The Renewable Energy-Water-Environment Nexus: Fundamentals, Technology, and Policy

By Shahryar Jafarinejad

The Renewable Energy-Water-Environment Nexus: Fundamentals, Technology, and Policy explores the connections between renewable energy, water, and the environment, along with their integration in the context of awareness, technologies, challenges, opportunities, and solutions. The book introduces different renewable energy technologies, including the importance of their development, use for a sustainable future, and their interrelationships. In-depth chapters then examine specific sub-relationships, focusing on renewable energy and water, renewable energy and the environment, and water and the environment. Available methods and tools for analyzing the renewable energy-water-environment nexus, including life cycle assessment of renewable energy systems are also covered.

The last section of the book highlights key technologies and opportunities in the nexus, considering areas such as innovative cooling systems for thermoelectric plants to reduce or eliminate the use of water for cooling, reduction of water use in biofuels production, sea waves for desalination, grid management, energy storage systems, and hydrogen technologies, examining the integration of renewable energy, water, and environment-related policies, and discussing the application of artificial intelligence and nanotechnology techniques.

• Introduces key technologies for efficient management and the integration of renewables, water resources, and the environment
• Provides methods and tools for analyzing the nexus, and for evaluating sustainability of renewable energy systems
• Considers the applications of artificial intelligence and nanotechnology, as well as policy

• Language: English
• Publisher: Elsevier Science
• Release date: Aug 31, 2023
• ISBN: 9780443134401

Book preview

Preface

The societal conflict between environmental protection and meeting the energy and water demands of our growing population needs have put tremendous pressure and focus on sustainable development regionally, nationally, and globally. There is an increasing interest and need to develop and use renewable energy (RE) technologies to meet the world’s energy needs while reducing reliance on fossil fuels, decreasing overall pollution, reducing greenhouse gas emissions toward mitigating the extent of climate change and the resulting impacts on society, and protecting our planet for future generations. RE technologies, water infrastructure and use, and the environment are closely intertwined and have complex interrelationships, with these linkages being both direct and indirect. It is crucial to acknowledge and consider the RE–water–environment (REWE) nexus for a sustainable future as we focus resources on basic research, commercialization of technologies, and advancing policy. Further, doing so has great potential for benefiting the economy by improving system efficiencies and overall sustainability.

Postsecondary education and training of industry personnel are vital for preparing a trained and qualified workforce of scientists, engineers, and technicians for the RE and water industries as well as broader societal and awareness by technical personnel and policymakers. This book can be a comprehensive introduction and reference for students of chemical engineering, civil and environmental engineering, mechanical engineering, and other related disciplines. It can also be used by researchers, lecturers, professionals, industrial and governmental sectors, and policymakers.

There are interrelated aspects to the REWE nexus, including institutional/governmental, political or regulatory, economic, social, and technological factors. This book aims to highlight the principles, technology, and policies related to REWE nexus in the context of historical awareness, present challenges, opportunities, and solutions, but the included material is not exhaustive on these topics. Chapter 1 introduces different RE technologies and ranks the renewable sources that contribute most to a sustainable future. Chapter 2 summarizes the life cycle assessment (LCA) of RE technologies to evaluate/analyze their environmental sustainability while highlighting some areas of potential. Chapter 3 discusses bioenergy production from different biomasses and its LCA. Prospects of environmental and techno-sustainability evaluation of RE technologies are described in Chapter 4. Chapter 5 focuses on providing an introduction to the concept and issues surrounding the REWE nexus. The RE–water nexus, RE–environment nexus, and water–environment nexus are discussed in greater detail in Chapters 6–8, respectively, to highlight specific subrelationships. Chapter 9 focuses on technology development in the nexus of RE, water, and the environment. Nanotechnology applications to the REWE nexus are summarized in Chapter 10. The REWE nexus analysis which involves the development of tools that facilitate the decision-making process around the implementation and operation of facilities by mitigating conflicts among stakeholders is discussed in Chapter 11. Chapter 12 discusses artificial intelligence techniques applied to the nexus of RE, water, and the environment. Chapter 13 examines the integration of RE, water, and environment-related policies and highlights several relevant policies related to the REWE nexus.

Although the editors/authors/contributors believe that this book is scientifically and technically accurate, some errors may occur; thus, constructive suggestions and comments from readers (instructors, students, etc.) using the book are greatly appreciated. The editors will incorporate suggestions and corrections in future reprints or editions of this book.

The editors appreciate the reviewers’ comments, which improved the quality of this book, as well as the Senior Acquisitions Editor, Edward Payne; Editorial Project Manager, Rupinder Heron; Production Project Manager, Sujithkumar Chandran; Cover Designer, Christian J. Bilbow; and Copyright Coordinator, Dinesh N, who supported us in the preparation and publication of this book.

