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• Published: 08 May 2024

Is renewable energy sustainable? Potential relationships between renewable energy production and the Sustainable Development Goals

• Jing Tian   ORCID: orcid.org/0000-0002-5223-7494 1 ,
• Sam Anthony Culley 1 ,
• Holger Robert Maier   ORCID: orcid.org/0000-0002-0277-6887 1 &
• Aaron Carlo Zecchin   ORCID: orcid.org/0000-0001-8908-7023 1  

npj Climate Action volume  3 , Article number:  35 ( 2024 ) Cite this article

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• Climate-change mitigation
• Sustainability

This article has been updated

Given the key role renewable energy plays in averting the impending climate crisis, assessments of the sustainability of renewable energy systems (RESs) are often heavily skewed towards their environmental benefits, such as reductions in carbon emissions. However, RES projects also have the potential to actively harm progress towards other aspects of sustainability, particularly when hidden within the energy generation process. Given the growing understanding of the ’dark side‘ of renewables, we must ask the question: Is renewable energy sustainable? To gain a better understanding of this issue, we analyzed the degree of alignment of seven aspects of the renewable energy production process with the Sustainable Development Goals (SDGs) and their targets for six renewable energy types categorizing the relationships as either enablers or inhibitors. This information makes it possible for decision- and policy- makers to move beyond carbon tunnel vision to consider the wider impacts of RESs on sustainable development.

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Introduction.

Achieving net zero carbon emissions is the holy grail of climate change policies, with the transition to renewable energy sources often considered the hero in this quest. While the need to transition to renewables is unquestioned, the myopic pursuit of achieving net zero emissions has resulted in ’carbon tunnel vision 1 ‘ (i.e., a focus on the ability of renewables to reduce carbon emissions at the expense of the consideration of wider impacts), as a consequence of which the broader environmental, social and economic impacts (both positive and negative) of the transition are generally ignored. This means that we are now in treacherous territory, as the switch to renewables to address the current climate crisis could unwittingly create a cascade of other problems for future generations. Consequently, there is a need to better understand the potential positive and negative impacts of renewable energy systems so that we can ensure that the transition to renewables can occur in a sustainable manner.

In order to meet this need, we present a high-level overview of the potential enabling (positive) and inhibiting (negative) relationships between renewable energy systems (RESs) and the United Nation’s Sustainable Development Goals (SDGs) 2 , based on a review of the literature (see Fig. 1 caption for details and definitions). We pay particular attention to how these relationships vary for different types of renewable energy systems (biomass, hydropower, solar, geothermal, wind, wave & tidal 3 ) and how the various aspects of the renewable energy production process affect the environmental, social and economic elements of sustainability as characterized by the SDGs 4 . This enables us to obtain a better understanding of (i) the degree of sustainability of renewable energy systems, (ii) the impacts of adopting carbon tunnel vision, and (iii) what we need to do to broaden our vision to achieve more sustainable outcomes.

SDGs are grouped according to the categories of social, environmental and economic factors based on the Wedding Cake Model 52 . Specific targets recognized in the 2030 Agenda for Sustainable Development 2 (excluding government implementation targets) are grouped under each associated SDG and ordered clockwise. As was done in previous papers 53 , connections shown in green in ( a ) indicate a renewable energy project can potentially enable achieving a SDG target (this is equivalent to the concepts of reinforcing 54 providing synergies 55 and accomplishing 53 SDG targets). Connections shown in orange in ( b ) indicate a renewable energy project can potentially inhibit progress towards a SDG target (this is equivalent to the concepts of undermining 54 , providing trade-offs 55 and inhibiting 53 progress). Full results of the assessment for each target can be found in the Supplementary Information . Note that SDGs 4, 5, and 10 are excluded from this study since no direct relationships with quantitative indicators could be identified in literature. Given that SDG 16 and SDG 17 are at the heart of the SDG synergies, serving as fundamental interconnections to all other goals 56 , they are also excluded from our study. This is an original figure that was produced by the authors using AutoCAD.

How sustainable are renewable energy systems?

While the transition from fossil fuels to renewable energy sources is strongly associated with positive impacts on climate action (SDG 13), there can also be a number of inhibiting relationships with this SDG (Fig. 1b ). Such cases primarily involve the flaring (i.e., burning) of greenhouse gas, leading to emissions during certain types of renewable energy production (e.g., the generation of carbon emissions 5 and the leakage of methane during transportation and storage 6 for biomass production; the release of greenhouse gases when drilling for geothermal energy 7 ; and disturbing deep underwater sediments (e.g., particles settled at the bottom of water bodies) during the operation of hydropower plants 8 ). More importantly, renewable energy systems can also have potential enabling and inhibiting relationships with a number of other SDGs within the environmental category, including life below water (SDG 14), life on land (SDG 15) and clean water and sanitation (SDG 6).

Impacts related to life below water (SDG 14) are primarily associated with the production of wave and tidal power, with potential enabling relationships including enhancing the protection of coastal areas, as the installation of barriers and turbines can contribute to nutrient accumulation for coral protection 1 , 9 , and potential inhibiting relationships including threats to marine life, such as the harming of bird populations by offshore wind farms 10 , 11 . For life on land (SDG 15), potential enabling relationships include the repurposing of natural land, such as establishing wind and solar farms on degraded land 12 , whereas potential inhibiting relationships include the degradation of land quality when biomass contributes to soil erosion and degradation through the use of energy crops and the collection of crop residuals 13 . Regarding clean water and sanitation (SDG 6), potential enabling relationships include improved water-use efficiency 14 , 15 and potential inhibiting relationships relate to the reduced availability of drinking water, such as the contamination of underground aquifers from geothermal exploration, the tainting of potable surface water as a result of the leakage of biomass feedstock, and the allocation of significant water resources for hydropower infrastucture 16 , 17 .

In addition to their impact on the production of affordable and clean energy (SDG 7), renewable energy systems can also affect a range of other SDGs in the social category, including no poverty (SDG 1), zero hunger (SDG 2), good health and well-being (SDG 3), and sustainable cities and communities (SDG 11). However, in contrast to SDG 7, where renewable energy systems solely act as enablers, for these other SDGs, they can act as both inhibitors and enablers. For example, in relation to no poverty (SDG 1), potential inhibiting relationships stem from the intermittency of wind and solar energy sources 18 , while enablers could relate to the improvement of living standards through the provision of usable energy 19 . As far as zero hunger (SDG 2) is concerned, potential inhibiting relationships include the reduction of land availability for food production due to renewable energy installations 13 , with potential enabling relationships pertaining to the integration of RESs into agricultural farms (e.g., shading crops with solar panels) 20 , which has the potential to enhance resilience and productivity within the agriculture sector. Regarding good health and well-being (SDG 3), inhibiting relationships could include illnesses caused by harmful chemicals inadvertently released into the air and water, such as hazardous wastewater from geothermal energy production 21 , while potential enabling relationships include the prevention of respiratory infections and disease related to carbon pollution 22 . Finally, in relation to sustainable cities and communities (SDG 11), inhibiting relationships could arise from the environmental impact of RESs on modern cities, such as foul odours from biomass conversion, alterations in the microclimate caused by wind turbines and hydropower dams 23 and light pollution from solar panels 24 . In contrast, potential enabling relationships might relate to reduced damage to heritage land compared with that caused by the exploitation of conventional energy sources 12 , 25 .

RESs also have potential enabling and inhibiting relationships with various economic SDGs, including decent work and economic growth (SDG 8), industry, innovation and infrastructure (SDG 9) and responsible consumption and production (SDG 12). In relation to decent work (SDG 8), potential enabling relationships include the provision of decent work opportunities within emerging RES projects 26 , while inhibiting relationships relate to the likely reduction in job availability in the fossil fuel industry 27 , 28 . As far as industry, innovation and infrastructure (SDG 9) is concerned, potential enabling relationships include decreased carbon intensity through soil carbon sequestration and CO 2 recycling, while inhibiting relationships could relate to bioenergy and hydropower, for which energy sources require transportation, potentially increasing carbon intensity 29 . With regard to responsible consumption and production (SDG 12), enabling relationships could include improved management of natural resources, where waste and recyclable materials as waste can be utilized as a bioenergy source 30 , whereas potential inhibiting relationships include encroachment on natural resources and the generation of hazardous waste 15 , 21 .

What is the impact of carbon tunnel vision?

In order to obtain a more holistic and comprehensive understanding of the impact carbon tunnel vision has on broader aspects of sustainability, the relationships in Fig. 1 are decomposed by renewable energy type and aspect of the energy production process (Fig. 2 ). The different types of renewables considered include biomass, hydropower, solar, geothermal, wind, and wave & tidal, as these are the most commonly used sources, given current technologies. The aspects of the renewable energy production process considered include source selection, conversion and associated operational requirements, re-use, waste production, storage and transmission & distribution (Fig. 3 ), as these can differ for different types of RESs and include lesser-known elements of the renewable energy supply chain that often receive diminished attention. In the absence of this more nuanced understanding, it is easy to underestimate both the negative and positive sustainability impacts of renewable energy production on SDGs, making it more difficult to escape the currently adopted carbon tunnel vision, as detailed in subsequent sections.

SDG targets are presented by a single value and are divided into three principal spheres—social, economic, and environmental—which are depicted on the vertical axis. The horizontal axis categorizes the six renewable energy types. Within each type, the seven aspects of the energy production process (see Fig. 3 ) are presented in two rows, where connections are shown between a SDG, renewable energy type and aspect of the renewable energy production process. A green index color represents ‘enablers,’ while the orange index color signifies ‘inhibitors’. A lack of highlighting indicates the absence of identified evidence from literature, although it is important to note that this does not necessarily imply the absence of a relationship per se, just that this was outside of the boundary of consideration used here (more details are provided in the Supplementary Information ). This is an original figure that was produced by the authors using the Microsoft Excel Spreadsheet Software.

These aspects are presented within the context of the operational input-process-output concept. Source selection is considered as the first aspect, noting that the storing of potential energy is where impacts emerge—there are no direct impacts from renewable energy types with kinetic energy sources. The process of converting the source into energy can influence SDGs, both through the conversion process itself (i.e., plant location) and the associated operational requirements. After the completion of the renewable energy production process step and before the generation of the output, by-products can either be re-used elsewhere or go to waste. The production outputs can be divided into two parts: storage for local use and operational support, and transmission and distribution for grid connection or delivery. This is an original figure that was produced by the authors using Microsoft PowerPoint.

Underestimation of negative sustainability impacts

As can be seen from Fig. 2 , one of the major impacts of adopting carbon tunnel vision is that, by solely focusing on climate action (SDG 13) and the production of affordable and clean energy (SDG 7), the vast majority of inhibiting relationships between renewable energy production and the SDGs (i.e., the orange cells in Fig. 2 ) are ignored, which is likely to result in a distorted view of the sustainability of RESs. However, it should be noted that the focus on net zero emissions might not be the only reason for the lack of consideration of the potentially negative impacts of renewables on sustainability. This is because inhibiting relationships are primarily associated with the less well-known and understood aspects of the renewable energy production process (such as conversion and associated operational requirements, re-use and the generation of waste), rather than the more well-known and better understood processes (such as those associated with source selection, storage and transmission & distribution).

These potentially negative impacts affect a range of SDGs (Fig. 2 ). For example, operational requirements of renewable energy projects can have a negative impact on SDG 2 (zero hunger) because the development of RESs competes with the agricultural sector for natural resources such as water and minerals, along with land use 15 . This is particularly the case for bioenergy, as energy farming may occupy agriculturally viable land 13 , 16 . The conversion process and storage of energy can have a negative impact on SDG 11 (sustainable cities and communities), as renewable energy plants and storage facilities can unintentionally encroach on cultural and heritage lands, especially sacred lands of First Nations people (i.e., for indigenous peoples who are the earliest known inhabitants of an area), posing a potential infringement on indigenous rights 25 , 31 . Similarly, the conversion process can have a negative impact on SDG 15 (life on land), as renewable energy facilities are likely to cause damage to the biodiversity of surrounding areas (i.e. natural wildlife) 32 , 33 .

In most cases, the inhibiting relationships between the aspects of the renewable energy production process and the SDGs are specific to a particular renewable energy type. For example, the storage component of the source selection step (Fig. 3 ) can negatively impact SDG 12 (responsible consumption and production) in the case of biomass and hydropower. For the former, this is because the feedstock required for bioenergy production necessitates the use of storage facilities, like warehouses or hubs for biomass storage and pre-processing 34 , thereby increasing material resource use and land occupation. For the latter, this is because the storage of water required for hydropower production necessitates the use of dams or reservoirs for storage and collection, potentially altering and using surrounding natural resources 21 , 35 . In contrast, this is not the case for solar, wind and wave & tidal energy (Fig. 3 ).

Similarly, the conversion process (Fig. 3 ) can result in an inhibitive relationship with SDG 14 (life below water) for hydropower, wind and wave & tidal. For hydropower, this is due to the potential to artificially alter aquatic ecosystems and redirect the flow of rivers 21 , 35 . For wind power, this is because of the potential contribution of offshore wind farms to biofouling and the generation of underwater noise 36 , whereas for wave & tidal power, tidal barriers can modify the flow of water and wave patterns 1 , 9 . However, the same does not apply to biomass, solar, or geothermal. This demonstrates that particular care must be taken to understand the inhibiting factors for different renewable energy types in order to obtain a comprehensive understanding of their impact on sustainability.

Underestimation of positive sustainability impacts

Figure 2 also highlights that another significant impact of adopting carbon tunnel vision by only considering SDG 13 (climate action) is the lack of consideration of a large number of the other positive SDG impacts of renewable energy production, which is also likely to result in a distorted assessment of the sustainability of RESs. As can be seen in Fig. 2 , all types of RESs exhibit potentially enabling relationships with all of the social (i.e., SDGs 1 - 3, 7, 11) and economic (i.e., SDGs 8, 9, 12) aspects of sustainability. In addition, the components of the renewable energy production process where these occur are generally the same. For example, for SDG 1 (Target 1.5: build resilience to environmental, economic and social disasters), there is a potentially enabling relationship with source selection, transmission & distribution, and storage. This is because renewable energy can directly assist individuals in impoverished conditions by providing them access to electricity, thereby reducing their risk of suffering from local disasters 37 . For SDG 2 (zero hunger), there is a potentially enabling relationship with transmission and storage, attributable to the efficiency and advanced integrated farming techniques that can be enhanced when food production is paired with RESs 38 . Similarly, for SDG 3 (good health and well-being), there is a potential enabling relationship from using renewable energy (conversion, transmission & distribution and storage), as this can reduce the risk of cardiovascular diseases caused by air pollution (PM2.5, PM10) 22 , as well as chronic respiratory disease resulting from the burning of traditional energy sources like coal and fuel 39 . For SDG 15 (life on land), there is a potentially enabling relationship with the conversion process, as renewable energy plants do not require further deforestation for installation and can repurpose degraded land, such as deserts or areas suffering from soil erosion 12 .

However, some of these enabling relationships only apply to specific combinations of renewable energy type and aspects of the energy production process. For example, biomass and hydropower can have a positive impact on SDG 6 (clean water and sanitation) and SDG 11 (sustainable cities and communities) because they are able to use municipal wastewater as one of their energy sources 30 , 40 , thereby purifying water and reusing it as a product or by-product 41 . Additionally, bioenergy, geothermal energy and hydropower can have a positive impact on SDG 12 (responsible consumption and production), as bioenergy production can result in the generation of fertilizer as a by-product, thereby reducing material usage and promoting recycling 42 , 43 , hydropower can supply clean water to downstream areas 44 , and geothermal energy can provide heating/irrigation water for direct applications such as greenhouse farming 45 .

How do we broaden our vision?

As highlighted in the previous sections, while renewable energy sources are a strong enabler of climate action, as well as a number of other SDGs, they can also have a range of negative social, environmental and economic impacts. Consequently, there are several significant conclusions to draw that affect how we should think about climate policy:

Ignoring the potential negative impacts of RESs in the singular pursuit of net zero carbon emissions has the potential to result in disastrous consequences and the perverse outcome that solutions intended to increase the sustainability of humankind actually have the opposite effect. We need to heed the lessons of history to avoid another “hole in the ozone layer” by trying to “fix” a specific issue without considering all potential consequences in an integrated fashion. For policy makers, this can be combated by more cross-agency participation in the management of renewable energy zones and planning, so that trade-offs of a proposed solution can be more apparent.

