Geothermal energy is heat energy derived from the Earth’s interior. Underground reservoirs of hot water, known as geothermal resources, exist at various temperatures and depths below the Earth’s surface. These resources are not human-made, but naturally occurring. Wells can be drilled into these reservoirs to access this thermal energy. These wells, ranging in depth from a few feet to several miles, can tap into steam and very hot water within the underground reservoirs, bringing them to the surface. This steam and very hot water have a variety of applications, ranging from electricity generation to heating and cooling.
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Geothermal Electricity Generation
Applications of geothermal energy encompass electricity generation, heating and cooling, and direct use for various purposes. Hot rocks, fluid, and permeability provide the ideal conditions for generating electricity from geothermal energy. Fluid circulates through hot rocks, absorbing their heat energy. This fluid becomes heated itself, and the absorbed heat energy converts into steam. Steam drives turbines, harnessing its kinetic energy to produce electricity. Turbines produce electricity through the rotation driven by steam.
Geothermal Heating and Cooling
Naturally occurring underground reservoirs of hot water can be used to heat and cool buildings. The stable temperature of the subsurface can be utilized to heat and cool buildings effectively. Geothermal heat pumps provide heating and cooling, leveraging the ground as a heat sink. These pumps absorb excess heat from buildings during warmer seasons and act as a heat source, providing warmth during colder periods. District heating and cooling systems utilize geothermal energy to heat and cool groups of buildings, campuses, and entire communities. These systems effectively heat and cool a range of structures, promoting energy efficiency.
Harnessing Geothermal Energy for Diverse Purposes
Geothermal direct use applications rely on wells to access hot water from the subsurface. Wells used for direct geothermal applications are typically deeper than those for heat pumps. Wells draw hot water from the subsurface, providing a direct source of thermal energy. Hot water from geothermal sources can be used directly for various purposes, eliminating the need for conversion. Direct use of hot water includes providing hot water to buildings, space heating, and heat for industrial processes.
The Advantages of Geothermal Energy
Geothermal energy is a renewable source of energy, ensuring its sustainability. Heat flowing from Earth’s interior is continuously replenished by the decay of naturally occurring radioactive elements. Geothermal energy will remain available for billions of years, ensuring a reliable and sustainable energy source. Geothermal power plants produce electricity consistently, providing a reliable energy source. These plants can operate 24 hours a day, 7 days a week, regardless of weather conditions. Furthermore, they can adjust their electricity generation to respond to changes in demand.
U.S. geothermal resources can be harnessed for power production, heating, and cooling, promoting domestic energy independence. These resources can be utilized without importing fuel, reducing reliance on foreign energy sources. Geothermal power plants have a small footprint, minimizing their land use impact. These plants use less land per gigawatt-hour than coal, wind, and solar photovoltaic power stations, minimizing their environmental impact.
Geothermal heat pumps can be retrofitted into existing buildings, promoting energy efficiency and sustainability. These pumps can be seamlessly integrated into new buildings, offering a sustainable and efficient heating and cooling solution. Modern geothermal power plants emit no greenhouse gases, contributing to cleaner air and a healthier environment. These plants have life cycle emissions four times lower than solar PV, showcasing their environmental advantage. Modern geothermal power plants have life cycle emissions six to 20 times lower than natural gas, highlighting their significant environmental benefits. Geothermal power plants consume less water on average over their lifetime energy output than most conventional electricity-generation technologies, promoting water conservation.
Understanding Geothermal Energy
Geothermal energy is thermal energy extracted from the Earth’s crust, harnessing the Earth’s internal heat. It combines energy from the planet’s formation with energy from radioactive decay, showcasing its multifaceted origins. Geothermal energy has been exploited as a source of heat and/or electric power for centuries, demonstrating its long history of use. Geothermal heating, using water from hot springs, has been used for bathing since Paleolithic times, showcasing its ancient origins. Geothermal heating has been utilized for space heating since Roman times, demonstrating its long-standing role in providing warmth. Geothermal power is the generation of electricity from geothermal energy, harnessing the Earth’s internal heat for power production. Geothermal power has been used since the 20th century, marking its emergence as a modern energy source.
Geothermal plants produce power at a constant rate, ensuring a reliable and consistent energy supply. These plants produce power regardless of weather conditions, showcasing their independence from weather fluctuations. Geothermal resources are theoretically more than adequate to supply humanity’s energy needs, highlighting their vast potential.