Shahryar Jafarinejad and Bryan S. Beckingham

February 2023

1

Renewable energy for a sustainable future

Gabriela Allegretti¹, Marco Antonio Montoya² and Edson Talamini³,    ¹Brazilian Institute of Bioeconomy (INBBIO), Porto Alegre, Brazil,    ²Faculty of Economics, Administrative and Accounting Sciences, University of Passo Fundo, Passo Fundo, Brazil,    ³Department of Economics, Interdisciplinary Center for Studies and Research in Agribusiness - CEPAN, Universidade Federal do Rio Grande do Sul - UFRGS, Porto Alegre, Brazil

Abstract

Renewable energy is fundamental in building a sustainable future, expected to increase from 11% today to 28% of the total primary energy consumed worldwide by 2050. However, some sources can contribute more to a sustainable future, even among renewables. This chapter overviews the relative share, growth rate, major consuming sectors, greenhouse gas emissions, global warming potential (GWP), renewability, and job generation of the major renewable sources. Based on the literature survey, by rating the sources according to the values found for GWP, renewability, and clean job generation, this chapter ranks the renewable sources that contribute most to a sustainable future. The results suggest that bioenergy contributes the most, followed by solar, geothermal, wind, hydropower, and marine. It is concluded that all renewable sources can contribute to a sustainable future. The challenge for each country is to identify the best mix of alternatives to convert natural energy flows into electricity, heat, fuel, and biomass.

Keywords

Photovoltaic; concentrating solar power; biomass; biofuels; wind; tidal; energy sustainability

1.1 Introduction

The challenge humankind is facing today is to supply human needs in a growing population world, keeping security for food, energy, and water (Amulya et al., 2016). Until the beginning of this century, this growth was founded on fossil fuels which exposed, besides the finitude of these resources, to the environmental consequences related to greenhouse gas (GHG) emissions, pollutants, and climate changes (Ang et al., 2022; Duarah et al., 2022; Wang & Wang, 2015). Large-scale fossil fuel consumption releases high levels of CO2 into the atmosphere each year, contributing to global warming and warning of severe health risks to humans and the environment (Okeke et al., 2022). Renewable energies (REs) emerge as a possibility to fill this gap and ensure the pathway for a sustainable world.

RE is the energy produced from natural sources that are naturally replenished at a lower rate than is consumed. It is virtually inexhaustible but limited in the amount of energy available per unit of time (IEA, 2022). Among RE sources, hydropower, solar, wind, bioenergy (biomass, biofuel, and biogas), geothermal, and marine are highlighted. Despite the particularities, each source can contribute to the sustainability issues like carbon emissions and global warming potential (GWP), employment generation, pollutants emissions, resource depletion, and renewability rate. Thus, it is worth noting that renewability per technology may not be enough to ensure sustainability. Allegretti et al. (2022) reported that long-term sustainable structural changes need to be planned based on renewable sources focusing on the lowest net emission intensity and highest renewability.

The production and use of RE have been encouraged as a part of the global sustainable development strategy. Since 2015, this commitment has been stated by 196 countries in the Sustainable Development Goals (SDGs), particularly in SDG-7 (Affordable and Clean Energy), SDG-12 (Responsible Consumption and Production), and SDG-13 (Climate Action) (UN, 2022). Currently, RE sources provide around 11% of the world’s primary energy (OWD, 2022). However, the share of renewables in national energy matrices varies among countries. Norway, Brazil, and Sweden have a higher relative percentage of RE balance (71.56%, 46.22%, and 50.92%, respectively) (OWD, 2022) compared to China, the United States, and Germany (14.95%, 10.66%, and 19.45%, respectively) (IEA, 2022).

RE is an opportunity for all countries, especially developing ones, to ensure their energy security in the long term (REN21, 2020; Chu et al., 2023; Nizami et al., 2017). The availability of natural capital, in the form of stocks and flows, is an advantage that some countries have already exploited to generate energy through technological innovation (Mancini et al., 2017; Odum, 1988). The huge challenge is the development of technologies to extract the maximum work capacity of these sources in a way to reduce fossil fuels use. Biorefineries are one example of biomass exploitation that are evolving in the last years to extract all energetic potential in the form of energy and materials (T. Liu et al., 2022; Welfle et al., 2020).

RE has impacted economic sectors in different ways. With fleet electrification, the transport sector is going to be one of the most impacted sectors worldwide. The engine technologies and the variety of sources to generate electricity already allow the transition from fossil to RE in the road sector of developed countries (Dumortier et al., 2022; Tsai et al., 2023). In the same way, biofuels are already an option for emerging countries like Brazil and Indonesia to clean their road sector through the blend with ethanol and biodiesel (Das & Gundimeda, 2022; Liaquat et al., 2010; Maia & Bozelli, 2022). The aerial transportation sector is responsible for 2% of global anthropogenic CO2 emissions. It will be the next sector to benefit from RE through sustainable aviation fuels (SAFs) in the short term (Ng et al., 2021; Prussi et al., 2021).

