Economic, Societal, and Environmental Impacts of Available Energy Sources: A Review

Abstract

The impacts that the available energy sources have had on society, the environment, and the economy have become a focus of attention in recent years, generating polarization of opinions. Understanding these impacts is crucial for rational evaluation and the development of strategies for economic growth and energy security. This review examines such impacts of the main energy resources currently exploited or in development, including fossil fuels, geothermal, biomass, solar, hydropower, hydrogen, nuclear, ocean, and wind energies on society through analysis and comparison. It is essential to consider how high energy demand influences energy prices, the workforce, and the environment and to assess the advantages and disadvantages of each energy source. One significant finding from this review is that the levelized cost of energy (LCOE) may vary substantially depending on the energy source used and show substantial ranges for different applications of the same energy source. Nuclear energy has the lowest LCOE range whereas ocean energy has the highest LCOE range among the nine energy sources considered. Fossil fuels were found to have the most substantial societal impacts, which involved on the positive side providing by far the largest number of jobs and highest tax revenues. However, on the negative side, fossil fuels, biomass, and nuclear energy sources pose the most significant health threats and social well-being impacts on communities and societies compared to other energy sources. On the other hand, solar, ocean and wind energy pose the lowest risk in terms of health and safety, with solar and wind also currently providing a substantial number of jobs worldwide. Regarding environmental consequences, fossil fuels generate the highest greenhouse gas (GHG) emissions and have the highest adverse impacts on ecosystems. In contrast, nuclear, ocean, solar and wind energies have the lowest GHG emissions and low to moderate impacts on ecosystems. Biomass, geothermal and hydropower energy sources have moderate to high ecosystem impacts compared to the other energy sources. Hydropower facilities require the most materials (mainly concrete) to build per unit of energy generated, followed by wind and solar energy, which require substantial steel and concrete per unit of energy generated. The lack of substantial materials recycling causes associated with solar and wind energy sources. All the energies that use thermal power generation process consume substantial quantities of water for cooling. The analysis and comparisons provided in this review identified that there is an urgent need to transition away from large-carbon-footprint processes, particularly fossil fuels without carbon capture, and to reduce the consumption of construction materials without recycling, as occurs in many of the existing solar and wind energy plants. This transition can be facilitated by seeking alternative and more widely accessible materials with lower carbon footprints during manufacturing and construction. Implementing such strategies can help mitigate climate change and have a positive impact on community well-being and economic growth.

1. Introduction

Energy can be produced from many kinds of resources. Some energy sources are classified as renewable energy because they are replenished at a greater rate than they are consumed. On the contrary, non-renewable energy sources are those that are consumed at a rate greater than they are naturally replenished. Nevertheless, consuming any energy source is not free of charge; it comes at a price. This review discusses the impacts of nine energy sources: fossil fuels, geothermal, bioenergy, solar, wind, hydropower, ocean, nuclear, and hydrogen.

To understand the impacts of each energy source it is vital to know how each energy source originates. Solar energy originates from the sun’s radiation emissions, which are available worldwide to be captured by solar panels and converted to electricity using photovoltaic panels and/or extracted using various solar thermal processes. Bioenergy uses organic materials such as agricultural products residues, and animal waste to produce energy. Bioenergy can be characterized into two main types: biomass and biofuels. Biomass retrieves the energy from plant and algae-based resources [1] including crop wastes, forest residues, purpose-grown grasses, microalgae, woody energy crops, urban wood waste, and food waste. Biofuels, on the other hand, involve materials that can be transformed into liquids—for example, biodiesel and ethanol. The energy that is derived from air movement in the atmosphere is classified as wind energy and originates from solar inputs to the atmosphere. Wind energy is exploited to spin turbines that capture its kinetic energy and then convert it primarily into electricity. Geothermal energy exploits heat generated from within the Earth. The Earth’s interior contains various radioactive materials that decay at various rates generating energy, along with convection and circulation in the Earth’s mantle which ultimately creates geothermal hot spots and volcanic activity that heat fluids in the Earth’s crust. Hot fluids in the sub-surface can be produced to the surface to be used for heat and to generate electricity. Hydropower extracts the kinetic energy from water due to its gravitational movements by passing flowing water through turbines to generate electricity. This can be achieved on a large scale using dams which impound water in artificial reservoirs and use the elevation difference of water flowing from inside to outside the dam. Ocean energy uses tidal and wave kinetic water movements (lunar and solar driven) and/or the difference in seawater salinity and temperature between different parts of the ocean to generate electricity. Ocean energy systems remain at an early stage of development with several wave and tidal extraction methods undergoing pilot testing. The ocean energy systems being tested mainly focus on wave energy converters (WEC) and tidal power plants (TPP), but their efficiency needs to be substantially improved for large-scale exploitation. Theoretically, the oceans hold vast clean energy resources that could make a significant contribution to meeting the world’s total energy demand [2].

Unlike the previously mentioned energy sources, fossil fuels (coal, oil, and gas) are non-renewable energy sources that are formed from the decomposition of plants and animals (organic materials) buried over millions of years. Fossil fuels dominate the energy consumed for transportation, power generation, space heating, and industrial processes worldwide accounting for 82% of supply [3]. This is at odds with the widely stated objective to cut greenhouse gas emissions (GHG) by 43% by 2030 from 2019 levels to achieve the internationally agreed climate goals of the Paris Agreement to maintain global warming to <2 °C above pre-industrial levels [4]. During the burial, increasing temperature and pressure transform the organic matter into kerogen and coal depending on its composition. The kerogen, also depending on its composition, generates oil and/or natural gas with increasing temperature, and the coal generates primarily dry gas. These fluid hydrocarbon products partly remain in their source rocks (mainly shales and coals) and partly migrate into porous reservoirs, where under certain geological conditions, they become trapped. Coal can be mined and used for space heating and power generation. Fluid hydrocarbons (gas and oil) are extracted from porous reservoirs and source rocks and consumed for various energy uses. Crude oil is for the most part refined to separate it into useful energy products, particularly gasoline, diesel, kerosene (jet fuel), and liquid petroleum gases (LPG) used especially for transportation fuels but also in smaller quantities for space heating and petrochemical manufacture. Natural gas is primarily consumed for electricity generation, space heating, and petrochemical generation.

All matter in the universe is created from atoms, and the energy that holds the nuclei of the atom together is called nuclear energy. The release of nuclear energy can be achieved through two processes: the fission (splitting) or fusion (combining) of atoms’ nuclei. The nuclear energy released during the fission of uranium-based fuels is harnessed by commercial nuclear plants to generate heat from which electricity is generated in thermal (steam-driven) turbines [5]. Nuclear fusion remains at the research and development stage and is unlikely to be exploited in commercial-scale power plants for several decades.

Hydrogen is also a potential energy source that can be generated from renewable and non-renewable resources. Hydrogen has much potential as a clean energy source with projects and technologies being developed in recent years to exploit it more extensively for a range of uses [6]. Hydrogen efficiency and emissions depend on how it is produced and from what resources. It can be produced on a commercial scale relatively cheaply by synthesis gas reformation (non-renewable) or by water electrolysis, fermentation of biomass, and other renewable organic materials (renewable). However, such methods remain expensive and technically challenging from the infrastructure perspective. When used as a fuel in fuel cell technology, the only by-product is water vapor. However, depending on the conditions in which hydrogen is combusted in thermal power plants, substantial oxide of nitrogen pollutants can be generated [7].

Energy supply plays a vital role in sustaining all human life today and it is used in many ways. It enables various functions ranging from commercial, industry, transportation, and residential sectors. Figure 1 provides the US approximate breakdown of energy consumption in the residential and commercial sectors highlighting the importance of cooling, heating, and lighting of homes and buildings [8].

Based on statistics quoted by the International Energy Administration (IEA), approximately 40% of the energy consumed worldwide in 2022 was used to power residential buildings and offices. Fossil fuels in the form of natural gas, petroleum products, and coal, and the electricity generated from them, are the main sources of energy consumed by the residential sector. The International Energy Agency (IEA) also indicated that residential energy consumption in the past 30 years had increased by 20.8 quads (1 quad is 1 quadrillion (1015) British thermal units (BTU)), equivalent to approximately one-fifth of total global energy consumption (98 quads). All forms of transport depend upon an energy source. According to the IEA’s World Energy Outlook [9], 22% of global energy is consumed by all forms of transport (i.e., trucks, airplanes, ships, automobiles, etc.). The amount of driven millage by energy-powered road transportation vehicles was estimated by the IEA [9] to be nearly 3 trillion miles. The transportation sector’s energy supply is 92% derived from fossil fuels, mainly petroleum products but some natural gas, and 8% electricity. The industrial sector is also a major energy consumer and a major contributor to economic prosperity, growth, and employment. According to the IEA [9], 38% of the world’s energy consumption powers industrial activities. Industries use energy in multiple forms varying from the heat and power in manufacturing, refining, petrochemical and mineral extraction processes. Based on the United States Government’s Energy Information Administration (EIA), the energy sources that are used to supply the industrial sector are diverse [10]. As well as fossil fuels (the dominant source of industrial energy consumption), most renewable energy sources are also used for industrial and residential purposes in the USA.

A major limitation of renewable energy sources is that they are limited to specific locations due either to resource availability (geothermal, hydropower) or climatic/meteorological conditions (solar, wind, ocean energy sources). Biomass can be transported around the world, so it is not specifically limited by location. However, its usage is constrained by economic characteristics—specifically its cost of feedstock supply, including transportation costs [10].

Global energy demand has been progressively increasing since the industrial revolution of the nineteenth century [11]. Annual fluctuation in global energy demand tends to be driven by economic growth/recession trends. As energy demand continues to grow and new technologies develop to enable various energy sources to be exploited more cost-effectively and efficiently, the energy mix continues to change over time [12]. According to the IEA, the energy required for global transportation by all its sectors, especially light-duty road vehicles, heavy-duty road vehicles, and aviation, is expected to grow substantially by 2050 [9]. Vehicles operated by internal combustion (petroleum product) engines could lead the demand for fossil fuels to increase by 3 million barrels/day. However, much uncertainty surrounds this forecast depending on the cost reductions and energy efficiency technology breakthroughs that may lead to much greater uptake of rechargeable electric vehicles and or fuel-cell-powered transport systems. The IEA predicts that the retail and trade movements of consumer product—together with the worldwide movements of individuals and bulk cargoes, which have increased significantly in past decades—could lead to an increase in global transportation energy consumption of some 25% in 2050.

