Contenido

Cuando se hace referencia a fuentes de energía, los términos "energía sostenible" y "energía renovable" a menudo se usan indistintamente, sin embargo, los proyectos particulares de energía renovable a veces plantean importantes preocupaciones de sostenibilidad. Las tecnologías de energía renovable son contribuyentes esenciales para la energía sostenible, ya que generalmente contribuyen a la seguridad energética mundial, reduciendo la dependencia de los recursos de combustibles fósiles,[9]​ y brindando oportunidades para mitigar los gases de efecto invernadero.[9]​ Se han realizado diversos trabajos de análisis de costo-beneficio realizados por una gran variedad de especialistas y agencias para determinar las vías más baratas y rápidas para descarbonizar el suministro de energía del mundo, y el tema es de gran controversia, en particular sobre el papel de la energía nuclear.[10]​[11]​[12]​[13]​[14]​.

Hydroelectricity

Among renewable energy sources, hydroelectric plants have the advantage of being long-lived: many existing plants have operated for more than 100 years. In addition, hydroelectric plants are clean and have low emissions. Criticisms leveled at large-scale hydropower plants include: the dislocation of people living where the reservoirs are planned and the release of significant amounts of carbon dioxide during reservoir construction and flooding.[15]​.

However, high emissions have been found to be associated only with shallow reservoirs in warm (tropical) locations, and recent innovations in turbine technology are enabling the efficient development of low-impact hydroelectric projects on the river stream.[16] In general, hydroelectric plants produce much lower greenhouse gas emissions than other types of generation.

Hydropower, which experienced intense development during the growth of electrification in the 19th and 20th centuries, is experiencing a resurgence of development in the 21st century. The areas of greatest hydropower growth are the booming economies of Asia. China is the leader of development; However, other Asian nations are installing hydropower at a rapid pace. This growth is driven by an increase in energy costs, especially imported energy, and by widespread desires for more domestic, clean, renewable and affordable generation.

Geothermal

Technologies in use for geothermal production include dry steam plants, flash steam plants and binary cycle plants. Geothermal electricity generation is currently used in 24 countries, while geothermal heating is used in 70 countries.[17] International markets grew at an average annual rate of 5 percent over the three years to 2015, and global geothermal power capacity is expected to reach 14.5–17.6 GW in 2020.[18]

Geothermal energy is considered a sustainable and renewable energy source because heat extraction is small compared to the heat content of the Earth.[19] Greenhouse gas emissions from geothermal power stations are on average 45 grams of carbon dioxide per kilowatt-hour of electricity, or less than 5 percent of that of conventional coal plants.[17] As a renewable energy source for power and heating, geothermal energy has the potential to satisfy 3-5% of global demand by 2050. With economic incentives, it is estimated that by 2100 it will be possible to satisfy 10% of global demand.[20]​.

Biomass

Biomass briquettes are increasingly used in the developing world as an alternative to charcoal. The technique involves converting almost any plant matter into compressed briquettes that typically have about 70% of the heating value of charcoal. There are relatively few examples of large-scale briquette production. One exception is in North Kivu, in eastern Democratic Republic of the Congo, where forest clearing for charcoal production is considered the biggest threat to mountain gorilla habitat. Virunga National Park staff have successfully trained and equipped over 3,500 people to produce biomass briquettes, replacing charcoal produced illegally within the national park and creating important employment for people living in extreme poverty in conflict-affected areas.[21]​.

Biofuel

Brazil has one of the world's largest renewable energy programs, involving the production of fuel ethanol "Ethanol (fuel)") from sugar cane, and ethanol now provides 18 percent of the country's automotive fuel. As a result of this, along with the exploitation of domestic deepwater oil sources, Brazil, which years ago had to import a large portion of the oil needed for domestic consumption, achieved complete oil self-sufficiency.[22][23][24]​.

Most cars on the road in the United States can run on blends of up to 10% ethanol, and motor vehicle manufacturers already produce vehicles designed to run on much higher ethanol blends. Ford, DaimlerChrysler and GM are among the companies selling "flex-fuel" cars, trucks and minivans that can use gasoline and ethanol blends, from pure gasoline to 85% ethanol (E85). As of mid-2006, there were approximately six million E85-compatible vehicles on United States roads.[25]​.

Biofuels may be defined as "renewable", but may not be "sustainable" due to land degradation. As of 2012, 40% of US corn production goes into ethanol. Ethanol occupies a large percentage of "Clean Energy Use" when, in fact, it is still debatable whether ethanol should be considered a "Clean Energy".[26]​.

According to the International Energy Agency, new bioenergy (biofuels) technologies being developed today, especially cellulosic ethanol biorefineries, could allow biofuels to play a much larger role in the future than previously thought.[27] Cellulosic ethanol can be obtained from plant matter composed primarily of non-edible cellulose fibers that form the stems and branches of most plants. Crop residues (such as corn stalks, wheat straw, and rice straw), wood residues, and municipal solid waste are potential sources of cellulosic biomass. Dedicated energy crops, such as switchgrass, are also promising sources of cellulose that can be produced sustainably in many regions of the United States.[28]​.

Wind

In Europe in the 19th century, there were about 200,000 windmills, slightly more than the modern wind turbines of the 21st century.[29] They were mainly used to grind grain and pump water. The era of coal-powered steam engines replaced this early use of wind power.

Some of the second generation renewables, such as wind power, have high potential and have already had relatively low production costs. At the end of 2008, the capacity of wind farms worldwide was 120,791 megawatts (MW), which represented an increase of 28.8 percent over the year,[31]​ and wind power produced approximately 1.3% of global electricity consumption.[32]​.

In 2006, wind energy represented approximately 20% of electricity use in Denmark, 9% in Spain and 7% in Germany. The installed wind capacity in the EU is mainly offshore and reached 14.6 GW in 2021 and is expected to increase at least 25 times by 2030, using the great potential of the 5 EU sea basins.[33]​.

The total cumulative wind electricity generation capacity installed worldwide has increased rapidly since then and, as of the end of 2020, stands at 733 GW. Since 2010, more than half of all new wind energy was added outside the traditional markets of Europe and North America, mainly driven by the continued boom in China, India, Brazil, Vietnam among other countries. By 2020 the 10 largest producers can be seen in the table below:[34]​[35]​

[36]​.

Solar heating

Solar heating systems are a well-known second generation technology and generally consist of solar thermal collectors, a fluid system to move heat from the collector to its point of use, and a reservoir or tank for heat storage and later use. The systems can be used to heat domestic hot water, pool water, or for space heating.[37]​ The heat can also be used for industrial applications or as energy input for other uses, such as refrigeration equipment.[38]​ In many climates, a solar heating system can provide a very high percentage (20 to 80%) of domestic hot water energy. The energy received from the sun by the earth is electromagnetic radiation. Ranges of visible, infrared, ultraviolet, X-ray, and radio wave light received by Earth through solar energy. The greatest radiation power comes from visible light. Solar energy is complicated because of the changes in seasons and from day to night. Cloud cover can also increase the complications of solar energy, and not all of the sun's radiation reaches Earth because it is absorbed and scattered by clouds and gases within Earth's atmospheres.[39]​.

Solar thermal plants have been successfully operating commercially in California since the late 1980s, including the largest solar power plant of any type, the 350 MW Solar Power Generation Systems. Nevada Solar One is another 64MW plant that recently opened.[40] Other parabolic plants being proposed are two 50MW plants in Spain and a 100MW plant in Israel.[41]​.

solar electricity

In the 1980s and early 1990s, most PV modules provided remote area power supply, but since about 1995, industry efforts have increasingly focused on developing integrated PV buildings and power plants for grid-connected applications (see article on PV plants for more details). Currently, the largest photovoltaic power plant in North America is the Nellis Solar Power Plant (15 MW).[42]​[43]​ There is a proposal to build a solar power plant in Victoria, Australia, which would be the largest photovoltaic plant in the world, at 154 MW.[44]​[45]​ Other large photovoltaic plants include the Girassol solar power plant (62 MW),[46]​ and the Solar Park Waldpolenz (40 MW).[47]​.

Large national and regional research projects on artificial photosynthesis are designing nanotechnology-based systems that use solar energy to split water into hydrogen fuel.[48]​ and a proposal has been made for a global artificial photosynthesis project[49]​ In 2011, researchers at the Massachusetts Institute of Technology (MIT) developed what they call an "artificial leaf", which is capable of splitting water into hydrogen and oxygen directly from solar energy when dropped into a glass of water. One side of the "Artificial Leaf" produces hydrogen bubbles, while the other side produces oxygen bubbles.[50]​.

Most solar power plants today are made of a series of similar units where each unit is continuously adjusted, for example with some stepper motors, so that the light converter remains in the focus of sunlight. The cost of focusing light on converters, such as high-power solar panels, Stirling engine, etc., can be drastically reduced with simple and efficient rope mechanics.[51]​ In this technique, many units are connected with a network of ropes, so that pulling two or three ropes is enough to keep all the light converters focused simultaneously as the sun's direction changes.

Japan and China have national programs aimed at commercial-scale space solar power (SBSP). The Chinese Academy of Space Technology (CAST) won the 2015 SunSat International Design Competition with this video of its multi-swivel joint design. Proponents of SBSP claim that space-based solar power would be clean, consistent, and global, and could scale to meet all planetary energy demand.[20]​ A recent multi-agency industry proposal (which echoed the Pentagon's 2008 recommendation) won the SECDEF/SECSTATE/USAID D3 (Diplomacy, Development, Defense) Innovation Challenge.[52]​.

ocean energy

Portugal has the world's first commercial wave farm, the Aguçadora Wave Park, under construction in 2007 and inaugurated on September 23, 2008. The farm used three Pelamis P-750 machines that were expected to generate 2.25 MW.[54][55]​ and costs were estimated at 8.5 million euros. Due to technical problems with the Pelamis P-750 machines, they were returned to the port of Leixões in November 2008. Funding for a wave farm in Scotland was announced in February 2007 by Scottish Executive, at a cost of over £4 million, as part of a £13 million funding package for ocean energy in Scotland. The farm will be the largest in the world with a capacity of 3 MW generated by four Pelamis machines.[56]​.