Modern manufacturing and smart cities can take advantage of using RE sources to build a more sustainable industrial and urban environment in the future. The construction sector is progressively adopting new technologies and designs to efficiently use RE in heating, cooling, and lighting systems. Incorporating RE into buildings can be done through solar panels or wind turbines installed on the roof or exterior walls (Chong et al., 2016), solar water heaters (Wang et al., 2015), geothermal energy for heating and cooling (geothermal district heating—GeoDH) (Romanov & Leiss, 2022), pelletized wood biomass for boilers (Marigo et al., 2022), small-scale hydroelectric systems, passive solar design to the direct use of solar sunlight for heating (Morrissey et al., 2011; Stevanović, 2013), green roofs for thermal isolation (Berardi et al., 2014; Besir & Cuce, 2018), energy-efficient windows designed to reduce the heat loss (Zhang et al., 2016), and light-emitting diode lighting (Chinchero et al., 2020).

Currently, RE generation employs 12.7 million people worldwide, directly and indirectly, from energy components manufacturing to installation and maintenance, which means a growth rate of almost 74% between 2012 and 2021 (IRENA and ILO, 2022). The social impact of these technologies goes further than the health and environmental benefits that society captures from clean energy production and consumption (Yang et al., 2022). It generates wealth through good wages paid by skilled jobs, especially in developing and emerging countries. It also reduces electricity costs and generates income from surplus energy sold back to the power grid (Ang et al., 2022; Topcu & Tugcu, 2020).

In addition to jobs and income generation, the sustainable and clean energy economy must rely on RE sources and improved energy efficiency to mitigate adverse environmental impacts (Mohsin et al., 2021; Yushchenko & Patel, 2016; Żywiołek et al., 2022). The transition to a large-scale clean energy economy requires energy production to occur decentralized rather than concentrated in large-scale power plants (Javid et al., 2021). Decentralization allows for optimizing the use of natural energy flows and their conversion into biomass or electricity. This is especially important in the case of solar radiation for biomass and electricity, wind streams for electricity, and geological features for geothermal energy exploitation. On the other hand, the decentralization of production and the mix of the renewable and nonrenewable sources requires smart electrical grids to manage flows and integrate renewables into the power distribution grid (Hossain et al., 2016; Tan et al., 2021).

The big challenge for a RE-based economy lies in storing the electricity derived from natural flows. Battery development and pumped storage hydropower (PSH) are possible alternatives but are still limited in sustainability and capacity, respectively (Ma et al., 2014; Qiu et al., 2022; Sovacool, 2022). Public policies and government incentives can accelerate the transition to a clean energy economy by stimulating the installation of new energy production plants, technology development, the supply of a clean energy grid to the consumer market, and the generation of clean jobs and new sources of income (Liu et al., 2019; Lu et al., 2020; Yi, 2013, 2014).

Although RE sources present benefits for building a more sustainable future, the economic, social, and environmental contributions may differ from one to the other. This chapter discusses the overview of the relative share, growth rate, major consuming sectors, GHG emissions and GWP, renewability, and job generation of hydropower, solar, wind, geothermal, bioenergy, and marine sources. Based on the benchmarks found in the literature, this chapter proposes ranking the analyzed energy sources according to their performance for GWP, jobs generation, and renewability rate.

The following sections present and discuss each of the mentioned renewable sources about (1) their relative participation in the global energy matrix and the global renewable matrix, (2) GHG emissions and their potential in global warming, (3) issues related to renewability, and (4) social impacts like direct and indirect jobs created.

1.2 Renewable energy technologies

1.2.1 Hydropower

The production and consumption of hydroelectricity began in the 1900s. Today, it ranks fourth among the energy sources consumed worldwide. By 2020, the amount of hydropower electricity exceeded that of traditional biomass (wood) for the first time, accounting for 6.8% of the world’s total energy consumption. Only oil, coal, and gas have a larger relative share than hydroelectricity (OWD, 2022).

Despite their relevance in the world energy matrix, hydroelectric plants have been dropping their relative importance among the sources of RE generation due to the growth in production and consumption of other sources, such as wind and solar. In 2000, hydropower supplied 2,701,015 GWh of energy, representing 94.94% of the amount of RE consumed worldwide that year. Although, 4,476,230 GWh was consumed in 2020, this amount represented only 59.94% of the world’s RE consumption (Table 1.1). Even so, this energy source showed a growth rate in consumption on the order of 2.53% per year between 2000 and 2020, sustained mainly by renewable hydroelectric generation.

Table 1.1

Source: Data from IRENASTAT. (2022). Power Capacity and Generation. https://www.irena.org/Data/Downloads/IRENASTAT.