Discovering Earth’s Potential
Most extraction of geothermal energy occurs in areas near tectonic plate boundaries, where geothermal activity is more pronounced. The cost of generating geothermal power decreased by 25% during the 1980s and 1990s, making it more economically viable. Technological advances have continued to reduce costs and expand the amount of viable geothermal resources, making it more accessible. The US Department of Energy estimated that power from a plant built today costs about $0.05/kWh, demonstrating the affordability of geothermal energy. Geothermal power was available worldwide in 2019, showcasing its global reach and accessibility.
Geothermal power amounted to 13,900 megawatts (MW) in 2019, demonstrating its significant contribution to global energy production. Geothermal power provided heat for district heating, space heating, spas, industrial processes, desalination, and agricultural applications as of 2010, highlighting its diverse applications. Geothermal power provided 28 gigawatts of heat as of 2010, demonstrating its substantial contribution to thermal energy production. The geothermal industry employed about one hundred thousand people in 2019, showcasing its significant economic impact.
The Evolution of Geothermal Energy
The adjective “geothermal” originates from the Greek roots γῆ (gê) meaning Earth, and θερμός (thermós) meaning hot, reflecting its connection to Earth’s internal heat. The oldest known pool fed by a hot spring was built in the Qin dynasty in the 3rd century BCE, demonstrating the ancient use of geothermal energy. Hot springs have been used for bathing since at least Paleolithic times, showcasing the ancient practice of using geothermal resources for well-being. The oldest known spa is at the site of the Huaqing Chi palace, showcasing the historical importance of geothermal energy for relaxation and healing.
The Romans conquered Aquae Sulis, now Bath, Somerset, England, showcasing their recognition of the value of geothermal resources. The Romans used hot springs to supply public baths and underfloor heating, showcasing their innovative use of geothermal energy. Admission fees for baths represent the first commercial use of geothermal energy, marking the early economic value of Earth’s heat.
The world’s oldest geothermal district heating system is in Chaudes-Aigues, France, showcasing the long history of using geothermal energy for heating. This system has been operating since the 15th century, demonstrating the longevity and reliability of geothermal energy for heating. The earliest industrial exploitation of geothermal energy began in 1827, marking the start of using Earth’s heat for industrial processes. This involved the use of geyser steam to extract boric acid from volcanic mud, showcasing its early applications in resource extraction. This exploitation took place in Larderello, Italy, establishing a historical hub for geothermal energy production.
The US’s first district heating system was powered by geothermal energy, showcasing its early adoption for heating in the United States. Located in Boise, Idaho, this system was built in 1892, demonstrating the early adoption of geothermal energy for heating in the United States. This system was copied in Klamath Falls, Oregon, in 1900, showcasing the early spread of geothermal energy technology for heating. The world’s first known building to utilize geothermal energy as its primary heat source is the Hot Lake Hotel in Union County, Oregon, showcasing the early use of geothermal energy for building heating. The Hot Lake Hotel began using geothermal energy as its primary heat source in 1907, demonstrating the early adoption of geothermal energy for building heating. A geothermal well was used to heat greenhouses in Boise in 1926, showcasing the early adoption of geothermal energy for agricultural applications. Geysers were used to heat greenhouses in Iceland and Tuscany at about the same time as Boise, showcasing the simultaneous development of geothermal energy applications in different regions.
Charles Lieb developed the first downhole heat exchanger in 1930, marking a significant innovation in geothermal energy technology. Lieb used this innovation to heat his house, demonstrating the practical application in residential heating. Geyser steam and water began heating homes in Iceland in 1943, showcasing the early adoption of geothermal energy for residential heating in Iceland.
Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904 at the Larderello steam field, marking a significant milestone in geothermal power generation. Conti successfully lit four light bulbs with this generator, demonstrating the feasibility of using geothermal energy for electricity production. The world’s first commercial geothermal power plant was built in Larderello in 1911, marking the beginning of commercial-scale geothermal power production. This was the only industrial producer of geothermal power until New Zealand built a plant in 1958, showcasing the early dominance of Larderello in geothermal power production. The Larderello power plant produced some 594 megawatts in 2012, demonstrating its continued contribution to geothermal power production.