It is a well-established trend that as nations become more developed, their energy demand and consumption also grow. The increase in global energy demand reflects the collective efforts of nations to develop economically and improve living standards. Development relies mostly on technologies. Reliable access to affordable technologies in developed countries consumes enormous quantities of energy and, in turn, drives increasing energy demand. Figure 2 compares increasing energy consumption from 1990 to 2019 in kW hours by different global countries. The substantial growth in energy consumption in China during that period stands out [12].

As demand for energy relentlessly increases, particularly in the most populated regions of the world, it brings with it substantial social, economic, and environmental impacts (good and bad). The magnitude of these impacts are driven by a variety of factors including the pace of technological advancement, population growth, economic development, and change in consumption patterns [10]. However, meeting continuously rising energy demand is carries significant challenges. Higher energy unit prices can lead to energy inflation constraining economic growth, and the release of greenhouse gases (GHG) have potentially life-threatening (to all global species) environmental impacts associated with global warming and climate change. Energy shortages associated with price increases and access to supply can cause social instability and energy poverty.

Determining the economic viability of alternative energy supply mixes is important to making strategic decisions on infrastructure investments that will influence economic growth, costs of living and energy-consumption related GHG emissions. On the other hand, environmental sustainability requires a clear view of the impacts that distinctive energy sources have on the local and global environment to sanction effective and affordable climate-change mitigation strategies. Energy security of supply is of primary concern, particularly for energy-resource-poor nations and those with limited resources to build new infrastructure, and failure to address it risks dire social and economic consequences. Understanding the impacts of different energy sources on society, the environment, and the economy (the focus of this review) requires in-depth analysis at the local, regional, and global scales.

The remainder of this review is organized as follows: Section 2 addresses the impacts of nine specific energy sources; Section 3 (Results and Discussion) provides comparisons of the economic viability of the energy sources based on their levelized cost of energy, and their relative social and environmental impacts. Section 4 (Recommendations) identifies the actions required to improve the sustainability and viability of each energy source. Section 5 (Conclusions) states the key findings of the review based on the information provided and discussed in the foregoing sections.

2. Impacts of Specific Energy Sources

2.1. Economic Impacts of Energy Sources

A key cause of major disturbances in global trade over many decades and sudden inflationary periods has been strong fluctuations in energy prices, particularly those of fossil fuels [13]. Maintaining an abundant, affordable, storable, and secure energy supply offers the best strategy to fortify a nation’s economy and protect it in times of global energy supply shortfalls or sudden disruptions in supply chains.

2.1.1. Fossil Fuel

Most economic analysis emphasizes that energy supply forms the backbone of the global economy, and the trading and movement of fossil fuels has underpinned this for decades. Fossil fuels constitute some of the most highly valued industrial sectors, which have contributed substantially to global development by meeting the continuous growth in energy demand. The sectors are dominated—upstream, midstream, and downstream—by some of the world’s largest companies, both national and international. Those companies and the service companies that sustain them are investing substantial capital to develop more sustainable strategies to locate and produce new fossil fuel reservoirs with the stated intention to mitigate the GHG emissions involved in doing so. The fossil fuel sectors remain the primary provider of energy to the world’s largest economies and energy consumers. Consequently, the global economy remains fossil-fuel-dependent, despite the politically stated intentions of many nations to substantially reduce that dependence over the coming decades. The G-20 nations have assigned investments of approximately USD 100 billion for fossil fuel production and development over approximately the past decade. Indeed, the largest European national economies (based on GPD) have apportioned nearly EUR 78 billion for that purpose in recent years [14]. The value of private equities’ investments in fossil fuels were valued at approximately USD 39 billion in 2018, the highest market revenue since 2008.

The impact the fossil fuels on the economy of some oil-rich regions is enormous, as exemplified by Alaska. Oil alone is responsible for nearly 50% of Alaska’s economy, and the tax structure of Alaska is almost 100% dependent on oil production. In 2012, the Prudhoe Bay oil field generated some USD 170 billion revenue, contributing nearly 90% of the state’s income. Economic analysts have predicted that by removing the fossil fuel sector from Alaska’s economy could likely cause its population, personal income, and jobs to halve [15]. On a national scale, many of the major oil- and gas-producing countries such as Norway and several Organization of Petroleum Exporting Countries (OPEC) members have economies that remain dominated and sustained by fossil-fuel revenues.

The levelized cost of energy (LCOE) provides the average cost of a unit of electricity throughout a power plants life cycle [16]. This covers operations and maintenance (OM) costs and considers the initial capital investment requirements [17]. An LCOE evaluation therefore considers:

• Initial investments or capital costs (capex);
• Average rate of electricity production;
• The operating and maintenance costs over the plant lifetime;
• The power plant’s lifetime;
• Discount rate to adjust for time value.

In assessing the economic viability of a power plant, it is useful to compare LCOE to the magnitude of the initial capex requirement to construct it.

The 2021 levelized costs of energy (LCOE) [18] ranges pertaining to specific fossil fuels were: for coal-fired plants from USD 0.05 to USD 0.15 per kWh; for natural-gas-fired plants from USD 0.04 to USD 0.10 per kWh; and oil-product-fired plants from USD 0.08 to USD 0.20 per kWh. For the same period (2021), the average unit capex requirements for these plants were: coal-fired plants from USD 1500 to USD 3000 capex per kW of capacity; natural-gas-fired plants from USD 800 to USD 1500 per kWh; and, for oil-product-fired plants from USD 1500 to USD 3500 per kW [18]. Figure 3 demonstrates that fossil fuels continue to offer some of the lowest cost alternatives for large-scale centralized electricity generation.

However, in global economic terms, the role that crude oil and coal play is slowly diminishing. Economic concerns exist relating to the economic dependence on fossil fuels and their negative environmental impacts. Figure 3 presents the oil intensity changes from 1990 to 2014 of selected major economies and the global economy. Oil intensity represents the quantity of fossil fuel (metric ton of oil equivalent) consumed to generate one unit of economic yield. It reveals that oil intensity has declined substantially over that period [19].

Figure 3 reveals that GDP growth doesn’t depend so heavily on fossil fuel consumption as it did two decades ago. This suggests that it is possible to achieve economic growth in many regions at a slower rate of growth in energy supply. OPEC in 2022 projected oil prices would be approximately USD 80/bbl in 2025 and USD 128/bbl in 2040. Growth in oil demand was expected to reach 900 kbbl/day per year in 2025, followed by a lower growth of oil supply would result in oil supply balancing demand of 103.5 mbbl/day per year in 2040.

2.1.2. Geothermal Energy

Geothermal power plant costs are typically divided into two main categories: (1) surface costs including the costs of surface exploration, construction and infrastructure design, operation and maintenance; and (2) the subsurface costs covering drilling, well completion and downhole maintenance. The LCOE of a typical geothermal power plant would range from USD 0.04 up to USD 0.14 kW/h [20].

The initial investment costs for a geothermal powerplant depend on plant size and electricity production rate. Global investments in geothermal power plants range between USD 2000 per kW and USD 5000 per kW [20]. However, there are substantial drilling costs and risks associated with high-temperature geothermal projects and the long-term sustainability of the deep sub-surface reservoirs. The capital cost breakdown of a typical high-temperature geothermal project is displayed in Figure 4, identifying that drilling and related infrastructure components typically account for about 40% of the total project costs. Over time the temperature and fluid circulation in the subsurface reservoirs often degrade and require additional drilling or stimulation to maintain it, which can add substantially to project life-cycle costs [17].

The geothermal market is potentially large globally but has grown very slowly in the past three decades and is developed in relatively few countries. The United States revenues from the total electricity production derived from geo-power plants is about USD 1.5 billion per year, with the expected revenues from geothermal energy in the next 20 years expected to range from USD 20 to USD 40 billion [17]. The US tax revenues from geothermal power plants are also significant. For example, in Nevada, the amount of energy produced in 2019 from geothermal power plants was 240 MW of electricity (i.e., equivalent to 3 Mbbl of oil), raising USD 800,000 in state taxes and about USD 1.7 million in property taxes. Additionally, the US Bureau of Land Management received royalties and rents from geothermal power plants a portion of which is returned to the state.

There is a growing use of low-temperature geothermal energy in the form of ground-source heat pumps for commercially competitive space heating of large and small buildings [21]. Studies have shown that in moderate-to-high-latitude conditions, ground-source heat pumps are more effective than air-source heat pumps for space heating [22]. There is considerable potential for such low-temperature geothermal heating around the world, not just in the high-heat-flow (volcanic) regions where the large-scale geothermal power generation projects are typically located.

2.1.3. Biomass Energy

The use of biomass for energy generation can have positive economic impacts for some regions/nations by reducing the costs and dependence on energy imports [23]. However, increased use of biomass for power generation and/or crops for biofuels can have negative economic impacts by causing crop prices to increase and reducing the growth of crops for food production. Zhang et al. [24] assessed the impact that biofuel have on corn prices and other feedstocks, observing a 20% to 40% increase in corn prices between 2012–2013. That study suggested that increased biofuel production could result in corn prices increasing by 53% by 2025. Biomass/crop feedstock prices substantially impact biomass energy LCOE. The estimated LCOE of electricity produced from biomass plants was estimated to range from USD 0.07 to USD 0.15 LCOE per kWh in 2020, with estimated capital costs for building new biomass plants ranging from USD 2000 to about USD 6000 per kW of energy capacity [25]. Feedstock costs contribute 80% of operating and production costs of biomass plants [24,26,27].

A factor that needs to be considered when accessing the economic value of biomass power plants is that the energy density of biomass is substantially less than that of fossil fuels. This results in lower energy conversion efficiency and plants with larger footprints than fossil fuel plants of the same capacity.

2.1.4. Solar Photovoltaic (PV) Energy

Investments in solar (PV) energy can lead to a variety of economic benefits however the magnitude of such benefits vary substantially depending on geographic location [28]. The LCOE of solar PV energy in 2021 ranged from USD 0.03 to USD 0.08 per kWh [9]. This LCOE decreased substantially over the past two decades and is projected to further decrease over the coming decade, whereas solar PV energy capital costs ranged from USD 1000 to USD 3000 per kW of capacity in 2021.

A substantial amount of solar PV energy revenue is supported by tax reduction incentives. For example, the Rajasthan PV plant (India) involved investments of about USD 1.4 billion in 2020, with revenues expected to reach USD 5.2 billion by 2025, contributing to a reduction in fossil fuel imports but reducing the tax revenues for the Government. The upfront costs associated with large solar power plants (PV and thermal) are high, and if the components are not manufactured in-country, then they represent a substantial import burden. Solar PV plant costs are divided into approximately 75% Capex and 25% OM. However, on the economic upside, when the facilities are built and operational, there are no fuel costs involved in operating them, thereby reducing the energy imports for energy-consuming nations and reducing exposure to fluctuations in international fossil fuel and biomass prices. In terms of energy efficiency of PV plants, it is important to factor in the energy consumed in manufacturing and installing the PV panels.