RESs have enabling relationships with a much broader range of SDGs, not just climate action (SDG 13) and affordable and clean energy (SDG 7), which, if ignored, can significantly underestimate their positive impact on sustainability. This includes the potential to improve the living conditions of communities through the creation of employment opportunities, improved access to resources or reduced health risks, as well as through supporting the biodiversity of the surrounding environment. While there is mounting political pressure to deliver on decarbonization targets, these synergies are at risk of not being capitalized on, and the multiple benefits of implementing renewable energy projects need to be framed in a more holistic way.

By identifying the potential inhibiting and enabling relationships between RESs and the SDGs, this paper provides a blueprint for sustainability assessments that will enable us to broaden our vision beyond considering the impacts of renewables on net-zero emissions to considering the full range of sustainability impacts, allowing for more structured conversations to occur within project management and policy development. This includes an awareness of all potential negative and positive impacts of different types of renewables on different elements of sustainability, as well as for which aspect(s) of the renewable energy production process they occur. Such awareness is especially important for the aspects for which management decisions determine whether sustainability impacts are enabling or inhibiting. For example, the conversion process can have both positive and negative impacts on SDG 11 (sustainable cities and communities), depending on how the government and local society manage their strategy for the preservation, protection, and conservation of all cultural and natural heritage. Similarly, operation and transmission & distribution can have both positive and negative impacts on SDG 8 (decent work and economic growth), depending on the degree to which renewable energy sources are able to promote GDP growth 46 and create more job opportunities with fair pay 47 . To further the ability for renewable energy projects to be more sustainable, future work on this topic should focus on ways to quantity the impact renewable energy projects can have on the SDGs identified, to allow for more direct comparisons for decision makers 48 , 49 , and policy makers alike 50 , 51 .

The enabling and inhibiting relationships between renewable energy sources and the SDGs identified in this paper provide a step toward the information needed to develop climate policy and associated action plans that ensure that we can achieve net zero emissions by implementing RESs in a sustainable manner. This will enable us to address the climate crisis in a manner that avoids mistakes of the past and creates a positive future for our planet.

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Acknowledgements

The authors would like to thank the Future Fuels Cooperative Research Centre for providing funding for this work through project RP1.2-04. The authors would also like to thank the anonymous reviewers of this paper, whose comments have improved its quality significantly.

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Tian, J., Culley, S.A., Maier, H.R. et al. Is renewable energy sustainable? Potential relationships between renewable energy production and the Sustainable Development Goals. npj Clim. Action 3 , 35 (2024). https://doi.org/10.1038/s44168-024-00120-6

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Cost, environmental impact, and resilience of renewable energy under a changing climate: a review

• ReviewPaper
• Open access
• Published: 28 October 2022
• Volume 21 , pages 741–764, ( 2023 )

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• Ahmed I. Osman   ORCID: orcid.org/0000-0003-2788-7839 1 ,
• Lin Chen 2   na1 ,
• Mingyu Yang 3 ,
• Goodluck Msigwa 4 ,
• Mohamed Farghali 5 , 6 ,
• Samer Fawzy 1 ,
• David W. Rooney 1 &
• Pow-Seng Yap 4  

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Energy derived from fossil fuels contributes significantly to global climate change, accounting for more than 75% of global greenhouse gas emissions and approximately 90% of all carbon dioxide emissions. Alternative energy from renewable sources must be utilized to decarbonize the energy sector. However, the adverse effects of climate change, such as increasing temperatures, extreme winds, rising sea levels, and decreased precipitation, may impact renewable energies. Here we review renewable energies with a focus on costs, the impact of climate on renewable energies, the impact of renewable energies on the environment, economy, and on decarbonization in different countries. We focus on solar, wind, biomass, hydropower, and geothermal energy. We observe that the price of solar photovoltaic energy has declined from $0.417 in 2010 to $0.048/kilowatt-hour in 2021. Similarly, prices have declined by 68% for onshore wind, 60% for offshore wind, 68% for concentrated solar power, and 14% for biomass energy. Wind energy and hydropower production could decrease by as much as 40% in some regions due to climate change, whereas solar energy appears the least impacted energy source. Climate change can also modify biomass productivity, growth, chemical composition, and soil microbial communities. Hydroelectric power plants are the most damaging to the environment; and solar photovoltaics must be carefully installed to reduce their impact. Wind turbines and biomass power plants have a minimal environmental impact; therefore, they should be implemented extensively. Renewable energy sources could decarbonize 90% of the electricity industry by 2050, drastically reducing carbon emissions, and contributing to climate change mitigation. By establishing the zero carbon emission decarbonization concept, the future of renewable energy is promising, with the potential to replace fossil fuel-derived energy and limit global temperature rise to 1.5 °C by 2050.

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Introduction

Due to their high energy density, fossil fuels are the primary energy source worldwide; however, fossil fuel combustion produces greenhouse gases; approximately 35% of greenhouse gases are emitted by existing power plants (Maamoun et al., 2020 ). In addition, China's coal-fired power plants emit 42% of nitrous oxides and 38% of sulfur dioxides, for a total of 40% of the heat-trapping greenhouse gases, thereby increasing global temperature (Yang et al., 2020 ). Over 300 natural disasters were caused by climate change in 2018, affecting more than 68 million people and causing approximately $131.7 billion in economic losses, with storms, wildfires, floods, and droughts accounting for 93%. Particularly alarming is the fact that the wildfire's financial losses in 2018 are nearly equivalent to the decade's total losses. Moreover, food, crop yields, water, health, the occurrence of infectious diseases, human habitats, infrastructure, and ecosystems are vulnerable to climate change (Farghali et al., 2022 ; Fawzy et al., 2020 ).

It is anticipated that energy demand will increase by 56% by 2040 (Rahman et al., 2022 ). If the same policy of reliance on fossil fuels is continued, increasing energy demand will increase greenhouse gas emissions. Consequently, mitigating climate change is necessary to avoid these outcomes. Renewable energy sources play a crucial role in achieving carbon neutrality, reducing global warming and climate change, and meeting the Paris Agreements' 2 °C target. Renewable energy sources are considered to be affordable, sustainable, and free-obtained energy. Figure  1 depicts the various renewable energy sources and their proportional contribution to electricity production.

Source: Rahman et al., ( 2022 )

Share of renewable energy sources in electricity generation in gigawatt% from a total of 2587.6 gigawatts. The largest contributor to electricity production is hydropower. Solar and wind energy together account for 50% of the total electricity share. Geothermal, ocean, and biomass-based power plants account for slightly more than 6%.

Utilizing renewables is crucial for decarbonizing the energy sector and combating climate change, but solar, hydropower, and wind availability depends on weather conditions and future climate changes. In addition, less research has been conducted on the environmental effects of using renewable energy sources. Therefore, this review was conducted to discuss (i) the most widely used renewable energy sources, (ii) the needs and costs of renewable energy, (iii) the impacts of climate change on renewable energy sources and their future prospective under climate change scenarios, and (iv) the potential environmental impacts caused by renewable energy sources and the most environmentally friendly renewable sources.

The need for renewable energy

Almost 80% of the global population lives in countries that are net importers of fossil fuels (IRENAd, 2022 ). Due to their dependence on foreign fossil fuels, approximately six billion people are vulnerable to geopolitical shocks and crises (AaH et al., 2021 ). In contrast, renewable energy sources are available in all nations, but their full potential has yet to be realized. The International Renewable Energy Agency (IRENA) estimates that by 2050, 90% of the world's energy can and should come from renewable sources (IRENAb, 2018 ).

In addition, the excessive use of fossil fuels and non-renewable energy sources contributes to global warming by emitting large quantities of greenhouse gases (Chen et al., 2022a ). Controlling greenhouse gas emissions from energy production and consumption is crucial to combating climate change. To achieve the Paris Agreement's goal of limiting global temperature rise to 1.5 °C–2 °C by 2100, energy systems require rapid, immediate, and sustained innovation and the effective use of renewable energy across all sectors (Fawzy et al., 2020 ). The demand and growth of renewable energy in the transportation, buildings, industrial, and power sectors are summarized in Table 1 based on the critical energy use sectors identified by the  IRENA.

The urgency to combat climate change and achieve sustainable development strengthens the global renewable energy transition momentum in an era of global environmental degradation. A sustainable energy future is within reach due to the development of green buildings, green energy and power use in industry, green transportation, decreased costs of renewable energy, increased energy efficiency and continued technological advancements, and informed policymaking. This shift is gaining traction, but it must accelerate to contribute to global sustainable development. According to the development and research on the use of renewable energy in critical sectors (Table 1 ), the building sector accounts for 70% of the Kingdom of Saudi Arabia's energy consumption. In order to sustain the construction industry, renewable energy is essential. However, the development of renewable energy is hindered by policies, finances, technology, and culture. In addition, India's urgent need for policies promoting the use of renewable energy in the construction industry was demonstrated. According to studies, using renewable energy in the industrial sector can save money and protect the environment from the dangers of fossil fuel emissions. However, government level awareness campaigns regarding the significance of energy conservation are required.

In addition, several studies in China and Europe have demonstrated that even when a high proportion of renewable energy is used in power plants, their capacity utilization is low and that renewable energy exhibits significant monthly variations, resulting in seasonal or even interannual structural imbalances in energy supply. The study concluded that by 2020, Ireland had achieved a 15% contribution of renewable energy in transportation. In Denmark, however, sustainable bioenergy consumption is possible if 100% renewable energy systems are utilized in the transportation sector, which is technically feasible given that the costs are comparable to those of fossil fuel alternatives. Thus, renewable energy can theoretically replace fossil fuels in the four key sectors, but policy and culture influence renewables in practice. In the future, there will also be a need for greater government and relevant authority support for the use of renewable energy, as well as the promotion of energy conservation and renewable energy acceptance campaigns.

This section examines the need for renewable energy in four key sectors across multiple nations. The research demonstrates that policy, technology, finance, and culture influence the use of renewable energy. Therefore, global support for adopting renewable energy and developing policies to promote sustainable development will need to be strengthened in the future.

Types of renewable energies

Renewable energy is energy that is derived from natural resources. In order to achieve carbon neutrality, the global share of renewable energy is projected to increase from 14% in 2018 to approximately 74% in 2050, requiring an eightfold annual increase. Renewable energy can be evaluated from the perspective of sustainability and its technical characteristics, such as integration with other resources, energy efficiency, and operating costs (Bortoluzzi et al., 2021 ). These factors assist policymakers in selecting a specific renewable energy source to meet market demand. Identifying the most viable renewable energy source is essential; consequently, defining the renewable energy resource is vital.

Accordingly, renewable energy technologies reported in the literature are categorized, as depicted in Fig.  2 , into (i) solar energy, also known as photovoltaic energy, and generated from sunlight (Bortoluzzi et al., 2021 ; Farrell et al., 2019 ). Solar energy includes solar photovoltaic grid-connected, solar photovoltaic isolated, and thermal solar energy (Bortoluzzi et al., 2021 ; Karunathilake et al., 2019 ; Pang et al., 2022 ). This energy source is one of the most rapidly expanding clean sources of global energy production (Campos-Guzmán et al., 2019 ). (ii) Wind energy is the utilization of wind power to generate electricity for residential and industrial use (Konneh et al., 2019 ; Ren and Lutzen, 2017 ). A wind turbine is utilized for the conversion of wind energy to electricity. The wind operation can primarily be used as a small-scale wind energy system, which supplies specific regions, and a wind-connected energy grid system, which makes it possible to construct electricity grids similar to wind farms (Bortoluzzi et al., 2021 ; Yazdani et al., 2018 ). Wind and solar energies are two sources of clean energy, but they are weather-dependent. Thus, it is essential to consider weather changes when choosing such energy sources (Campos-Guzmán et al., 2019 ). (iii) Geothermal energy is derived from the earth's heat or the steam of hot rocks (Bortoluzzi et al., 2021 ). Geothermal energy can provide industrial-scale electricity and heat (Rani et al., 2019 ). (iv) Biomass energy is derived from both plant and animal sources. The energy is produced through the combustion of wood, agricultural residues such as crop and animal waste, and other organic feedstocks (Osman et al., 2019a ). Biomass is incinerated to generate heat and/or electricity or converted into biofuel and biogas using anaerobic digestion, gasification, or pyrolysis/hydrothermal carbonization (Farghali et al., 2022 ; Osman et al., 2021a ; Rahman et al., 2022 ). Biomass pyrolysis produces biochar that can be used effectively for climate change mitigation as a readily available negative emission technology; this is in addition to the renewable energy produced from the process in the form of excess heat (Fawzy et al., 2022 ; Osman et al., 2022 ). Energy from waste can be considered a subset of biomass energy when waste derived from animal, human, or vegetable sources is considered (Akor et al., 2021 ; Al-Wahaibi et al., 2020 ; Osman et al., 2019b ). The wastes may be incinerated or anaerobically digested to produce heat and/or electricity (Farghali et al., 2022 ; Osman et al., 2022 , 2021b ; Rahman et al., 2022 ). (v) Hydropower is obtained by converting the potential energy of water into kinetic energy (Çolak and Kaya, 2017 ). Hydroelectricity is generated by constructing dams on rivers. Water at a greater altitude is precipitated onto the hydroturbine, which generates electricity. Hydroelectricity generates approximately 1150 gigawatts on a global scale and is the largest renewable energy source (Rahman et al., 2022 ). Table 2 provides a comprehensive listing of the potential renewable energy sources.

Renewable energy types. Various renewable energy sources can be used to produce energy that can replace fossil fuels and as a tool for climate change mitigation strategies. The most common energy sources are solar, wind, geothermal, hydropower, and biomass. Hydrothermal is the leading energy source, with the capacity to generate 1,150 gigawatts of electricity

Cost of renewable energies

Renewable energy will soon be the cheapest source of energy in the majority of the world. The costs of renewable energy technologies are falling dramatically, as shown in Table 3 . Between 2010 and 2021, the cost of solar energy decreased by 88% (IRENAa, 2022 ). The costs associated with onshore and offshore wind energy decreased by 68% and 60%, respectively. Renewable energy is becoming more attractive everywhere, particularly in low and middle-income countries, where the majority of future energy demand will originate. With prices falling, a substantial portion of the future power supply will probably come from low-carbon sources. By 2030, renewable energy sources could provide 65% of the world's total electricity supply, and by 2050, they could decarbonize 90% of the electricity industry, significantly reducing carbon emissions and assisting in climate change mitigation. Although solar and wind power costs are expected to be higher in 2022 and 2023 compared to pre-pandemic levels owing to overall heightened commodity and freight prices, the International Energy Agency predicts that their competitiveness will improve due to steeper increases in gas and coal prices.

Renewable energy generation capacity introduced in 2021 was 257 gigawatts, which is 41% higher than the 182 gigawatts added in 2019. Renewable generation capacity worldwide increased more than fourfold between 2000 and 2021, from 754 gigawatts to 3,064 gigawatts (IRENAa, 2022 ). Thus, renewable energy will become the primary energy source with the lowest cost, especially when combined with the fossil fuel crisis and net-zero emission initiatives (Yang et al., 2022 ). Solar photovoltaics contributed the most to renewable energy addition in 2021, with an added capacity of 133 gigawatts (IRENAa, 2022 ). In addition, wind power capacity addition was 93 gigawatts in 2021, of which 72 gigawatts were onshore. In 2021, the generation capacity of hydropower increased by 23 gigawatts, doubling the 11 gigawatts in 2020.

In 2021, bioenergy power generation grew by an additional 10.3 gigawatts, compared to the 9.1 gigawatts added in 2020. Away from these resources, geothermal power additions were modest in 2021, and only 110 megawatts of concentrated solar power capacity added to the grids. Therefore, the share of renewables growth for the total power generation capacity reached 81% in 2021, making renewables account for at least half of all new net energy additions worldwide since 2012 (IRENAa, 2022 ).

Cost of solar energy

By 2021, over 843 gigawatts of solar photovoltaic systems had been installed worldwide, representing a 21-fold increase in solar energy since 2010. In addition, 133 gigawatts of newly installed systems were established during 2021 alone, which was a 13% increase from 2020. These new capacity additions were the highest among all renewable energy sources that year (IRENAa, 2022 ).