In 2007, the world's first turbine to create commercial quantities of energy using tidal energy was installed in the narrows of Strangford Lough in Ireland. The 1.2MW underwater tidal electricity generator takes advantage of the rapid tidal flow in the lake, which can be up to 4m/s. Although the generator is powerful enough to power up to a thousand homes, the turbine has minimal environmental impact, as it is almost completely submerged and the rotors spin slowly enough that they do not pose any danger to wildlife.[57][58]​.

Enabling technologies for renewable energies

Solar and wind energy are intermittent energy sources that supply electricity 10 to 40% of the time. To compensate for this characteristic, it is common to link its production with existing hydroelectricity or natural gas generation. In regions where this is not available, wind and solar can be combined with significantly more expensive pumped storage hydroelectricity.

Heat pumps and thermal energy storage are classes of technologies that can enable the utilization of renewable energy sources that would otherwise be inaccessible due to a temperature too low for use or a time lag between energy availability and when it is needed. By increasing the temperature of the available renewable thermal energy, heat pumps have the additional property of harnessing electrical energy (or in some cases, mechanical or thermal energy) by using it to extract additional energy from a low-quality source (such as seawater, lake water, soil, air, or waste heat from a process).

Thermal storage technologies allow heat or cold to be stored for periods of time ranging from hours to overnight to seasonal, and may involve the storage of sensible heat (i.e., by changing the temperature of a medium) or latent heat (i.e., through phase changes of a medium, such as between water and sleet or ice). Short-term thermal storage can be used to regulate maximums in electrical distribution or district heating systems. The types of renewable or alternative energy sources that can be enabled include natural energy (for example, collected through solar thermal collectors, or dry cooling towers used to collect winter cold), waste energy (for example, from HVAC equipment, industrial processes, or power plants), or surplus energy (for example, such as seasonally from hydroelectric projects or intermittently from wind farms). The Drake Landing solar community (Alberta, Canada) is illustrative. Thermal energy storage allows the community to obtain 97% of its heat year-round from solar collectors on garage roofs, which accumulate in the summer. Types of sensible heat storage include insulated tanks, clusters of boreholes in substrates ranging from gravel to bedrock, deep aquifers, or shallow cased wells that are insulated on top. Some types of storage are capable of storing heat or cold between opposing seasons (especially if very large), and some storage applications require the inclusion of a heat pump. Latent heat is usually stored in ice tanks or what are called phase change materials (PCM).

There is considerable controversy over whether nuclear energy can be considered sustainable. Some forms of nuclear energy (those that are capable of "burning" nuclear waste through a process known as nuclear transmutation, such as an Integral Fast Reactor), could fall into the category of "Green Energy").

Some people, including Greenpeace founder and first member Patrick Moore,[61]​[62][63]​ George Monbiot,[64]​ Bill Gates[65]​ and James Lovelock[66]​ have specifically classified nuclear energy as green energy. Others, including Phil Radford[67]​[68]​ of Greenpeace, disagree, stating that the problems associated with radioactive waste and the risk of nuclear accidents (such as the Chernobyl disaster) represent an unacceptable risk to the environment and humanity. However, newer nuclear reactor designs are capable of using what is now considered "nuclear waste" until it is no longer (or dramatically less) dangerous, and have design features that greatly minimize the possibility of a nuclear accident. These designs have not yet been commercialized.

Avanzar hacia la sostenibilidad energética requerirá cambios no solo en la forma en que se suministra la energía, sino también en la forma en que se utiliza, y es esencial reducir la cantidad de energía necesaria para entregar diversos bienes o servicios. Las oportunidades de mejora en el lado de la demanda de la ecuación de energía son tan ricas y diversas como las del lado de la oferta y, a menudo, ofrecen importantes beneficios económicos.[69]​.

La energía renovable y la eficiencia energética a veces se dice que son los "pilares gemelos" de la política energética sostenible. Ambos recursos deben desarrollarse para estabilizar y reducir las emisiones de dióxido de carbono. La eficiencia ralentiza el crecimiento de la demanda energética, de modo que el aumento de los suministros de energía limpia puede hacer grandes recortes en el uso de combustibles fósiles. Si el uso de energía crece demasiado rápido, el desarrollo de energía renovable perseguirá un objetivo en retroceso. Un análisis histórico reciente ha demostrado que la tasa de mejoras en la eficiencia energética en general se ha visto superada por la tasa de crecimiento de la demanda de energía, que se debe a un crecimiento económico y demográfico continuo. Como resultado, a pesar de los aumentos de eficiencia energética, el uso total de energía y las emisiones de carbono relacionadas han seguido aumentando. Por lo tanto, dados los límites termodinámicos y prácticos de las mejoras de eficiencia energética, es esencial reducir el crecimiento de la demanda de energía.[70]​ Sin embargo, a menos que los suministros de energía limpia se conecten rápidamente, la desaceleración del crecimiento de la demanda solo comenzará a reducir las emisiones totales; también es necesario reducir el contenido de carbono de las fuentes de energía. Cualquier visión seria de una economía energética sostenible requiere compromisos tanto de energías renovables como de eficiencia.[71]​.

La energía renovable (y la eficiencia energética) ya no son sectores especializados que solo son promovidos por gobiernos y ambientalistas. El aumento de los niveles de inversión y el hecho de que gran parte del capital proviene de actores financieros más convencionales, sugiere que las opciones de energía sostenible ahora se están convirtiendo en la corriente principal.[72]​.

De acuerdo con un análisis de tendencias del Programa de las Naciones Unidas para el Medio Ambiente, las preocupaciones por el cambio climático, junto con los altos precios del petróleo") y el creciente apoyo gubernamental, están impulsando el aumento de las tasas de inversión en las industrias de energía sostenible. Según el PNUMA, la inversión global en energía sostenible en 2007 fue superior a los niveles anteriores, con $ 148 mil millones de dinero recaudado en 2007, un aumento del 60% en comparación con 2006. El total de transacciones financieras en energía sostenible, incluida la actividad de adquisición, fue de $ 204 mil millones.[73]​.

Los flujos de inversión en 2007 se ampliaron y diversificaron, haciendo del panorama general una mayor amplitud y profundidad del uso sostenible de la energía. Los principales mercados de capital son "ahora totalmente receptivos a las compañías de energía sostenible, apoyadas por un aumento en los fondos destinados a la inversión en energía limpia".[73]​.

Smart grid technology

Smart grid refers to a class of technology that people use to bring utility electricity delivery systems into the 20th century, using computer-based remote control and automation.[74] These systems are made possible by two-way communication technology and computer processing that has been used for decades in other industries. They are beginning to be used in electrical networks, from power plants and wind farms to electricity consumers in homes and businesses. They offer many benefits to utilities and consumers, primarily in large improvements in energy efficiency in the electrical grid and in the homes and offices of energy users.[74]​.

La energía verde incluye procesos energéticos naturales que se pueden aprovechar con poca contaminación. La energía verde es la electricidad generada a partir de fuentes de energía renovables.[75]​ Algunas definiciones también pueden incluir la energía derivada de la incineración de residuos.

Algunos han argumentado que aunque la energía verde es un esfuerzo encomiable para resolver el creciente consumo de energía en el mundo, debe ir acompañada de un cambio cultural que fomente la disminución del apetito energético en el mundo.[76]​.

En varios países con acuerdos de transportistas comunes, los acuerdos de venta minorista de electricidad hacen posible que los consumidores compren electricidad ecológica (electricidad renovable) de su proveedor de servicios públicos o de un proveedor de energía ecológica.

Cuando se compra energía de la red eléctrica, la energía que llega al consumidor no necesariamente se generará a partir de fuentes de energía verde. La compañía local de servicios públicos, la compañía eléctrica o el grupo de energía estatal compran su electricidad a los productores de electricidad que pueden estar generando a partir de combustibles fósiles, fuentes de energía energía nuclear o renovable. En muchos países, la energía verde en la actualidad proporciona una cantidad muy pequeña de electricidad, que generalmente contribuye con menos del 2 al 5% al conjunto. En algunos estados de los EE. UU., los gobiernos locales han formado grupos regionales de compras de energía mediante el uso de Community Choice Aggregation y Solar Bonds para lograr una mezcla renovable del 51% o superior, como en la Ciudad de San Francisco.[77]​.

Al participar en un programa de energía verde, un consumidor puede tener un efecto en las fuentes de energía utilizadas y, en última instancia, podría estar ayudando a promover y expandir el uso de energía verde. También están haciendo una declaración a los responsables políticos de que están dispuestos a pagar una prima de precio para respaldar la energía renovable. Los consumidores de energía verde obligan a las empresas de servicios públicos a aumentar la cantidad de energía verde que compran de la piscina (lo que reduce la cantidad de energía no verde que compran), o bien financian directamente la energía verde a través de un proveedor de energía verde. Si no hay suficientes fuentes de energía verde disponibles, la empresa de servicios públicos debe desarrollar otras nuevas o contratar a un proveedor de energía de terceros para proporcionar energía verde, lo que hace que se construya más. Sin embargo, no hay forma de que el consumidor pueda verificar si la electricidad comprada es "verde" o no.

En algunos países, como los Países Bajos, las compañías de electricidad garantizan la compra de una cantidad igual de "energía verde" que utilizan sus clientes de energía verde. El gobierno holandés exime a la energía verde de los impuestos sobre la contaminación, lo que significa que la energía verde no es más cara que la otra.