Return on investment (ROI) versus time is a useful benchmark with which to assess the value of installing PV power plants rather than using other energy sources. Of course, the ROI will vary depending on location based on solar intensity and sunshine hours over the course of a year. Considering the Rajasthan PV plant, if the same plant were constructed and operated in the Sahara Desert, it would produce more energy and achieve a faster payback and higher ROI.

Over the past two decades, solar PV efficiency has increased by about 40% and efficiency improvements continue to be achieved, progressively enhancing their long-term value, increasing ROI, and reducing payback time. At current efficiencies, large-scale solar PV plants are becoming commercially viable without subsidies or tax incentives in many countries. In the United States, for example, the rapid growth in large-scale solar PV plants has been sustained over recent years with the support of substantial tax incentives, but soon, these should no longer be required. For large-scale solar power contributions to the energy mix of a region, it is desirable to coordinate it with substantial short-term energy storage. If this is not done, the energy supply remains intermittent, and when there is oversupply (during long sunny periods or during off-peak times of day) much of the power generated is either wasted or curtailed. Solar power curtailments are a growing issue in large solar markets, e.g., Texas (USA) [29] and Germany [30].

2.1.5. Hydrogen Energy

Hydrogen generated from renewable resources remains expensive to produce but is expected to become a key large-scale renewable power source in the longer term. The versatility of renewable hydrogen as an energy source makes it a potentially attractive option but to harness it requires substantial infrastructure to both produce it and then store it under pressure [31]. Global investments in hydrogen energy were forecast to rise by about 33% from 2021 to 2026 [32]. In 2022 electrolyze capacity for renewable hydrogen production was about 700 MW and expected to rise to about 2 GW during 2023, with a substantial portion of that capacity being built in China.

The current demand for hydrogen, mainly generated from non-renewable fossil-fueled processes, is approximately used 55% for ammonia synthesis, 20% for methanol production, and 25% for various crude oil refining processes (e.g., hydrocracking). The developing hydrogen energy markets are usefully divided into “merchant” hydrogen, produced onsite in bulk and transported to customers, and “captive” hydrogen, generated and consumed on-site by industrial, commercial, or residential users. The global hydrogen market at the present time comprises of 95% captive hydrogen, which is expected to continue to dominate the hydrogen market over the next decade. As more investments are sanctioned for water-electrolysis-driven renewable hydrogen and methane-reformation-driven non-renewable hydrogen, the merchant hydrogen market is expected to grow substantially. In the United States, merchant hydrogen market annual revenues in 2021 reached USD 4 billion and are expected to increase about 10% by 2024.

The LCOE for hydrogen power plants ranged from USD 0.05 to USD 0.18 per kWh, with capex cost requirements varying between USD 1500 to USD 5000 per kW of capacity in 2020 [9]. However, renewable hydrogen plants are at the upper end of these ranges, making renewable hydrogen prices considerably higher than fossil fuels. Based on the US market, hydrogen costs USD 4.64/kg, compared to fossil fuels costing USD 1.5/kg [33]. However, some analysts predict that the costs of water-electrolysis-driven and methane-reforming-driven hydrogen production will fall substantially by 2030. There is an expectation that global investments exceeding USD 300 billion will be sanctioned for 200 new hydrogen production plants by 2030. Such investment would be equivalent to an increase in the global economy of about 1.7% and contribute nearly USD 6.7 trillion in market capitalization [33]. The three largest proposed hydrogen projects are: North Sea H₂ production (Netherlands; valued at USD 20 billion); Pilbara hydrogen plant (Australia; valued at USD 15 billion); and the Neom hydrogen plant (Saudi Arabia, valued at USD 5 billion). Some project that cumulative hydrogen sales in the next 30 years could exceed USD 2.5 trillion. However, to achieve that substantial technological improvements are required to reduce production costs, particularly of renewable hydrogen, and to provide affordable and safe hydrogen transportation and storage infrastructure. Large-scale underground hydrogen gas storage would be required, in reservoirs like those used for many decades to store natural gas. However, there are many technical issues that need to be resolved before underground hydrogen storage sites can be developed on a commercial basis [34].

Hydrogen is the least dense gas, making it necessary to store and transport it under pressure. This is technically challenging and adds substantially to its LCOE. Hydrogen can be stored either as a gas or as a liquid (under cryogenic conditions), the latter being more expensive but potentially safer. Hydrogen storage and infrastructure investments would need to reach about USD 630 billion by 2030 if the hydrogen production growth forecasts mentioned are to be achieved [32].

2.1.6. Hydropower Energy

Large-scale hydropower facilities involving concrete dams are expensive to build and highly dependent on geographic and climatic conditions for their long-term viability. The infrastructure involved includes dams, large artificial water reservoirs, fish ladders, turbines, and control facility buildings, which take between 5 and 15 years of operation to pay back the investments [35]. In the US, hydropower plants with a capacity of 80 GW repaid their capital costs from 2010 to 2016 by generating yearly revenue of USD 1.26 billion. Once hydropower infrastructure is in place, it has no fuel cost burden, providing it with very low marginal costs of generation. However, many hydropower plants are susceptible to fluctuating climatic condition, particularly droughts.

Hydropower plants contribute nearly 7% of the total global energy market. The economic value of a hydropower plants can be assessed by considering the costs of alternative energy supply avoided by their presence [36]. The average costs of hydropower plants of various scales are summarized in

Table 1. Hydropower plant cost for large and small facilities and plant upgrades [38].

Category	Installed Costs (USD/kW)	Operations and Maintenance Costs (%/years of Installed Costs)	LCOE
Large Hydro	1050–7650	2–2.5	0.02–0.19
Small Hydro	1300–8000	1–4	0.02–0.27
Refurbishment/Upgrade	500–1000	1–6	0.01–0.05

. To relate the operations and maintenance costs percentages (Table 1) to actual projects costs, China announced in 2013 that their hydropower plants incur operations and maintenance costs of about USD 4.8 per MWh, which are substantially lower than those of coal power plants, which incurred operations and maintenance costs of about USD 14.59 per MWh [37]. LCOE for hydropower plants are very low in comparison with most other energy sources. Based on IRENA data, for small-scale hydropower plants, LCOE ranges from USD 0.02 to USD 0.27 per kWh. For large hydropower plants, LCOE ranges from USD 0.02 to USD 0.19 per kWh [38].

A breakdown of the capital costs of a large hydropower project into its components is presented in Figure 5 [38]. It is apparent that the water reservoir (including the dam), tunnel powerhouse, and shafts account for more than 50% of the capital costs.

Hydropower plants are mature energy technologies that have been constructed and operated at a large range of scales for many decades. There is an expectation that hydropower construction projects will continue to fall as new civil engineering techniques are developed. An additional key value of some hydropower facilities is that they can be used as both short-term and long-term energy storage facilities on a large scale in the form of pumped-storage facilities [39]. Indeed, pumped storage facilities can store large quantities of electricity—much more than other forms of energy storage—in the form of potential energy. With the upsurge in construction of large-capacity intermittent renewable energy plants, energy storage facilities, including pumped hydropower, are in high demand, and many new pumped storage facilities are under construction around the world for that purpose.

2.1.7. Nuclear Energy

Large-scale nuclear power plants provide large-scale baseload energy in many countries. The long-term value of nuclear power plants is strongly linked to their upfront capital costs, which make the largest contribution (about 65%) to their LCOE, which ranges from USD 0.025 to USD 0.15 [40]. Nuclear power plants incur capital costs that range between USD 4000 to USD 7000 per kW of capacity. Licensing and regulatory fees for nuclear power plants are substantial and influence their economic viability. Regulators’ fees are USD 60 million per reactor, with vendor technology licensing—depending on reactor design—ranging from USD 180 to USD 240 million [40]. The annual discount factor applied (ranging from 3% to 10%) when valuing nuclear power plants has a substantial impact on their estimated long-term value and LCOE because these plants typically operate for 50 years or longer. Discount factors also act to diminish the cost contributions of decommissioning costs, which can be high, and a huge financial burden when actually incurred [41] but are often only incurred between 50 and 100 years after the nuclear power plants are built. Improved modular designs of modern reactors are focused on reducing the long-term decommissioning costs.

The LCOE of nuclear power plants are less sensitive to fuel prices than natural gas or coal power plants. For instance, by doubling uranium fuel prices from USD 25 per lb of U₃O₈ to USD 50 per lb of U₃O₈ increases LCOE from USD 0.5 to USD 0.62 per kWh (a 24% increase) [40]. For natural gas power plants, every 10% increase in fuel prices increases the LCOE by 7%, making them much more sensitive to fuel prices than nuclear power plants.

The nuclear power industry contributes approximately 500,000 jobs within the United States, which amounts to USD 60 billion of US annual GPD in addition to the tax revenues benefits to the local economy. For example, the Ginna nuclear power plant (580 MWe) in New York (USA) contributes a yearly revenue of USD 350 million and has an overall impact on the New York economy of USD 450 million per year. The closure of the Ginna power plant would therefore create a substantial economic shortfall for the state and the country with a loss of jobs, tax revenues and GDP. In Europe, it is estimated that each GW of nuclear power capacity built involves about EUR 9.3 billion of capital investment. Additionally, every euro spent in building Europe’s nuclear power capacity contributed to an increase in GDP of approximately EUR 4 and created 3.2 jobs [41].

Safety concerns with large nuclear power plants make it difficult to garner support for new large-scale nuclear power projects in many countries. In particular, the Fukushima nuclear power plant accident [42]—caused by a 15 m Tsunami in 2011—which caused a major direct impact on the Japanese economy, with clean up and plant recovery costing in excess of USD 200 billion and still ongoing, caused Germany to commence decommissioning of its nuclear power plant fleet and some other countries to curtail their nuclear power development projects. The development of small modular reactors (SMR) offers a smaller scale alternative for nuclear power that offers potential in the future to provide lower-cost, safer, quicker-to-build, and easier-to-operate alternatives to the traditional large scale nuclear power plants [43].