Hydroelectricity remains a relevant alternative for the future. Expectations from the International Energy Agency (IEA, 2021) point to a 19% increase in power generation by 2030, adding 850 TWh. The International Renewable Energy Agency (IRENA)’s projections are even more optimistic and indicate a 30% growth compared to 2020 (IRENA, 2022). On a longer horizon, installed capacity is projected to double to 2000 GW and generate more than 7000 TWh of electricity by 2050, where PSH could make a considerable contribution. The increase in hydroelectricity generation capacity is expected to come from large projects in emerging economies and developing countries, mainly in Africa, Asia, and Latin America (IEA, 2022).

The generation and consumption of hydroelectric power are strategic for the stability of the energy matrix and the mitigation of GWP. Besides being a renewable source, its CO2-eq emission rates are considered zero by the Intergovernmental Panel on Climate Change (IPCC) (IPCC, 2020). However, one must consider the life cycle involving the construction process, flooding, and generation of hydroelectricity and the different variables that can affect emission levels. For hydropower plants in cold climate regions, 15 g CO2-eq/kWh is considered a common GHG emission factor (Gagnon & van de Vate, 1997), but there are disagreements. For example, Steinhurst et al. (2012) assumed 20 g CO2-eq/kWh as a global emission factor. A higher emission factor was considered by Hertwich (2013), who adopted 85 g CO2/kWh and 3 g CH4/kWh, assuming that these values can be multiplied by an uncertainty factor equal to 2. In a more extensive study considering 119 hydropower plants, Räsänen et al. (2018) identified that emission levels range from 0.2 to 1994 g CO2-eq/kWh over a 100-year life cycle, with a median in the order of 26 g CO2-eq/kWh. Emission levels depend on numerous variables and do not include environmental impacts such as river fragmentation, deforestation, and biodiversity loss, among others (Huđek et al., 2020).

The renewability of this energy source deserves to be highlighted. By transforming the potential energy of water flows into electricity, hydropower plants have high rates of renewability. As stated by Frey and Linke (2002), the ‘fuel’ for hydropower is water which, in itself, is renewable, and is not consumed in the electricity-generating process, although some confuse renewability with sustainability. Dewulf et al. (2000) defined the renewability—parameter for assessing the sustainability of technologies—as the fraction of RE consumption concerning the total exergy consumption. Using such an indicator, Dewulf and Van Langenhove (2005) pointed out a renewability index of 0.99 (99%) in hydroelectric plants because of the high use of renewable resources. Zhang et al. (2019) found 52% of renewability in small hydropower, while Brown and Ulgiati (2002) reported 68.84% in an 85 MW hydropower plant.

Hydropower plants supply energy to different sectors of economic activity, especially electricity, gas and water, petroleum, chemical, nonmetallic mineral products, education, health and other services, and private households services, in which this energy source participates with 25.45%, 11.4%, 4.40%, and 1.39%, respectively (Table 1.2).

Table 1.2

Source: Elaborated by the authors based on (IRENASTAT, 2022a) and (MRIO, 2022).

The production and consumption of hydroelectricity contribute to the mitigation of GHG emissions, economic development, and job creation. Large and small projects to be developed in emerging economies and developing countries should expand energy access, reduce poverty, and promote social development (IEA, 2021b). Hydropower was the third most important source of employment, generating approximately 2.37 million direct jobs in 2021. China, India, and Brazil were leading countries in developing employment in the sector, with 37%, 17.6%, and 7.5% of the direct jobs generated, respectively. These jobs are distributed between production activities (64%), construction and installation (30%), and operations and maintenance (6%) (IRENA and ILO, 2022). Based on IRENA and ILO (2022) data, it can be obtained that the job generation rate of hydropower plants is in the order of 1.74 jobs per MW of installed capacity (2,370,000 jobs/1,360,502 MW) (IRENADATA, 2022; IRENASTAT, 2022a; IRENA and ILO, 2022).

1.2.2 Solar

Among the fastest-growing global RE sources in the last 20 years, solar energy stands out, with an annual growth rate of 32.26% between 2000 and 2020 (IRENA, 2022). The increased competitiveness of solar, combined with cost reduction and the growth of conversion efficiency promoted by successive technological improvements, allowed the final world consumption to jump from 1331 GWh in 2000 to 843,855 GWh in 2020 (IRENA, 2022; Ang et al., 2022). Even so, it represents only 1.53% of the world’s primary energy consumption in 2021—2702 TWh (OWD, 2022).

Solar energy generation is based on the capturing ionized energy from radiation emitted by the sun, which can be used to produce energy from two methods: (1) directly, producing electrical energy from photovoltaic (PV) cells, and (2) indirectly, using solar thermal collectors that appropriate the excess heat not used to generate thermal energy (Jacob et al., 2022).

The predominant technology to appropriate solar energy is solar PV. Even showing a conversion efficiency of 31% (Ang et al., 2022; Shockley & Queisser, 1961), this technology contributed to supplying 10.95% of the world’s RE consumption in 2020, which represents the highest annual rate of growth among renewables (34.69% p.a.) (IRENA, 2022).