Local green energy systems

Those dissatisfied with the third-party grid approach to green energy via the electrical grid can install their own locally-based renewable energy system. Renewable energy electrical systems, from solar to wind to even local hydropower in some cases, are some of the many types of renewable energy systems available locally. Additionally, for those interested in heating and cooling their home using renewable energy, geothermal heat pump systems that take advantage of the earth's constant temperature, which is around 7 to 15 degrees Celsius a few meters underground and increases considerably at greater depths, are an option to conventional natural gas and oil. Additionally, in geographic locations where the Earth's crust is especially thin, or near volcanoes (as is the case in Iceland) there is the potential to generate even more electricity than would be possible elsewhere, thanks to a more significant temperature gradient in these locations.

The advantage of this approach in the United States is that many states offer incentives to offset the cost of installing a renewable energy system. In California, Massachusetts, and several other U.S. states, a new approach to community energy delivery called Community Choice Aggregation has given communities the means to apply for a competitive electricity provider and use municipal revenue bonds to finance the development of local green energy resources. People are usually assured that the electricity they are using is actually produced from a green energy source that they control. Once the system is paid off, the owner of a renewable energy system will produce their own renewable electricity at virtually no cost and can sell the excess to the local utility at a profit.

Using green energy

Renewable energy, after its generation, must be stored in a medium for use with autonomous devices and vehicles. Additionally, to provide domestic electricity in remote areas (i.e. areas that are not connected to the main electrical grid), energy storage is required for use with renewable energy. The energy generation and consumption systems used in the latter case are usually autonomous energy systems.

Some examples are:

• - energy carriers such as hydrogen, liquid nitrogen, compressed air, oxyhydrogen, batteries, to power vehicles.

• - flywheel energy storage, hydroelectricity with pumped storage is more usable in stationary applications (for example, to power homes and offices). In home energy systems, energy conversion can also be done to reduce odor. For example, organic matter, such as cow dung and organic matter that can decompose, can be converted into biochar. To eliminate emissions, carbon capture and storage is used.

Generally, however, renewable energy is derived from the main electrical grid. This means that most of the energy storage is not used, as the main electrical grid is organized to produce the exact amount of energy that is consumed at that particular time. Power production in the main power grid is always configured as a combination of (large-scale) renewable power plants as well as other power plants such as fossil fuel power plants and nuclear power. However, this combination, which is essential for this type of energy supply (such as wind turbines, solar power plants, etc.) can only occur when the wind blows and the sun shines. This is also one of the main drawbacks of the system, since fossil fuel power plants are polluting and are the main cause of global warming (nuclear power is an exception). While fossil fuel power plants can also be made emission-free (through carbon capture and storage) as well as renewable (if the plants are converted to, for example, biomass), the best solution is to phase out the power plants over time. Nuclear power plants can also be more or less eliminated from their nuclear waste problem by using nuclear reprocessing and newer plants such as fast breeder plants and nuclear fusion plants.

Renewable energy power plants provide a constant flow of energy. For example, hydroelectric plants, ocean thermal plants and osmotic power plants provide energy at a regulated rate and are therefore sources of energy available at any time (even at night, windy times, etc.). However, at present, the number of steady flow renewable energy plants alone is too small to meet power demands at the time of day when irregularly produced renewable energy plants cannot produce power.

In addition to reducing the impact of fossil fuels and nuclear power plants, another option is the distribution and immediate use of energy from exclusively renewable sources. In this configuration, energy storage is also not necessary. For example, TREC has proposed distributing solar energy from the Sahara to Europe. Europe can distribute wind and ocean energy to the Sahara and other countries. In this way, energy is produced at any given time as at any point on the planet as the sun or the wind rises or the ocean waves and currents stir. However, this option is probably not possible in the short term, as fossil fuel and nuclear energy remain the main energy sources in the main electricity grid and it will not be possible to replace them overnight.

Green energy and labeling by region

Directive 2004/8/EC of the European Parliament and of the Council of 11 February 2004 on the promotion of cogeneration based on useful heat demand in the internal energy market[78] includes Article 5 (Guarantee of origin of electricity for high efficiency cogeneration).

European environmental NGOs have launched an eco-label for green energy. The ecolabel is called EKOenergy. Establishes criteria for sustainability, additionality, consumer information and monitoring. Only a portion of the electricity produced by renewable sources meets the EKOenergy criteria.[79]​.

A green energy supply certification scheme was launched in the UK in February 2010. This implements the guidelines of the Energy Regulator, Ofgem, and establishes requirements for transparency, the comparison of sales for renewable energy supplies and additionality.[80]​.

The United States Department of Energy (DOE), the Environmental Protection Agency "Environmental Protection Agency (United States)") (EPA), and the Center for Resource Solutions (CRS)[81]​ recognize the voluntary purchase of electricity from renewable energy sources (also called renewable electricity or green electricity) as green power.[82]​.

The most popular way to purchase renewable energy as revealed by NREL data is through the purchase of Renewable Energy Certificates (RECs). According to a survey by the Natural Marketing Institute (NMI),[83]​ 55 percent of American consumers want companies to increase their use of renewable energy.[82]​.

The DOE selected six companies for its 2007 Green Power Supplier Awards, including Constellation NewEnergy; 3Degrees ; Planet Sterling; SunEdison; Pacific Power and Rocky Mountain Power; and Silicon Valley Power. The combined green energy provided by those six winners equals more than 5 billion kilowatt-hours per year, which is enough to power nearly 465,000 average American homes. In 2014, Arcadia Power made RECS available to homes and businesses in all 50 states, allowing consumers to use "100% green energy," as defined by the EPA's Green Energy Partnership.[84][85]​

The United States Environmental Protection Agency (USEPA) Green Power Partnership is a voluntary program that supports organizational procurement of renewable electricity by offering expert advice, technical assistance, tools and resources. This can help organizations reduce the transaction costs of purchasing renewable energy, reduce their carbon footprint, and communicate their leadership to key stakeholders.[86]​.

Nationwide, more than half of all U.S. electricity customers now have the option to purchase some type of green energy product from a retail electricity provider. About a quarter of the nation's utilities offer green energy programs to customers, and voluntary retail sales of renewable energy in the United States totaled more than 12 billion kilowatt-hours in 2006, up 40% from the previous year.

Existen numerosas organizaciones dentro de los sectores académico, federal y comercial que realizan investigaciones avanzadas a gran escala en el campo de la energía sostenible. Esta investigación abarca varias áreas de enfoque en todo el espectro de energía sostenible. La mayor parte de la investigación está dirigida a mejorar la eficiencia y aumentar el rendimiento energético general.[91]​ Múltiples organizaciones de investigación con apoyo federal se han centrado en la energía sostenible en los últimos años. Dos de los laboratorios más destacados son los Laboratorios Nacionales Sandia") y el Laboratorio Nacional de Energía Renovable (NREL), ambos financiados por el Departamento de Energía de los Estados Unidos y respaldados por varios socios corporativos.[92]​ Sandia tiene un presupuesto total de $ 2.4 mil millones[93]​ mientras que NREL tiene un presupuesto de $ 375 millones.[94]​.

La producción científica hacia sistemas de energía sostenible está aumentando de manera exponencial, ya que creció de aproximadamente 500 artículos de revistas en inglés solo sobre energía renovable en 1992 a casi 9,000 artículos para 2011.[95]​.

Biomass is biological material derived from living or recently living organisms. It most often refers to plants or plant-derived materials that are specifically called lignocellulosic biomass.[96] As an energy source, biomass can be used directly through combustion to produce heat, or indirectly after conversion into various forms of biofuel. The conversion of biomass into biofuel can be achieved by different methods that are broadly classified into: thermal, chemical and biochemical methods. Wood remains the largest source of biomass energy today; examples include forestry waste, such as dead trees, tree branches and stumps, yard trimmings, wood chips, and even municipal solid waste. In the second sense, biomass includes plant or animal matter that can be converted into fibers or other industrial chemicals, including biofuels. Industrial biomass can be grown from numerous types of plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane), bamboo,[98] and a variety of tree species, ranging from eucalyptus to oil palm (palm).

Biomass, biogas and biofuels are burned to produce heat/energy and in doing so, harm the environment. Pollutants such as sulfur oxides (SO), nitrous oxides (NO) and particulate matter (PM) are produced from this combustion; The World Health Organization estimates that air pollution causes 7 million premature deaths each year.[99]​ Biomass combustion is a major contributor.[99][100][101]​.

Ethanol biofuels

As the primary source of biofuel in North America, many organizations are conducting research in the area of ​​ethanol production. At the federal level, the USDA conducts a large amount of research on ethanol production in the United States. Much of this research is oriented toward the effect of ethanol production on domestic food markets.[102] The National Renewable Energy Laboratory has conducted several ethanol research projects, primarily in the area of cellulosic ethanol.[103] Cellulosic ethanol has many benefits over traditional corn-based ethanol. It does not directly remove or conflict with the food supply because it is produced from wood, grasses, or inedible parts of crops. plants.[104]​ Additionally, some studies have shown that cellulosic ethanol is more cost-effective and economically sustainable than corn-based ethanol.[105]​ Even if we used the entire corn crop we have in the United States and converted it to ethanol, it would only produce enough fuel to cover 13 percent of total gasoline consumption in the United States.[106]​ Sandia National Laboratories") conducts internal research on cellulosic ethanol.[107]​ and is also a member of the Joint BioEnergy Institute (JBEI), a research institute founded by the United States Department of Energy with the goal of developing cellulosic biofuels.[108]​.

Other biofuels

From 1978 to 1996, the National Renewable Energy Laboratory experimented with algal fuel production in the "Aquatic Species Program".[109] A self-published paper by Michael Briggs, in the Biofuels Group at the University of New Hampshire, provides estimates for the realistic replacement of all motor vehicle fuels with biofuels using algae that have a natural oil content greater than 50%, which Briggs suggests it may be grown in algae ponds at wastewater treatment plants.[110] These oil-rich algae can then be extracted from the system and processed into biofuels, and the dried remainder can be reprocessed to create ethanol. The production of algae for oil extraction for biofuels has not yet been done on a commercial scale, but feasibility studies have been carried out to arrive at the above performance estimate. During the biofuel production process, algae actually consume the carbon dioxide in the air and convert it to oxygen through photosynthesis.[111] In addition to its projected high yield, algaculture, unlike food crop-based biofuels, does not involve a decrease in food production, as it does not require cropland or fresh water. Many companies are pursuing algal bioreactors for various purposes, including scaling up biofuel production to commercial levels.[112]​[113]​.