Solar energy costs must be quantified to promote the benefits and future of renewable energies. The levelized cost of energy (LCOE) of crystalline and amorphous silicon photovoltaic panels in different local climates was the subject of one study. The LCOE and lifetime of the crystalline silicon panels were $0.143 (21 years), $0.138 (32 years), $0.172 (25 years), and $0.159 (40 years) for mid-altitude desert, humid subtropical, humid continental, and maritime climates, respectively (Flowers et al., 2016 ). The amorphous silicon panels had LCOE values and life spans of $0.141 (17 years), $0.201 (14 years), and $0.227 (17 years) for mid-altitude desert, humid subtropical, and maritime climates, respectively. The study identified crystalline silicon panels as the most viable due to their low degradation rates. Another research studied the LCOE of bifacial solar farms considering land and module costs. The research suggested that for places with limited and expensive land, solar panels should be laid flat to maximize land utilization. Additionally, areas with high module costs and latitudes above 300 should tilt the bifacial modules at 100–150, achieving a LCOE reduction of 2–6% (Patel et al., 2019 ). The authors suggest that a proper choice of photovoltaic panel technology should be implemented to achieve affordable solar energy. IRENAa ( 2022 ) reported that in Europe, crystalline solar photovoltaics costs decreased by approximately 91% between December 2009 and December 2021.

Hybrid energy systems are essential for reducing the overall cost of renewable energy sources. Using NASA (National Aeronautics and Space Administration) and HOMER (Hybrid Optimization of Multiple Electric Renewables) data, researchers in Iran analyzed the cost of 103 hybrid solar–wind systems. The results indicated an 87–100% potential for using solar and wind energy (Jahangiri et al., 2019 ). The cheapest solar hybrid system at Jask station costs $0.592/kilowatt-hour and consists of two solar cells, one diesel generator, eleven batteries, and one converter, while the cheapest wind hybrid system at Bandarabbass station costs $0.586/kilowatt-hour and consists of one wind turbine, one diesel generator, ten batteries, and one converter. The authors emphasized that Iran's renewable energy industry faces obstacles due to the availability of inexpensive fossil fuels and the high dollar exchange rate. Solar concentrating collectors, photovoltaics, a double-effect absorption heat pump, and thermal storage were studied as another hybrid system for heating and cooling buildings. The results indicated that the solar system could provide 31.1% of a hospital's heating and cooling loads while saving 64.2% on energy costs (Chen et al., 2022b ). More hybrid systems can be explored here to further reduce solar energy costs. Overall, the global weighted average levelized cost of electricity for solar photovoltaic projects established in 2021 was decreased by approximately 88% from 2010, representing a 13% year-on-year decline, from 0.055 $/kilowatt-hour in 2020 to 0.048 $/kilowatt-hour in 2021 (IRENAa, 2022 ).

In summary, the costs of solar energy are primarily influenced by technology, climate, and national policies; consequently, with advanced technology and favorable renewable energy policies, the costs will continue to decline in the future.

Cost of wind energy

The offshore wind energy sector is one of the renewable energy sources that can operate without requiring a large amount of land; however, due to construction technology and grid connection challenges, offshore wind farms are more expensive to construct than onshore wind farms (Msigwa et al., 2022 ). A study was conducted on the costs of offshore wind energy in Southeast Asia, specifically Singapore, where wind conditions are unfavorable. Considering reduction potential of 14% capital costs, 63% submarine power cable costs, and 36.5% operation and maintenance costs, the study found that the LCOE of an offshore wind farm is 32 cents/kilowatt-hour, which is higher compared to solar photovoltaics, which cost approximately 12 cents/kilowatt-hour (Nian et al., 2019 ). The study suggested that a significant change in the levelized cost of energy (LCOE) of an offshore wind farm in Singapore could be achieved by increasing the wind power plant's load factor, which is only 12%. Enhanced turbine designs and the relocation of turbines as far as 300 km from the coast can increase the load factor. Another study was conducted in Egypt for 7 megawatts of wind turbines at various locations in the Mediterranean Sea with fixed platforms 5 km from the coast and 60 m deep (Abdelhady et al., 2017 ). The results indicated that capacity factors ranged from 55% to 63%, with LCOE ranging from $0.075 to $0.079 per kilowatt-hour, which is competitive with other renewable energies in Egypt and is half the cost of offshore wind energy in Europe. The authors recommend additional research on offshore wind farm technology to bring costs down to parity with onshore wind farms.

Due to technological advancements and favorable renewable energy costs, the wind energy industry has exhibited a declining cost trend. A study of onshore wind energy in the European Union, USA, and Norway between 2008 and 2016 revealed a trend toward larger machines with a decline in capital and financing costs. During the study period, the project capital costs decreased by 10% to €1422/megawatt, and the LCOE decreased by 33% to €48/megawatt-hour, with the decrease attributable to a change in specific power, financing, and capital costs (Duffy et al., 2020 ). Denmark had the lowest LCOE at €34 per megawatt-hour, while Ireland had the highest, at €68 per megawatt-hour. The price difference between Denmark and Ireland is attributable to Denmark's more favorable renewable energy policies, which reduce the cost of wind energy. Another study on Pakistan wind farms showed that the lifetime LCOE for a windfarm producing 142 gigawatt-hours per year was $0.11371 per kilowatt-hour and $0.04092 per kilowatt-hour for 1–10 and 11–20 years, respectively (Hulio and Jiang, 2018 ). The initial ten years of LCOE are more expensive due to the loan repayment and interest rates that must be paid in full during the initial ten years of the project. According to Table 3 , the global levelized cost of electricity for onshore wind projects established in 2021 decreased by 15%, from $0.039/kilowatt-hour in 2020 to $0.033/ kilowatt-hour in 2021. In addition, the global average levelized cost of electricity for onshore and offshore wind decreased by 68% and 60%, respectively. IRENAa ( 2022 ) reported that the average global levelized cost of electricity for offshore wind decreased by 60% between 2010 and 2021, from $0.188 per kilowatt-hour to $0.075 per kilowatt-hour.

The average LCOE for newly constructed projects in Europe decreased by 29% between 2020 and 2021, from 0.092 to 0.065 dollars per kilowatt-hour. Between 2010 and 2021, the global average installed costs decreased by 41%, from $4876/kilowatt to $2858/kilowatt. Increasing developer experience, product standardization, industrialization, regional manufacturing and service hubs, and economies of scale have contributed to price reductions. These declines have also been aided by deployment and, in many cases, manufacturing policies that have facilitated growth (IRENAa, 2022 ).

To summarize, offshore wind energy costs are currently more expensive than onshore. Nevertheless, technological development and favorable policies further reduce costs until they are comparable.

Cost of biomass energy

Several feedstocks and various technologies can be used to produce energy or electricity from biomass (Al-Mawali et al., 2021 ). The adapted technology may include biomass pyrolysis and gasification, both of which are still in the developmental phase but are being tested commercially. Direct co-firing, combustion in stoker boilers, anaerobic digestion, landfill gas, municipal solid waste incineration, and combined heat and power systems are established technologies. Available low-cost biomass, such as agricultural by-products, provides highly competitive, dispatchable sources of electricity. However, transportation costs are responsible for the high price of biomass. In Switzerland, research has been conducted on the transport of biomass, including firewood, woodchips, and solid and liquid manure, along various transport chains. The results revealed that transportation costs ranged from 24 Swiss francs/ton of dry matter for the transport of slurry by underground pipe to 340 Swiss francs/ton of dry matter for transporting coniferous wood by farmers (Schnorf et al., 2021 ). Due to a decrease in volume and an increase in empty trips, the transportation costs for the farmers' chain were higher. In addition, loading and unloading accounted for up to 65% of total manure transportation costs. The author suggested transporting biomass raw materials in large quantities and over short distances to reduce costs.

The cost of harvesting equipment is an additional aspect of biomass energy costs to consider. In Michigan, USA, the fixed-to-machine cost ratios for cut-to-length harvesting systems (30%, 70%, and 100%) ranged between 50% and 60%, whereas those for whole-tree harvesting systems ranged between 30% and 50% (Zhang et al., 2016 ). Productivity, equipment purchase price, and annual scheduled hours had the greatest effect on harvesting expenses.

Due to its availability and affordability, biomass energy is also employed in cooking. The economic viability of firewood, charcoal, biogas, jatropha oil, and crop residue briquettes was examined in Kenyan and Tanzanian villages. The calculations of life cycle costs revealed that jatropha oil had the highest costs, while firewood burned in efficient stoves had the lowest. The briquettes were competitive with charcoal. In Kitui Kenya, using advanced maendeleo, rocket, and envirofit stoves reduced the life cycle cost per meal by 30%, 55%, and 57%, respectively (Okoko et al., 2018 ).  In Moshi Tanzania, using kuni chache and okoa stoves reduced the life cycle cost per meal cooked by 49% and 69%, respectively. The charcoal production in Moshi Tanzania was found to be expensive due to royalty fees charged by the government, which account for up to 80% of the cost ranging between $0.1 and $0.2/meal. In contrast, charcoal in Kitui Kenya was cheap, ranging from $0.03–0.04 per meal due to the absence of royalty fees.

In addition to the commercial production of biomass energy, the residential use of biomass energy, particularly in rural areas, is a cost-sensitive; therefore, appropriate incentives are required to promote the use of low-cost biomass energy. Between 2010 and 2021, the average global LCOE of bioenergy for power projects decreased from $0.078/kilowatt-hour in 2010 to $0.067/kilowatt-hour in 2021, lower than the cost of electricity from fossil fuel-fired systems. The global installed price for newly commissioned bioenergy is set at $2353/kilowatt in 2021 compared to $2634/ kilowatt in 2020 (IRENAa, 2022 ). But the cost of bioenergy is varied between countries, with $0.057/kilowatt-hour in India, $0.060/kilowatt-hour in China, $0.088/kilowatt-hour in Europe, and $0.097/kilowatt-hour in North America. Variations in bioenergy costs are caused by several factors, such as feedstock type, feedstock cost and availability, conversion process, and power production process. Transportation, equipment, technology, and policies significantly impact the cost of commercial and residential biomass energy use.

Cost of hydropower energy

Hydropower production costs depend on the construction, equipment, operation, and maintenance expenses. Micro-hydropower plants are necessary for rural and underdeveloped areas to have access to electricity. The cost of micro-hydropower plants utilizing locally manufactured equipment was quantified in Nepal. The results showed that the average price per kilowatt at Crossflow and Pelton sites were $505/kilowatt and $605/kilowatt, respectively (Butchers et al., 2022 ). The generator, penstock, and turbine sub-systems account for almost half of the total costs of the hydropower plant sub-systems. The initial cost of a micro-hydropower plant is around 6 cents/hour, while solar and wind plants cost 10 cents/hour and 7 cents/hour, respectively (Elbatran et al., 2015 ). The cost of starting up a micro-hydropower plant is divided into civil works (40%), turbine and generator (30%), control equipment (22%), and management cost (8%). The initial costs of construction and equipment for hydropower plants are the highest, and hydropower production at a lower cost requires careful planning.

Another study used the upgraded Hydropower’s Environmental Costs Analysis Model (HECAM II) to model the costs of a hydropower plant with the Bakhtiari dam in Iran as a case study. The total cost, revenue, and the benefit-to-cost ratio were $79.13/megawatt-hour, $203/megawatt-hour, and 2.57, respectively (Tajziehchi et al., 2022 ). Another research on the costs of hydropower plants in Ecuador showed that the latest Ecuador hydropower projects of Coca Codo Sinclair, Sopladora, Minas San Francisco, Delsintagua, and Manduriacu had prices that were 79%, 34%, 21%, 12%, and 119% more expensive than the IRENA’s averages (Naranjo-Silva et al., 2022 ). In addition, the cost of hydropower energy was $2,018/kilowatt, which is 37% higher than the IRENA 2020 cost of $1,472/kilowatt. Without proper planning from the onset of the project, hydropower can be costly in this situation. In general, the average global levelized cost of electricity of newly commissioned hydropower systems in 2021 was $0.048/kilowatt-hour—4% higher than the $0.046/kilowatt-hour recorded in 2020 and 23% higher than the systems commissioned in 2010. However, this cost is still lower than the cost of the newly commissioned fossil fuel-fired systems, which range between $0.054 and $0.167/kilowatt-hour (IRENAa, 2022 ).

In conclusion, the initial costs of hydropower plant construction are high relative to operation and maintenance costs; therefore, hydropower projects must be managed properly from the outset to be profitable.

Cost of geothermal energy

The use of geothermal energy for heating buildings and water is widespread. In Geneva, Switzerland, a geothermal district heating cost analysis was conducted. The LCOE for geothermal energy alone for different decision paths was between 59 and 553 Swiss Franc/megawatt-hour (Pratiwi and Trutnevyte, 2022 ). The lowest LCOE was obtained on the decision path of the annual heat demand of 400 gigawatt-hours/year, geothermal coverage of 40% in a centralized system, linear heat density of 8 megawatt-hours/(meter⋅year), and well depth is 2500 meters with a maximum geothermal flowrate per well doublet of 80 liter/second. In contrast, the highest LCOE was on a decision path with an annual heat demand of 100 gigawatt-hours/year and geothermal coverage of 10% with a geothermal flow rate of less than 20 liter/second. Another research in Bangladesh showed that the geothermal energy costs were reduced with increasing capacity and time with a minimum price of €2.8/kilowatt-hour for a 150 megawatts plant. The initial costs of setting up the power plant are $2500 per kilowatt, with operation and maintenance costs at $0.01–0.03 per kilowatt-hour with 90% availability. Initial costs for geothermal power plants vary widely, necessitating careful decision-making to ensure that the energy produced is affordable.

Another research studied the environmental life cycle costing (ELCC) for enhanced geothermal systems in Reykjanes, Iceland, and Vendenheim, France. The ELCC for the Reykjanes project was about 14.47–15.78 million euros, with most costs from investment and drilling, while that of Vendenheim was about 91.90–113.97 million euros, with most costs from the plant, well drilling, and operations and maintenance (Cook et al., 2022 ). The mean LCOE for the Reykjanes project was €16.5/megawatt-hour/year, while that of the Vendenheim project was €45/megawatt-hour/year. In Serbia, the geothermal energy heating price was €0.37/m 2 , which is lower than natural gas and coal ranging between €0.99–1.17/m 2 (Milanović Pešić et al., 2022 ). Hence, geothermal prices vary widely depending on the type of power plant.

To summarize, geothermal energy prices are competitive with other energy sources and are lower than those of other energy sources; however, the costs of different power plants vary greatly depending on the technology employed.

Impact of climate change on renewable energies

Using fossil fuels for energy production was the primary cause of climate change and global warming. Renewable energy sources are crucial in preventing carbon emissions and mitigating climate change. However, renewable resources such as solar, wind, and hydropower depend on current weather and future climate variability. Consequently, accurately evaluating the viability of a low-carbon and sustainable energy technology can be made more certain by studying the impact of future climate and estimating the variation in renewable energy sources. Climate changes, such as increasing temperatures, extreme winds, rising sea levels, and decreased precipitation, will be one of the century's greatest societal challenges. This section will examine how climate change affects various renewable energy sources.

Impact on wind energy

Climate change may alter atmospheric dynamics, affecting wind patterns in terms of spatial distribution and temporal variability, posing a threat to wind power generation (Solaun and Cerdá, 2020 ). Susini et al. ( 2022 ) investigated the impact of climate change on the offshore wind energy sector in the North and Irish Seas by analyzing changes in climate averages and extreme events for the period 2081–2100 under the Representative Concentration Pathway-8.5 scenario. The results indicate a slight decrease in wind energy production and a reduction in all climate indicators (mean and extreme wind speed, wind power density, operating hours, total generation, and capacity factor). Similarly, Doddy Clarke et al. ( 2021 ) analyzed wind power generation in the Irish region offshore and onshore under Representative Concentration Pathways-4.5 and Representative Concentration Pathways-8.5 scenarios for 2041–2060 and 2081–2100, respectively. The research results also demonstrate an overall reduction in wind energy (less than 2%) in future climate scenarios. From a seasonal perspective, wind energy is expected to decrease by approximately 6% in the summer and increase slightly by 1.1% in winter. At the same time, under the scenarios that consider greenhouse gas emissions and land use; precisely, the Shared Socioeconomic Pathways-8.5 (intensive emissions) and Shared Socioeconomic Pathways-4.5 (moderate emissions) scenarios, onshore wind energy resources in North America and Canada are expected to decrease. In particular, under the Shared Socioeconomic Pathways-8.5 scenario, wind generation intensity reduces by an overall 15% and up to 40%, respectively in northern regions such as Quebec and Nunavut in Canada and Alaska in the USA (Martinez and Iglesias, 2022 ).