New technologies have been developed to improve the conversion efficiency of PV cells, like concentrated PV. The system is based on concentrating sunlight capture through lenses and mirrors (concentration optics) that direct the radiation to a small area of PV receivers. Such technology shows a conversion efficiency of 40% (IEA, 2021a), which can be increased in the short term due to more significant reduction costs (85%) compared to other technologies, or by its association with solar thermal technologies (Ang et al., 2022).

One of the challenges to improving PV cell efficiency is plate temperature reduction, which interferes with energy use. For this purpose, the floating PV technology allows the panels installed on water surfaces such as lakes, dams, and reservoirs to be cooled and improves the efficiency of PV cells. Besides this technical advantage, the technology shows social and environmental benefits like land use preservation, the reduction of algae development in reservoirs, and the positive impact on water stress with evapotranspiration diminishing (Cazzaniga et al., 2018).

Although sometimes advertised as a carbon-free source, when evaluating all steps of the life cycle of solar energy generation (material extraction, manufacturing, construction, operation maintenance, and disposal or decommissioning), this characteristic is not confirmed (Nugent & Sovacool, 2014). There is variability in the level of energy emissions per kWh generated among technologies, depending on the material and the energy source used. In a solar PV system without F-gases and using exclusively RE sources, the emissions intensity is lower than 1 g CO2-eq/kWh. In a solar PV system with F-gases using nonrenewable sources like coal, the energy emission intensity arrives at 218 g CO2-eq/kWh. Considering a technological average, Nugent and Sovacool (2014) considered solar PV a low-intensity emission (49.91 g CO2-eq/kWh) only behind hydropower and biogas through anaerobic digestion. Ren et al. (2020), comparing different energy sources, showed solar PV in Italy with carbon emissions of 144 g CO2-eq/kWh and concentrated solar power in China with 36.3 g CO2-eq/kWh.

Besides the PV options, another solar appropriation technology is solar thermal energy. The radiation energy is converted to thermal energy, usually used in industrial and domestic processes to heat water, the environment, or even for energy generation (Masera et al., 2023). This technology is the most efficient in absorbing solar radiation, reaching 90% (Chang et al., 2020). However, it has been strongly affected by the intermittency of solar radiation, which, unavoidably, demands subsystem installation for thermal storage to take all their capacity for energy generation (Chang et al., 2020).

Solar is the third biggest RE source in installed capacity with 627 GW (REN21, 2020), mainly used in domestic (22.09%); electricity, gas, and water (23.29%); and service (51.18%) sectors (Table 1.2). However, with the fleet electrification tendency desired by many developed countries, this source will significantly impact the transport sector in the medium run as it represented only 1.3% of the gross production value in 2020 (Table 1.2).

Analyzing renewable characteristics, the fact of using the most available input on Earth, the sun does not make it a 100% renewable source. Following the energy sources renewability classification proposed by Dewulf and Van Langenhove (2005), solar energy loses only by hydropower due to nonrenewable resources used for construction (0.981 versus 0.990). The most considerable described difference between both renewable sources is efficiency. Solar energy, due to partially converting radiation in electricity, has an index of 0.13 compared to the generation of kinetic energy from water in hydroelectric plants, which has an index of 0.77. Comparing the renewability to another source, Zhang et al. (2019), using emergy analysis, ranked PV energy at 0.02% compared to 0.63% of geothermal energy in Italy. Using the same metric, Fan et al. (2021) analyzed a concentrating solar power plant in China and found a renewability rate of 16.13%. When comparing different electricity production systems, those authors related that solar PV had the worst emergy sustainability index (ESI = 0.02) compared to the wind (48.3) and hydropower (41.6).

Even with this characteristic, the huge concern about renewability is long term due to the technological residue. IRENA (2022) stems that solar waste will increase from 0.2 Mt in 2021 to 4 Mt in 2030, 50 Mt in 2040, and more than 200 Mt in 2050, mainly from developed countries. Even considering the recycling and reuse of these materials, public policies in several countries must be deployed aiming to regulate accountability, standardization, and certification of this recycling process, including developing research and technologies that mitigate this impact.

The exponential growth of solar energy generation in the last decades has taken an increase in global direct (manufacturing, installation, and operation) and indirect (plant lifetime maintenance) employment which went from 4 million in 2020 to 4.3 million in 2021 (IRENA and ILO, 2022). Asian countries account for 79% of the PV generation jobs in the world, with China responsible for 63% of jobs in the manufacturing and installation stages. The remaining jobs are in German, Brazil, India, and the United States, especially in the PV installation stage (IRENA and ILO, 2022). The intensity of workers per unit of energy in this source was 6.04 jobs per MW of installed electricity capacity in 2021 (5,139,000 jobs/849,473 MW) (IRENADATA, 2022; IRENASTAT, 2022a; IRENA and ILO, 2022). Another social advantage to be highlighted from this source, especially in developing countries, is the possibility of generating extra income from the sale of excess energy to the power grid due to high solar radiation incidence (Ang et al., 2022).