Several groups in various sectors are conducting research on Jatropha curcas, a poisonous bush-like tree that produces seeds considered by many to be a viable source of oil as a feedstock for biofuels.[114] Much of this research focuses on improving the overall oil yield per acre of Jatropha through advances in genetics, soil science, and horticultural practices. SG Biofuels, a San Diego-based Jatropha developer, has used molecular genetics and biotechnology to produce elite hybrid Jatropha seeds that show significant improvements in yield compared to first-generation varieties.[115]​ The Center for Sustainable Energy Agriculture (CfSEF) is a Los Angeles-based nonprofit research organization dedicated to Jatropha research in the areas of plant science, agronomy, and horticulture. Successful exploration of these disciplines is projected to increase Jatropha farm production yields by 200-300% over the next ten years.[116]​.

Thorium

There are potentially two sources of nuclear energy. Fission is used in all current nuclear power plants. Fusion is the reaction that exists in stars, including the sun, and is not practical for use on Earth as fusion reactors are not yet available. However, nuclear energy is politically and scientifically controversial due to concerns about radioactive waste disposal, safety, risks of a serious accident, and technical and economic problems in decommissioning old power plants.[117]

Thorium is a fissile material used in thorium-based nuclear power. The thorium fuel cycle claims several potential advantages over the uranium fuel cycle, including greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation[118][119][120], and reduced production of plutonium and actinides.[120]​ Therefore, it is sometimes referred to as sustainable.[121]​.

Solar

The main obstacle preventing large-scale implementation of solar power generation is the inefficiency of current solar technology. Currently, photovoltaic (PV) panels only have the capacity to convert about 24% of the sunlight that hits them into electricity.[122] At this rate, solar energy still presents many challenges to widespread deployment, but steady progress has been made in reducing manufacturing costs and increasing photovoltaic efficiency. Both Sandia National Laboratory and the National Renewable Energy Laboratory (NREL) have funded solar research programs. The NREL solar program has a budget of around $75 million[123] and develops research projects in the areas of photovoltaic (PV) technology, solar thermal energy, and solar radiation.[124] The budget for Sandia's solar division is unknown, however, it represents a significant percentage of the company's $2.4 billion budget. laboratory.[125]​ Several academic programs have focused on solar research in recent years. The Solar Energy Research Center (SERC) at the University of North Carolina (UNC) has the sole purpose of developing cost-effective solar technology. In 2008, researchers at the Massachusetts Institute of Technology (MIT) developed a method to store solar energy by using it to produce hydrogen from water.[126]​ Such research is aimed at addressing the obstacle facing solar development of energy storage for use. during nighttime hours when the sun is not shining. In February 2012, North Carolina-based Semprius Inc., a solar development company backed by the German company Siemens, announced that it had developed the world's most efficient solar panel. The company claims that the prototype converts 33.9% of the sunlight it receives into electricity, more than double the previous high-level conversion rate.[127] Large projects on artificial photosynthesis or solar fuels are also underway. many developed nations.[128]​.

Space-based solar power satellites seek to overcome storage problems and provide civilization-scale power that is clean, constant and global. Japan and China have active national programs aimed at commercial-scale space-based solar power (SBSP), with both nations hoping for orbiting demonstrations in the 2030s.

Wind energy research dates back several decades to the 1970s, when NASA developed an analytical model to predict the power generation of wind turbines during high winds.[130] Today, both Sandia National Laboratory and the National Renewable Energy Laboratory have programs dedicated to wind research. The Sandia laboratory focuses on advancing materials, aerodynamics and sensors.[131] Wind projects NREL focus on improving the energy output of wind plants, reducing their capital costs, and making wind energy more profitable overall.[132]​ The Field Laboratory for Optimized Wind Energy (FLOWE) at Caltech was established to research renewable approaches to wind energy technology practices that have the potential to reduce the cost, size, and environmental impact of wind energy production.[133]​ The president of Sky WindPower Corporation believes that wind turbines will be able to produce electricity at one cent/kWh at an average that, compared to coal-generated electricity, is a fraction of the cost.[134]​.

A wind farm is a group of wind turbines on the same site used to produce electrical energy. A large wind farm may consist of several hundred individual wind turbines, covering an extended area of ​​hundreds of square miles, but the land between the wind turbines may be used for agricultural or other purposes. A wind farm can also be located offshore.

Many of the largest operational onshore wind farms are located in the United States and China. The Gansu wind farm in China has over 5,000 MW installed with a goal of 20,000 MW by 2020. China has several other "wind energy bases" of similar size. The High Wind Energy Center in California is the largest onshore wind farm outside China, with a capacity of 1,020 MW of power.[135]​ Europe leads the use of wind energy with almost 66 GW, approximately 66 percent of the global total, with Denmark leading the way according to countries with per capita installed capacity.[136]​ As of February 2012, the Walney wind farm in the United Kingdom is the offshore wind farm. largest in the world with 367 MW, followed by the Thanet wind farm (300 MW), also in the United Kingdom.

There are many large wind farms under construction, including BARD Offshore 1 (400 MW), Clyde Wind Farm (350 MW), Greater Gabbard Wind Farm (500 MW), Lincs Wind Farm (270 MW), London Array (1000 MW), Lower Snake River Wind Project (343 MW), Macarthur Wind Farm (420 MW), Shepherds Flat Wind Farm (845 MW) and Sheringham shoal (317 MW).

In 2022, wind energy generation in the world increased with a record of 265 TWh (14% growth), reaching more than 2,100 TWh[137]​.

Although Enerdata provides quantitative values ​​of the use of wind and solar energy together, it is worth noting that in 2020 the share of these energies grew at a rapid and constant rate (+1.2 points), reaching 9.5% worldwide. The country that experienced the highest growth in 2020 was Australia, a country where the share of wind and solar energy in the energy supply grew by 2.9 points.[138]​.

Geothermal energy is produced by harnessing the thermal energy created and stored within the earth. It arises from the radioactive decay of an isotope of potassium and other elements found in the Earth's crust.[139]​ Geothermal energy can be obtained by drilling into the ground, much like oil exploration, and is then transported using a heat transfer fluid (e.g., water, brine, or steam).[139]​ Geothermal systems that are primarily dominated by water have the potential to provide greater benefits to the system and will generate more energy.[140]​ Within these liquid-dominated systems, there are potential concerns of subsidence and contamination of groundwater resources. Therefore, protection of groundwater resources is necessary in these systems. This means that careful reservoir production and engineering is necessary in liquid-dominated geothermal reservoir systems.[140]​ Geothermal energy is considered sustainable because thermal energy is constantly replenished.[141]​ However, the science of geothermal energy generation is still young and developing economic viability. Several entities, such as the National Renewable Energy Laboratory[142]​ and Sandia National Laboratories")[143]​ are conducting research toward the goal of establishing a proven science around geothermal energy. The International Geothermal Research Center (IGC), a German geoscience research organization, focuses primarily on geothermal energy development research.[144]​.

Hydrogen

More than $1 trillion of federal money has been spent on research and development of hydrogen and a means for energy storage in the United States. (2012)[145]​ Both the National Renewable Energy Laboratory[146]​ and Sandia National Laboratories")[147]​ have departments dedicated to hydrogen research. Hydrogen is useful for energy storage and for use in airplanes and ships, but is not practical for automobile use, as it is not very efficient compared to using a battery, for the same cost a person can travel three times as far using a battery. Electric vehicle battery .[148] Despite that opinion, Japanese automakers Toyota and Honda currently offer hydrogen fuel cell-powered passenger vehicles for sale in Japan and the US. Experimental hydrogen fuel cell city buses are currently operational in two US transit districts: Costa County, California, and in Connecticut.[149]

Around the world, many subnational governments (regions, states and provinces) have aggressively pursued investments in sustainable energy. In the United States, California's leadership in renewable energy was recognized by The Climate Group when it awarded former Governor Arnold Schwarzenegger its inaugural award for international climate leadership in Copenhagen in 2009. coal.[151] South Australia has also had the highest per capita consumption of domestic solar panels in Australia following the Rann Government's introduction of solar power laws and related educational campaign to install solar photovoltaic installations on the roofs of prominent public buildings, including parliament. , museum, airport and Adelaide Showgrounds pavilions and schools.[152]​ Rann, Australia's first climate change minister, passed legislation in 2006 setting targets for renewable energy and emissions cuts, the first legislation in Australia to do so.[153]​.

Furthermore, in the European Union there is a clear tendency to promote policies that encourage investments and financing of sustainable energy in terms of energy efficiency, innovation in the exploitation of energy and development of renewable resources, with greater consideration of environmental aspects and sustainability.[154]​.

In October 2018, the American Council for an Energy Efficient Economy (ACEEE) published its “State Energy Efficiency Scorecard.” The scorecard concluded that states and electric utilities continue to expand energy efficiency measures to meet clean energy goals. In 2017, the United States spent $6.6 billion on electrical efficiency programs. $1.3 billion was spent on natural gas efficiency. These programs resulted in savings of 27.3 million megawatt hours (MWh) of electricity.[155]​.

Among the scientific journals related to the interdisciplinary study of sustainable energy are:

• - Energy and environmental science.

• - Energy for sustainable development.

• - Energy policy.

• - Renewable and Sustainable Energy Magazine.

• - Renewable and sustainable energy reviews.

• - Electric vehicle.

• - Energy hierarchy.

• - Hydrogen economy.