Pacific Gas and Electric began operation of the first US geothermal power plant at The Geysers in California in 1960, marking the beginning of geothermal power production in the United States. The original turbine at The Geysers lasted for more than 30 years, demonstrating the durability of geothermal power plant equipment. The original turbine produced 11 MW net power, showcasing its early contribution to geothermal power generation in the United States. The binary cycle power plant was first demonstrated in the USSR in 1967, marking a significant development in geothermal power technology. This technology was introduced to the US in 1981, expanding its use for geothermal power generation. The binary cycle power plant allows the generation of electricity from much lower temperature resources, expanding the potential of geothermal energy production. A binary cycle plant came on-line in Chena Hot Springs, Alaska, in 2006, showcasing the expansion of geothermal power generation to new regions. This plant produced electricity from a record low temperature of 57 °C (135 °F), demonstrating the versatility of this technology in utilizing lower-temperature geothermal resources.
A Continuous Source of Energy
The Earth has an internal heat content of 1031 joules (3·1015 TWh), showcasing the vast amount of thermal energy within the planet. This heat content is about 20% residual heat from planetary accretion, highlighting the origin of a portion of Earth’s heat. The remainder is attributed to past and current radioactive decay of naturally occurring isotopes, highlighting the ongoing process of heat generation within the planet. A 5275 m deep borehole in the United Downs Deep Geothermal Power Project in Cornwall, England, found granite with very high thorium content, suggesting a potential source of geothermal energy. Radioactive decay of thorium is believed to power the high temperature of the rock, indicating a potential source of geothermal energy.
Earth’s interior temperature and pressure are high enough to cause some rock to melt, generating magma and contributing to geothermal activity. The solid mantle behaves plastically, allowing for the movement of magma and contributing to geothermal activity. Parts of the mantle convect upward, carrying heat from the Earth’s core towards the surface and contributing to geothermal energy production. These parts are lighter than the surrounding rock, driving their upward movement and contributing to geothermal activity. Temperatures at the core-mantle boundary can reach over 4000 °C (7200 °F), demonstrating the extreme heat within the Earth’s interior.
Earth’s internal thermal energy flows to the surface by conduction, gradually transferring heat from the core towards the crust. This energy flows at a rate of 44.2 terawatts (TW), showcasing the massive amount of heat flowing towards the surface. Earth’s internal thermal energy is replenished by radioactive decay of minerals, ensuring a continuous source of heat within the planet. This energy is replenished at a rate of 30 TW, highlighting the continuous energy generation within the planet. These power rates are more than double humanity’s current energy consumption from all primary sources, showcasing the vast potential of geothermal energy to meet global energy demands. Most of the Earth’s energy flux is not recoverable, emphasizing the need for efficient and targeted extraction methods.
The Geothermal Gradient
The top layer of the surface to a depth of 10 m (33 ft) is heated by solar energy during the summer and cools during the winter, showcasing the seasonal influence on surface temperatures. The geothermal gradient of temperatures through the crust is 25–30 °C (45–54 °F) per km of depth in most of the world, showcasing the gradual increase in temperature with depth. Conductive heat flux averages 0.1 MW/km2, highlighting the average rate of heat flow through the Earth’s crust.
Values of conductive heat flux are much higher near tectonic plate boundaries, indicating increased geothermal activity in these areas. These values are higher near tectonic plate boundaries, reflecting the thinner crust and increased geothermal activity in these regions. The crust is thinner near tectonic plate boundaries, allowing for greater heat flow and contributing to higher conductive heat flux in these areas. Values of conductive heat flux may be further augmented by combinations of fluid circulation, including magma conduits, hot springs, and hydrothermal circulation, amplifying the geothermal activity in these areas.
Thermal efficiency and profitability of electricity generation from geothermal energy are particularly sensitive to temperature, emphasizing the importance of high-temperature resources. Applications of geothermal energy receive the greatest benefit from a high natural heat flux, highlighting the advantage of areas with significant geothermal activity. High natural heat flux is most easily obtained from a hot spring, providing a readily available source of geothermal energy. The next best option is to drill a well into a hot aquifer, accessing geothermal energy through a more targeted approach. An artificial hot water reservoir may be built by injecting water to hydraulically fracture bedrock, creating a man-made source of geothermal energy. Systems using this last approach are called enhanced geothermal systems (EGS), showcasing the technology’s role in expanding geothermal energy production.