Russo et al. ( 2022 ) estimated the influence of climate change on the future of wind energy generation. The authors found a 20% variation up to 2030, a 40% variation from 2040 to 2060, and a 100% variation from 2070 to 2100. Regionally, South America will be the most vulnerable to climate change, with a 60% expected variation from 2040 to 2060, contrary to Europe, which is more stable. The results in this section show that climate change has a negative impact on wind energy. With the increase in the climate change and severe weather problems, several countries and regions worldwide would have a continuous trend of decreasing wind energy production.

Impact on solar energy

As solar energy becomes an increasingly important renewable energy source in the future, so it is crucial to investigate the effect of climate change on solar energy's spatial and temporal variability. Oka et al. ( 2020 ) analyzed the effect of future climate change on solar energy in Fukushima Prefecture, Japan, under three representative concentration pathways and seven global climate models. The investigation results showed that photovoltaic power generation is expected to increase under all scenarios (2030, 2050, and 2070) with average annual growth rates of 1.7%, 3.9%, and 4.9%, respectively. Meanwhile, Gil et al. ( 2018 ) used a high-resolution model to generate regionalized scenarios of climate change in Spain to study the future solar radiation resource changes in the Iberian Peninsula. The scenario analysis revealed that future solar irradiance would increase, and the solar resource quality is anticipated to improve. Russo et al. ( 2022 ) modeled a maximum of 20% variation in solar energy worldwide from 2070 to 2100. The authors emphasized that solar is the least affected energy source by climate change.

Similarly, using data from three different downscaled global climate models, de Jong et al. ( 2019 ) predicted that surface solar radiation is expected to increase over most of Brazil between 2070 and 2080 period compared to the end of the twentieth century, with a possible average increase of 3.6% in the northeastern region of Brazil. In contrast, by the end of the century, the annual average solar potential is expected to decline by an average of 4% over much of the African continent and 6% in the Horn of Africa as a direct result of decreasing solar radiation and increasing air surface temperatures, as found through the high-resolution climate experiments (Bichet et al., 2019 ). Losada Carreño et al. ( 2020 ) found that as a result of climate change, direct normal irradiance, global horizontal irradiance, and surface air temperature in Texas increased by 5%, 4%, and 10%, respectively; these changes resulted in an increase in the solar capacity factor from -0.6% to + 2.5% for the entire state of Texas. As a result, the solar capacity factor tends to increase in regions with insufficient solar resources, while it tends to decrease in regions with abundant solar resources.

This section specifies that the effects of climate change would generally boost photovoltaic power generation, but there are some areas where solar energy becomes weaker. The research found that solar energy generation is increasing in regions with initially insufficient solar resources, while it is decreasing in regions with abundant solar resources. Therefore, the global impact of climate change on solar energy is predominantly positive, except for a few locations where solar power was originally abundant.

Impact on biomass energy

Changes in rainfall patterns, temperature, carbon dioxide levels, drought, and air moisture caused by climate change affect biomass productivity, growth, chemical composition, and soil microbial communities (Freitas et al., 2021 ), thus affecting biomass energy potential. Therefore, the application of biomass energy is directly determined by the impact of climate change on biodiversity. Nunez et al. ( 2019 ) found that the fraction of remaining species and the fraction of remaining area would decrease significantly by 14% to 35% during a global average temperature increase of 1 °C to 2 °C, representing the extinction of many species and thus the scarcity of biomass energy. It is anticipated that climate change will impact all levels of biodiversity, from species to biome, and that continued warming on a global scale coupled with more frequent extreme weather events will put more pressure on all organisms on Earth (Habibullah et al., 2022 ; Sintayehu, 2018 ). Under climate change, lignocellulosic biorefineries can be markedly affected, as shown in Fig.  3 .

Impact of climate change on biomass. Climate change can have a greater impact on biomass yields. In addition, climate change may negatively impact the carbohydrate–fiber structure of biomass, alter the protein and nutrient content, and negatively impact the food and bioenergy uses of crops. Reduced biomass yields and traits increase the use of chemical fertilizers, resulting in environmental pollution

Abiotic stressors and climate change substantially impact cellulosic ethanol yields and other value-added biorefineries by reducing the availability and yield of biomass, such as energy crops or agricultural residues, and by altering the metabolic pathways of plants (Freitas et al., 2021 ). Zhao et al. ( 2017 ) found that a one-degree Celsius increase in temperature could reduce global wheat yields by 6.0%, maize by 7.4%, rice by 3.2%, and soybean by 3.1%. The combined stresses of high temperature and drought decreased maize and wheat photosynthesis rates, leaf, and plant length, total dry weight, and eventually plant yields (Hussain et al., 2019 ; Sattar et al., 2020 ). Climate change negatively impacts plant growth and yield, affecting bioenergy potential and food supply.

This section explains that climate change has a negative impact on biomass due to the fact that climate change issues and extreme weather can devastate certain organisms and thus reduce biodiversity. Moreover, biodiversity may restrict the use of biomass, so climate change indirectly has a negative impact on biomass.

Impact on hydropower energy

Hydropower is an essential renewable energy source, but hydropower may be negatively impacted by climate-related changes in hydrological conditions, such as river flow and reservoir storage. Liu et al. ( 2016 ) used 8 global hydrological model simulations under climate scenario data for Representative Concentration Pathways-2.5 and Representative Concentration Pathways-8.5 to predict the future changes in gross hydropower potential and developed hydropower potential in China. The results of the study indicate that the developed hydropower potential would decrease From −2.2% to −5.4% (0.7–1.7% of the total installed hydropower capacity) in 2020–2050 and from −1.3% to −4% (0.4−1.3% of the total installed hydropower capacity) in 2070–2099. Meanwhile, by investigating Representative Concentration Pathways-2.6, Representative Concentration Pathways-4.5, and Representative Concentration Pathways-8.5 conditions, Guo et al. ( 2021 ) found that the near-term hydroelectric power generation decreased by 10.981 megawatts, 12.933 megawatts, and 14.765 megawatts, respectively, and the long-term hydroelectric power generation decreased by 21.922 megawatts, 23.649 megawatts, and 26.742 megawatts, respectively. Similarly, Teotónio et al. ( 2017 ) found a potential 41% reduction in hydropower generation in 2050 by assessing the impact of climate change on the Portuguese hydroelectric system.

Precipitation and ambient temperature variations impact hydropower generations (Mello et al., 2021 ; Turner et al., 2017 ). Changes in the runoff, rainfall, streamflow frequency, and extended are among the factors affecting hydropower power production (de Jong et al., 2021 ; Solaun and Cerdá, 2019 ; Yalew et al., 2020 ). Russo et al. ( 2022 ) estimated that global variations in hydropower potential would fall within − 5% to 5%, with the highest effect being mid-to-long term.

This section focuses on the impact that climate change can have on hydroelectric power. Numerous simulation studies have demonstrated that the future efficiency of hydropower energy in many nations will decrease, with a maximum reduction of 41% in hydropower generation.

Impact on geothermal energy

Geothermal energy exists as heat in the interior of the earth, and the source of this heat is related to the internal structure and physical processes that occur there. Geothermal energy is, therefore, primarily influenced by the structure of the earth's crust. Hence, Adaramola ( 2017 ) elaborates on the advantages of geothermal energy in providing base-load power for daily human life, regardless of seasonal problems or climate change. Thus, geothermal energy can supplement intermittently generated renewable energy sources (such as wind or solar). Geothermal resources are typically located several kilometers underground (Adaramola, 2017 ). Meanwhile, the World Energy Assessment, the United Nations Development Programme, the United Nations Development in Economic and Social Affairs, and the World Energy Council have worked together to demonstrate that geothermal energy has the greatest potential value among all renewable energy sources. However, geothermal power development lags significantly behind wind and solar photovoltaic power at the present time (Adaramola, 2017 ).

This section highlighted that geothermal energy will not be affected by climate change, as it is primarily influenced by the structure of the earth's crust and the physical processes within the earth's interior.

Impact of renewable energies on the environment

According to the World Health Organization, nearly 99% of the world's population breathes unhealthy air, and more than 13 million people die annually from preventable environmental causes, including air pollution (World Health Organization, 2022 ). Primarily, the combustion of fossil fuels generates fine particulate matter and nitrogen dioxide. In 2018, air pollution from fossil fuels caused daily health and economic losses of approximately $8 billion (United Nations a, 2018 ). Switching to renewable energy sources, such as solar and wind, aids in combating climate change, air pollution, and health problems. Therefore, Table 4 analyzes the positive and negative environmental effects of increasing renewable energy use in various regions.

Increasing environmental degradation and climate instability effectively force the global community to reduce carbon emissions and, as a result, reduce its impact on climate change. Renewable energy sources are one method for combating climate change, which belongs to conventional mitigation technologies. In Egypt, Nassar et al. ( 2019 ) have shown that if renewable energy is used as a permanent energy source, by the end of 2022, rocket launchers will reduce carbon dioxide emissions to 46,405 × 10 3 tons of carbon dioxide, generating a price of $433,427.6 × 10 3 based on certified emission reduction return and fuel savings would amount to 19,066 kilotons. Furthermore, according to the analysis of the environmental impact of the use of renewable energy in each country in Table 4 , we find that the use of renewable energy in BRICS (Brazil, Russia, India, China and South Africa), Europe, the USA, and Japan has a positive impact on the environment, i.e., a reduction in carbon dioxide emissions over the whole life cycle, thus reducing global warming and contributing to sustainable development. In contrast, Table 4 reveals an exponential increase in total carbon emissions after installing renewable energy systems in some remote regions of India. Although studies have shown that renewable energy in remote areas can improve the quality of life of local villagers and create employment opportunities, the increased carbon dioxide emissions have a negative effect on the environment. As given in Table 4 , the majority of studies conducted since 2016 indicate that the use of renewable energy has a positive impact on the environment, which may be a result of the concerted global effort to develop and use renewable energy since the 2015 Paris Agreement to achieve a controlled global temperature rise of 1.5 °C -2 °C. Therefore, in the future, renewable energy sources such as solar, wind, and biomass will also need to be improved.

On the other hand, Rahman et al. ( 2022 ) reviewed all the environmental impacts of each type of renewable source, as shown in Table 5 . The authors classified the consequences into several classes, including air, soil, water, human-related, and miscellaneous concerns. In terms of air impacts, hydroelectric power plants are primarily responsible for changes in temperature and precipitation caused by greenhouse gas emissions. Solar photovoltaics and concentrated solar power also generate greenhouse gas emissions and ozone depletion. Except for biomass energy, all renewable sources impact nature in aquatic environments. Particularly, hydropower caused eutrophication and an increase in suspended sediments. In addition to drying out rivers, altering lagoons and deltas, causing floods, and altering water temperature and oxygen levels, hydropower plants have an impact on ecosystems. The submerged power plants frequently hinder the movement of sailing vessels and disrupt the defense of the coastline. In conclusion, hydroelectric has the greatest impact on the aquatic environment, while geothermal plants and biomass have the least.

A hydroelectric power plant poses a threat to soil, specifically by causing soil desiccation and soil erosion. The hydropower generated by a dam may cause rivers downstream to dry up, causing soil degradation and further affecting vegetation and local communities. Large land areas are also required for biomass, solar, wind, and hydropower, impacting land use for agricultural purposes. Long-term land use diminishes their effectiveness and fertility, affecting wildlife and the demand for deforestation. Moreover, many power plants contribute to air and soil pollution during the installation, maintenance, and removal phases. Hydropower plants cause extreme land impacts.

Some renewable plants are disruptive to animals and people. Except for solar photovoltaics, which is noiseless during operation, almost all power plants produce noise during installation, operation, and maintenance. Wind turbines and concentrating solar power generate visual effects while floating oceanic types can hinder the movement of aircraft and sea transport. The resettlement of the resident is an additional concern. In general, hydropower and geothermal power plants impact human health most.

This section examines the impact of renewable energy sources on the environment. The study demonstrates that using renewable energy in most regions and nations positively affects the environment by directly reducing carbon dioxide emissions. However, renewable energy in some remote regions may have adverse environmental impact. To summarize, renewable energy is environmentally friendly and can contribute to sustainable development in the world.

Economic impact of renewable energy

In 2020, the fossil fuel industry was subsidized to $5.9 trillion, including explicit subsidies, tax exemptions, and unaccounted for health and environmental losses (Yale Environment, 2021 ). By 2030, approximately $4 trillion per year must be spent on renewable energy, including expenditures on technology and infrastructure, to achieve net-zero carbon emissions (International Energy Agency, 2021 ). The initial cost may be challenging for many nations with limited resources, and many will require financial and technical assistance to complete the transition. However, renewable energy investments will be profitable. Reducing pollution and climate impacts could save the world up to $4.2 trillion annually by 2030 (United Nations b, 2020 ). In addition, efficient, dependable renewable technologies may establish a system that is less susceptible to market shocks and increase energy resilience and security by diversifying power supply options. Utilizing renewable energy contributes to economic growth, generates millions of jobs, and improves people's quality of life. Consequently, Fig.  4 examines renewable energy investment and its impact in several countries.

Renewable energy from an economic point of view. The figure analyzes the impact of renewable energy use from an economic aspect. GDP refers to gross domestic product, and USD refers to the United States dollar. Data from IRENAc ( 2016 )

To achieve deep decarbonization of the energy system, such an investment would have enormous socioeconomic benefits and requires approximately $130 trillion in new investments. The transformation of energy systems could add $98 trillion to global gross domestic product (GDP) between 2016 and 2050 compared to the business-as-usual scenario, nearly triple the employment in the renewable energy industry to $42 million, increase energy efficiency-related employment to $21 million, and increase grid flexibility-related employment to $15 million (IRENAc, 2016 ). According to Fig.  4 , we can observe that Ireland already has a positive impact on gross domestic product from + 0.2% to + 1.3% in 2020 due to the use of renewable energy. In addition, Chile expects renewable energy to contribute + 0.63% to a gross domestic product by 2028, approximately $2.24 billion. Europe, Germany, Japan, Mexico, the UK, and the USA are expected to positively impact the economy by 2030, contributing + 0.46%, + 3%, + 0.9%, + 0.2%, + 0.8%, and + 0.6% to gross domestic product, respectively. Saudi Arabia is expected to generate a + 4% impact on gross domestic product in 2032, approximately $51 billion. Overall, renewable energy positively impacts most countries' economies, with a relatively significant contribution of 4% to Saudi Arabia's gross domestic product and a relatively small impact of 0.2% on Mexico's gross domestic product. The research demonstrates that using renewable energy will contribute to the growth of national economies.

This section examines the economic impact of renewable energy use in several nations. The study demonstrates that using renewable energy will directly increase gross domestic product (GDP) and improve the economy, with the highest expected growth rate of + 4% in Saudi Arabia and the lowest expected growth rate of + 0.2% in Mexico.

Renewable energy and decarbonization by countries

China has made significant advances in the research and development of renewable energy technologies, as evidenced by the consistent growth and improvement of low-speed wind power generation technologies, wind power consumption and grid technologies, and energy storage technologies. China provides approximately two-thirds of the world's solar panels and nearly 50% of the world's wind turbines (Liu, 2019 ). Developing a hydrogen energy system based on a multi-energy complementary system simultaneously increases renewable energy consumption, thereby reducing the negative impact on the grid system (Li et al., 2020 ). The Chinese government has clearly defined the medium- and long-term development goals and directions in terms of geothermal energy. China will continue to promote geothermal heating, geothermal water heating, and underground source heat pump technology to meet environmental and water conservation requirements (Hou et al., 2018 ). India has taken various measures to enhance the use of renewable energy and decarbonization, including improving energy entrepreneurship, democratizing energy trade, allowing private sector participation in energy trade, rationalizing renewable energy procurement, using strict and regulated energy auction procedures, fostering reputable stakeholders, developing and leveraging venture capital, periodically revising tariffs, regulating polluting industries, tracking renewable energy procurement channels in the long term, and incentivizing green energy imports (Thapar et al., 2016 ). The Japanese government has proposed the concept of "benchmark utilization," which requires power companies to fulfill yearly renewable energy development and utilization obligations. Otherwise, the government will be forced to carry out the enterprise’s regular rectification and may even impose a high fine of 1 million yen (Liu, 2019 ).

This section focuses primarily on the development strategies for renewable energy utilization in China, India, and Japan. China has developed specific technologies for low-speed wind power generation, wind power consumption, electricity grid technology, and energy storage. China also adopts geothermal heating, geothermal water heating, and underground source heat pump technologies as significant development directions. India has taken numerous steps, primarily relating to the renewable energy market and decarbonization policy. The Japanese government has implemented the concept of "baseline utilization" in an effort to expand the use of renewable energy.