2.1.8. Ocean Energy

Although ocean energy (wave energy converter (WEC) and tidal power plant (TPP)) power generation remains at the early development stage, it offers huge potential, particularly at higher latitudes in nations with substantial coastlines subjected to high tidal reaches. In some such locations (e.g., United Kingdom; northern North America), ocean energy has the potential to play a more substantial future economic role [2]. There is substantial ongoing research and pilot testing of ocean energy devices—for example, in the European Marine Energy Centre (EMEC) in Scotland. However, the marine environment is highly abrasive, corrosive, and dynamic requiring robust facilities made of non-corrosive materials. In the long-term, operating conditions operation and maintenance costs are likely to be high for both WEC and TPP facilities. Hence, LCOE for ocean energy systems deployed in favorable locations in Europe and China are estimated to range from USD 0.12 per kWh to USD 0.16 per kWh, whereas in northeast Australia, the LCOE is estimated to range from USD 0.08 per kWh to USD 0.10 per kWh. However, LCOE with current technologies ranges up to USD 0.40 per kWh, applying discount rates of 10%, and with capital costs estimated to range from to USD 3000 to USD 8000 per kW of capacity [2,9].

Significant cost reductions and plant energy efficiency improvements are required to make these technologies commercially viable on a large scale [44]. Applying such improvements, ocean energy LCOE could be reduced to USD 0.15 per kWh and at that LCOE could make a substantial contribution to the energy economy and security of energy supply [45].

2.1.9. Wind Energy

Electricity generation from wind energy is achieved by onshore and offshore wind farms each consisting of arrays of multiple turbines elevated above ground on towers [46]. As wind is an intermittent resource, it requires backup power systems to cover when the wind is not blowing [47]. Turbine technologies have improved substantially over the past two decades, and their individual capacities have increased to about 12 MW onshore and about 18 MW offshore [48]. The introduction of floating wind turbines over the past decade has made it possible to deploy wind turbines effectively in deeper water far from the shoreline [48]. Wind energy facilities can have substantial influences on the economy through direct revenues, and indirectly, by providing economic benefits and cheaper energy to local communities. For example, Texas (USA), achieved an 11% electricity price reduction and increased tax revenues within recent years by implementing large-scale land-based wind energy systems.

Table 2. Wind energy cost breakdown and levelized cost of energy 2021 [49].

		Land Based	Offshore		Distributed
Parameter	Unit	Utility Scale Land Based	Utility Scale (Fixed Bottom)	Utility Scale (Floating)	Single Turbine (Residential)	Single Turbine (Commercial)	Single Turbine (Large)
Wind turbine Rating	MW	3	8	8	20 (kW)	100 (kW)	1.5
CAPEX	USD/kW	1501	3871	5577	5675	4300	3540
Fixed Charge Rate (FCR) “real”	%	5.88	5.82	5.82	5.88	5.42	5.42
Operational Expenditures	USD/kW/yr	40	111	118	35	35	35
Net Annual Energy Production	MWh/MW/yr	3775	4295	3336	2580	2846	3326
LCOE	USD/MWh	34	78	133	143	94	68

presents LCOE for land-based, offshore and distributed wind power facilities [49]. Land-based wind energy turbines achieve the lowest LCOE of USD 0.034/kWh with a capex of USD 1501/kW and operation and maintenance costs of US USD 40/kW/y. For offshore and distributed wind energy turbines, LCOE ranges from USD 0.078/kWh to USD 0.143/kWh, with capex for offshore facilities ranging from USD 3900/kW to USD 5600/kW.

In 2019, wind farms constructed on private land in Texas (USA) provided USD 706 million to local farmers from land lease agreements which were implemented through three different types of contracts: (1) fixed payments, (2) revenue-based payments, (3) combinations of (1) and (2). The total tax revenues generated from wind energy turbines in the USA for federal, state, and local authorities were estimated to be USD 7000 per MW of installed capacity. Wind energy is responsible for providing up to 10% of electricity in the USA and attracted USD 20 billion of investment to the United Stated economy and generated an estimated USD 2 billion in tax revenue in 2022 [46]. Europe has attracted investments for multiple large-scale wind energy project developments with capital investment requirements of EUR 3 to EUR 5 billion from 2018 to 2020 [46].

In recent years, offshore wind developments have been led by the United Kingdom, with the world’s largest offshore wind farm commencing electricity production in October 2023. The 3.6 GW Dogger Bank Wind Farm is located 130 km off the coast of eastern England and is being built in three 1.2 GW stages [50]. Many more large-scale offshore wind projects are planned for the UK and northern Europe over the coming decade.

2.2. Societal Impacts of Energy Sources

Assessing the impact a source of energy has on the social sector is vital to ensuring that communities benefit from energy investment decisions. Social considerations are also important in the understanding and implementation of sustainable energy development strategies.

2.2.1. Fossil Fuels

Fossil Fuels have significant positive and negative impacts on the social sector across the World. Fossil fuels sustain the global employment of approximately 32 million employees, with about 30% of those jobs associated with fuel distribution and marketing. In some oil-rich regions, the oil industry is responsible for most employment and attracts substantial inward migration over time to those regions, e.g., Alaska. However, on the downside, fossil fuels are responsible for substantial climate change, significant adverse effects on society, and environmental pollution both during their extraction and processing and their consumption. That pollution is associated with negative health consequences leading to premature deaths, particularly from lung and heart disease, various forms of cancer, and breathing-related illnesses. The health impacts of certain aromatic hydrocarbons present in crude oils, in some refined products, and in the petrochemical manufactured from them (e.g., toluene, xylene, gasoline, benzene, and ethylbenzene) can be particularly harmful to all forms of life. Global fossil-fuel-related deaths continued to increase and were estimated at 8 million in 2019.

2.2.2. Geothermal Energy

The geothermal energy sector has minimal direct impacts on the social sector but moderate indirect effects. Most geothermal energy employment opportunities occur during the construction phase and are temporary in a specific area with service contractors. In 2021, there were 196,000 individuals employed in the geothermal energy sector worldwide. China employed about 78,900 and the European Union about 60,000 individuals, whereas only about 8000 individuals were employed in the United States [20]. However, there are additional service company employees employed in drilling, exploration, and construction activities.

Table 3. Geothermal and natural gas employment rates per MW [51].

Power Source	Construction Employment (Jobs/MW)	OM Employment (Jobs/MW)	Total Employment for 500 MW Capacity (Person-Years)
Geothermal	4	1.7	27,050
Natural Gas	1	0.1	2460

compares the employment rate for geothermal power plants with gas-fired power plants on a jobs/MW of capacity basis. Compared to natural gas power plants, it is apparent that geothermal facilities are more labor-intensive, bringing more jobs to local communities but adding to the labor costs of operating the power plants [51].

However, geothermal energy facilities are accompanied by some health risks due to exposure to radiation from some of the materials brought to the surface during drilling and production, including toxic gases. These harmful materials include arsenic, hydrogen sulfide, radon, mercury, and benzene, which—if inhaled/ingested—have serious and sometimes fatal health consequences [20]. These materials can also cause contamination of surface and groundwaters, having both human health and wider negative ecosystem impacts.

Noise, particularly during the drilling operations, creates another community nuisance associated with geothermal power plants. However, during daily geothermal power plant operational processes, noise is generated from pumps, turbines, and generators, and in the USA, average noise from geothermal facilities was estimated to be 120 dB [20].

2.2.3. Biomass Energy

Operating a biomass energy plant is labor-intensive and therefore creates significant local jobs. They also provide jobs and revenue more broadly across those rural areas growing and/or harvesting the feedstocks that include both crops and agricultural and forest waste materials.

A total of 716,000 global jobs were estimated to be associated with biomass energy production (power and biofuels) in 2020. A 40-million-gallon ethanol fuel plant in the USA was estimated to provide between 4000 and 7000 job with annual payroll costs amounting to USD 200 million. In Brazil, the biomass/biofuel industry sustains about 11% of the workforce, providing hundreds of thousands of jobs [52].

On the downside, biomass energy production puts upward pressure on food crop prices and causes much land to be dedicated to production of its feedstocks (particularly, sugar cane, soybean, oil seed, and corn) rather than to growing food products. As this trend continues to grow it is likely to destabilize local and international food-crop markets. Analysis suggests that in Europe, biomass energy production by 2025 is expected to increase by 16% in plant-based oils and 10% in oil seeds, with the likely outcome of at least a 2.5% increase in crop prices, repeating some of the market impacts that occurred in 2011 and 2013 [52].

Like the negative health effects of fossil fuel combustion, burning biomass and the emissions associated with it can have similar impacts on human health (e.g., neurological disorders, heart attacks, breathing difficulties, and birth defects) and ecosystem wellbeing [53].

2.2.4. Solar Energy

Solar energy, particularly PV, is one of the fastest-growing energy sources and has created, and continues to create, substantial employment around the world. Those jobs are associated with solar panel manufacture and installation, solar plant operation and maintenance, and in extracting the raw materials (silica and many rare metals) involved. In 2019, such employment was estimated to amount to 3.9 million jobs globally, representing more than one third of the renewable energy workforce. The solar thermal sector, used particularly for commercial and domestic water heating, also provides substantial manufacturing and installation jobs around the world. Some forecasts suggest that by 2050, solar panels could provide 300 million direct and indirect job opportunities [54].

However, concerns exist associated with the manufacturing processes of solar panels. Substantial quantities of toxic substances are used in the preparation and purification of the semi-conductor components. These include most industrial acids and solvents, and in part of the manufacturing process, substantial silicon dust is generated. Inhaling or ingesting these substances can lead to significant health issues [54]. Another major social concern about the manufacture of solar energy materials is where that manufacture takes place. In countries that import nearly all the solar panels they install (e.g., United Kingdom) the local communities see none of the employment benefits from that manufacture. Hence, when developing and expanding solar energy, from a social-benefit perspective, it is essential for the manufacture of the bulk of the components to occur in country and to not depend on imported components.

2.2.5. Hydrogen Energy

The hydrogen energy sector is relatively diverse involving fuel cells for power generation and transportation, as fuel for combustion in power plants, and to manufacture carbon-free chemicals such as ammonia for use in energy storage and as industrial feedstock [55]. This is an emerging sector with substantial opportunity to grow if commercial viability can be achieved, Deloitte [56] forecast that the clean (green) hydrogen market has the potential to grow to USD 1.4 trillion per year by 2050 and support 2 million jobs globally per year between 2030 and 2050. However, to do so it has some serious technical and commercial hurdles to overcome. Some analysts forecast that if it can overcome these hurdles it could generate 2.5 million new jobs in the United States and 6.5 million jobs globally by 2025 [33], although that seems unlikely. Nevertheless, the industry is now offering above-average salaries in the USA for technical expertise.