1.2.3 Wind

The conversion of wind’s kinetic energy into electricity has shown high growth rates. In 2021, it was the seventh most consumed primary energy source in the world, with 4872 TWh. This amount of consumption represented 2.8% of the total primary energy consumed worldwide. Despite the relatively modest share, it is worth noting the pace at which wind energy has been growing in the energy matrix. In 1999, wind energy was responsible for only 0.1% of the total energy consumed. More than a decade later, the participation rate has grown by 2800%. The average annual growth rate in wind energy consumption between 1999 and 2021 was 47.8% p.a., the second highest among the major primary energy sources (OWD, 2022). The growth rate is higher than that based on IRENA data which is shown in Table 1.1.

According to estimates by IRENA, wind power is expected to be the source that will grow the most in the coming decades, alongside PVs (IRENA, 2022). Installed capacity for onshore wind power generation is expected to be fourfold compared to 2020, reaching 3000 GW by 2030 and 6170 GW by 2050. On the other hand, offshore generation is expected to be eleven times larger and generate approximately 380 GW by 2030. The expansion in installed capacity is expected to provide 24% of the total electricity required worldwide. The necessary investments in onshore wind power are expected to increase 3.7 times by 2030, estimated to be $299 billion annually. Offshore production is expected to receive annual investments 6.4 times that of 2021, reaching a value of $114 billion annually. The regions where the most significant investments in onshore wind energy are projected by 2050 are North America, Asia, and Latin America. In Oceania and Europe, offshore production is expected to show the largest relative growth (IRENA, 2022).

Wind power is almost entirely consumed by intermediate economic activities, which consumed 99.89% in 2020 (Table 1.2). The electricity, gas, and water sectors account for 97.95% of wind power consumption worldwide. It is the main type of RE used by the sector (25.33%), second only to hydroelectricity (69.34%). The share of wind power in final demand is relatively low and corresponds to only 0.30% of the total RE consumed by households and governments. Advances in the electrification of the vehicle fleet make transportation a potentially relevant sector for wind energy use in the future (Hossain, 2021).

The GHG emission reduction targets justify the growing share of wind power in the world energy matrix. The IPCC considers the CO2-eq emissions from wind power to be null (IPCC, 2020). However, studies point to the presence of CO2-eq emissions when considering the life cycle from turbine installation, production, and recycling, even if at relatively low levels. Studies using the life cycle assessment (LCA) methods indicate variations in emission levels, influenced by onshore versus offshore (Arvesen & Hertwich, 2012; Raadal et al., 2014), wind speed (Padey et al., 2012), materials used in turbine manufacturing, materials used in turbine foundation (steel, concrete), size of the wind farm, location (Wang & Wang, 2015), turbine generating capacity (Arvesen & Hertwich, 2012; Tremeac & Meunier, 2009), wind turbine conceptual designs (Raadal et al., 2014), turbine lifetime (Padey et al., 2012), and LCA method (Wang & Wang, 2015).

Depending on the configuration of variables, emissions can range from 2 to 86 g CO2-eq/kWh, but specific values of 13.4, 28.7, and 29.7 g CO2-eq /kWh have been found for different LCA methods (Wang & Wang, 2015). While Arvesen and Hertwich (2012), Yang and Chen (2013), Raadal et al. (2014), and Nugent and Sovacool (2014) reported 6, 32 (19±13), 7.2, 18 to 31.4, and 0.4 to 364.8 (mean 34.11) g CO2-eq/kWh, respectively, Tremeac and Meunier (2009) found values of 15.8 and 46.4 g CO2-eq/kWh for turbines with a generation capacity of 4.5 MW and 250 W, respectively. Similar emission ranges were identified in a broad review conducted by Dolan and Heath (2012), with values ranging from 1.7 to 81 g CO2-eq/kWh, and by Pulselli et al. (2022), with values ranging from 26 to 79 g CO2-eq/kWh. When these values were subjected to consistent gross system boundaries and values for several essential system parameters, emissions were reduced by 47% (3.0–45 g CO2-eq/kWh). Wind speed can significantly reduce the relative CO2-eq/kWh emissions. In an analysis considering a lifetime of 10 to 30 years for wind turbines, Padey et al. (2012) found 8.7–76.7 g CO2-eq/kWh in winds with speeds below 6.5 m/s and 4.5–22.2 g CO2-eq/kWh in winds with speeds above 6.5 m/s. In other words, installing wind turbines in locations with faster and more constant wind flows can reduce emissions per kWh to less than half. Overall, the results show that wind power can fully compete with other low-GHG emission electricity technologies, such as nuclear, PV, and hydropower (Raadal et al., 2014). In addition to GHG emissions, other environmental impacts are associated with wind power generation, such as noise pollution, bird and bat fatalities, land surface impacts (Wang & Wang, 2015), toxicity, and resource depletion (Arvesen & Hertwich, 2012).