Nigeria utilizes distributed generation models and smart grids to increase the use of renewable energy and decarbonization. The use of distributed generation will ensure that electricity production is not dependent on a centralized grid that is occasionally disrupted. Connecting distributed generation to the grid creates a smart grid and rationalizes the electrical infrastructure (Ogbonnaya et al., 2019 ). South Africa offers a range of programs for renewable energy manufacturing and funding mechanisms for renewable energy project development, including the establishment of a Green State Fund and a Memorandum of Agreement with the Development Bank of Southern Africa, the Industrial Development Cooperation Green Energy Efficiency Fund to provide loan incentives, registration of renewable energy technologies with the Clean Development Mechanism, and the possibility of generating carbon credits for market-based carbon financing (Msimanga and Sebitosi, 2014 ).

This section examines the implementation of renewable energy strategies in the African countries of Nigeria and South Africa. Nigeria has adopted distributed generation, created a smart grid to increase the use of renewable energy, and optimized the nation's electricity infrastructure. Meanwhile, South Africa offers various renewable energy manufacturing programs and financing mechanisms for renewable energy project development to encourage renewable energy technologies and make solar energy the primary focus of renewable energy technology development.

The government of the UK has adopted distributed energy measures to facilitate the integration of renewable energy into the future grid, thereby reducing energy centralization and removing capacity constraints. In addition, the government has provided additional assistance for the private sector to fully integrate distributed energy sources to reduce the complexity of the financial and energy markets (Raybould et al., 2020 ). Within the UK, the Welsh region has the potential to develop a wide range of marine renewable technologies because of the region’s tidal solid content, high tidal energy areas, and limited space for wave energy resources. The UK government has introduced the Tidal and Wave Energy Demonstration Zone to facilitate importing equipment from companies worldwide with the related technologies (Roche et al., 2016 ). Belgium has the largest scale, composition, and efficiency of public research and development funding invested in European innovation for renewable energy technologies. Green technology research receives 35% of the European Union's total budget of 95.5 billion euros. Belgium has the highest proportion of available public research and development support, at 63%. As a result, Belgium focuses not only on producing renewable energy technologies at the national level but also on the efforts of scientific and technological researchers, allocating a substantial amount of funding to green technology research (Gasser et al., 2022 ).

This section examines renewable energy initiatives by reviewing the UK and Belgium in Europe. The government of the UK has adopted distributed energy measures to reduce energy concentration and make room for renewable energy development. Simultaneously, the UK has been developing marine renewable energy technologies, and the government has established demonstration zones for tidal and wave energy to attract investment in renewable energy technologies. From the national government to frontline researchers, Belgium is committed to developing renewable energy technologies and has received substantial European Union funding for green technology research.

Australia was the first nation to legislate a renewable energy development target in 2001 when Australia enacted a mandatory renewable energy target. Specifically, Australia has widely implemented incentives such as financial subsidies, tax breaks, and credits in numerous areas of renewable energy use, particularly the transportation sector, which has a high energy demand. Grants of up to a maximum of 20,000 Australian dollars and a reduction of 0.38 Australian dollars per liter of ethanol in the federal excise tax are available to E10 ethanol blend operators (Nelson et al., 2013 ). The New Zealand government has adopted an energy efficiency policy and has set a target of 90% renewable energy by 2025. The use of distributed generation technologies, the development of battery storage technologies, and the large-scale use of smart grids and electric vehicles are relevant and practical measures that New Zealand is taking to meet renewable energy targets (Verma et al., 2018 ).

This section examines the actions taken by Australia and New Zealand in Oceania to promote renewable energy development. Australia has implemented numerous incentives, including financial subsidies, tax breaks, and credits, to encourage the growth of the renewable energy sector. In the meantime, New Zealand has developed energy efficiency policies and promoted the use of distributed generation technologies, the development of battery storage technologies, smart grids, and the widespread adoption of electric vehicles.

North and South America

Policymakers in the USA have increased renewable energy production by encouraging industrial output in the industrial sector with tax credits and subsidies. In addition, policymakers have protected renewable energy producers by establishing dedicated funds for them and proposing market-specific financing schemes (Jamil et al., 2022 ). The systematic use of energy auctions in Brazil to support public policies has resulted in energy security, improved electricity efficiency, and increased energy supply diversification, particularly for renewable energy. Energy auctions have been incorporated into Brazil's electricity market and can be incorporated into the country's institutional and policy framework (Tolmasquim et al., 2021 ).

This section summarizes the US and Brazilian renewable energy development strategies. In order to support renewable energy businesses, policymakers in the USA have promoted renewable energy production through tax breaks and economic subsidies and have introduced specific financing schemes for renewable energy markets. Systematically, in Brazil, energy auctions have been used to support public policy and promote the diversification of renewable energy supply.

Based on the development of renewable energy and decarbonization strategies for various nations, we have compiled Table 6 as a summary. The survey results indicate that the specific measures for developing renewable energy in each nation are divided into government policy support and research on renewable energy technologies, which can provide guidance for nations that have not yet developed renewable energy use. Reducing taxes on renewable energy can be an effective incentive for companies to expand their renewable energy projects. At the same time, improving renewable energy laws and regulations can better regulate the energy trade market and strengthen the capital injection mechanism. Since each country has a unique geographical location, each nation’s renewable energy advantages vary, and other regions must concentrate on developing renewable energy with inherent advantages.

Here, we reviewed the potential of renewable energy sources in decarbonization policy and the impact of climate change on the expansion of renewable energy sources. About 80% of the world's population resides in net importers of fossil fuels, leaving approximately 6 billion people susceptible to geopolitical shocks and energy crises. In contrast, renewable energy sources are available in all nations, but their full potential is not being realized. By 2050, approximately 90% of the world's energy will come from renewable sources. Excluding geothermal and hydropower-derived energy, renewable energy technology costs have decreased significantly since 2010. In Europe, the cost of solar and wind-generated electricity per kilowatt-hour in 2021 was four to six times less than that of fossil fuels in 2022. Between January and May of 2022, wind and solar generation alone in Europe prevented at least $50 billion in fossil fuel imports. With prices declining, new power supply has a significant portion of the future to supply 65% of the world's total electricity by 2030 and to decarbonize 90% of the electricity industry by 2050, thereby drastically reducing carbon emissions and contributing to climate change mitigation.

Understanding the effects of climate change on producing renewable energy is crucial for achieving a sustainable future. Wind, hydropower, biomass, and geothermal energy were found to have the greatest effects, while solar energy had the least. Long-term climate change has a greater impact than short and medium-term climate variations. In addition, future decarbonization efforts are necessary for expanding and establishing renewables to reduce reliance on fossil fuels, save the environment from pollution and climate change, and reduce dependence on fossil fuels. Future research should emphasize increasing climate model estimates to evaluate the entire energy generation system rather than focusing solely on a single energy source to identify decarbonization strategies.

In this review, the environmental effects of renewable energy sources have also been thoroughly investigated. Consideration is given to all renewable energy sources, including solar, wind, hydropower, geothermal, and biomass. Each renewable energy source has different environmental impacts depending on the renewable energy source type, location, scale, and implementation method. However, these effects can be mitigated through careful choice and utilization of renewable energy sources. Using a building's rooftop, for instance, the impact of solar power on land can be significantly mitigated. Considering the severity of the environment, hydropower plants are the most harmful renewable energy source. Future actions should be taken to prevent hydropower plants and restore typical rivers once dependence on fossil fuels is eliminated. Wind and biomass energy are the most environmentally friendly energy sources.

To achieve net-zero emissions by 2050, renewable energy sources must be established by 2030 at the cost of $4 trillion annually. The initial expense may be prohibitive for many nations, which may require financial and technical assistance to complete the energy transition. However, by achieving net-zero carbon emissions, renewable energy investments will be profitable and could save up to $4.2 trillion annually. Additionally, renewables are less susceptible to market shocks and increase each country's energy security. Understanding the role of renewable energy implementation in all nations to reduce reliance on fossil fuels and mitigate climate change will aid policymakers and decision-makers in promoting the widespread use of renewable energy sources, particularly environmentally friendly ones.

Abbreviations

The levelized cost of energy

International renewable energy agency

Hydropower’s environmental costs analysis model

Environmental life cycle costing

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Acknowledgements

Dr. Ahmed I. Osman and Prof. David W. Rooney wish to acknowledge the support of The Bryden Centre project (Project ID VA5048), which was awarded by The European Union’s INTERREG VA Programme, managed by the Special EU Programmes Body (SEUPB), with match funding provided by the Department for the Economy in Northern Ireland and the Department of Business, Enterprise and Innovation in the Republic of Ireland.

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Ahmed I. Osman and Lin Chen have contributed equally to this work.

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School of Chemistry and Chemical Engineering, David Keir Building, Queen’s University Belfast, Stranmillis Road, Belfast, BT9 5AG, Northern Ireland, UK

Ahmed I. Osman, Samer Fawzy & David W. Rooney

School of Civil Engineering, Chongqing University, Chongqing, 400045, China

School of Materials Science Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China

Mingyu Yang

Department of Civil Engineering, Xi’an Jiaotong-Liverpool University, Suzhou, 215123, China

Goodluck Msigwa & Pow-Seng Yap

Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, 080-8555, Japan

Mohamed Farghali

Department of Animal and Poultry Hygiene & Environmental Sanitation, Faculty of Veterinary Medicine, Assiut University, Assiut, 71526, Egypt

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Osman, A.I., Chen, L., Yang, M. et al. Cost, environmental impact, and resilience of renewable energy under a changing climate: a review. Environ Chem Lett 21 , 741–764 (2023). https://doi.org/10.1007/s10311-022-01532-8

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David Pimentel, Megan Herz, Michele Glickstein, Mathew Zimmerman, Richard Allen, Katrina Becker, Jeff Evans, Benita Hussain, Ryan Sarsfeld, Anat Grosfeld, Thomas Seidel, Renewable Energy: Current and Potential Issues: Renewable energy technologies could, if developed and implemented, provide nearly 50% of US energy needs; this would require about 17% of US land resources, BioScience , Volume 52, Issue 12, December 2002, Pages 1111–1120, https://doi.org/10.1641/0006-3568(2002)052[1111:RECAPI]2.0.CO;2

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The United States faces energy shortages and increasing energy prices within the next few decades ( Duncan 2001 ). Coal, petroleum, natural gas, and other mined fuels provide 75% of US electricity and 93% of other US energy needs ( USBC 2001 ). On average, every year each American uses about 93,000 kilowatt-hours (kWh), equivalent to 8000 liters of oil, for all purposes, including transportation, heating, and cooling ( USBC 2001 ). About 12 kWh (one liter of gasoline) costs as much as $0.50, and this cost is projected to increase significantly in the next decade ( Schumer 2001 ).

The United States, having consumed from 82% to 88% of its proved oil reserves ( API 1999 ), now imports more than 60% of its oil at an annual cost of approximately $75 billion ( USBC 2001 ). General production, import, and consumption trends and forecasts suggest that within 20 years the United States will be importing from 80% to 90% of its oil. The US population of more than 285 million is growing each year, and the 3.6 trillion kWh of electricity produced annually at a cost of $0.07 to $0.20 per kWh are becoming insufficient for the country's current needs. As energy becomes more scarce and more expensive, the future contribution of renewable energy sources will be vital ( USBC 2001 ).

Fossil fuel consumption is the major contributor to the increasing concentration of carbon dioxide (CO 2 ) in the atmosphere, a key cause of global warming ( Schneider et al. 2000 ). Global warming reduces agricultural production and causes other biological and social problems ( Schneider et al. 2000 ). The United States, with less than 4% of the world population, emits 22% of the CO 2 from burning fossil fuels, more than any other nation. Reducing fossil fuel consumption may slow the rate of global warming ( Schneider et al. 2000 ).

Diverse renewable energy sources currently provide only about 8% of US needs and about 14% of world needs (table 1) , although the development and use of renewable energy is expected to increase as fossil fuel supplies decline. Several different technologies are projected to provide the United States most of its renewable energy in the future: hydroelectric systems, biomass, wind power, solar thermal systems, photovoltaic systems, passive energy systems, geothermal systems, biogas, ethanol, methanol, and vegetable oil. In this article, we assess the potential of these various renewable energy technologies for supplying the future needs of the United States and the world in terms of land requirements, environmental benefits and risks, and energetic and economic costs.

Hydroelectric systems

Hydropower contributes significantly to world energy, providing 6.5% of the supply (table 1) . In the United States, hydroelectric plants produce approximately 989 billion kWh (1 kWh = 860 kilocalories [kcal] = 3.6 megajoules), or 11% of the nation's electricity, each year at a cost of $0.02 per kWh ( table 2 ; USBC 2001 ). Development and rehabilitation of existing dams in the United States could produce an additional 60 billion kWh per year (table 3) .

Hydroelectric plants, however, require considerable land for their water storage reservoirs. An average of 75,000 hectares (ha) of reservoir land area and 14 trillion liters of water are required per 1 billion kWh per year produced ( table 2 ; Pimentel et al. 1994 , Gleick and Adams 2000 ). Based on regional estimates of US land use and average annual energy generation, reservoirs currently cover approximately 26 million ha of the total 917 million ha of land area in the United States ( Pimentel 2001 ). To develop the remaining best candidate sites, assuming land requirements similar to those in past developments, an additional 17 million ha of land would be required for water storage (table 3) .

Despite the benefits of hydroelectric power, the plants cause major environmental problems. The impounded water frequently covers valuable, agriculturally productive, alluvial bottomland. Furthermore, dams alter the existing plants, animals, and microbes in the ecosystem ( Ligon et al. 1995 , Nilsson and Berggren 2000 ). Fish species may significantly decline in river systems because of these numerous ecological changes ( Brown and Moyle 1993 ). Within the reservoirs, fluctuations of water levels alter shorelines, cause downstream erosion, change physiochemical factors such as water temperature and chemicals, and affect aquatic communities. Sediments build up behind the dams, reducing their effectiveness and creating another major environmental problem.

Biomass energy systems

Although most biomass is burned for cooking and heating, it can also be converted into electricity. Under sustainable forest conditions in both temperate and tropical ecosystems, approximately 3 dry metric tons (t) per ha per year of woody biomass can be harvested sustainably ( Birdsey 1992 , Repetto 1992 , Trainer 1995 , Ferguson 2001 ). Although this amount of woody biomass has a gross energy yield of 13.5 million kcal, approximately 33 liters of diesel fuel per ha, plus the embodied energy, are expended for cutting and collecting the wood for transport to an electric power plant. Thus, the energy input–output ratio for such a system is calculated to be 1:22.

The cost of producing 1 kWh of electricity from woody biomass is about $0.058, which is competitive with other systems for electricity production (table 2) . Approximately 3 kWh of thermal energy is expended to produce 1 kWh of electricity, an energy input–output ratio of 1:7 ( table 2 ; Pimentel 2001 ).

Per capita consumption of woody biomass for heat in the United States amounts to 625 kilograms (kg) per year. In developing nations, use of diverse biomass resources (wood, crop residues, and dung) ranges from 630 kg per capita ( Kitani 1999 ) to approximately 1000 kg per capita ( Hall 1992 ). Developing countries use only about 500 liters of oil equivalents of fossil energy per capita, compared with nearly 8000 liters of oil equivalents of fossil energy used per capita in the United States.

Woody biomass could supply the United States with about 1.5 × 10 12 kWh (5 quads thermal equivalent) of its total gross energy supply by the year 2050, provided that approximately 102 million ha were available (table 3) . A city of 100,000 people using the biomass from a sustainable forest (3 t per ha per year) for electricity would require approximately 200,000 ha of forest area, based on an average electrical demand of slightly more than 1 billion kWh (electrical energy [e]) (860 kcal = 1 kWh) (table 2) .

The environmental effects of burning biomass are less harmful than those associated with coal, but more harmful than those associated with natural gas ( Pimentel 2001 ). Biomass combustion releases more than 200 different chemical pollutants, including 14 carcinogens and 4 cocarcinogens, into the atmosphere ( Alfheim and Ramdahl 1986 , Godish 1991 ). Globally, but especially in developing nations where people cook with fuelwood over open fires, approximately four billion people suffer from continuous exposure to smoke ( World Bank 1992 , WHO/UNEP 1993 , Reddy et al. 1997 ). In the United States, wood smoke kills 30,000 people each year ( EPA 2002 ). However, the pollutants from electric plants that use wood and other biomass can be controlled.