Contenido

Cuando se hace referencia a fuentes de energía, los términos "energía sostenible" y "energía renovable" a menudo se usan indistintamente, sin embargo, los proyectos particulares de energía renovable a veces plantean importantes preocupaciones de sostenibilidad. Las tecnologías de energía renovable son contribuyentes esenciales para la energía sostenible, ya que generalmente contribuyen a la seguridad energética mundial, reduciendo la dependencia de los recursos de combustibles fósiles,[9]​ y brindando oportunidades para mitigar los gases de efecto invernadero.[9]​ Se han realizado diversos trabajos de análisis de costo-beneficio realizados por una gran variedad de especialistas y agencias para determinar las vías más baratas y rápidas para descarbonizar el suministro de energía del mundo, y el tema es de gran controversia, en particular sobre el papel de la energía nuclear.[10]​[11]​[12]​[13]​[14]​.

Hydroelectricity

Among renewable energy sources, hydroelectric plants have the advantage of being long-lived: many existing plants have operated for more than 100 years. In addition, hydroelectric plants are clean and have low emissions. Criticisms leveled at large-scale hydropower plants include: the dislocation of people living where the reservoirs are planned and the release of significant amounts of carbon dioxide during reservoir construction and flooding.[15]​.

However, high emissions have been found to be associated only with shallow reservoirs in warm (tropical) locations, and recent innovations in turbine technology are enabling the efficient development of low-impact hydroelectric projects on the river stream.[16] In general, hydroelectric plants produce much lower greenhouse gas emissions than other types of generation.

Hydropower, which experienced intense development during the growth of electrification in the 19th and 20th centuries, is experiencing a resurgence of development in the 21st century. The areas of greatest hydropower growth are the booming economies of Asia. China is the leader of development; However, other Asian nations are installing hydropower at a rapid pace. This growth is driven by an increase in energy costs, especially imported energy, and by widespread desires for more domestic, clean, renewable and affordable generation.

Geothermal

Technologies in use for geothermal production include dry steam plants, flash steam plants and binary cycle plants. Geothermal electricity generation is currently used in 24 countries, while geothermal heating is used in 70 countries.[17] International markets grew at an average annual rate of 5 percent over the three years to 2015, and global geothermal power capacity is expected to reach 14.5–17.6 GW in 2020.[18]

Geothermal energy is considered a sustainable and renewable energy source because heat extraction is small compared to the heat content of the Earth.[19] Greenhouse gas emissions from geothermal power stations are on average 45 grams of carbon dioxide per kilowatt-hour of electricity, or less than 5 percent of that of conventional coal plants.[17] As a renewable energy source for power and heating, geothermal energy has the potential to satisfy 3-5% of global demand by 2050. With economic incentives, it is estimated that by 2100 it will be possible to satisfy 10% of global demand.[20]​.

Biomass

Biomass briquettes are increasingly used in the developing world as an alternative to charcoal. The technique involves converting almost any plant matter into compressed briquettes that typically have about 70% of the heating value of charcoal. There are relatively few examples of large-scale briquette production. One exception is in North Kivu, in eastern Democratic Republic of the Congo, where forest clearing for charcoal production is considered the biggest threat to mountain gorilla habitat. Virunga National Park staff have successfully trained and equipped over 3,500 people to produce biomass briquettes, replacing charcoal produced illegally within the national park and creating important employment for people living in extreme poverty in conflict-affected areas.[21]​.

Biofuel

Brazil has one of the world's largest renewable energy programs, involving the production of fuel ethanol "Ethanol (fuel)") from sugar cane, and ethanol now provides 18 percent of the country's automotive fuel. As a result of this, along with the exploitation of domestic deepwater oil sources, Brazil, which years ago had to import a large portion of the oil needed for domestic consumption, achieved complete oil self-sufficiency.[22][23][24]​.

Most cars on the road in the United States can run on blends of up to 10% ethanol, and motor vehicle manufacturers already produce vehicles designed to run on much higher ethanol blends. Ford, DaimlerChrysler and GM are among the companies selling "flex-fuel" cars, trucks and minivans that can use gasoline and ethanol blends, from pure gasoline to 85% ethanol (E85). As of mid-2006, there were approximately six million E85-compatible vehicles on United States roads.[25]​.

Biofuels may be defined as "renewable", but may not be "sustainable" due to land degradation. As of 2012, 40% of US corn production goes into ethanol. Ethanol occupies a large percentage of "Clean Energy Use" when, in fact, it is still debatable whether ethanol should be considered a "Clean Energy".[26]​.

According to the International Energy Agency, new bioenergy (biofuels) technologies being developed today, especially cellulosic ethanol biorefineries, could allow biofuels to play a much larger role in the future than previously thought.[27] Cellulosic ethanol can be obtained from plant matter composed primarily of non-edible cellulose fibers that form the stems and branches of most plants. Crop residues (such as corn stalks, wheat straw, and rice straw), wood residues, and municipal solid waste are potential sources of cellulosic biomass. Dedicated energy crops, such as switchgrass, are also promising sources of cellulose that can be produced sustainably in many regions of the United States.[28]​.

Wind

In Europe in the 19th century, there were about 200,000 windmills, slightly more than the modern wind turbines of the 21st century.[29] They were mainly used to grind grain and pump water. The era of coal-powered steam engines replaced this early use of wind power.

Some of the second generation renewables, such as wind power, have high potential and have already had relatively low production costs. At the end of 2008, the capacity of wind farms worldwide was 120,791 megawatts (MW), which represented an increase of 28.8 percent over the year,[31]​ and wind power produced approximately 1.3% of global electricity consumption.[32]​.

In 2006, wind energy represented approximately 20% of electricity use in Denmark, 9% in Spain and 7% in Germany. The installed wind capacity in the EU is mainly offshore and reached 14.6 GW in 2021 and is expected to increase at least 25 times by 2030, using the great potential of the 5 EU sea basins.[33]​.

The total cumulative wind electricity generation capacity installed worldwide has increased rapidly since then and, as of the end of 2020, stands at 733 GW. Since 2010, more than half of all new wind energy was added outside the traditional markets of Europe and North America, mainly driven by the continued boom in China, India, Brazil, Vietnam among other countries. By 2020 the 10 largest producers can be seen in the table below:[34]​[35]​

[36]​.

Solar heating

Solar heating systems are a well-known second generation technology and generally consist of solar thermal collectors, a fluid system to move heat from the collector to its point of use, and a reservoir or tank for heat storage and later use. The systems can be used to heat domestic hot water, pool water, or for space heating.[37]​ The heat can also be used for industrial applications or as energy input for other uses, such as refrigeration equipment.[38]​ In many climates, a solar heating system can provide a very high percentage (20 to 80%) of domestic hot water energy. The energy received from the sun by the earth is electromagnetic radiation. Ranges of visible, infrared, ultraviolet, X-ray, and radio wave light received by Earth through solar energy. The greatest radiation power comes from visible light. Solar energy is complicated because of the changes in seasons and from day to night. Cloud cover can also increase the complications of solar energy, and not all of the sun's radiation reaches Earth because it is absorbed and scattered by clouds and gases within Earth's atmospheres.[39]​.

Solar thermal plants have been successfully operating commercially in California since the late 1980s, including the largest solar power plant of any type, the 350 MW Solar Power Generation Systems. Nevada Solar One is another 64MW plant that recently opened.[40] Other parabolic plants being proposed are two 50MW plants in Spain and a 100MW plant in Israel.[41]​.

solar electricity

In the 1980s and early 1990s, most PV modules provided remote area power supply, but since about 1995, industry efforts have increasingly focused on developing integrated PV buildings and power plants for grid-connected applications (see article on PV plants for more details). Currently, the largest photovoltaic power plant in North America is the Nellis Solar Power Plant (15 MW).[42]​[43]​ There is a proposal to build a solar power plant in Victoria, Australia, which would be the largest photovoltaic plant in the world, at 154 MW.[44]​[45]​ Other large photovoltaic plants include the Girassol solar power plant (62 MW),[46]​ and the Solar Park Waldpolenz (40 MW).[47]​.

Large national and regional research projects on artificial photosynthesis are designing nanotechnology-based systems that use solar energy to split water into hydrogen fuel.[48]​ and a proposal has been made for a global artificial photosynthesis project[49]​ In 2011, researchers at the Massachusetts Institute of Technology (MIT) developed what they call an "artificial leaf", which is capable of splitting water into hydrogen and oxygen directly from solar energy when dropped into a glass of water. One side of the "Artificial Leaf" produces hydrogen bubbles, while the other side produces oxygen bubbles.[50]​.

Most solar power plants today are made of a series of similar units where each unit is continuously adjusted, for example with some stepper motors, so that the light converter remains in the focus of sunlight. The cost of focusing light on converters, such as high-power solar panels, Stirling engine, etc., can be drastically reduced with simple and efficient rope mechanics.[51]​ In this technique, many units are connected with a network of ropes, so that pulling two or three ropes is enough to keep all the light converters focused simultaneously as the sun's direction changes.

Japan and China have national programs aimed at commercial-scale space solar power (SBSP). The Chinese Academy of Space Technology (CAST) won the 2015 SunSat International Design Competition with this video of its multi-swivel joint design. Proponents of SBSP claim that space-based solar power would be clean, consistent, and global, and could scale to meet all planetary energy demand.[20]​ A recent multi-agency industry proposal (which echoed the Pentagon's 2008 recommendation) won the SECDEF/SECSTATE/USAID D3 (Diplomacy, Development, Defense) Innovation Challenge.[52]​.

ocean energy

Portugal has the world's first commercial wave farm, the Aguçadora Wave Park, under construction in 2007 and inaugurated on September 23, 2008. The farm used three Pelamis P-750 machines that were expected to generate 2.25 MW.[54][55]​ and costs were estimated at 8.5 million euros. Due to technical problems with the Pelamis P-750 machines, they were returned to the port of Leixões in November 2008. Funding for a wave farm in Scotland was announced in February 2007 by Scottish Executive, at a cost of over £4 million, as part of a £13 million funding package for ocean energy in Scotland. The farm will be the largest in the world with a capacity of 3 MW generated by four Pelamis machines.[56]​.