A major positive development decision for the development of seven regional hydrogen hubs in the USA was progressed in October 2023, when the US Government awarded USD 7 billion in federal grants to accelerate their development. There were twenty applicants for these grants by consortia distributed across the USA [57]. The seven projects are listed in

Table 4. United States hydrogen hubs awarded federal grants in October 2023. Adapted from Otillar [57].

Hydrogen Hub	Funding Amount	Geographic Location	Feedstock	Production Capacity	Notable Corporate Partners
Appalachian Regional Clean Hydrogen Hub (ARCH2)	USD 925 million	West Virginia, Ohio, Pennsylvania, Kentucky	Natural gas	Unknown	EQT Corporation, Battelle, GTI Energy, Allegheny Science & Technology
California Hydrogen Hub (ARCHES)	USD 1.2 billion	California	Renewables, biomass	500 mt/day by 2030; 45,000 mt/day by 2045	Amazon, Brookfield Renewable, EDP Renewables, Hyundai, Pacific Gas & Electric
Gulf Coast Hydrogen Hub (HyVelocity)	USD 1.2 billion	Texas	Natural gas, renewables	9000 mt/day	Chevron, ExxonMobil, Fortescue Future Industries, Invenergy, Orsted, Shell
Heartland Hydrogen Hub (HH2H)	USD 925 million	Minnesota, North Dakota, South Dakota	Natural gas, nuclear	Unknown	Xcel Energy, Marathon Petroleum Corporation, TC Energy, Bakken Energy
Mid-Atlantic Clean Hydrogen Hub (MACH2)	USD 750 million	Delaware, New Jersey, Pennsylvania	Renewables, nuclear	85 mt/day to 600 mt/day	Monroe Energy, PBF Energy, Southeastern Pennsylvania Transportation Authority
Midwest Alliance for Clean Hydrogen (MachH2)	USD 1 billion	Illinois, Indiana, Michigan	Natural gas, renewables, nuclear	Unknown	AirLiquide, Exelon, ArcelorMittal, bp America, Constellation Energy
Pacific Northwest Hydrogen Hub (PNW H2)	USD 1 billion	Washington, Oregon, Montana	Renewables	50 mt/day to 100 mt/day	bp America, Amazon, Puget Sound Energy, Plug Power

. One of them (HyVelocity) is being led by major oil industry corporations in the Texas and the Louisiana Gulf Coast as a joint venture. Partners in that project include ExxonMobil, Chevron, Air Liquide, Mitsubishi Power Americas, AES, Sempra, and Orsted. Collectively, the seven hubs intend to produce 3 Mt/year of clean hydrogen, about one-third of the USA’s stated goal for clean hydrogen supply by 2030. These hubs will also eliminate 25 Mt/ year of CO₂ emissions from energy end users. The US DOE has the stated objective in making these awards of reducing the cost of clean hydrogen by 80% to USD 1/kg over the coming decade and reducing CO₂ emissions generated in hydrogen production to <2 kg of carbon/ kg of hydrogen manufactured.

On the downside, hydrogen combustion—although free of carbon emissions depending on the processes used—does generate NOx emissions, which degrade air quality and can lead to negative health and ecosystem damage [7,33]. Throughout the process of steam methane reforming (SMR) to produce non-renewable hydrogen, NOx and several volatile organic compounds (VOC), as well as CO₂ emissions, are formed. Public concerns over safety of hydrogen production and storage plants exist due to the risks of explosions and fires associated with leakage from pressurized facilities. Therefore, there are both positive benefits of green hydrogen energy (avoidance of carbon emissions and substantial job creation) and potential negative impacts (NOx emissions, increased hazards, and—in the short-term, at least—higher production and storage costs).

2.2.6. Hydropower Energy

Hydropower offers multiple social benefits including employment, freshwater storage, flood control, and in some cases recreational and water sports facilities [58]. However, it does come with substantial downsides including a large land footprint, substantial carbon emissions during construction, and in many cases large population displacements (e.g., tens of million individuals displaced by the Three Gorges Dam facility in China and 55 million individuals displaced in the past decade in India) [59], leading to local populations losing their homes and livelihoods.

The job opportunity forecasts for the USA, hydropower industry based on its expected growth made in 2018 were 120,000 by 2030 and 500,000 by 2050, up from 66,500 jobs in 2018 [60]. A breakdown of those potential jobs is provided in Figure 6.

In 2020, hydropower contributed 2.3 million jobs worldwide [57]. However, climate changes bring with it much uncertainty with respect to rainfall on which hydropower plants are dependent. Periods of floods interspersed with extended droughts can lead to unreliable energy contributions from the hydropower sector, as has been the case in the western states of the USA in recent years and many other parts of the world with large existing hydropower infrastructure (e.g., Brazil). The development of new large-scale projects in remote areas can lead to negative “boomtown” impacts [58] with an influx of a large migrant work population for several years during construction that subsequently disappears. In most situations, such occurrences have negative social consequences for the indigenous rural communities.

2.2.7. Nuclear Energy

The nuclear sector does not maintain a good public image, primarily because of the risks of substantial, long-lasting health and environmental damage associated with the large-scale, high-profile accidents (e.g., Chernobyl and Fukushima) and leakages that have occurred. The inadequate handling, treatment and long-term storage of nuclear waste (with low-level and high-level radioactive contamination) associated with many nuclear power plants, and its long-lasting legacy, is another issue of major public and environmental concern [41].

Despite the major downsides, nuclear energy has substantial social upsides in terms of its potential for large-scale, low-cost, carbon-free power generation well suited to provide baseload supply. Moreover, various irradiation technologies used in the food processing and medical industries provide substantial societal benefits. The nuclear power sector is a major employer. For instance, it accounts for approximately 50,000 jobs in the European Union, where for every EUR 1 invested in nuclear energy, approximately three jobs are created directly and indirectly. In the United States, the Ginna 580 MW nuclear power plant (New York State) provides approximately 700 direct jobs and 1000 to 1200 indirect job, generating an annual income of USD 100 million [61]. Worldwide the nuclear energy sector provides approximately 100,000 jobs. The new generation of large-scale and SMR reactors offer the potential to overcome many of the downsides of the old nuclear powerplants and many believe that nuclear power offers the fastest route to reducing CO₂-emissions on a global scale and mitigating the impacts of climate change.

2.2.8. Ocean Energy

Public opinions are mixed on the perceived benefits of ocean energy. As a carbon-free energy source, its benefits are acknowledged, but there are substantial concerns about its potential impact on marine and coastal environments, including fisheries; impacts on all marine life; marine navigation (commercial and leisure); visual impacts; and negative impacts on tourism and property prices in some areas [62]. Therefore, large-scale tidal reach projects in populated and scenic regions are not met with widespread public support. Consequently, to successfully implement such projects requires careful planning with designs, installation and operating strategies that mitigate these concerns.

In some circumstances, particularly remote and isolated coastal areas and islands, ocean energy plants offer the potential to support rural communities with low-cost, cheap power supply and employment. However, for ocean energy to be effective in such locations, it would need to be implemented at a relatively modest scale to match local energy demand. Nevertheless, approximately 25 local jobs, mainly in operation and maintenance (OM) roles, would likely be generated by 100 MW ocean energy plant [62]. The least visually intrusive ocean energy systems are WEC devices positioned in deep water many kilometers offshore with transmission cables submerged and secured on the seafloor. The industry has a long way to go to have a major social impact on communities via employment opportunities or in providing reliable local renewable energy supply.

2.2.9. Wind Energy

Surveys of public approval regarding the deployment of onshore wind turbines in the USA and UK. over the past decade have received social acceptance ratings of 70% [63]. However, a substantial part of that approval is from the urban population, which is not impacted visually or audibly by their deployment, whereas the rural communities that live close by windfarms are much less positive. This difference has led to a “social gap” between high apparent approval ratings yet strong local objections to plans to deploy these facilities in people’ neighborhood. In the U.K., social studies have shown that property owners/purchasers are prepared to pay from GBP 650 to GBP 1400 per year to avoid living within 2 km of a wind farm. Clearly adverse visual and noise impact are negative social consequence of for communities living close to wind farms [60]. For these reasons, populations are much more approving of offshore wind farms.

In the United States, wind farms provided 117,000 full time jobs in 2020, with O&M jobs often involving residents or inward migration to the vicinity of wind farms [64]. Wind power represents the second fastest growing energy source (after solar PV) in the USA, and its capacity has grown exponentially over the past two decades. Up to 2020, wind power capacity was exclusively focus onshore, but since then large offshore wind projects have been sanctioned for deployment off the north-eastern coast, and licensing is underway for deployments offshore California [65]. The LCOE of offshore wind in 2022, according to that EERE report, varied between USD 0.06 /kWh and USD 0.12 /kWh in 2022. However, substantial inflation of offshore facilities and service costs worldwide have caused this sector to run into commercial viability problems in 2023, with the average levelized cost of a subsidized offshore wind plant in the USA rising to USD 0.114 / kWh in 2023.

In the USA, onshore wind facilities employ between 7 and 11 individuals per 100 MWh of electricity generated. On the other hand, China and Brazil employ 550,000 and 260,000 workers, respectively, in the wind power sector [64]. Globally, wind energy is responsible for employing 3.3 million people, directly in onshore or offshore plants, and indirectly in the O&M service sectors. According to the International Renewable Energy Agency (IRENA) [66], renewables jobs nearly doubled worldwide in the past decade, rising to 13.7 million in 2022, and were dominated by the solar PV and wind energy sectors.

2.3. Environmental Impacts of Energy Sources

2.3.1. Fossil Fuels

Combustion processes that play an integral part in fuel production upon using fossil fuels emits harmful greenhouse gases (GHG) including carbon dioxide (CO₂) [67]. In addition to combustion, fugitive emissions of methane (CH₄) during production and transport of fossil fuels and the deliberate flaring and venting of natural gas, also contribute to GHG accumulations in the atmosphere. These emissions are highly connected to climate change since they are responsible for trapping heat inside Earth’s atmosphere. Although fossil fuels have high energy densities making them attractive options for energy transportation and storage and provide significant economic benefits to the economy and industry, they come at a significant environmental cost. The CO₂ emissions per kWh of energy produced for the fossil fuels are [68]. Coal-fired power plants range from 2.2 lb/kWh to 2.7 lb/kWh; natural-gas-fired power plants range from 0.9 lb/kWh to 1.2 lb/kWh; and petroleum product (oil)-fired power plants range from 2.0 lb to 2.7 lb per kWh [67]. Of course, the ultimate generators of those emissions are the utilities, companies, and individuals that have willingly purchased and consumed (combust) these in-demand fossil fuels. Therefore, collectively, almost all of the human race is responsible for these GHG emissions, not just the fossil-fuel-producing companies, including the impacts on the environment, climate, and health that have resulted from fossil fuel combustion [69,70].