For many centuries, wind power has provided energy to pump water and to run mills and other machines. Today, turbines with a capacity of at least 500 kW produce most commercially wind-generated electricity. Operating at an ideal location, one of these turbines can run at maximum 30% efficiency and yield an energy output of 1.3 million kWh (e) per year ( AWEA 2000a ). An initial investment of approximately $500,000 for a 500 kW capacity turbine ( Nelson 1996 ), operating at 30% efficiency, will yield an input–output ratio of 1:5 over 30 years of operation (table 2) . During the 30-year life of the system, the annual operating costs amount to $40,500 ( Nelson 1996 ). The estimated cost of electricity generated is $0.07 per kWh (e) (table 2) .

In the United States, 2502 megawatts (MW) of installed wind generators produce about 6.6 billion kWh of electrical energy per year ( Chambers 2000 ). The American Wind Energy Association ( AWEA 2000b ) estimates that the United States could support a capacity of 30,000 MW by the year 2010, producing 75 billion kWh (e) per year at a capacity of 30%, or approximately 2% of the annual US electrical consumption. If all economically feasible land sites were developed, the full potential of wind power would be about 675 billion kWh (e) ( AWEA 2000b ). Offshore sites could provide an additional 102 billion kWh (e) ( Gaudiosi 1996 ), making the total estimated potential of wind power 777 billion kWh (e), or 23% of current electrical use.

Widespread development of wind power is limited by the availability of sites with sufficient wind (at least 20 kilometers [km] per hour) and the number of wind machines that the site can accommodate. In California's Altamont Pass Wind Resource Area, an average of one 50 kW turbine per 1.8 ha allows sufficient spacing to produce maximum power ( Smith and Ilyin 1991 ). Based on this figure, approximately 13,700 ha of land is needed to supply 1 billion kWh per year (table 2) . Because the turbines themselves occupy only approximately 2% of the area, most of the land can be used for vegetables, nursery stock, and cattle ( DP Energy 2002 , NRC 2002 ). However, it may be impractical to produce corn or other grains because the heavy equipment used in this type of farming could not operate easily between the turbines.

An investigation of the environmental impacts of wind energy production reveals a few hazards. Locating the wind turbines in or near the flyways of migrating birds and wildlife refuges may result in birds colliding with the supporting towers and rotating blades ( Kellet 1990 ). For this reason, Clarke (1991) suggests that wind farms be located at least 300 meters (m) from nature reserves to reduce the risk to birds. The estimated 13,000 wind turbines installed in the United States have killed fewer than 300 birds per year ( Kerlinger 2000 ). Proper siting and improved repellant technology, such as strobe lights or paint patterns, might further reduce the number of birds killed.

The rotating magnets in the turbine electrical generator produce a low level of electromagnetic interference that can affect television and radio signals within 2 to 3 km of large installations ( IEA 1987 ). Fortunately, with the widespread use of cable networks or line-of-sight microwave satellite transmission, both television and radio are unaffected by this interference.

The noise caused by rotating blades is another unavoidable side effect of wind turbine operation. Beyond 2.1 km, however, the largest turbines are inaudible even downwind. At a distance of 400 m, the noise level is about 56 decibels ( IEA 1987 ), corresponding roughly to the noise level of a home air-conditioning unit.

Solar thermal conversion systems

Solar thermal energy systems collect the sun's radiant energy and convert it into heat. This heat can be used directly for household and industrial purposes or to produce steam to drive turbines that produce electricity. These systems range in complexity from solar ponds to electricity-generating parabolic troughs. In the material that follows, we convert thermal energy into electricity to facilitate comparison with other solar energy technologies.

Solar ponds.

Solar ponds are used to capture radiation and store the energy at temperatures of nearly 100 degrees Celsius (°C). Constructed ponds can be made into solar ponds by creating a layered salt concentration gradient. The layers prevent natural convection, trapping the heat collected from solar radiation in the bottom layer of brine. The hot brine from the bottom of the pond is piped out to use for heat, for generating electricity, or both.

For successful operation of a solar pond, the salt concentration gradient and the water level must be maintained. A solar pond covering 4000 ha loses approximately 3 billion liters of water per year (750,000 liters per ha per year) under arid conditions ( Tabor and Doran 1990 ). The solar ponds in Israel have been closed because of such problems. To counteract the water loss and the upward diffusion of salt in the ponds, the dilute salt water at the surface of the ponds has to be replaced with fresh water and salt added to the lower layer.

The efficiency of solar ponds in converting solar radiation into heat is estimated to be approximately 1:4 (that is, 1 kWh of input provides 4 kWh of output), assuming a 30-year life for the solar pond (table 2) . Electricity produced by a 100 ha (1 km 2 ) solar pond costs approximately $0.15 per kWh ( Kishore 1993 ).

Some hazards are associated with solar ponds, but most can be avoided with careful management. It is essential to use plastic liners to make the ponds leakproof and prevent contamination of the adjacent soil and groundwater with salt. The degradation of soil quality caused by sodium chloride can be avoided by using an ammonium salt fertilizer ( Hull 1986 ). Burrowing animals must be kept away from the ponds by buried screening ( Dickson and Yates 1983 ).

Parabolic troughs.

Another solar thermal technology that concentrates solar radiation for large-scale energy production is the parabolic trough. A parabolic trough, shaped like the bottom half of a large drainpipe, reflects sunlight to a central receiver tube that runs above it. Pressurized water and other fluids are heated in the tube and used to generate steam, which can drive turbogenerators for electricity production or provide heat energy for industry.

Parabolic troughs that have entered the commercial market have the potential for efficient electricity production because they can achieve high turbine inlet temperatures ( Winter et al. 1991 ). Assuming peak efficiency and favorable sunlight conditions, the land requirements for the central receiver technology are approximately 1100 ha per 1 billion kWh per year (table 2) . The energy input–output ratio is calculated to be 1:5 (table 2) . Solar thermal receivers are estimated to produce electricity at a cost of approximately $0.07 to $0.09 per kWh ( DOE/EREN 2001 ).

The potential environmental impacts of solar thermal receivers include the accidental or emergency release of toxic chemicals used in the heat transfer system ( Baechler and Lee 1991 ). Water scarcity can also be a problem in arid regions.

Photovoltaic systems

Photovoltaic cells have the potential to provide a significant portion of future US and world electrical energy ( Gregory et al. 1997 ). Photovoltaic cells produce electricity when sunlight excites electrons in the cells. The most promising photovoltaic cells in terms of cost, mass production, and relatively high efficiency are those manufactured using silicon. Because the size of the unit is flexible and adaptable, photovoltaic cells can be used in homes, industries, and utilities.

However, photovoltaic cells need improvements to make them economically competitive before their use can become widespread. Test cells have reached efficiencies ranging from 20% to 25% ( Sorensen 2000 ), but the durability of photovoltaic cells must be lengthened and production costs reduced several times to make their use economically feasible.

Production of electricity from photovoltaic cells currently costs $0.12 to $0.20 per kWh ( DOE 2000 ). Using mass-produced photovoltaic cells with about 18% efficiency, 1 billion kWh per year of electricity could be produced on approximately 2800 ha of land, which is sufficient to supply the electrical energy needs of 100,000 people ( table 2 ; DOE 2001 ). Locating the photovoltaic cells on the roofs of homes, industries, and other buildings would reduce the need for additional land by an estimated 20% and reduce transmission costs. However, because storage systems such as batteries cannot store energy for extended periods, photovoltaics require conventional backup systems.

The energy input for making the structural materials of a photovoltaic system capable of delivering 1 billion kWh during a life of 30 years is calculated to be approximately 143 million kWh. Thus, the energy input–output ratio for the modules is about 1:7 ( table 2 ; Knapp and Jester 2000 ).

The major environmental problem associated with photovoltaic systems is the use of toxic chemicals, such as cadmium sulfide and gallium arsenide, in their manufacture ( Bradley 1997 ). Because these chemicals are highly toxic and persist in the environment for centuries, disposal and recycling of the materials in inoperative cells could become a major problem.

Hydrogen and fuel cells

Using solar electric technologies for its production, gaseous hydrogen produced by the electrolysis of water has the potential to serve as a renewable fuel to power vehicles and generate electricity. In addition, hydrogen can be used as an energy storage system for various electric solar energy technologies ( Winter and Nitsch 1988 , MacKenzie 1994 ).

The material and energy inputs for a hydrogen production facility are primarily those needed to build and run a solar electric production facility, like photovoltaics and hydropower. The energy required to produce 1 billion kWh of hydrogen is 1.4 billion kWh of electricity ( Ogden and Nitsch 1993 , Kreutz and Ogden 2000 ). Photovoltaic cells (table 2) currently require 2800 ha per 1 billion kWh; therefore, a total of 3920 ha would be needed to supply the equivalent of 1 billion kWh of hydrogen fuel. The water required for electrolytic production of 1 billion kWh per year equivalent of hydrogen is approximately 300 million liters per year ( Voigt 1984 ). On a per capita basis, this amounts to 3000 liters of water per year. The liquefaction of hydrogen requires significant energy inputs because the hydrogen must be cooled to about −253°C and pressurized. About 30% of the hydrogen energy is required for the liquefaction process ( Peschka 1992 , Trainer 1995 ).

Liquid hydrogen fuel occupies about three times the volume of an energy equivalent of gasoline. Storing 25 kg of gasoline requires a tank weighing 17 kg, whereas storing 9.5 kg of hydrogen requires a tank weighing 55 kg ( Peschka 1987 , 1992 ). Although the hydrogen storage vessel is large, hydrogen burns 1.33 times more efficiently than gasoline in automobiles ( Bockris and Wass 1988 ). In tests, a Plymouth liquid hydrogen vehicle, with a tank weighing about 90 kg and 144 liters of liquid hydrogen, has a cruising range in traffic of 480 km with a fuel efficiency of 3.3 km per liter ( MacKenzie 1994 ). However, even taking into account its greater fuel efficiency, commercial hydrogen is more expensive at present than gasoline. About 3.7 kg of gasoline sells for about $1.20, whereas 1 kg of liquid hydrogen with the same energy equivalent sells for about $2.70 ( Ecoglobe 2001 ).

Fuel cells using hydrogen are an environmentally clean, quiet, and efficient method of generating electricity and heat from natural gas and other fuels. Fuel cells are electrochemical devices, much like storage batteries, that use energy from the chemical synthesis of water to produce electricity. The fuel cell provides a way to burn hydrogen using oxygen, capturing the electrical energy released ( Larminie and Dicks 2000 ). Stored hydrogen is fed into a fuel cell apparatus along with oxygen from the atmosphere, producing effective electrical energy ( Larminie and Dicks 2000 ). The conversion of hydrogen into direct current (DC) using a fuel cell is about 40% efficient.

The major costs of fuel cells are the electrolytes, catalysts, and storage. Phosphoric acid fuel cells (PAFCs) and proton exchange membrane fuel cells (PEMs) are the most widely used and most efficient. PAFCs have an efficiency of 40% to 45%, compared to diesel engine efficiency of 36% to 39%. However, PAFCs are complex and have high costs because they operate at temperatures of 50° to 100°C ( DOE 1999 ). A fuel cell PEM engine costs $500 per kW, compared to $50 per kW for a gasoline engine ( DOE 1999 ), leading to a total price of approximately $100,000 for an automobile running on fuel cells ( Ogden and Nitsch 1993 ). These prices are for specially built vehicles, and the costs should decline as they are mass-produced. There is high demand for fuel cell–equipped vehicles in the United States ( Larminie and Dicks 2000 ).

Hydrogen has serious explosive risks because it is difficult to contain within steel tanks. Mixing with oxygen can result in intense flames because hydrogen burns more quickly than gasoline and diesel fuels ( Peschka 1992 ). Other environmental impacts are associated with the solar electric technologies used in hydrogen production. Water for the production of hydrogen may be a problem in arid regions of the United States and the world.

Passive heating and cooling of buildings

Approximately 20% (5.5 kWh × 10 12 [19 quads]) of the fossil energy used each year in the United States is used for heating and cooling buildings and for heating hot water ( USBC 2001 ). At present only about 0.3 quads of energy are being saved by technologies that employ passive and active solar heating and cooling of buildings (table 3) , which means that the potential for energy savings through increased energy efficiency and through the use of solar technologies for buildings is tremendous. Estimates suggest that the amount of energy lost through poorly insulated windows and doors is approximately 1.1 × 10 12 kWh (3.8 quads) each year—the approximate energy equivalent of all the oil pumped in Alaska per year ( EETD 2001 ).

Both new and established homes can be fitted with solar heating and cooling systems. Installing passive solar systems in new homes is less costly than retrofitting existing homes. Based on the cost of construction and the amount of energy saved, measured in terms of reduced heating and cooling costs over 10 years, the estimated returns of passive solar heating and cooling range from $0.02 to $0.10 per kWh ( Balcomb 1992 ).

Improvements in passive solar technology are making it more effective and less expensive than in the past ( Bilgen 2000 ). Current research in window design focuses on the development of “superwindows” with high insulating values and “smart” or electrochromic windows that can respond to electric current, temperature, or sunlight to control the admission of light energy ( Roos and Karlsson 1994 , DOE 2000 ).

Although none of the passive heating and cooling technologies requires land, they are not without problems. Some indirect problems with land use may arise, concerning such issues as tree removal, shading, and rights to the sun ( Simpson and McPherson 1998 ). Glare from collectors and glazing may create hazards to automobile drivers and airline pilots. Also, when houses are designed to be extremely energy efficient and airtight, indoor air quality becomes a concern because of indoor air pollutants. However, well-designed ventilation systems with heat exchangers can take care of this problem.

Geothermal systems

Geothermal energy uses natural heat present in Earth's interior. Examples are geysers and hot springs, like those at Yellowstone National Park in the United States. Geothermal energy sources are divided into three categories: hydrothermal, geopressured–geothermal, and hot dry rock. The hydrothermal system is the simplest and most commonly used one for electricity generation. The boiling liquid underground is utilized through wells, high internal pressure drives, or pumps. In the United States, nearly 3000 MW of installed electric generation comes from hydrothermal resources, and this figure is projected to increase by 1500 MW within the next 20 years ( DOE/EIA 1991 , 2001 ).

Most of the geothermal sites for electrical generation are located in California, Nevada, and Utah ( DOE/EIA 1991 ). Electrical generation costs for geothermal plants in the West range from $0.06 to $0.30 per kWh ( Gawlik and Kutscher 2000 ), suggesting that this technology offers potential to produce electricity economically. The US Department of Energy and the Energy Information Administration ( DOE/EIA 1991 , 2001 ) project that geothermal electric generation may grow three- to fourfold during the next 20 to 40 years. However, other investigations are not as optimistic and, in fact, suggest that geothermal energy systems are not renewable because the sources tend to decline over 40 to 100 years ( Bradley 1997 , Youngquist 1997 , Cassedy 2000 ). Existing drilling opportunities for geothermal resources are limited to a few sites in the United States and the world ( Youngquist 1997 ).

Potential environmental problems with geothermal energy include water shortages, air pollution, waste effluent disposal, subsidence, and noise ( DOE/EIA 1991 ). The wastes produced in the sludge include toxic metals such as arsenic, boron, lead, mercury, radon, and vanadium ( DOE/EIA 1991 ). Water shortages are an important limitation in some regions ( OECD 1998 ). Geothermal systems produce hydrogen sulfide, a potential air pollutant; however, this product could be processed and removed for use in industry ( Bradley 1997 ). Overall, the environmental costs of geothermal energy appear to be minimal relative to those of fossil fuel systems.

Wet biomass materials can be converted effectively into usable energy with anaerobic microbes. In the United States, livestock dung is normally gravity fed or intermittently pumped through a plug-flow digester, which is a long, lined, insulated pit in the earth. Bacteria break down volatile solids in the manure and convert them into methane gas (65%) and carbon dioxide (35%) ( Pimentel 2001 ). A flexible liner stretches over the pit and collects the biogas, inflating like a balloon. The biogas may be used to heat the digester, to heat farm buildings, or to produce electricity. A large facility capable of processing the dung from 500 cows costs nearly $300,000 ( EPA 2000 ). The Environmental Protection Agency ( EPA 2000 ) estimates that more than 2000 digesters could be economically installed in the United States.

The amount of biogas produced is determined by the temperature of the system, the microbes present, the volatile solids content of the feedstock, and the retention time. A plug-flow digester with an average manure retention time of about 16 days under winter conditions (−17.4°C) produced 452,000 kcal per day and used 262,000 kcal per day to heat the digester to 35°C ( Jewell et al. 1980 ). Using the same digester during summer conditions (15.6°C) but reducing the retention time to 10.4 days, the yield in biogas was 524,000 kcal per day, with 157,000 kcal per day used for heating the digester ( Jewell et al. 1980 ). The energy input–output ratios for the digester in these winter and summer conditions were 1:1.7 and 1:3.3, respectively. The energy output of biogas digesters has changed little over the past two decades ( Sommer and Husted 1995 , Hartman et al. 2000 ).