In 2007, the world's first turbine to create commercial quantities of energy using tidal energy was installed in the narrows of Strangford Lough in Ireland. The 1.2MW underwater tidal electricity generator takes advantage of the rapid tidal flow in the lake, which can be up to 4m/s. Although the generator is powerful enough to power up to a thousand homes, the turbine has minimal environmental impact, as it is almost completely submerged and the rotors spin slowly enough that they do not pose any danger to wildlife.[57][58]​.

Enabling technologies for renewable energies

Solar and wind energy are intermittent energy sources that supply electricity 10 to 40% of the time. To compensate for this characteristic, it is common to link its production with existing hydroelectricity or natural gas generation. In regions where this is not available, wind and solar can be combined with significantly more expensive pumped storage hydroelectricity.

Heat pumps and thermal energy storage are classes of technologies that can enable the utilization of renewable energy sources that would otherwise be inaccessible due to a temperature too low for use or a time lag between energy availability and when it is needed. By increasing the temperature of the available renewable thermal energy, heat pumps have the additional property of harnessing electrical energy (or in some cases, mechanical or thermal energy) by using it to extract additional energy from a low-quality source (such as seawater, lake water, soil, air, or waste heat from a process).

Thermal storage technologies allow heat or cold to be stored for periods of time ranging from hours to overnight to seasonal, and may involve the storage of sensible heat (i.e., by changing the temperature of a medium) or latent heat (i.e., through phase changes of a medium, such as between water and sleet or ice). Short-term thermal storage can be used to regulate maximums in electrical distribution or district heating systems. The types of renewable or alternative energy sources that can be enabled include natural energy (for example, collected through solar thermal collectors, or dry cooling towers used to collect winter cold), waste energy (for example, from HVAC equipment, industrial processes, or power plants), or surplus energy (for example, such as seasonally from hydroelectric projects or intermittently from wind farms). The Drake Landing solar community (Alberta, Canada) is illustrative. Thermal energy storage allows the community to obtain 97% of its heat year-round from solar collectors on garage roofs, which accumulate in the summer. Types of sensible heat storage include insulated tanks, clusters of boreholes in substrates ranging from gravel to bedrock, deep aquifers, or shallow cased wells that are insulated on top. Some types of storage are capable of storing heat or cold between opposing seasons (especially if very large), and some storage applications require the inclusion of a heat pump. Latent heat is usually stored in ice tanks or what are called phase change materials (PCM).

There is considerable controversy over whether nuclear energy can be considered sustainable. Some forms of nuclear energy (those that are capable of "burning" nuclear waste through a process known as nuclear transmutation, such as an Integral Fast Reactor), could fall into the category of "Green Energy").

Some people, including Greenpeace founder and first member Patrick Moore,[61]​[62][63]​ George Monbiot,[64]​ Bill Gates[65]​ and James Lovelock[66]​ have specifically classified nuclear energy as green energy. Others, including Phil Radford[67]​[68]​ of Greenpeace, disagree, stating that the problems associated with radioactive waste and the risk of nuclear accidents (such as the Chernobyl disaster) represent an unacceptable risk to the environment and humanity. However, newer nuclear reactor designs are capable of using what is now considered "nuclear waste" until it is no longer (or dramatically less) dangerous, and have design features that greatly minimize the possibility of a nuclear accident. These designs have not yet been commercialized.

Avanzar hacia la sostenibilidad energética requerirá cambios no solo en la forma en que se suministra la energía, sino también en la forma en que se utiliza, y es esencial reducir la cantidad de energía necesaria para entregar diversos bienes o servicios. Las oportunidades de mejora en el lado de la demanda de la ecuación de energía son tan ricas y diversas como las del lado de la oferta y, a menudo, ofrecen importantes beneficios económicos.[69]​.

La energía renovable y la eficiencia energética a veces se dice que son los "pilares gemelos" de la política energética sostenible. Ambos recursos deben desarrollarse para estabilizar y reducir las emisiones de dióxido de carbono. La eficiencia ralentiza el crecimiento de la demanda energética, de modo que el aumento de los suministros de energía limpia puede hacer grandes recortes en el uso de combustibles fósiles. Si el uso de energía crece demasiado rápido, el desarrollo de energía renovable perseguirá un objetivo en retroceso. Un análisis histórico reciente ha demostrado que la tasa de mejoras en la eficiencia energética en general se ha visto superada por la tasa de crecimiento de la demanda de energía, que se debe a un crecimiento económico y demográfico continuo. Como resultado, a pesar de los aumentos de eficiencia energética, el uso total de energía y las emisiones de carbono relacionadas han seguido aumentando. Por lo tanto, dados los límites termodinámicos y prácticos de las mejoras de eficiencia energética, es esencial reducir el crecimiento de la demanda de energía.[70]​ Sin embargo, a menos que los suministros de energía limpia se conecten rápidamente, la desaceleración del crecimiento de la demanda solo comenzará a reducir las emisiones totales; también es necesario reducir el contenido de carbono de las fuentes de energía. Cualquier visión seria de una economía energética sostenible requiere compromisos tanto de energías renovables como de eficiencia.[71]​.

La energía renovable (y la eficiencia energética) ya no son sectores especializados que solo son promovidos por gobiernos y ambientalistas. El aumento de los niveles de inversión y el hecho de que gran parte del capital proviene de actores financieros más convencionales, sugiere que las opciones de energía sostenible ahora se están convirtiendo en la corriente principal.[72]​.

De acuerdo con un análisis de tendencias del Programa de las Naciones Unidas para el Medio Ambiente, las preocupaciones por el cambio climático, junto con los altos precios del petróleo") y el creciente apoyo gubernamental, están impulsando el aumento de las tasas de inversión en las industrias de energía sostenible. Según el PNUMA, la inversión global en energía sostenible en 2007 fue superior a los niveles anteriores, con $ 148 mil millones de dinero recaudado en 2007, un aumento del 60% en comparación con 2006. El total de transacciones financieras en energía sostenible, incluida la actividad de adquisición, fue de $ 204 mil millones.[73]​.

Los flujos de inversión en 2007 se ampliaron y diversificaron, haciendo del panorama general una mayor amplitud y profundidad del uso sostenible de la energía. Los principales mercados de capital son "ahora totalmente receptivos a las compañías de energía sostenible, apoyadas por un aumento en los fondos destinados a la inversión en energía limpia".[73]​.

Smart grid technology

Smart grid refers to a class of technology that people use to bring utility electricity delivery systems into the 20th century, using computer-based remote control and automation.[74] These systems are made possible by two-way communication technology and computer processing that has been used for decades in other industries. They are beginning to be used in electrical networks, from power plants and wind farms to electricity consumers in homes and businesses. They offer many benefits to utilities and consumers, primarily in large improvements in energy efficiency in the electrical grid and in the homes and offices of energy users.[74]​.

La energía verde incluye procesos energéticos naturales que se pueden aprovechar con poca contaminación. La energía verde es la electricidad generada a partir de fuentes de energía renovables.[75]​ Algunas definiciones también pueden incluir la energía derivada de la incineración de residuos.

Algunos han argumentado que aunque la energía verde es un esfuerzo encomiable para resolver el creciente consumo de energía en el mundo, debe ir acompañada de un cambio cultural que fomente la disminución del apetito energético en el mundo.[76]​.

En varios países con acuerdos de transportistas comunes, los acuerdos de venta minorista de electricidad hacen posible que los consumidores compren electricidad ecológica (electricidad renovable) de su proveedor de servicios públicos o de un proveedor de energía ecológica.

Cuando se compra energía de la red eléctrica, la energía que llega al consumidor no necesariamente se generará a partir de fuentes de energía verde. La compañía local de servicios públicos, la compañía eléctrica o el grupo de energía estatal compran su electricidad a los productores de electricidad que pueden estar generando a partir de combustibles fósiles, fuentes de energía energía nuclear o renovable. En muchos países, la energía verde en la actualidad proporciona una cantidad muy pequeña de electricidad, que generalmente contribuye con menos del 2 al 5% al conjunto. En algunos estados de los EE. UU., los gobiernos locales han formado grupos regionales de compras de energía mediante el uso de Community Choice Aggregation y Solar Bonds para lograr una mezcla renovable del 51% o superior, como en la Ciudad de San Francisco.[77]​.

Al participar en un programa de energía verde, un consumidor puede tener un efecto en las fuentes de energía utilizadas y, en última instancia, podría estar ayudando a promover y expandir el uso de energía verde. También están haciendo una declaración a los responsables políticos de que están dispuestos a pagar una prima de precio para respaldar la energía renovable. Los consumidores de energía verde obligan a las empresas de servicios públicos a aumentar la cantidad de energía verde que compran de la piscina (lo que reduce la cantidad de energía no verde que compran), o bien financian directamente la energía verde a través de un proveedor de energía verde. Si no hay suficientes fuentes de energía verde disponibles, la empresa de servicios públicos debe desarrollar otras nuevas o contratar a un proveedor de energía de terceros para proporcionar energía verde, lo que hace que se construya más. Sin embargo, no hay forma de que el consumidor pueda verificar si la electricidad comprada es "verde" o no.

En algunos países, como los Países Bajos, las compañías de electricidad garantizan la compra de una cantidad igual de "energía verde" que utilizan sus clientes de energía verde. El gobierno holandés exime a la energía verde de los impuestos sobre la contaminación, lo que significa que la energía verde no es más cara que la otra.