Geothermal Resources
Estimates of the potential for electricity generation from geothermal energy vary sixfold, ranging from 0.035 to 2 TW, reflecting the uncertainty in assessing geothermal resources. These estimates vary depending on the scale of investments, indicating the significant influence of funding on geothermal development. Upper estimates of geothermal resources assume wells as deep as 10 kilometres (6 mi), showcasing the potential for accessing deeper geothermal resources. 20th-century wells rarely reached more than 3 kilometres (2 mi) deep, indicating the recent advancements in drilling technology that allow for access to deeper geothermal resources. Wells of this depth are common in the petroleum industry, suggesting the potential for adapting oil and gas drilling technology for geothermal energy production.
Geothermal Power
Geothermal power is electrical power generated from geothermal energy, harnessing Earth’s internal heat for electricity production. Dry steam, flash steam, and binary cycle power stations have been used for generating geothermal power, showcasing the different technologies available for harnessing Earth’s heat for electricity production. Geothermal electricity was generated in 26 countries as of 2010, showcasing the global reach and adoption of geothermal power generation.
Worldwide geothermal power capacity amounted to 15.4 gigawatts (GW) in 2019, demonstrating its significant contribution to global electricity production. This capacity was 23.86 percent or 3.68 GW in the United States in 2019, highlighting its significant contribution to U.S. electricity production. Geothermal energy supplies a significant share of the electrical power in Iceland, El Salvador, Kenya, the Philippines, and New Zealand, showcasing the prominent role of geothermal energy in these countries’ energy systems. Geothermal power is considered a renewable energy, highlighting its sustainability and long-term availability. Heat extraction rates are insignificant compared to the Earth’s heat content, ensuring the long-term sustainability of geothermal energy production.
The Benefits of Geothermal Energy
Greenhouse gas emissions of geothermal electric stations are on average 45 grams of carbon dioxide per kilowatt-hour of electricity, significantly lower than fossil fuel power plants. These emissions are less than 5 percent of that of coal-fired plants, demonstrating the significantly reduced environmental impact of geothermal energy production. Geothermal electric plants were traditionally built on the edges of tectonic plates, where geothermal activity is more pronounced, highlighting the geographic limitations of early geothermal power generation. The development of binary cycle power plants enables enhanced geothermal systems over a greater geographical range, expanding the potential of geothermal energy production. Improvements in drilling and extraction technology enable enhanced geothermal systems over a greater geographical range, expanding the potential of geothermal energy production. Demonstration projects of enhanced geothermal systems are operational in Landau-Pfalz, Germany, and Soultz-sous-Forêts, France, showcasing the practical implementation of this technology. An earlier effort of enhanced geothermal systems was shut down in Basel, Switzerland, due to triggered earthquakes, highlighting the potential risks associated with this technology. Other demonstration projects of enhanced geothermal systems are under construction in Australia, the United Kingdom, and the US, showcasing the continued development and expansion of this technology.
Myanmar has over 39 locations capable of geothermal power production, highlighting the country’s significant geothermal potential.
Geothermal Heating
Geothermal heating is the use of geothermal energy to heat buildings and water for human use, showcasing its diverse applications in providing warmth and comfort. Humans have utilized geothermal heating since the Paleolithic era, showcasing its long history of use for providing warmth and comfort. Seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004, showcasing the widespread adoption of geothermal heating for providing warmth and comfort. 28 GW of geothermal heating satisfied 0.07% of global primary energy consumption as of 2007, demonstrating its significant contribution to global energy supply.
The thermal efficiency of geothermal heating is high, highlighting its energy efficiency and reduced reliance on other energy sources. Capacity factors of geothermal heating tend to be low, reflecting the seasonal nature of heating demands and the need for efficient management. These factors are around 20%, reflecting the seasonal nature of heating demands and the need for efficient management. The heat of geothermal heating is mostly needed in the winter, highlighting the seasonal nature of this energy application and the need for efficient storage and distribution.
Ground Source Heat Pumps
Cold ground contains heat, showcasing the potential for utilizing Earth’s thermal energy even in colder regions. Ground temperature is consistently at the Mean Annual Air Temperature below 6 meters (20 ft), highlighting the stable temperature of the subsurface for geothermal energy applications. The Mean Annual Air Temperature can be extracted with a ground source heat pump, showcasing the technology’s ability to harness the Earth’s thermal energy.