In developing countries such as India, biogas digesters typically treat the dung from 15 to 30 cattle from a single family or a small village. The resulting energy produced for cooking saves forests and preserves the nutrients in the dung. The capital cost for an Indian biogas unit ranges from $500 to $900 ( Kishore 1993 ). The price value of one kWh of biogas in India is about $0.06 ( Dutta et al. 1997 ). The total cost of producing about 10 million kcal of biogas is estimated to be $321, assuming the cost of labor to be $7 per hour; hence, the biogas has a value of $356. Manure processed for biogas has little odor and retains its fertilizer value ( Pimentel 2001 ).

Biofuels: Ethanol, methanol, and vegetable oil

Petroleum, essential for the transportation sector and the chemical industry, makes up approximately 40% of total US energy consumption. Clearly, as the supply diminishes, a shift from petroleum to alternative liquid fuels will be necessary. This analysis focuses on the potential of three fuel types: ethanol, methanol, and vegetable oil. Burned in internal combustion engines, these fuels release less carbon monoxide and sulfur dioxide than gasoline and diesel fuels; however, because the production of most of these biofuels requires more total fossil energy than they produce as a biofuel, they contribute to air pollution and global warming ( Pimentel 2001 ).

Ethanol production in the United States using corn is heavily subsidized by public tax money ( Pimentel 2001 ). However, numerous studies have concluded that ethanol production does not enhance energy security, is not a renewable energy source, is not an economical fuel, and does not ensure clean air. Furthermore, its production uses land suitable for crop production ( Weisz and Marshall 1980 , Pimentel 1991 , Youngquist 1997 , Pimentel 2001 ). Ethanol produced using sugarcane is more energy efficient than that produced using corn; however, more fossil energy is still required to produce a liter of ethanol than the energy output in ethanol ( Pimentel et al. 1988 ).

The total energy input to produce 1000 liters of ethanol in a large plant is 8.7 million kcal ( Pimentel 2001 ). However, 1000 liters of ethanol has an energy value of only 5.1 million kcal and represents a net energy loss of 3.6 million kcal per 1000 liters of ethanol produced. Put another way, about 70% more energy is required to produce ethanol than the energy that ethanol contains ( Pimentel 2001 ).

Methanol can be produced from a gasifier–pyrolysis reactor using biomass as a feedstock ( Hos and Groenveld 1987 , Jenkins 1999 ). The yield from 1 t of dry wood is about 370 liters of methanol ( Ellington et al. 1993 , Osburn and Osburn 2001 ). For a plant with economies of scale to operate efficiently, more than 1.5 million ha of sustainable forest would be required to supply it ( Pimentel 2001 ). Biomass is generally not available in such enormous quantities, even from extensive forests, at acceptable prices. Most methanol today is produced from natural gas.

Processed vegetable oils from sunflower, soybean, rape, and other oil plants can be used as fuel in diesel engines. Unfortunately, producing vegetable oils for use in diesel engines is costly in terms of both time and energy ( Pimentel 2001 ).

Transition to renewable energy alternatives

Despite the environmental and economic benefits of renewable energy, the transition to large-scale use of this energy presents some difficulties. Renewable energy technologies, all of which require land for collection and production, must compete with agriculture, forestry, and urbanization for land in the United States and the world. The United States already devotes as much prime cropland per capita to food production as is possible, given the size of the US population, and the world has only half the cropland per capita that it needs for a diverse diet and an adequate supply of essential nutrients ( USBC 2001 , USDA 2001 ). In fact, more than 3 billion people are already malnourished in the world ( WHO 1996 , 2000 ). According to some sources, the world and US population could double in the next 50 and 70 years, respectively; all the available cropland and forest land would be required to provide vital food and forest products ( PRB 2001 ).

As the growing US and world populations demand increased electricity and liquid fuels, constraints like land availability and high investment costs will restrict the potential development of renewable energy technologies. Energy use is projected on the basis of current growth to increase from the current consumption of nearly 100 quads to approximately 145 quads by 2050 ( USBC 2001 ). Land availability is also a problem, with the US population increasing by about 3.3 million people each year ( USBC 2001 ). Each person added requires about 0.4 ha (1 acre) of land for urbanization and highways and about 0.5 ha of cropland ( Vesterby and Krupa 2001 ).

Renewable energy systems require more labor than fossil energy systems. For example, wood-fired steam plants require several times more workers than coal-fired plants ( Pimentel et al. 1988 , Giampietro et al. 1998 ).

An additional complication in the transition to renewable energies is the relationship between the location of ideal production sites and large population centers. Ideal locations for renewable energy technologies are often remote, such as deserts of the American Southwest or wind farms located kilometers offshore. Although these sites provide the most efficient generation of energy, delivering this energy to consumers presents a logistical problem. For instance, networks of distribution cables must be installed, costing about $179,000 per kilometer of 115-kilovolt lines ( DOE/EIA 2002 ). A percentage of the power delivered is lost as a function of electrical resistance in the distribution cable. There are five complex alternating current electrical networks in North America, and four of these are tied together by DC lines ( Casazz 1996 ). Based on these networks, it is estimated that electricity can be transmitted up to 1500 km.

A sixfold increase in installed technologies would provide the United States with approximately 13.1 × 10 12 (thermal) kWh (45 quads) of energy, less than half of current US consumption (table 1) . This level of energy production would require about 159 million ha of land (17% of US land area). This percentage is an estimate and could increase or decrease, depending on how the technologies evolve and energy conservation is encouraged.

Worldwide, approximately 408 quads of all types of energy are used by the population of more than 6 billion people (table 1) . Using available renewable energy technologies, an estimated 200 quads of renewable energy could be produced worldwide on about 20% of the land area of the world. A self-sustaining renewable energy system producing 200 quads of energy per year for about 2 billion people would provide each person with about 5000 liters of oil equivalents per year—approximately half of America's current consumption per year, but an increase for most people of the world ( Pimentel et al. 1999 ).

The first priority of the US energy program should be for individuals, communities, and industries to conserve fossil fuel resources by using renewable resources and by reducing consumption. Other developed countries have proved that high productivity and a high standard of living can be achieved with the use of half the energy expenditure of the United States ( Pimentel et al. 1999 ). In the United States, fossil energy subsidies of approximately $40 billion per year should be withdrawn and the savings invested in renewable energy research and education to encourage the development and implementation of renewable technologies. If the United States became a leader in the development of renewable energy technologies, then it would likely capture the world market for this industry ( Shute 2001 ).

This assessment of renewable energy technologies confirms that these techniques have the potential to provide the nation with alternatives to meet approximately half of future US energy needs. To develop this potential, the United States would have to commit to the development and implementation of non–fossil fuel technologies and energy conservation. The implementation of renewable energy technologies would reduce many of the current environmental problems associated with fossil fuel production and use.

The immediate priority of the United States should be to speed the transition from the reliance on nonrenewable fossil energy resources to reliance on renewable energy technologies. Various combinations of renewable technologies should be developed, consistent with the characteristics of the different geographic regions in the United States. A combination of the renewable technologies listed in table 3 should provide the United States with an estimated 45 quads of renewable energy by 2050. These technologies should be able to provide this much energy without interfering with required food and forest production.

If the United States does not commit itself to the transition from fossil to renewable energy during the next decade or two, the economy and national security will be at risk. It is of paramount importance that US residents work together to conserve energy, land, water, and biological resources. To ensure a reasonable standard of living in the future, there must be a fair balance between human population density and use of energy, land, water, and biological resources.

We thank the following people for reading an earlier draft of this article and for their many helpful suggestions: Louis Albright, Cornell University, Ithaca, NY; Allen Bartlett, University of Colorado, Boulder, CO; Richard C. Duncan, Institute on Energy and Man, Seattle, WA; Andrew R. B. Ferguson, Optimum Population Trust, Oxon, United Kingdom; Tillman Gerngross, Dartmouth College, Hanover, NH; O. J. Lougheed, Irkutsk, Siberia; Norman Myers, Oxford University, United Kingdom; Marcia Pimentel, Cornell University, Ithaca, NY; Nancy Rader, California Wind Energy Association; Kurt Roos, US Environmental Protection Agency, Washington, DC; Frank Roselle-Calle, King's College, London; Peter Salonius, Canadian Forest Service, Fredericton, New Brunswick, Canada; Jack Scurlock, Oak Ridge National Laboratory, Oak Ridge, TN; Henry Stone, Ionia, NY; Ted Trainer, University of New South Wales, Australia; Mohan K. Wali, Ohio State University, Columbus, OH; Paul B. Weisz, State College, PA; William Jewell, Cornell University, Ithaca, NY; Walter Youngquist, Eugene, OR.

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Table 1. Fossil and solar energy use in the United States and world, in kilowatt-hours and quads.

Table 2. Land resource requirements and total energy inputs for construction of facilities that produce 1 billion kilowatt-hours of electricity per year.

Table 3. Current and projected US gross annual energy supply from various renewable energy technologies, based on the thermal equivalent and required land area.

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Challenges in Renewable Energy

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Renewable energy  has emerged as a vital solution to the pressing global challenges of climate change and energy security. 

By harnessing natural resources like  sunlight, wind , water, geothermal heat, and biomass, renewable energy offers  a cleaner and more sustainable alternative to traditional fossil fuels . 

As the demand for clean energy continues to grow globally, it is important to understand and  address the challenges  that impede the widespread adoption of renewable energy sources.

In this article, we will explore the major hurdles faced by the renewable energy sector and delve into potential solutions to overcome these obstacles.

Overview of Renewable Energy Sources

source: https://news.energysage.com/five-types-of-renewable-energy-sources/

To grasp the challenges inherent in renewable energy, it is essential to understand the major sources driving the transition.

Solar power  is abundant and highly accessible. It harnesses the sun’s energy through photovoltaic panels, converting it into electricity. 

The challenge lies in solar power’s intermittency, as it relies on daylight availability and weather conditions. Advances in energy storage systems are crucial to mitigate this issue.

Wind power  utilizes wind turbines to generate electricity. It is a mature technology with significant potential. 

However, the intermittency of wind patterns and the need for vast areas for wind farms present challenges. Balancing wind power with other energy sources and enhancing grid flexibility is vital for a reliable energy supply.

Hydropower  taps into the kinetic energy of flowing or falling water to generate electricity. 

While it is a clean and reliable source, its feasibility depends on geographical features and potential environmental impacts . Finding a balance between energy generation and ecosystem preservation is key.

Geothermal energy  reaps the Earth’s heat from deep within its core. It provides a constant source of energy but is geographically limited to areas with substantial  geothermal  resources. 

Expanding exploration efforts and developing advanced drilling technologies are essential for its growth.

Biomass energy  derives from organic matter, such as agricultural waste, wood pellets, or dedicated energy crops. 

Although biomass is a versatile energy source, problems include feedstock availability, land use conflicts, and emissions management.

Major Challenges in Renewable Energy

• Intermittency and Variability : Renewable energy sources are subject to fluctuation due to weather conditions or time of day. This intermittency poses challenges to grid stability and necessitates effective  energy storage  solutions to store excess energy during peak production for use during low-generation periods.
• Cost and Economics : While renewable energy costs have decreased significantly over the years, initial capital investments remain high. Additionally, the levelized cost of electricity (LCOE) for renewables must be competitive with fossil fuels to encourage broader adoption. Continued advancements in technology and economies of scale are crucial for cost reductions.
• Infrastructure and Grid Integration : The transition to renewable energy requires extensive infrastructure development, including expanding transmission networks to connect remote renewable resources to population centers. Upgrading existing grids to accommodate bidirectional power flow and balancing supply and demand is vital for smooth integration.
• Public Acceptance and Policy Support : Renewable energy projects often face opposition, known as  NIMBY (Not In My Backyard) sentiment , due to concerns about visual impacts, noise, or potential environmental consequences. Furthermore, inconsistent government policies and regulatory barriers can hinder renewable energy growth. Ensuring public acceptance and providing stable policy frameworks are essential for overcoming these challenges.

Technological Innovations and Potential Solutions

source: https://www.freepik.com/free-photo/bulb-solar-panel-eolic-fan_926538.htm

• Advancements in Energy Storage : Energy storage technologies play a critical role in addressing intermittent renewable energy generation. Batteries and grid-scale storage systems enable the efficient utilization of excess energy during high-generation periods. Additionally, the use of hydrogen as an energy carrier shows promise for long-duration storage and diverse energy applications.
• Smart Grids and Digitalization : Implementing smart grids enables efficient demand-side management, facilitating load balancing and reducing energy waste. Digitalization improves grid optimization, real-time monitoring, and control, enhancing the integration of renewable energy sources and maximizing their utilization. Smart grids also enable the seamless integration of electric vehicles, further promoting clean energy adoption.
• Research and Development : Continued investment in research and development is vital for overcoming renewable energy challenges. Improving the efficiency and performance of renewable technologies, developing new materials and technologies, and exploring innovative approaches will drive progress in the field. Collaboration between industry, academia, and governments is key to fostering innovation.
• Grid Flexibility and Virtual Power Plants : Grid flexibility refers to the ability to balance supply and demand fluctuations in real time.  Virtual power plants (VPPs)  integrate multiple renewable energy sources, energy storage systems, and demand response mechanisms. By aggregating these resources, VPPs can optimize energy generation and consumption, enhance grid stability, and provide ancillary services to support the overall grid operation.
• Blockchain Technology :  Blockchain technology  offers potential solutions for energy sector challenges, including enhancing traceability and transparency in renewable energy transactions, optimizing peer-to-peer energy trading, and enabling more efficient grid management. Smart contracts and decentralized platforms can facilitate secure and automated energy transactions, empowering consumers to participate in the energy market.
• Advanced Monitoring and Predictive Analytics : Deploying advanced monitoring systems and predictive analytics in renewable energy installations can optimize performance, detect faults, and facilitate predictive maintenance. Real-time monitoring of renewable energy assets allows for early detection of issues, enabling prompt actions to prevent system failures and maximize energy generation.
• Artificial Intelligence and Machine Learning : Artificial intelligence (AI) and machine learning (ML) algorithms can optimize renewable energy generation and consumption by analyzing vast amounts of data. AI and ML can enable accurate weather forecasting for renewable energy generation, optimize energy distribution and storage, and improve load forecasting, enhancing grid management and efficiency.

Case Studies and Success Stories

source: https://unsplash.com/photos/eIBTh5DXW9w

Examining countries leading in renewable energy adoption provides valuable insights into overcoming challenges. 

For instance,  Denmark  has successfully integrated wind power into its grid , utilizing flexible electricity markets and interconnections with neighboring countries. 

Germany  has made significant strides in solar power deployment, driven by favorable policies and incentives.

Costa Rica  has made remarkable progress in renewable energy adoption, with over  98% of its electricity generation coming from renewable sources .

Notable projects around the world showcase innovative solutions to renewable energy challenges. 

The Hornsdale Power Reserve in  Australia , the largest lithium-ion battery installation, has helped stabilize the grid and support renewable energy integration. 

The Three Gorges Dam in  China  demonstrates the potential of hydropower, powering millions of homes while addressing environmental concerns.

Lessons learned from these case studies emphasize the importance of long-term planning, policy support, technological innovation, and collaboration between stakeholders.

Future Outlook and Recommendations

To overcome challenges in renewable energy , several key actions and strategies are necessary:

• Policy and Regulatory Framework Improvements : Governments must establish consistent, long-term policies and regulatory frameworks that provide clear incentives, promote  investment , and ensure a level playing field for renewables. This includes streamlining permitting processes and addressing regulatory barriers.
• Continued Investment in Research and Development : Governments, industry leaders, and research institutions should allocate resources to advance renewable energy technologies. This involves improving efficiency, reducing costs, and exploring emerging technologies such as floating solar, offshore wind, and next-generation energy storage.
• Collaborative Efforts and International Cooperation : Cooperation between countries and stakeholders is crucial for addressing global renewable energy challenges. Sharing best practices, knowledge, and resources can accelerate progress and foster innovation. International agreements and initiatives like the Paris Agreement play a vital role in promoting collaboration.
• Public Awareness and Education : Raising public awareness about the importance of renewable energy and dispelling misconceptions are essential for fostering support and acceptance. Education and outreach programs can help inform communities about the benefits and realities of renewable energy, enabling informed decision-making.
• Renewable Energy Market Design : Evolving market designs to value the flexibility, reliability, and environmental benefits of renewable energy is essential. Implementing market mechanisms that incentivize renewable energy integration, provide fair compensation for grid services, and facilitate the trading of renewable energy certificates can create a level playing field and stimulate further investments in renewable energy.
• Circular Economy Approach : Adopting a circular economy approach in the renewable energy sector can maximize resource efficiency and minimize waste. Emphasizing recycling and repurposing of renewable energy components, such as solar panels and wind turbine blades, will reduce environmental impacts and create new opportunities for the industry.