Acidification of oceans: nearly a quarter of GHG emitted by fossil fuel production and consumption are absorbed by sea water and distributed through the World’s oceans. This has caused the pH level of ocean waters to fall substantially due to increasing acidity. As a result, the process of building coral reefs and ocean ecosystems more generally have been greatly affected, putting many species at risk. Increase in extreme weather events: Extreme weather and the natural disasters sometimes associated with them have become more frequent because of climate change. From 2016 to 2020, USD 605.4 billion was spent on dealing with the damage consequences of extreme weather events in the USA, including hurricanes, wildfires, floods, and severe storms. Air pollution: Nitrogen oxides (NOx), carbon monoxide (CO), oxides of sulfur (SOx), mercury (Hg), volatile organic compounds (VOC) and particulate matter (PM) are among the most harmful air pollutants resulting from the production/combustion of fossil fuels. These pollutant gases cause acidification (“acid rain”), resulting in the lowering oxygen levels in the near-ground-level atmosphere, causing extensive damage to ecosystems through eutrophication, and the poor air quality also causes substantial human health problems. The rise in global sea level: The progressive rise in atmospheric temperatures causes the polar ice sheets and mountain glaciers to gradually melt. That meltwater enters the oceans and causes sea level to rise and inundate low-lying coastal areas. All coastal areas, particularly those with low-lying shorelines, are now obliged to dedicate funds and take actions to try and protect vulnerable coastal areas. If climate change is allowed to continue, such coastal protection efforts will not be successful in the long term. Water pollution and oil spills: The effects of oil and petrochemical spills in water at the Earth’s surface pose a threat to human welfare, aquatic life, and ecosystems in general and also threaten the potential contamination of groundwater. In addition, water consumption by the oil and gas production sector has increased substantially in the past two decades due to the fracture stimulation requirements of tight (low permeability) reservoirs. The wastewater generated by fracture-stimulation processes contains many environmentally damaging and some toxic substances, including chlorine, lead, and arsenic. If the produced and flowback waters are not adequately handled and treated, they can cause water pollution and extensive ecosystem damage. Plastic pollution: Almost 99% of plastic production is from petrochemicals derived from fossil fuels. Unfortunately, many plastics are not biodegradable and when discarded in the form of waste or litter remain in some form in the environment. The amount of plastic waste that accumulates yearly is 300 million tons, distributed around the world. Of these, tens of millions of tons end up as macro- and microfragments in the ocean and enter the food chain, some ultimately into humans via the consumption of seafood. Additionally, GHG emissions from petrochemical/ plastic manufacturing are substantial. For example, the USA petrochemical industry is estimated to contribute 250 Mt of GHG emissions to the atmosphere annually, second to the power generation industry in magnitude.

2.3.2. Geothermal Energy

Air quality: Geothermal energy production typically adheres to the global clean air standards with respect to GHG emissions, with their main emissions being water vapor. There are some gas emissions brought to the surface in the produced fluids from the wellbores during the production of hot water/steam. However, power plants that operate closed-loop systems return most of these to the sub-surface reservoirs [20]. Solid wastes: Geothermal energy projects do produce some solid wastes, particularly associated with the drilling of the wells, and these contain some naturally radioactive materials that need to be disposed of. Some mineral deposits, including those of sulfur, are precipitated from some geothermal fluids. If not handled and treated correctly those solid wastes can cause damage if released to the environment. Land use and site footprints: Geothermal power plants involve construction on designated land areas, the area of which depends on the plant capacity and process technologies employed. Generally, geothermal power plants require 1 to 8 acres per megawatt of electricity produced [20]. However, boreholes also require drilling and production sites that contribute to their overall footprint. Induced earthquakes: Drilling and stimulating geothermal wellbores can cause induced seismic activities/earthquakes by altering the sub-surface stress regime and stimulating existing but dormant faults to activate. For example, in 2017, at the Pohang geothermal power plant (South Korea), a 5.7-magnitude induced earthquake leading to 59 injuries [20] was attributed to surface swelling caused by injected fluids.

Table 5. Environmental Impacts of geothermal power plants [51].

Impact	Probability of Occurring	Severity of Consequence	Duration of Impact
Air quality emissions	Low	Medium	Short-term
Surface water discharge	Medium	Low to medium	Short-term to long-term
Underground contamination	Low	Medium	Long-term
Land subsidence	Low	Low to medium	Long-term
High noise levels	High	Medium to high	Short-term
Well blowouts	Low	Low to medium	Short-term
Conflicts with cultural and archaeological features	Low to medium	Medium to high	Short-term to long-term
Social economic problems	Low	Low	Short-term
Chemical or thermal contamination	Medium	Medium to high	Short-term to long-term
Solid waste disposal	Medium	Medium to high	Short-term

provides a summary of geothermal environmental impact including clean air quality, solid wastes, land footprint, noise levels, subsurface contaminations, and surface water discharges.

2.3.3. Biomass Energy

Similar to fossil fuels, the majority of biomass energy sources require combustion, whereas other biomass processes involve fermentation (e.g., ethanol manufacture) or other transformation processes (e.g., biodiesel), all of which release GHG as emissions. To partially offset GHG releases, new biomass must be continuously planted and grown to photosynthesize. The biomass energy industries are major contributors to deforestation, using substantial quantities of water and emitting pollution during their harvesting, transportation, and consumption.

• Deforestation: wood (harvested timber) and forest waste is a major feedstock for the biomass energy sector. If not managed carefully and accompanied by replanting, this can cause severe environmental problems, including ecosystem damage or loss, soil erosion, and deforestation. Unfortunately, many biomass supply chains are not managed in a sustainable way such as to avoid ecosystem damage [53].
• Water use: Biomass power plants, like other thermal power plants, use substantial quantities of water in the generation of power. In arid areas, this can be problematic for the environment and put a strain on the water required for agriculture.
• Pollution: The combustion of many forms of biomass leads to polluting emissions, including GHG and particulate matter (PM). The PM generated consists of a large range of materials, some at the scale of a few microns, that can be absorbed into human (and animal) blood streams via respiration. This PM includes some carcinogenic (cancer-causing) elements and toxic metals, including mercury, arsenic, cadmium, and selenium. Such emissions are particularly harmful to the environment and human health when generated by multiple users of small-scale equipment (e.g., wood-burning stoves), as those emissions collectively degrade air quality and cannot be captured and treated as in larger centralized power plants [53].

2.3.4. Solar Energy

Unlike most energy sources that use water for cooling and operational purposes, the production of energy using solar PV does not use water in its energy generation process. PV in dusty locations does occasionally use water to clean the solar panel surfaces, but generally, PV has very low water intensity, which is positive for the environment.

Although solar PV does create GHG emissions during its operations, these are GHG emissions over a solar panel’s life cycle. The magnitude of GHG emitted during panel manufacturing, transportation, assembly, maintenance, dismantling, decommissioning recycling, and waste disposal significant [71].

The land footprint per unit of energy (ranging from 3.5 to 10 acres/MWh) generated is higher for solar PV than any of the other energy sources considered [72]. This is not a major issue when solar panels are deployed on the roofs of commercial or residential buildings or floated over a fractional area of reservoirs and water courses. However, when it is deployed on a large scale on agricultural or wilderness land surfaces, it causes major disruptions to the local ecosystems and local drainage. Concentrated solar (thermal) power plants (CSP) have an even greater land footprint ranging from 4 to 17 acres/MWh By 2035, 5.7 million acres in the USA may be occupied by commercial-scale solar power plant accounting for 0.3% of the total land area. This would likely have negative consequences for many local ecosystems.

The treatment and disposal of wastes from decommissioned solar power plants is a major, yet little addressed issue. Some estimates suggest that by 2050 the accumulated amount of solar panel waste could exceed 75 million metric tons unless more effective ways of recycling their materials can be established. The rate at which solar PV panels need to be replaced is substantially faster than originally envisaged [70]. Unfortunately, it is expensive to recycle them, meaning that most defunct PV panels end up in landfill sites. Some of the components they contain are potential environmental pollutants. Hence, there is an urgent need for the solar industry to be obliged to recycle these materials.

2.3.5. Hydrogen Energy

Hydrogen energy has the potential to be a very clean energy source, depending on how it is produced [31], how it is used (combustion versus fuel cell) [7], and how much leakage of hydrogen into the atmosphere occurs during its production, storage, and consumption [73]. It is clearly not without emissions problems or potential climate impacts. Hydrogen acts indirectly as a GHG in the atmosphere with short-term effects of about two decades. When hydrogen is released into the atmosphere via leakage, it reacts with hydroxyl radicals, causing them to lose their effectiveness, thereby boosting GHG impacts.

The small size of the hydrogen molecule means that it can leak easily from containment (pipelines and storage). This means that as the use of hydrogen expands more hydrogen can be expected to leak into the atmosphere and cause short-term negative GHG impacts. Hence, it is essential to improve steel pipeline integrity to better contain hydrogen in the new hydrogen gas hubs being developed. Additionally, it is important to rigorously monitor hydrogen facilities, including underground storage sites [31], for hydrogen leakage to improve our understanding of exactly how much hydrogen is escaping through leakage. Moreover, “green” hydrogen generated by renewable methods is likely to be less harmful than “blue” hydrogen produced from natural gas combined with carbon capture and storage (CCS), because the later involves leakage of some CH₄ and CO₂ as well as hydrogen [73].

Another key environmental issue for hydrogen is its association with substantial NOx emissions when it is combusted in power plants [7]. This means that hydrogen hub facilities also need to be carefully monitored for NOx emissions to verify their benefits to air quality compared to natural gas plants combined with CCS.

2.3.6. Hydropower Energy

Although hydropower plants do not generate GHG directly during their power generation operations, they can have substantial environmental impacts. Hydropower can contribute negatively to submerged land-based and natural aqueous habitats. The construction of hydropower plants in large-scale cases includes the construction of dams and reservoirs and in small-scale run-of-the-river designs diverts the flow of rivers. This often disrupts and/or obstructs fish migration, affecting the breeding processes, and potentially devastating fish stocks. The hydropower facilities may also change water flow patterns and temperatures that, coupled with turbine blade impacts can also affect aquatic ecosystems more generally [74]. The artificial reservoirs of large-scale hydropower projects have large areas that submerge and destroy formerly established terrestrial ecosystems. The static and oxygen-poor nature of the water in those reservoirs disrupts the natural flow of nutrients to the sections of the rivers and—in some cases—coastal and marine areas downstream of the dams, and that may lead to ecosystem imbalances.