Geothermal Reservoirs
Hydrothermal systems produce geothermal energy by accessing naturally occurring hydrothermal reservoirs, showcasing the use of naturally occurring geothermal resources. These systems come in either vapor-dominated or liquid-dominated forms, reflecting the diverse nature of geothermal resources. Vapor-dominated plants offer temperatures from 240 to 300 °C, providing high-temperature steam for power generation. These plants produce superheated steam, making them highly efficient for driving turbines and generating electricity. Liquid-dominated reservoirs (LDRs) are more common than vapor-dominated plants, showcasing their widespread availability for geothermal energy production. These reservoirs have temperatures greater than 200 °C (392 °F), providing sufficient heat for various geothermal applications. These reservoirs are found near volcanoes in/around the Pacific Ocean and in rift zones and hot spots, highlighting their geographic distribution and association with geothermal activity.
Harnessing Geothermal Energy
Flash plants are the common way to generate electricity from liquid-dominated reservoirs, showcasing their widespread use in harnessing geothermal energy for power production. Steam from the well is sufficient to power the plant in flash plants, eliminating the need for additional energy sources. Most wells generate 2–10 MW of electricity, showcasing the typical output of flash plants and their contribution to electricity production. Steam is separated from liquid via cyclone separators in flash plants, showcasing the technology’s efficient separation process. Steam drives electric generators in flash plants, converting thermal energy into electrical power. Condensed liquid returns down the well for reheating/reuse in flash plants, showcasing the technology’s efficient utilization of geothermal resources. Cerro Prieto in Mexico is the largest liquid system as of 2013, showcasing its significant contribution to geothermal power production. Cerro Prieto generates 750 MW of electricity, demonstrating its substantial output and contribution to electricity generation. Cerro Prieto has temperatures reaching 350 °C (662 °F), highlighting its high-temperature resources and potential for power generation.
Lower-temperature LDRs require pumping, reflecting the need for additional energy input for extracting geothermal energy from these resources. These reservoirs are common in extensional terrains, where geothermal activity is often found along faults. These reservoirs are common in the Western US and Turkey, showcasing the geographic distribution of this type of geothermal resource.
Water passes through a heat exchanger in a Rankine cycle binary plant, transferring heat from the geothermal fluid to a working fluid. Water vaporizes an organic working fluid in a Rankine cycle binary plant, converting thermal energy into mechanical energy. The organic working fluid drives a turbine in a Rankine cycle binary plant, converting the mechanical energy into electricity. Binary plants originated in the Soviet Union in the late 1960s, showcasing their early development in the field of geothermal power technology. Binary plants predominate in new plants, reflecting the advancements in geothermal technology and their efficiency in utilizing lower-temperature resources. Binary plants have no emissions, showcasing their environmental advantage over traditional fossil fuel power plants.
Engineered Geothermal Systems
An engineered geothermal system is a geothermal system that engineers have artificially created or improved, showcasing the human role in harnessing Earth’s heat. These systems are used in a variety of geothermal reservoirs that have hot rocks but lack sufficient natural reservoir quality, expanding the potential for geothermal energy production. These systems are used in reservoirs that have insufficient natural reservoir quality, such as insufficient geofluid quantity, rock permeability, or porosity, demonstrating their ability to overcome geological limitations. These systems are used to operate as natural hydrothermal systems, showcasing their ability to mimic natural geothermal processes.
Types of engineered geothermal systems include enhanced geothermal systems (EGS), closed-loop or advanced geothermal systems (AGS), and some superhot rock geothermal systems, showcasing the diverse approaches to harnessing Earth’s heat. Enhanced geothermal systems (EGS) actively inject water into wells, creating artificial fractures in the rock and increasing permeability for fluid flow. These systems heat the injected water, extracting thermal energy from the hot rocks, and then pump the heated water back out of the wells, completing the energy extraction process. Water is injected under high pressure in EGS, creating fractures and improving permeability for fluid flow. Water expands existing rock fissures in EGS, increasing permeability and facilitating fluid flow. Water enables the water to flow freely in EGS, facilitating heat transfer and energy extraction.