The high renewability of wind power results from the conversion of the kinetic energy flow of wind. The main elements affecting the renewability rate are associated with the manufacturing and transportation, installation, operation, maintenance, disassembly, and disposal of components of wind turbines (Chen et al., 2011). These authors used the nonrenewable energy investment in energy delivered as an indicator of the renewability of wind power in China. They found a value of 0.047, indicating that wind power requires 0.047 units of nonrenewable energy to generate 1 unit of electricity, revealing the process’s high renewability (95.3%). Using the renewability indicator of emergy analysis, Yang et al. (2013) calculated that wind power has 20% renewability in China, being more renewable than other energy sources such as thermal and PV. Emergy renewability rates of 14.6% and 23% were obtained by Yang and Chen (2016) and Yazdani et al. (2019), considering a lifetime of 21 and 20 years, respectively. A higher renewability value of 86.61% was reported by Brown and Ulgiati (2002).

In addition to its renewability and low emissions, wind power has contributed to employment and income generation. In 2021, approximately 1.371 million workers were employed in the wind power sector, representing just over 10% of direct and indirect jobs in the RE sector (IRENA and ILO, 2022). Over the last decade, the growth in the number of direct and indirect jobs in the wind power sector has exceeded 82%, second only to solar power among renewables. The activities of building the industrial base and infrastructure are necessary to support the growing offshore wind farm projects. Eighty-five percent of wind power jobs are concentrated in ten countries, with China alone accounting for almost half of the jobs (48%). However, countries such as India, Brazil, the Philippines, South Africa, and Mexico are expected to expand employment in the sector by 230, 115, 59, 37, and 29,000 positions by 2026, respectively. Despite this, job creation does not seem to be the main positive point of wind energy. The intensity of workers per unit of energy is relatively low, reaching the value of 1.66 jobs per MW of installed electricity capacity (1,370,000 jobs/823,484 MW) (IRENADATA, 2022; IRENASTAT, 2022a; IRENA and ILO, 2022).

1.2.4 Geothermal

Geothermal energy is the energy contained as heat in the Earth’s interior, which is converted into electricity by transferring heat from depth to subsurface regions by conduction and convection (Barbier, 2002). Geothermal energy began to be exploited in 1904 at Larderello, Italy, with an experimental 10 kW generator. Italy remained the only country producing geothermal energy until 1958 when New Zealand became the second-producing country. In the following decades, other countries began to explore geothermal energy. By 1975, Mexico, the United States, Russia, Japan, Iceland, and China were exploring their natural conditions for geothermal energy production (Lund et al., 2022).

Geothermal energy is not among the major sources of energy consumed in the world today. In 2000, geothermal energy consumption was 52,567 GWh, representing 1.8% of final renewable primary energy consumption. Although geothermal energy consumption grew in absolute value to 94,949 GWh in 2020, the relative share among renewables fell to 1.25% (Table 1.1). Considering that RE accounted for 11.4% of the total primary energy consumed worldwide in 2019 (OWD, 2022), the share of geothermal energy in the world’s primary energy consumption matrix can be estimated at approximately 0.14%.

Currently, the direct consumption of geothermal energy is 0.9 EJ. This figure is expected to increase more than fourfold by 2050 when consumption is estimated at 4.0 EJ (IRENA, 2022). The contribution of geothermal energy is also expected to grow in electricity generation. It is estimated that the share of renewable sources will reach 65% of the total electricity supplied by 2030. Geothermal energy is expected to contribute by expanding installed capacity for electricity generation by more than 47%, from 15.6 GW in 2021 (STATISTA, 2022) to more than 23 GW in 2030 (Salhein et al., 2022).

Geothermal energy has been used for different purposes, especially for direct consumption, as given above. In 2000, the main uses given to geothermal energy were bathing and swimming (41.67%), space heating (22.87%), geothermal heat pumps (12.15%), greenhouses and covered ground heating (6.04%), industrial process heating (5.33%), agricultural crop drying (0.54%), snow melting and air conditioning (0.51%), and other uses, such as earthquake monitoring, tourism, and animal husbandry (1.58%) (Lund & Freeston, 2001). Geothermal energy consumption occurs primarily in the electricity sector via grid-connected thermal power stations, which consumed 87.46% of this energy in 2020. The remainder (6.69%) was for final consumption, mainly by households, for space heating, appliances and lighting, water heating, cooking, and space cooling (Table 1.2) (DNV, 2022). The geothermal energy consumption structure scenario is relatively the same for 2050 (DNV, 2022).