Local green energy systems

Those dissatisfied with the third-party grid approach to green energy via the electrical grid can install their own locally-based renewable energy system. Renewable energy electrical systems, from solar to wind to even local hydropower in some cases, are some of the many types of renewable energy systems available locally. Additionally, for those interested in heating and cooling their home using renewable energy, geothermal heat pump systems that take advantage of the earth's constant temperature, which is around 7 to 15 degrees Celsius a few meters underground and increases considerably at greater depths, are an option to conventional natural gas and oil. Additionally, in geographic locations where the Earth's crust is especially thin, or near volcanoes (as is the case in Iceland) there is the potential to generate even more electricity than would be possible elsewhere, thanks to a more significant temperature gradient in these locations.

The advantage of this approach in the United States is that many states offer incentives to offset the cost of installing a renewable energy system. In California, Massachusetts, and several other U.S. states, a new approach to community energy delivery called Community Choice Aggregation has given communities the means to apply for a competitive electricity provider and use municipal revenue bonds to finance the development of local green energy resources. People are usually assured that the electricity they are using is actually produced from a green energy source that they control. Once the system is paid off, the owner of a renewable energy system will produce their own renewable electricity at virtually no cost and can sell the excess to the local utility at a profit.

Using green energy

Renewable energy, after its generation, must be stored in a medium for use with autonomous devices and vehicles. Additionally, to provide domestic electricity in remote areas (i.e. areas that are not connected to the main electrical grid), energy storage is required for use with renewable energy. The energy generation and consumption systems used in the latter case are usually autonomous energy systems.

Some examples are:

• - energy carriers such as hydrogen, liquid nitrogen, compressed air, oxyhydrogen, batteries, to power vehicles.

• - flywheel energy storage, hydroelectricity with pumped storage is more usable in stationary applications (for example, to power homes and offices). In home energy systems, energy conversion can also be done to reduce odor. For example, organic matter, such as cow dung and organic matter that can decompose, can be converted into biochar. To eliminate emissions, carbon capture and storage is used.

Generally, however, renewable energy is derived from the main electrical grid. This means that most of the energy storage is not used, as the main electrical grid is organized to produce the exact amount of energy that is consumed at that particular time. Power production in the main power grid is always configured as a combination of (large-scale) renewable power plants as well as other power plants such as fossil fuel power plants and nuclear power. However, this combination, which is essential for this type of energy supply (such as wind turbines, solar power plants, etc.) can only occur when the wind blows and the sun shines. This is also one of the main drawbacks of the system, since fossil fuel power plants are polluting and are the main cause of global warming (nuclear power is an exception). While fossil fuel power plants can also be made emission-free (through carbon capture and storage) as well as renewable (if the plants are converted to, for example, biomass), the best solution is to phase out the power plants over time. Nuclear power plants can also be more or less eliminated from their nuclear waste problem by using nuclear reprocessing and newer plants such as fast breeder plants and nuclear fusion plants.

Renewable energy power plants provide a constant flow of energy. For example, hydroelectric plants, ocean thermal plants and osmotic power plants provide energy at a regulated rate and are therefore sources of energy available at any time (even at night, windy times, etc.). However, at present, the number of steady flow renewable energy plants alone is too small to meet power demands at the time of day when irregularly produced renewable energy plants cannot produce power.

In addition to reducing the impact of fossil fuels and nuclear power plants, another option is the distribution and immediate use of energy from exclusively renewable sources. In this configuration, energy storage is also not necessary. For example, TREC has proposed distributing solar energy from the Sahara to Europe. Europe can distribute wind and ocean energy to the Sahara and other countries. In this way, energy is produced at any given time as at any point on the planet as the sun or the wind rises or the ocean waves and currents stir. However, this option is probably not possible in the short term, as fossil fuel and nuclear energy remain the main energy sources in the main electricity grid and it will not be possible to replace them overnight.

Green energy and labeling by region

Directive 2004/8/EC of the European Parliament and of the Council of 11 February 2004 on the promotion of cogeneration based on useful heat demand in the internal energy market[78] includes Article 5 (Guarantee of origin of electricity for high efficiency cogeneration).

European environmental NGOs have launched an eco-label for green energy. The ecolabel is called EKOenergy. Establishes criteria for sustainability, additionality, consumer information and monitoring. Only a portion of the electricity produced by renewable sources meets the EKOenergy criteria.[79]​.

A green energy supply certification scheme was launched in the UK in February 2010. This implements the guidelines of the Energy Regulator, Ofgem, and establishes requirements for transparency, the comparison of sales for renewable energy supplies and additionality.[80]​.

The United States Department of Energy (DOE), the Environmental Protection Agency "Environmental Protection Agency (United States)") (EPA), and the Center for Resource Solutions (CRS)[81]​ recognize the voluntary purchase of electricity from renewable energy sources (also called renewable electricity or green electricity) as green power.[82]​.

The most popular way to purchase renewable energy as revealed by NREL data is through the purchase of Renewable Energy Certificates (RECs). According to a survey by the Natural Marketing Institute (NMI),[83]​ 55 percent of American consumers want companies to increase their use of renewable energy.[82]​.

The DOE selected six companies for its 2007 Green Power Supplier Awards, including Constellation NewEnergy; 3Degrees ; Planet Sterling; SunEdison; Pacific Power and Rocky Mountain Power; and Silicon Valley Power. The combined green energy provided by those six winners equals more than 5 billion kilowatt-hours per year, which is enough to power nearly 465,000 average American homes. In 2014, Arcadia Power made RECS available to homes and businesses in all 50 states, allowing consumers to use "100% green energy," as defined by the EPA's Green Energy Partnership.[84][85]​

The United States Environmental Protection Agency (USEPA) Green Power Partnership is a voluntary program that supports organizational procurement of renewable electricity by offering expert advice, technical assistance, tools and resources. This can help organizations reduce the transaction costs of purchasing renewable energy, reduce their carbon footprint, and communicate their leadership to key stakeholders.[86]​.

Nationwide, more than half of all U.S. electricity customers now have the option to purchase some type of green energy product from a retail electricity provider. About a quarter of the nation's utilities offer green energy programs to customers, and voluntary retail sales of renewable energy in the United States totaled more than 12 billion kilowatt-hours in 2006, up 40% from the previous year.

Existen numerosas organizaciones dentro de los sectores académico, federal y comercial que realizan investigaciones avanzadas a gran escala en el campo de la energía sostenible. Esta investigación abarca varias áreas de enfoque en todo el espectro de energía sostenible. La mayor parte de la investigación está dirigida a mejorar la eficiencia y aumentar el rendimiento energético general.[91]​ Múltiples organizaciones de investigación con apoyo federal se han centrado en la energía sostenible en los últimos años. Dos de los laboratorios más destacados son los Laboratorios Nacionales Sandia") y el Laboratorio Nacional de Energía Renovable (NREL), ambos financiados por el Departamento de Energía de los Estados Unidos y respaldados por varios socios corporativos.[92]​ Sandia tiene un presupuesto total de $ 2.4 mil millones[93]​ mientras que NREL tiene un presupuesto de $ 375 millones.[94]​.

La producción científica hacia sistemas de energía sostenible está aumentando de manera exponencial, ya que creció de aproximadamente 500 artículos de revistas en inglés solo sobre energía renovable en 1992 a casi 9,000 artículos para 2011.[95]​.

Biomass is biological material derived from living or recently living organisms. It most often refers to plants or plant-derived materials that are specifically called lignocellulosic biomass.[96] As an energy source, biomass can be used directly through combustion to produce heat, or indirectly after conversion into various forms of biofuel. The conversion of biomass into biofuel can be achieved by different methods that are broadly classified into: thermal, chemical and biochemical methods. Wood remains the largest source of biomass energy today; examples include forestry waste, such as dead trees, tree branches and stumps, yard trimmings, wood chips, and even municipal solid waste. In the second sense, biomass includes plant or animal matter that can be converted into fibers or other industrial chemicals, including biofuels. Industrial biomass can be grown from numerous types of plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane), bamboo,[98] and a variety of tree species, ranging from eucalyptus to oil palm (palm).

Biomass, biogas and biofuels are burned to produce heat/energy and in doing so, harm the environment. Pollutants such as sulfur oxides (SO), nitrous oxides (NO) and particulate matter (PM) are produced from this combustion; The World Health Organization estimates that air pollution causes 7 million premature deaths each year.[99]​ Biomass combustion is a major contributor.[99][100][101]​.

Ethanol biofuels

As the primary source of biofuel in North America, many organizations are conducting research in the area of ​​ethanol production. At the federal level, the USDA conducts a large amount of research on ethanol production in the United States. Much of this research is oriented toward the effect of ethanol production on domestic food markets.[102] The National Renewable Energy Laboratory has conducted several ethanol research projects, primarily in the area of cellulosic ethanol.[103] Cellulosic ethanol has many benefits over traditional corn-based ethanol. It does not directly remove or conflict with the food supply because it is produced from wood, grasses, or inedible parts of crops. plants.[104]​ Additionally, some studies have shown that cellulosic ethanol is more cost-effective and economically sustainable than corn-based ethanol.[105]​ Even if we used the entire corn crop we have in the United States and converted it to ethanol, it would only produce enough fuel to cover 13 percent of total gasoline consumption in the United States.[106]​ Sandia National Laboratories") conducts internal research on cellulosic ethanol.[107]​ and is also a member of the Joint BioEnergy Institute (JBEI), a research institute founded by the United States Department of Energy with the goal of developing cellulosic biofuels.[108]​.

Other biofuels

From 1978 to 1996, the National Renewable Energy Laboratory experimented with algal fuel production in the "Aquatic Species Program".[109] A self-published paper by Michael Briggs, in the Biofuels Group at the University of New Hampshire, provides estimates for the realistic replacement of all motor vehicle fuels with biofuels using algae that have a natural oil content greater than 50%, which Briggs suggests it may be grown in algae ponds at wastewater treatment plants.[110] These oil-rich algae can then be extracted from the system and processed into biofuels, and the dried remainder can be reprocessed to create ethanol. The production of algae for oil extraction for biofuels has not yet been done on a commercial scale, but feasibility studies have been carried out to arrive at the above performance estimate. During the biofuel production process, algae actually consume the carbon dioxide in the air and convert it to oxygen through photosynthesis.[111] In addition to its projected high yield, algaculture, unlike food crop-based biofuels, does not involve a decrease in food production, as it does not require cropland or fresh water. Many companies are pursuing algal bioreactors for various purposes, including scaling up biofuel production to commercial levels.[112]​[113]​.