The technique of EGS was adapted from oil and gas fracking techniques, demonstrating the transfer of technology from the petroleum industry to geothermal energy production. Geologic formations are deeper in EGS than in fracking, reflecting the different targets and depths of these technologies. Toxic chemicals are not used in EGS, making it a more environmentally friendly technology compared to conventional fracking. Proppants such as sand or ceramic particles are used to keep the cracks open in EGS, maintaining permeability and enhancing fluid flow for efficient energy extraction. These proppants are used to produce optimal flow rates in EGS, maximizing energy extraction efficiency. Drillers can employ directional drilling to expand the reservoir size in EGS, increasing the volume of hot rocks available for energy extraction. Small-scale EGS have been installed in the Rhine Graben at Soultz-sous-Forêts in France and at Landau and Insheim in Germany, showcasing the practical implementation of this technology on a smaller scale.
Closed-loop geothermal systems, sometimes referred to as Advanced Geothermal Systems (AGS), are engineered geothermal systems containing subsurface working fluid, showcasing their innovative approach to energy extraction. The subsurface working fluid is heated in the hot rock reservoir in closed-loop systems, absorbing thermal energy from the Earth’s interior. This fluid stays inside a closed loop of deeply buried pipes in closed-loop systems, ensuring a continuous circulation and maximizing energy extraction efficiency. Deeply buried pipes conduct Earth’s heat in closed-loop systems, transferring thermal energy from the reservoir to the surface. The deep, closed-loop geothermal circuit has advantages, including no need for a geofluid, no requirement for permeable or porous hot rock, and zero loss of working fluid, showcasing the technology’s efficiency and sustainability.
Eavor™ is a Canadian-based geothermal startup that piloted their closed-loop system in shallow soft rock formations in Alberta, Canada, demonstrating the adaptability of this technology to different geological settings. The geothermal gradient proved to be insufficient for electrical power generation in Eavor™’s pilot project, demonstrating the need for further technological advancements to overcome limitations. The Eavor™ system successfully produced approximately 11,000 MWh of thermal energy during its initial two years of operation, showcasing the technology’s ability to generate significant thermal energy.
The Costs and Benefits of Geothermal Energy
Wind and solar energy have minimal operating costs, showcasing their economic advantage in the long term. Capital costs dominate in wind and solar energy, reflecting the initial investment required to set up these energy sources. Drilling accounts for over half the costs in geothermal energy, emphasizing the significant expense associated with accessing geothermal resources. Wells do not always produce exploitable resources, highlighting the risk associated with geothermal energy exploration. A typical well pair can produce 4.5 megawatts (MW), showcasing the potential output of a successful geothermal well.
A typical well pair costs about $10 million to drill, reflecting the significant investment required to develop a geothermal energy project. A typical well pair has a 20% failure rate, highlighting the risk associated with geothermal exploration and the need for careful site selection. The average cost of a successful well is $50 million, reflecting the high investment needed to develop geothermal energy projects.
Drilling geothermal wells is more expensive than drilling oil and gas wells of comparable depth, reflecting the challenging geological conditions encountered in geothermal reservoirs. Geothermal reservoirs are usually located in igneous or metamorphic rock, which is harder to penetrate than the sedimentary rock of typical hydrocarbon reservoirs, presenting challenges for drilling and extraction. Igneous or metamorphic rock is harder to penetrate than the sedimentary rock of typical hydrocarbon reservoirs, requiring specialized drilling techniques and equipment for geothermal energy extraction. Rock is often fractured in geothermal reservoirs, causing vibrations that damage bits and other drilling tools, presenting additional challenges for drilling operations. Fractured rock causes vibrations that damage bits and other drilling tools, requiring robust equipment and careful drilling practices for successful geothermal well construction.
Rock is often abrasive in geothermal reservoirs, wearing down drilling tools and increasing the cost of drilling operations. Rock often has high quartz content in geothermal reservoirs, which can be abrasive and wear down drilling tools, requiring specialized drilling techniques and equipment for efficient extraction. Rock sometimes contains highly corrosive fluids in geothermal reservoirs, requiring specialized materials and equipment to withstand the corrosive environment during drilling and extraction. Rock is hot in geothermal reservoirs, limiting the use of downhole electronics and requiring specialized temperature-resistant equipment for drilling and monitoring operations. Well casing must be cemented from top to bottom in geothermal wells, resisting the casing’s tendency to expand and contract with temperature changes, ensuring well integrity and preventing leaks. Oil and gas wells are usually cemented only at the bottom, reflecting the different geological conditions and pressures encountered in hydrocarbon reservoirs compared to geothermal reservoirs. Well diameters are considerably larger than typical oil and gas wells, accommodating the larger volume of geothermal fluids and equipment required for energy extraction.