Geothermal energy provides reliable and stable power, despite a relatively low efficiency in converting steam into energy, corresponding to 10%–17% of nuclear thermal power or fossil fuels (Anderson & Rezaie, 2019; Kulasekara & Seynulabdeen, 2019). In addition, it is among those with the lowest GWP due to low-GHG emissions, which can be 35%–80% lower than fossil fuel power plants (Buonocore et al., 2015). Although geothermal steam contains other gases, CO2 accounts for 85% of the volume and weight of the gases (Anderson & Rezaie, 2019). Carbon dioxide emissions depend on location and, consequently, the composition of the water and steam, and there can be variations of up to 20 times more CO2 between geothermal fields (Anderson & Rezaie, 2019). Parisi et al. (2019) compared five Italian geothermal power plants and obtained average emission levels of 254 g CO2-eq/kWh with a standard deviation of 28 g CO2-eq/kWh using the Monte Carlo simulation.

Emissions can also vary due to the power generation system used. Paulillo et al. (2019) evaluated the emissions from a ground source heat pump (GSHP) system in Iceland against values reported in the literature. They concluded that the calculated emissions ranged from 15 to 24 g CO2-eq/kWh, standing at lower levels than other studies indicating emissions in the range of 2–550 g CO2-eq/kWh for similar systems. In a more extensive study, Tomasini-Montenegro et al. (2017) compared four engineered geothermal systems (EGSs): dry steam, single-flash geothermal power generation plants, double-flash power plants, and binary cycle power plants, finding GWP of 670, 690, 15, and 5.7 g CO2-eq/kWh, respectively. The authors concluded that EGS emits an average of 50 g CO2-eq/kWh, ranging from 42 to 62 g CO2-eq/kWh. Operation activities are primarily responsible for emissions levels, followed by construction, drilling and additional wells, decommissioning, and disposal (Buonocore et al., 2015; Tomasini-Montenegro et al., 2017).

The conservation of the Earth’s internal heat ensures the long-term maintenance of geothermal energy generation. Because of this, the renewability of geothermal energy tends to be high since the energy source is the continuous cycle of natural geological events. Therefore, the share of nonrenewable resources tends to be relatively low compared to the amount of geothermal energy provided by nature. Using emergy analysis, Brown and Ulgiati (2002) compared several renewable and nonrenewable energy sources. They found that geothermal energy had the second highest renewability rate at 69.67%, behind only wind energy. This value is in line with that presented by Buonocore et al. (2015), who reported a renewability of 70% for a geothermal power plant. The renewability rate can be affected by the power generation system used. When comparing renewable source power generation systems, Zhang et al. (2019) found 48% renewability in a full flow system and 63% in a dry steam system.

In addition to the high renewability rate, other advantages are attributed to geothermal energy. Anderson and Rezaie (2019) listed the following items as advantages: lower land requirements (e.g., geothermal power plants require approximately 404 m²/GWh, less than 1335 m²/GWh by the wind), water savings (e.g., geothermal uses about 20 L/MWh of fresh water while other sources such as coal require over 1000 L/MWh), and reliability (e.g., the heat within the ground allows for continuous operation without interference from intermittent surface weather conditions).

On the other hand, geothermal energy also has restrictions or concerns. Air pollution from non-condensable gases (CO2, H2S, NH3, CH4, N2, and H2), water pollution in rivers and lakes from toxic chemicals in water and the condensate, land subsidence by removing fluids from the rock pores, seismicity events in geologically unstable zones by inducing high-pressure and water reinjection, and noise pollution with processes potentially generating noise levels between 75 and 122 dB are among the potential negative impacts (Anderson & Rezaie, 2019; Barbier, 2002). Additionally, Anderson and Rezaie (2019) further point to the need to maintain technological initiatives to improve the low efficiency of 55%–60% at best. Initial investments characterized by high upfront capital costs, long payback time, constraints to access resources, and the difficulty of modulation inhibit the expansion of generation capacity. Silica scaling, risk of geological changes, and hydrothermal eruption are other risks reported by Anderson and Rezaie (2019).

Beyond the environment, job creation is a relevant social and economic aspect of geothermal energy. According to IRENA and ILO (2022) data, the RE sector employed 7.3 million workers in 2012, of which 0.22 million were in other RE sources, including geothermal energy, concentrated solar power, heat pumps (ground-based), municipal and industrial waste, and ocean energy. In 2021, the number of jobs generated by these other sources was 0.431 million of the 12.7 million total jobs in renewables. Therefore in the last decade, the number of jobs generated in other renewable sources, including geothermal, grew by 95.4%, while the growth rate in RE jobs was 73.9%. Particularly, geothermal energy employed 196,000 workers worldwide in 2021, with China (78,900), European Union (60,000), and the United States (8000) being the countries with the highest number of employees (IRENA and ILO, 2022). Considering that the installed geothermal electricity capacity worldwide was 15,959 MW in 2021 (IRENASTAT, 2022a) and the number of workers employed was 196,000, the labor intensity in geothermal energy is 12.28 jobs per MW of installed capacity (196,000 jobs/15,959 MW) (IRENADATA, 2022; IRENASTAT, 2022a; IRENA and ILO,