Large-scale hydropower projects involve the construction of large dams made of steel and concrete. The manufacture of cement and steel is associated with substantial GHG emissions. Moreover, the land excavations and dam construction, often taking more than five years to complete, are also typically associated with substantial GHG emissions [75]. Some CO₂ emissions do occur over the lifetime of an artificial reservoir as the submerged vegetation within it decays. The magnitude of those emissions depends on the size of the reservoir and the nature of the submerged vegetation but is typically higher in tropical locations. Hydropower plants are estimated to generate CO₂ emissions in the range of 0.04 to 0.11 lb CO₂/kWh.

2.3.7. Nuclear Energy

Although nuclear power plants to not generate significant GHG during their electricity generation processes, the mining, processing, and enrichment of uranium fuel does involve GHG emissions [76]. Additionally, substantial concrete, steel, and other metallic materials are used in the site and plant construction, generating substantial GHG emissions. Nuclear plants are estimated to generate CO₂ emissions in the range of 0.03 to 0.10 lb CO₂/kWh [68].

The land footprint of nuclear power plants depends on their power capacity but is relatively small compared to those of other energy sources. A 1000 MW nuclear energy power plant is estimated to require a land area of 2.59 km² (1 m²) [76]. However, nuclear plants do have substantial impacts in terms of the volume of water they use for cooling and the impacts that their warm-water outflows have on the adjacent rivers and marine environments. Regulations typically control the water outflow temperatures and compositions (in terms of radioactive materials) within strict limits. Hence, the warm water impact in the form of thermal pollution on aquatic ecosystems is typically contained to local areas close to the plants [77].

In the absence of long-term nuclear waste treatment much of the spent reactor fuel remains stored around the world at the nuclear plant sites, with relatively little stored in long-term underground repositories. Hence, there is a risk of leakage of high-level nuclear waste due to natural disasters (e.g., severe earthquakes, tsunamis etc.), as occurred at Fukushima in 2011, or terrorist actions. Most reactors are built with multiple layers of protection and failsafe barriers to prevent such incidents, but a small risk remains that such events could occur [61].

2.3.8. Ocean Energy

Future ocean energy plants are estimated to generate CO₂ emissions in the range of 0.01 to 0.06 lb CO₂/kWh [68]. A major environmental concern for ocean energy plants (tidal- or wave-driven) is that they disrupt water flow, change wave heights, and alter sedimentation patterns along coastlines or in river estuaries and thereby have potentially negative impacts on aquatic ecosystems [62]. Underwater turbine noise and potential collision risks for fish and marine mammals are other concerns that require the careful design and deployment of such systems. The construction, installation, and decommissioning of ocean energy plants requires a certain amount of seabed and coastline disturbance. Moreover, the electromagnetic fields generated from power transmission cables on the seafloor, or on estuary and riverbeds, may also disrupt aquatic ecosystems. Detailed local studies should be conducted to quantify such impacts before specific ocean energy plant designs are approved for deployment.

2.3.9. Wind Energy

Although wind farms do not emit CO₂ or use water during their operations, they do have environmental impacts throughout their life cycle [78]. Wind farms are estimated to generate CO₂ emissions in the range 0.02 to 0.09 lb CO₂/kWh [68]. The construction of wind farms has a land area impact including the construction of access roads that can interfere with ecosystems. However, bird and bat impacts with the turbine blades are the most significant ecological impacts, which are becoming more significant as individual turbine units increase in size and wind farms of larger capacity are built. There are also potential offshore ecological impacts that require careful evaluation when planning and constructing large offshore wind farms [79]. The visual impacts of windfarms destroying the ascetic beauty of the natural environment are also of concern to many residents and tourists, although that is often not considered as substantial environmental damage.

Life cycle assessments reveal that the materials involved in the manufacture of wind turbines account up to 80% of their environmental impact [80]. However, some of those materials, particularly turbines blades made from plastic/fiberglass, are not easily recyclable and end up in landfill sites. On the basis that turbines and the turbine blades have an expected lifetime of 20 years, accumulated wind turbines waste is expected to amount to many millions of tons over the coming decades. The complete recycling of a 60 MW wind farm is estimated to have the potential to reduce emissions by 7351 tons of CO₂ [80]. If steps are not taken to improve the recycling of wind turbines, their environmental impacts will become major problems over the coming decades.

3. Results and Discussion

It is apparent from Section 2 that all nine of the main energy sources available bring problems as well as problems when they are deployed on a large scale. Fossil fuels deliver high energy density and fuels that are readily stored and transported along established global supply chain infrastructure. They also generate substantial employment and tax revenues worldwide along all components of their supply chains. However, from the environmental and social perspectives fossil fuels are the most problematic due to their substantial GHG emissions, and other air pollution components responsible for human health issues and ecosystem damage. However, the environmental impacts of hydropower and nuclear power are also substantial. Biomass offers low energy density and generates substantial pollutants when consumed, which can only partly be offset by continuous regrowth of biomass supply. Hydrogen power, ocean energy, and geothermal energy require substantial technology improvements and massive capital investment before they can be deployed on the scales to revival the other energy sources and relied upon to provide baseload energy supply around the world. Solar and wind energies have been the fastest-growing energy sources globally for the past two decades. From the air quality and emissions perspective, they offer excellent alternatives, but they have a high land footprint and substantial ecosystem impacts. One of the key long-term concerns with rapidly expanded solar and wind energy deployment is the recycling of the plant’s components. Now most solar PV cells and wind turbine parts (including blades) are not being recycled, which is unsustainable in the medium term.

3.1. Economic Comparison of Energy Sources

Relative affordability is of crucial importance when making choices between energy sources for potential future deployment. The range of levelized cost of energy (LCOE) compared to the capital costs of building a unit of capacity offers the best means of making such comparisons.

Table 6. 2021 estimates for LCOE and capital cost per unit of capacity for power generation plant using nine different energies. Numbers are from tables presented in Section 2.

Energy Source	Levelized Cost of Energy (USD/kWh)	Capital Cost (USD/kW)
Fossil Fuels Energy	Coal-fired plants: (0.05–0.15) Gas-fired plants: (0.04–0.10) Oil-fired plants: (0.08–0.20)	Coal Plants: (1500–3000) Gas Plants (800–1500) Oil-fired plants: 1500–3500)
Geothermal Energy	0.04–0.14	2000–5000
Biomass Energy	0.07–0.15	2000–6000
Solar Energy	0.03–0.08	1000–3000
Hydrogen Energy	0.05–0.18	1500–5000
Hydropower Energy	0.02–0.19	1000–8000
Ocean Energy	0.10–0.40	3000–8000
Nuclear Energy	0.025–0.15	4000–8000
Wind Energy	0.03–0.17	1000–6000

summarizes the LCOE and capital cost information.

Capacity factors of specific plants measure what percentage of the time they are operating. It has a substantial impact on LCOE. For instance, natural gas plants that operate as baseload power suppliers are designed to supply power all the time and their capacity factors are high and vary according to the maintenance downtime they incur. Such plants display much lower LCOE than peaking gas plants that only operate at peak times (sometimes only for a few weeks a year during winter cold periods). Another factor influencing LCOE is plant efficiency; more energy-conversion-efficient plants tend to have lower LCOE than less efficient plants. For example, combined cycle gas turbines achieve >=50% energy conversion compared to single-cycle gas turbines with energy conversion of <35%. Both the intermittency of operation and energy conversion efficiency are key factors influencing LCOE of solar- and wind-powered facilities.

Higher capital costs associated with offshore locations or drilling deep/difficult reservoirs (gas/geothermal/oil projects) lead to higher LCOE than similar-capacity projects incurring lower capital costs. High capital cost is a major challenge for scaling up green hydrogen power projects and ocean energy projects. It is also a challenge for many large-scale hydropower and nuclear projects when coupled with the long period needed to payback those investments, a factor that also causes LCOE to increase. Energy conversion efficiency and high OM costs are additional factors holding back many potential large-scale ocean energy projects. The low energy density of biomass can be improved to an extent by shredding and compacting biomass into dense pellets, but even with such efficiency improvements, the energy conversion efficiency is less than that of fossil fuels. Indeed, to counter these, substantial quantities of biomass are co-fired with coal in thermal power plants.

In summary, solar PV, onshore wind, and natural gas offer the commercial attractions of low LCOE and relatively low capital costs per unit of capacity (Table 6). Natural gas plants require a smaller land footprint and for a large capacity offer a faster payback than other options. Large geothermal, nuclear, and hydropower projects can also achieve very low LCOE but require more capital per unit of capacity, take longer to plan and build, and are typically associated with long payback periods. Renewable hydrogen power and ocean energy sources still require technological developments and cost efficiencies to demonstrate that they can compete with other mature energy sources considered. Biomass also does not compete effectively with other energy sources for large-scale supply due to its energy efficiency and large land footprint. Small- to medium-sized biomass plants are more likely to be commercially viable as periodic back-up to intermittent renewable energy sources.

3.2. Social Impact Comparison of Energy Sources

Fossil fuel energy sources are responsible for more employment and generate more tax revenue worldwide than any other energy source. Those fuels are also in high demand for power generation, space heating, and transportation because of their convenience, driven by their high energy density. However, fossil fuels have far greater negative climate, pollution, health, and ecosystem impacts than other energy sources. Hence, to become sustainable, the fossil fuel industry needs to invest heavily in GHG mitigation strategies, such as adopting various available carbon capture and storage options [81], and substantially improve its performance on natural gas flaring and fugitive emissions, leaks, and spills in the short-term. Failure to do so will lead to the fossil fuel industry being displaced by alternative renewable energy sources in many parts of the world, even though it will be more costly and inconvenient to do so. The fossil fuel industry’s destiny is in its own hands; it has so far been far too slow to adapt and respond to mitigate its emissions issues, but it will become increasingly difficult for it to continue with business as usual. Fossil fuels are therefore characterized as “poor” in terms of a social impact indicator.

The manner and pace in which the uptake of renewable energy alternatives has developed over the past decade has increasingly become data driven, with evidence that artificial intelligence is destined to play an increasing role in managing and deploying distributed energy sources more efficiently and effectively [82]. This is significant, as it will enable dispersed solar and wind energy resources to compete more effectively with centralized, large-scale power plants. More effective use of dispersed, distributed, and localized energy sources would certainly meet with substantial social approval in many nations, particularly as it would likely lead to more local employment in the energy OM sector. Another relevant social issue in many countries is the energy–power nexus [83] because energy sources that use large quantities of water put a strain on already difficult-to-allocate-and-replenish water resources. Those renewable energy sources that involve minimal water usage (i.e., solar and wind) are likely to be viewed with greater social approval as water resources become scarcer in certain areas.