Renewable energy offers a promising pathway to a sustainable future, but it is not without its challenges. 

Overcoming issues of intermittency, cost, infrastructure, and public acceptance requires collaborative efforts, technological innovation, and supportive policies. 

By investing in research and development, improving energy storage solutions, advancing grid integration technologies, and fostering public awareness, we can navigate the challenges and unlock the full potential of renewable energy. 

The path to a sustainable future lies in our collective commitment to addressing these challenges and embracing the transformative power of renewable energy.

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Should we worry about wasting renewable energy? Here’s why ‘spilling’ excess power is expected – and efficient

Senior Research Associate, Renewable Energy & Energy Systems Analyst, UNSW Sydney

Disclosure statement

Dylan McConnell's current position is supported by the 'Race for 2030' Cooperative Research Centre.

UNSW Sydney provides funding as a member of The Conversation AU.

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In Australia’s electricity system, more and more energy from sunlight and wind is being “spilled” – or not converted to electricity.

In the last year, the amount of renewable energy spilled was roughly equivalent to the annual consumption of 750,000 typical households, or three months of consumption for the state of South Australia. Some have attributed these dynamics as being driven by a “ solar power glut ”.

At face value, this seems like a terrible waste of renewable energy, even more so in the face of a slump in rate of renewable energy growth and the pressing need to reduce emissions.

But the story is more complex. Such spillage, also known as curtailment, is also an expected and efficient feature of renewable energy systems.

What is ‘spilled energy’?

The energy market operator defines spilled energy as “energy from variable renewable energy resources that could be generated but is unable to be delivered”.

It represents energy that could have been converted to electricity, but wasn’t. The unconverted energy simply remains in the environment.

It is typically broken down into two categories, based on the cause of the spillage. Firstly, there is curtailment based on the operation of the transmission network. Power generation can be constrained due to operation limits or congestion in the network, resulting in spilled energy. This can occur when there are too many generators in the same area, trying to send power through the same transmission line. Secondly, a generator may reduce output due to low market prices, which the operator calls “economic spill” also known as “economic curtailment”.

The amount of this curtailment has been growing in recent years. In the last 12 months this curtailed energy represents more than 8.5% of the total potential. This varies considerably by region, with as much 12% spilled in Victoria in the last year.

Why is spillage efficient?

It doesn’t make economic sense to try and utilise every renewable electron. The cost to store, transmit and utilise every single watt of power from a renewable energy source would be exorbitant.

For example, we don’t build additional highway lanes to accommodate traffic for the busiest single hour on an Easter weekend. In a similar way, it doesn’t make sense to build transmission to ensure every single watt is transferred. This would be expensive and result in severely underused infrastucture. For the more common weather conditions – when it isn’t blowing a gale or in the middle of a sunny day – the network would be considerably oversized.

Studies that model energy systems primarily powered by renewables commonly find it is more economically efficient to build additional renewable capacity, and spill some generation when there is an abundance of supply above demand.

The Integrated System Plan, a roadmap for the electricity system prepared by Australia’s energy market operator, projects an increase of renewable energy curtailment in the best case scenario. Approximately 20% of renewable generation is expected to be spilled by 2050. This is roughly equivalent to the current consumption of the state of New South Wales.

On one level, this shouldn’t be surprising.

Households often buy larger solar PV system relative to their consumption.

And it’s now common practice to install solar panels in excess of the capacity of the inverter to convert the power and send it to the home or grid. This is usually done to maximise use of the inverter and exports across a limited connection.

These two examples are broadly analogous to what happens on the grid, with economic curtailment and transmission-based curtailment.

Are current levels efficient?

At a system-wide level, current levels of spillage are above what was expected. The integrated system plan suggests curtailment rates of around 5% might be considered appropriate for today’s penetration of renewable energy, compared with the today’s level of around 8.5%. This difference relates to how things are working in the real world, including how rules around accessing transmission capacity currently work.

A recent discussion paper from the Australian Energy Market Commission highlights this mismatch, and suggest that “in the absence of reform, actual levels of curtailment are likely to exceed the levels forecast in the ISP”, pointing to issues with the current arrangements for generators accessing transmission capacity.

They imply the current system is resulting in higher than expected congestion, leading to increased costs for consumers and potentially unnecessary transmission builds. Managing transmission access remains a challenge for developers building new renewables projects.

Australia’s fleet of coal-fired power generators is another key driver of economic curtailment. While coal generators are more flexible than commonly understood, they have their limits. Specifically, they can only reduce operation down so far, to so-called minimum generation levels. Below these levels, they have to turn off completely, which is a costly exercise.

Coal generators therefore prefer to continue to generate, even at negative prices, rather than completely shut down. As a consequence, and to avoid paying to generate, renewable energy is spilled, rather than coal shutdown. In the context of the energy transition and the need to reduce emissions we actually have a glut of coal, rather than renewables.

Where to next?

The curtailment story is complex. On the one hand it is an expected phenomenon, and one we should get used to as we transition more toward a renewable-dominated electricity system. We should, however, be encouraging consumers to make use of this abundance of renewable generation where possible, such as by shifting their useage to the middle of the day .

On the other hand, some of these levels of curtailment are beyond what is expected. That’s in part because we still have an excess of coal power. We separately need to ensure grid congestion is properly managed, and access arrangements are reformed, to prevent unnecessary costs to consumers and renewable developers alike.

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Election latest: Starmer wins another TV debate poll - as Lib Dem leader handed speeding fine

Sir Keir Starmer may have come off worse in a snap poll of last night's TV debate against the prime minister, but two more published this morning suggest more voters reckon he actually won. For analysis of the Sunak vs Starmer show, listen to Politics At Jack And Sam's as you scroll.

Wednesday 5 June 2024 12:34, UK

• General Election 2024

Election news

• Bulletin: What you need to know this lunchtime
• Another poll puts Starmer ahead in TV debate
• Doubt cast on Tory tax claim by top civil servant
• Labour accuses Sunak of 'desperate lies' over claim
• Politics At Jack And Sam's: The Day… after the debate
• Lib Dem leader fined for speeding
• Campaigning takes back seat for D-Day commemorations
• Live reporting by Faith Ridler

Expert analysis

• Sam Coates: Sunak and Starmer couldn't wait to tear into each other
• Ed Conway: Why caps on migrant numbers don't really work
• Matthew Thompson: The story behind Lib Dem battle bus icons

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• Be in the audience for our election leaders event
• Trackers: Who's leading polls? | Is PM keeping promises?
• Campaign Heritage: Memorable moments from elections gone by
• Follow Sky's politics podcasts: Electoral Dysfunction | Politics At Jack And Sam's
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It's 12pm - and today has been all about last night's TV debate.

The campaign trails have slowed while party leaders attend memorial events commemorating the 80th anniversary of the D-Day landings in Portsmouth.

Here's what you need to know so far today:

• Reaction has been fierce after Rishi Sunak  claimed during last night's debate that a £38bn black hole in Labour's financial plans could force the party to rocket household bills by £2,000;
• Labour frontbencher Jonathan Ashworth told Sky News Mr Sunak had resorted to "desperate lies" with the allegation;
• In response, the Conservatives insisted their claim was based on "clear Labour policies, their own costings or official HMT [His Majesty's Treasury] costings using the lowest assumptions".
• However, doubt was also cast on Mr Sunak's claim by a senior Treasury civil servant , who wrote to Labour two days ago to warn them that the Tory assessment of their tax plans "should not be presented as having been produced by the civil service".
• Amid this tax row, Energy Secretary Claire Coutinho said the numbers were signed off by James Bowler, the Treasury's permanent secretary - who sent the letter to Labour.
• Ms Coutinho said: "They will not sign off things which are dodgy and, if anything, this underestimates the cost to families."
• This comes after what our deputy political editor Sam Coates described as a "snippy" debate. He says: "Both the Starmer and Sunak campaigns agree: the first head-to-head of the election campaign was - in many ways - a difficult watch";
• But two polls today suggest the public reckon the Labour leader came out better than Mr Sunak - a reversal of a snap poll last night which had the PM just ahead.
• Later today,  Rishi Sunak  will give a speech at the D-Day 80th anniversary event in Portsmouth, where he has already been spotted sat between Prince William and his wife;
• We've also spotted Liberal Democrat leader Sir Ed Davey and Labour's Sir Keir Starmer at the D-Day memorial;
• It's also emerged that Sir Ed has been fined for speeding on the motorway, for which he's apologised;
• Scottish Labour have been on the campaign trail, with leader Anas Sarwar suggesting that Rishi Sunak could be "going down the same rabbit hole" as his predecessors Boris Johnson and Liz Truss;
• And the SNP have criticised both Labour and the Conservatives for failing to address Scottish issues in their debate last night;

Here are some other stories you might want to read:

Our essential political podcast,  Politics At Jack And Sam's , is going out every week day through the election campaign to bring a short burst of everything you need to know about the day ahead as this election unfolds - here is today's edition .

Tap here to follow Politics At Jack At Sam's wherever you get your podcasts .

Prime Minister Rishi Sunak has just been addressing crowds in Portsmouth, who have gathered to mark the 80th anniversary of the D-Day landings.

He read a message from General Bernard Montgomery, which was given to all troops on the eve of D-Day in 1944.

The prime minister recalls how the commander in chief of the Allied forces told his men: "We have a great and righteous cause.

"I want every soldier to know that I have complete confidence in the successful outcome of the operations that we are about to begin."

You can follow updates from the memorial in our dedicated live blog:

We've got another public survey of who performed better in last night's TV debate between Rishi Sunak and Sir Keir Starmer.

According to a poll by JLP Partners, for The Sun newspaper, the Labour leader performed best.

That was the view of 53% of respondents, compared to 33% for the PM.

But Mr Sunak did much better among 2019 Tory voters - a demographic Sir Keir has been trying to win over.

Some 60% of them said the Conservative leader did better, compared to 33% for his opponent.

The results are based on a poll of 1,000 people.

It follows last night's snap poll by YouGov, which found 51% of people thought the debate was won by Mr Sunak, and a Savanta one this morning which came out in favour of Sir Keir ( more here ).

Liberal Democrat leader Sir Ed Davey has been fined for speeding after being caught doing 73mph in a 60mph zone on the M1 motorway.

Details of the case, dealt with under an administrative system called the Single Justice Procedure, were revealed by the Evening Standard newspaper today.

Sir Ed wrote a letter of explanation in which he said he had tried to pay a speeding ticket issued by Bedfordshire Police after he was caught speeding on the M1 near Caddington.

In a "genuine oversight", he inadvertently failed to provide his driving licence details so the matter was brought before magistrates to consider in March.

He was handed a £72 fine at Luton Magistrates' Court, with a £28 victim surcharge, and had three points added to his licence, court staff confirmed.

He was not asked to pay prosecution costs.

A Lib Dem spokesman said: "Ed inadvertently broke the speed limit on the M1, which he is sorry for.

"He has paid the fine and accepted the points on his licence."

By Jenness Mitchell , Scotland reporter

Anas Sarwar has told Sky News that if Labour enters Number 10 next month, it plans to set up GB Energy "straight away".

Speaking about the pledge to create a publicly owned clean energy company, the Scottish Labour leader said while there's a "time and a process in terms of identifying headquarters and all the rest of it… we want to get cracking with this".

Mr Sarwar said a site is yet to be identified.

He added: "What we've said is we want it to be headquartered in Scotland."

Mr Sarwar would not get drawn into where in the country, but added: "There's clearly huge potential in the northeast, and Aberdeen in particular where we have an energy hub right now - which is, of course, something we want to support and back those workers and those companies in that region."

Energy Secretary Claire Coutinho has claimed all Labour would do is "raise people's bills" if they won the election.

The cabinet minister told GB News: "You look at Ed Miliband's plans for energy in this country and all he would do is raise people's bills and raise taxes to pay for it."

While her priority is "cheaper energy", including tariff reforms to "save people £900 a year", the shadow energy secretary wants to "decarbonise further and faster than anybody", regardless of cost to "working families".

Labour leader Sir Keir Starmer has previously said his party's plans for a publicly-owned clean energy company would "close the door on (Russian President Vladimir) Putin" and shield UK billpayers from global shocks and increases in global oil and gas markets.

Anas Sarwar, the Scottish Labour leader, has reiterated his party's claim that Rishi Sunak told a "straight-up lie" over allegations of a £2,000 tax hike.

In last night's TV debate, Mr Sunak made a repeated claim that Labour's financial plans include a £38bn black hole.

The prime minister alleged this would result in a £2,000 tax rise per household, saying Labour's policies were costed by "independent Treasury officials".

However, a senior Treasury civil servant has sought to distance himself from this today (see 09.22 post).

Asked about allegations of a tax rise, Mr Sarwar said: "This is a straight-up lie from a desperate prime minister, Rishi Sunak, who is trying to scaremonger across the country because he wants to hide away from his own record."

Labour will only raise taxes on "the super rich", he said, citing closing the "non-dom tax loophole" and a windfall tax on oil and gas giants.

Mr Sarwar is asked why Sir Keir didn't mention the civil servant letter in the debate last night.

"We thought the prime minister would have more integrity than what he showed last night," he said.

"We didn't think he was the same ilk as the Liz Truss, the Boris Johnson-style politics. 

"But clearly Rishi Sunak wants to go down that same rabbit hole that those two field prime ministers went down."

By Olive Enokido-Lineham , OSINT producer 

Tweets falsely suggesting a woman who threw a milkshake at Nigel Farage at a campaign event yesterday have gained over two million views on X. 

Videos of the incident featuring the new leader of Reform UK as he left a pub in Clacton-on-Sea went viral on social media.

But a number of tweets that have gained a lot of attention, focus on another woman - who was not involved. 

One tweet featured a side-by-side image of Conservative supporter Emily Hewertson, posing next to Mr Farage alongside a picture of the woman who allegedly threw the milkshake.

The tweet, which does not mention Ms Hewertson by name and features a shrug face emoji captioned "the milkshake thickens", has gained over 2.3 million views alone.

While this was not the only tweet featuring Ms Hewertson, it's an example of how quickly such speculation can spread online.  

Other tweets which don't mention her by name and speculate whether she was involved have now been deleted.

In response to the online rumours, she confirmed she did not throw a milkshake at Mr Farage.

Conservative candidate for Wolverhampton North East Jane Stevenson also uploaded a video to X alongside Ms Hewertson, showing that they were in fact in Wolverhampton.

In the video she says: "Sorry Twitter, Emily is in Wolverhampton working in my office and I think she knows a bit better than to throw a milkshake over someone."

Essex Police said a 25-year-old woman from Clacton was arrested on suspicion of assault.

Ms Hewertson's Instagram bio also claims she is 24 years old, not 25.

She later tweeted that she hopes that the misidentification becomes a "lesson in how quickly an unsubstantiated lie about an individual can spread on social media".

This post is part of the Online Election project – a Sky News initiative to cover how the campaign is playing out online, led by Tom Cheshire who is our Online Campaign correspondent throughout. 

Our political correspondent Serena Barker-Singh is on the Labour "battle bus" today, which is making its way through the West Midlands down to Portsmouth.

She says that the visit comes with "tangible promises" from Labour, including new legislation to establish an Armed Forces Commissioner - and "strengthen the rights of veterans".

"It's clear the message he wants to send," Serena says. "And he is also hoping to get away from this tax row that has emerged from the debate" ( see our 9.05am post ).

She adds: "The Labour leader Keir Starmer will join members of the Royal Family, they are marking the 80th anniversary of D-Day and he'll be with military veterans and service personnel.

"And a ceremony in Portsmouth with the King."

Politicians from across the House of Commons are arriving in Portsmouth today to commemorate the 80th anniversary of the D-Day landings.

There has been a brief pause in the election campaign to allow for these commemorative events - and political foes and friends have been spotted mingling.

Labour leader Sir Keir Starmer, Liberal Democrat leader Sir Ed Davey and veterans minister Johnny Mercer were among the early arrivals - with Rishi Sunak also expected to attend.

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