Several groups in various sectors are conducting research on Jatropha curcas, a poisonous bush-like tree that produces seeds considered by many to be a viable source of oil as a feedstock for biofuels.[114] Much of this research focuses on improving the overall oil yield per acre of Jatropha through advances in genetics, soil science, and horticultural practices. SG Biofuels, a San Diego-based Jatropha developer, has used molecular genetics and biotechnology to produce elite hybrid Jatropha seeds that show significant improvements in yield compared to first-generation varieties.[115]​ The Center for Sustainable Energy Agriculture (CfSEF) is a Los Angeles-based nonprofit research organization dedicated to Jatropha research in the areas of plant science, agronomy, and horticulture. Successful exploration of these disciplines is projected to increase Jatropha farm production yields by 200-300% over the next ten years.[116]​.

Thorium

There are potentially two sources of nuclear energy. Fission is used in all current nuclear power plants. Fusion is the reaction that exists in stars, including the sun, and is not practical for use on Earth as fusion reactors are not yet available. However, nuclear energy is politically and scientifically controversial due to concerns about radioactive waste disposal, safety, risks of a serious accident, and technical and economic problems in decommissioning old power plants.[117]

Thorium is a fissile material used in thorium-based nuclear power. The thorium fuel cycle claims several potential advantages over the uranium fuel cycle, including greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation[118][119][120], and reduced production of plutonium and actinides.[120]​ Therefore, it is sometimes referred to as sustainable.[121]​.

Solar

The main obstacle preventing large-scale implementation of solar power generation is the inefficiency of current solar technology. Currently, photovoltaic (PV) panels only have the capacity to convert about 24% of the sunlight that hits them into electricity.[122] At this rate, solar energy still presents many challenges to widespread deployment, but steady progress has been made in reducing manufacturing costs and increasing photovoltaic efficiency. Both Sandia National Laboratory and the National Renewable Energy Laboratory (NREL) have funded solar research programs. The NREL solar program has a budget of around $75 million[123] and develops research projects in the areas of photovoltaic (PV) technology, solar thermal energy, and solar radiation.[124] The budget for Sandia's solar division is unknown, however, it represents a significant percentage of the company's $2.4 billion budget. laboratory.[125]​ Several academic programs have focused on solar research in recent years. The Solar Energy Research Center (SERC) at the University of North Carolina (UNC) has the sole purpose of developing cost-effective solar technology. In 2008, researchers at the Massachusetts Institute of Technology (MIT) developed a method to store solar energy by using it to produce hydrogen from water.[126]​ Such research is aimed at addressing the obstacle facing solar development of energy storage for use. during nighttime hours when the sun is not shining. In February 2012, North Carolina-based Semprius Inc., a solar development company backed by the German company Siemens, announced that it had developed the world's most efficient solar panel. The company claims that the prototype converts 33.9% of the sunlight it receives into electricity, more than double the previous high-level conversion rate.[127] Large projects on artificial photosynthesis or solar fuels are also underway. many developed nations.[128]​.

Space-based solar power satellites seek to overcome storage problems and provide civilization-scale power that is clean, constant and global. Japan and China have active national programs aimed at commercial-scale space-based solar power (SBSP), with both nations hoping for orbiting demonstrations in the 2030s.

Wind energy research dates back several decades to the 1970s, when NASA developed an analytical model to predict the power generation of wind turbines during high winds.[130] Today, both Sandia National Laboratory and the National Renewable Energy Laboratory have programs dedicated to wind research. The Sandia laboratory focuses on advancing materials, aerodynamics and sensors.[131] Wind projects NREL focus on improving the energy output of wind plants, reducing their capital costs, and making wind energy more profitable overall.[132]​ The Field Laboratory for Optimized Wind Energy (FLOWE) at Caltech was established to research renewable approaches to wind energy technology practices that have the potential to reduce the cost, size, and environmental impact of wind energy production.[133]​ The president of Sky WindPower Corporation believes that wind turbines will be able to produce electricity at one cent/kWh at an average that, compared to coal-generated electricity, is a fraction of the cost.[134]​.

A wind farm is a group of wind turbines on the same site used to produce electrical energy. A large wind farm may consist of several hundred individual wind turbines, covering an extended area of ​​hundreds of square miles, but the land between the wind turbines may be used for agricultural or other purposes. A wind farm can also be located offshore.

Many of the largest operational onshore wind farms are located in the United States and China. The Gansu wind farm in China has over 5,000 MW installed with a goal of 20,000 MW by 2020. China has several other "wind energy bases" of similar size. The High Wind Energy Center in California is the largest onshore wind farm outside China, with a capacity of 1,020 MW of power.[135]​ Europe leads the use of wind energy with almost 66 GW, approximately 66 percent of the global total, with Denmark leading the way according to countries with per capita installed capacity.[136]​ As of February 2012, the Walney wind farm in the United Kingdom is the offshore wind farm. largest in the world with 367 MW, followed by the Thanet wind farm (300 MW), also in the United Kingdom.

There are many large wind farms under construction, including BARD Offshore 1 (400 MW), Clyde Wind Farm (350 MW), Greater Gabbard Wind Farm (500 MW), Lincs Wind Farm (270 MW), London Array (1000 MW), Lower Snake River Wind Project (343 MW), Macarthur Wind Farm (420 MW), Shepherds Flat Wind Farm (845 MW) and Sheringham shoal (317 MW).

In 2022, wind energy generation in the world increased with a record of 265 TWh (14% growth), reaching more than 2,100 TWh[137]​.

Although Enerdata provides quantitative values ​​of the use of wind and solar energy together, it is worth noting that in 2020 the share of these energies grew at a rapid and constant rate (+1.2 points), reaching 9.5% worldwide. The country that experienced the highest growth in 2020 was Australia, a country where the share of wind and solar energy in the energy supply grew by 2.9 points.[138]​.

Geothermal energy is produced by harnessing the thermal energy created and stored within the earth. It arises from the radioactive decay of an isotope of potassium and other elements found in the Earth's crust.[139]​ Geothermal energy can be obtained by drilling into the ground, much like oil exploration, and is then transported using a heat transfer fluid (e.g., water, brine, or steam).[139]​ Geothermal systems that are primarily dominated by water have the potential to provide greater benefits to the system and will generate more energy.[140]​ Within these liquid-dominated systems, there are potential concerns of subsidence and contamination of groundwater resources. Therefore, protection of groundwater resources is necessary in these systems. This means that careful reservoir production and engineering is necessary in liquid-dominated geothermal reservoir systems.[140]​ Geothermal energy is considered sustainable because thermal energy is constantly replenished.[141]​ However, the science of geothermal energy generation is still young and developing economic viability. Several entities, such as the National Renewable Energy Laboratory[142]​ and Sandia National Laboratories")[143]​ are conducting research toward the goal of establishing a proven science around geothermal energy. The International Geothermal Research Center (IGC), a German geoscience research organization, focuses primarily on geothermal energy development research.[144]​.

Hydrogen

More than $1 trillion of federal money has been spent on research and development of hydrogen and a means for energy storage in the United States. (2012)[145]​ Both the National Renewable Energy Laboratory[146]​ and Sandia National Laboratories")[147]​ have departments dedicated to hydrogen research. Hydrogen is useful for energy storage and for use in airplanes and ships, but is not practical for automobile use, as it is not very efficient compared to using a battery, for the same cost a person can travel three times as far using a battery. Electric vehicle battery .[148] Despite that opinion, Japanese automakers Toyota and Honda currently offer hydrogen fuel cell-powered passenger vehicles for sale in Japan and the US. Experimental hydrogen fuel cell city buses are currently operational in two US transit districts: Costa County, California, and in Connecticut.[149]

Around the world, many subnational governments (regions, states and provinces) have aggressively pursued investments in sustainable energy. In the United States, California's leadership in renewable energy was recognized by The Climate Group when it awarded former Governor Arnold Schwarzenegger its inaugural award for international climate leadership in Copenhagen in 2009. coal.[151] South Australia has also had the highest per capita consumption of domestic solar panels in Australia following the Rann Government's introduction of solar power laws and related educational campaign to install solar photovoltaic installations on the roofs of prominent public buildings, including parliament. , museum, airport and Adelaide Showgrounds pavilions and schools.[152]​ Rann, Australia's first climate change minister, passed legislation in 2006 setting targets for renewable energy and emissions cuts, the first legislation in Australia to do so.[153]​.

Furthermore, in the European Union there is a clear tendency to promote policies that encourage investments and financing of sustainable energy in terms of energy efficiency, innovation in the exploitation of energy and development of renewable resources, with greater consideration of environmental aspects and sustainability.[154]​.

In October 2018, the American Council for an Energy Efficient Economy (ACEEE) published its “State Energy Efficiency Scorecard.” The scorecard concluded that states and electric utilities continue to expand energy efficiency measures to meet clean energy goals. In 2017, the United States spent $6.6 billion on electrical efficiency programs. $1.3 billion was spent on natural gas efficiency. These programs resulted in savings of 27.3 million megawatt hours (MWh) of electricity.[155]​.

Among the scientific journals related to the interdisciplinary study of sustainable energy are:

• - Energy and environmental science.

• - Energy for sustainable development.

• - Energy policy.

• - Renewable and Sustainable Energy Magazine.

• - Renewable and sustainable energy reviews.

• - Electric vehicle.

• - Energy hierarchy.

• - Hydrogen economy.