Geothermal and biomass energy sources both pose certain pollution and health impacts that damage their social standing. Public concern over lack of recycling and efficient waste handling of component materials in the solar and wind energy sectors are likely to increase as the accumulated mass of decommissioned PV panel and wind turbines increases as those industries expand. The use of large quantities of rare metals in solar storage and wind storage systems is also of social concern, as are where those materials come from and how the markets for those materials are managed and controlled.

Hydropower has a relatively high social rating because of its large scale, relatively low GHG emissions, and lack of major air-quality-related health issues but social concern exists about the high costs and large surface footprints of such facilities. Additionally, when large dams fail (either through accidents or terrorist actions), the damage can be catastrophic, with potentially large loss of life The hydropower sector does not create as much employment as the more distributed renewable energies (solar PV and wind). The ability to use some hydropower facilities as large-scale pumped-storage reservoirs makes them unique among available energy sources in being able to store large quantities of energy over short-, medium- and long-term time scales.

The public remains uncertain as to whether the renewable hydrogen energy sector or the ocean energy sector will be able to develop technologies within the next decade that can provide large-scale commercially competitive power generation without damage to the environment. It is very much up to these industries to demonstrate that they can do this; their long-term uptake and acceptance depends upon it.

The nuclear energy sector has the lowest social approval rating of all the energy sources considered, lower than the coal sector and substantially lower than the natural gas sector. The reason for this is public concern over the risk of major accidents and their impact on long-term public health. Consequently, the building of new plants has been limited over the past three decades due partly to high capital costs and long-term concerns over decommissioning liabilities and public perception, making governments and banks reluctant to financially support and sanction the necessary investments. However, new nuclear technologies have emerged, particularly SMR, that are beginning to receive more support with the recognition that the low GHG emissions and small footprints of nuclear facilities plants could play a useful role in decarbonizing the power sectors centralized generation facilities and balance the more distributed locations of solar PV and wind energy facilities. If nuclear is to play this role, then large investment needs to be made within the next few years for it have a timely impact in the battle against climate change.

Table 7. Comparative social impacts of nine energy sources. Numbers are from tables presented in Section 2.

Energy Source	Approximate Jobs Provided Globally (2021)	Health and Safety Impacts
Fossil Fuels Energy	32 million	High risk
Geothermal Energy	196 thousand	Medium risk
Biomass Energy	716 thousand	High risk
Solar Energy	4.3 million	Low risk
Hydrogen Energy	120 thousand	Medium risk
Hydropower Energy	2.3 million	Low to medium risk
Nuclear Energy	100 thousand	High risk
Ocean Energy	60 thousand	Low risk
Wind Energy	3.3 million	Low risk

compares the global employment provided and the health and safety risk associated with the nine energy sources considered. On the employment side, there is a huge gap between the fossil fuel sector and other energy sectors. However, hydropower, solar and wind do offer substantial employment with much better health and safety outcomes.

3.3. Environmental Impact Comparison of Energy Sources

Table 8. Key environmental impacts of energy sources. Numbers are from tables presented in Section 2.

Energy Source	Carbon Emissions (lb/kWh)	Ecosystem Impacts
Fossil Fuels Energy	Coal Plant: (2.2–2.7) Gas Plants: (0.9–1.2) Oil-fired plants: (2.0–2.7)	High Moderate to high High
Geothermal Energy	0.8–2.87	Moderate
Biomass Energy	0.51–0.88	Moderate to high
Solar Energy	0.09–0.20	Low to moderate
Hydrogen Energy	0.05–0.11	Low to moderate
Hydropower Energy	Small Plants: 0.04–0.08 Large Plants: 0.05–0.11	Moderate Moderate to high
Nuclear Energy	0.03–0.10	Low to moderate
Ocean Energy	0.01–0.06	Low to moderate
Wind Energy	0.02–0.09	Low to moderate

summarizes two of the most important environmental impacts of the energy sources considered: magnitude of carbon emissions and the level of ecosystem impacts. It is noteworthy that none of energy sources an unequivocal “low” for ecosystem impacts. On small-scale deployments solar PV and wind energy have the potential to do this, as wind energy does with many offshore deployments, and solar does when deployed on roof tops or over parts of reservoirs. However, the large footprints of large solar PV and land-based wind plants inevitably leads to ecosystem disruption.

Wind, ocean, and nuclear energy sources offer the lowest range of carbon emissions, followed closely by hydropower, renewable hydrogen, and solar power. These six renewable energies offer the best option for reducing carbon emissions in the short term. However, ocean energy and renewable hydrogen still require technological developments to be able to achieve such low emissions on a large scale at commercially competitive LCOE. On the other hand, natural gas, coal and biomass energy sources may be able to reduce their GHG emissions by extensive deployment of carbon capture and storage (CCS). Although large-scale CCS projects are beginning to be planned and sanctioned for construction, there is substantial doubt that this can be done without raising the LCOE of these energy sources to sub-commercial levels. The moderate-to-high ecosystem impacts are associated with fossil fuels, biomass, and large-scale hydropower projects (Table 8).

An additional relevant environmental/sustainability factor to consider is the quantity of materials required to construct large-scale plants for each energy source. Figure 7 and

Table 9. Material used in plant construction of different energy sources, the units for materials are tons/TWh, and the lifespans are expressed in years [87].

Category	Nuclear	Solar	Wind	Hydro	Gas (Load Following)	Gas (Load Following) + CCS	Coal	Coal + CCS
Concrete	1060	1220	4470	15,320	390	820	450	520
Steel	130	940	1450	330	320	970	160	1170
Aluminium	0.3	287.5	17.4	8.7	5.7	21.4	1.6	37.4
Copper	2.5	68	39.1	4.8	5.4	8.8	3	11.8
Capacity factor	85%	28%	35%	50%	30%	30%	85%	85%
Lifespan	60	30	30	100	60	60	60	60

display this information for five of the considered energy sources based on data published by IRENA [66,84,85]. For geothermal, biomass, renewable hydrogen and ocean energy systems are not included because plants this large are not being built with the technologies currently available for these energy sources.

The amounts of materials consumed by large hydropower projects, mainly concrete, dwarf the other energy sources at the scale considered in Figure 7 and Table 9. Wind and solar energy consume the next highest quantities of materials at this scale and require more steel than hydropower plants. Natural-gas- and coal-fired power plants combined with CCS consume slightly more of those two materials combined than nuclear plants. Concrete dominates the materials required for nuclear plants, and steel and concrete are both major components consumed by natural gas and coal plants when they are combined with CCS.

4. Recommendations

The key recommendations stemming from the assessments of the relative economic, societal, and environmental impacts of the nine energy sources evaluated are:

• For fossil fuels to be considered seriously as a long-term source of energy supply major steps need to be urgently taken to mitigate their GHG and other harmful emissions. CCS is most suitable for doing this but is costly, so steps need to be taken to make it more cost effective and efficient.
• For geothermal energy supplies, reducing the cost of drilling and finding techniques to more reliably assess long-term reservoir performance are required. Additionally, more efficient heat exchange processes need to be developed to exploit both heat and power from these resources at a range of subsurface temperatures.
• CCS also needs to be applied with biomass energy supplies to reduce emissions. Based on it relatively low energy efficiency co-firing it with coal in combination with CCS may be the most commercial attractive route for large-scale, sustainable biomass energy production
• Hydrogen power generation supply chains need to incorporate careful monitoring to demonstrate that they can adopt operating practices and designs that minimize hydrogen leakage. Moreover, combustion technologies need to be adjusted to minimize NOx emissions from hydrogen combustion power plants. Technology improvements to further reduce the costs of renewable hydrogen production are also required to demonstrate its commercial viability.
• Hydropower projects need to develop designs that minimize or mitigate their environmental impacts on river ecosystems and reduce their carbon footprints.
• Solar and wind power projects need to explore ways of reducing their large land footprints and consequential ecosystem impacts. Additionally, as a matter of urgency those industries need to develop comprehensive, coordinated, and publicly disclosed materials recycling programs to avoid the unsustainable accumulation of waste materials that is currently materializing.
• The nuclear power sector needs to demonstrate that the latest generation of reactor technologies can be deployed cost-effectively and in a timely manner with improved levels of protection with respect to sustaining the effects of severe natural disasters and terrorist actions.
• Ocean energy needs to urgently develop commercial-scale plants that demonstrate that it can be developed to generate power, efficiently, cost-effectively, and sustainably with low environmental impacts. If it does not achieve this soon, it will be bypassed in favor of other renewable energy options.

5. Conclusions

This review has described, assessed, and compared the economic, societal, and environmental impacts of nine energy sources, including fossil fuels and renewable alternatives. The relative full life-cycle costs of these energy sources are usefully compared based on recently published ranges of levelized cost of energy (LCOE) combined with the ranges of capital expenditure (capex) per unit of power capacity required to build power generation plants exploiting each energy source. The level of employment and tax revenues generated by each energy source were also considered in terms of economic and societal benefits. Health and safety impacts in the context of the severity of the problems caused by the pollutants emitted from each energy source were compared together with risk of accidental impacts on local communities. Each energy source was allocated a health and safety impact score on the basis of that assessment and the prevailing public perception of such impacts. The environmental impacts of each energy source were assessing in terms of the magnitude of carbon emissions per unit of energy generated and a rating of the degree of its ecosystem impacts. All the energy sources considered had some associated environmental impacts that cause concern. Other factors considered in the assessment were the qualitative level of water consumption by each energy source, the quantity and type of materials used in initial plant construction, and decommissioning and recycling requirements. The findings indicate that all the energy sources assessed have positive and negative aspects regarding their the economic, societal, and environmental impacts.

The findings of this report reveal that while all energy sources have inherent trade-offs, understanding these nuances is critical for optimizing energy portfolio. As such, the recommendation for policymakers and industry leaders is clear; concerted actions are necessary to refine these energy solutions by focusing on reducing environmental impacts whilst balancing the economic and social benefits. Such strategic guidance requires governments involved in the energy supply sectors to improve performance of resource production and energy generation such that they can collectively make the best possible contribution to a more sustainable energy mix. This is essential to mitigate the adverse impacts of climate change and ensure the sustainability of the energy system.