Plant construction cost about €2–5 million per MW of electrical capacity as of 2007, reflecting the significant investment required to build a geothermal power plant. Well drilling cost about €2–5 million per MW of electrical capacity as of 2007, further reflecting the significant investment required to develop a geothermal energy project. The break-even price of geothermal energy was 0.04–0.10 € per kW·h as of 2007, showcasing the economic viability of geothermal energy production.
Enhanced geothermal systems tend to be on the high side of the cost ranges, reflecting the more complex technology and geological challenges involved in their development. Capital costs of enhanced geothermal systems are above $4 million per MW, emphasizing the significant investment required to develop this advanced technology. The break-even point for enhanced geothermal systems is above $0.054 per kW·h, reflecting the high capital costs and technological challenges associated with this advanced technology.
Private investments were the main source of funding for renewable energy between 2013 and 2020, showcasing the growing private sector interest in sustainable energy development. Private investments comprised approximately 75% of total financing for renewable energy between 2013 and 2020, demonstrating the significant role of private capital in driving renewable energy growth. The mix between private and public funding varies among different renewable energy technologies, reflecting their market appeal and readiness, showcasing the diverse financial landscape of the renewable energy sector. Geothermal energy received just 32% of its investment from private sources in 2020, reflecting the need for increased private sector participation to further accelerate geothermal development.
The Energy Sector Management Assistance Program (ESMAP) report “Socioeconomic Impacts of Geothermal Energy Development” highlights the substantial socioeconomic benefits of geothermal energy development, showcasing its positive impact on communities. Socioeconomic benefits of geothermal energy development exceed those of wind and solar by generating an estimated 34 jobs per megawatt, demonstrating its greater employment potential. Geothermal projects contribute to skill development through practical on-the-job training and formal education, strengthening the local workforce and fostering a skilled workforce in the geothermal sector. These projects strengthen the local workforce by expanding employment opportunities, providing training and education, and fostering a skilled workforce in the geothermal sector. Geothermal development leads to improved infrastructure, skill-building programs, and revenue-sharing models, promoting sustainable economic growth and community development. This development enhances access to reliable electricity and heat, boosting agricultural productivity and food security, promoting economic development and improving the lives of people in rural communities. Geothermal development is committed to advancing gender equality and social inclusion, offering job opportunities, education, and training to underrepresented groups, ensuring fair access to the benefits of geothermal development. These efforts are instrumental in driving domestic economic growth, increasing fiscal revenues, and contributing to more stable and diverse national economies, showcasing the wider economic benefits of geothermal development. These efforts offer significant social benefits such as better health, education, and community cohesion, showcasing the positive societal impact of geothermal energy development.
Challenges and Risks
Geothermal projects have several stages of development, each phase carrying associated risks and requiring careful planning and management for successful implementation. Many projects are canceled during the stages of reconnaissance and geophysical surveys, reflecting the uncertainty and risk associated with geothermal exploration, highlighting the need for robust exploration techniques and risk assessment. Reconnaissance and geophysical surveys are often unsuitable for traditional lending, demonstrating the need for innovative financing mechanisms to support early-stage geothermal exploration. Later stages of geothermal project development can often be equity-financed, showcasing the growing private sector interest in investing in mature geothermal projects.
Precipitate scaling is a common issue encountered in geothermal systems, occurring when the system is situated in carbonate-rich formations, highlighting a potential challenge for geothermal energy production. This scaling occurs when fluids extracting heat from the subsurface dissolve fragments of the rock during their ascent towards the surface, leading to the deposition of minerals as the fluids cool, showcasing the geochemical processes involved in scaling. Fluids extracting heat from the subsurface cool subsequently, leading to the precipitation of dissolved cations out of solution, showcasing the thermodynamic processes driving scaling. Dissolved cations precipitate out of solution as the fluids cool, leading to the formation of calcium scale, showcasing the specific mineral composition of scale. Calcium scale formation is known as calcite scaling, highlighting the specific type of scaling occurring in geothermal systems. This scaling can decrease flow rates, reducing the efficiency of geothermal energy production, and can necessitate system downtime for maintenance, highlighting the negative impact of scaling on geothermal operations.
The Future of Geothermal
Geothermal energy is considered sustainable, showcasing its long-term viability and minimal environmental impact. The heat extracted from geothermal reservoirs is small compared to the Earth’s heat content, ensuring a sustainable source of energy for the long term. Earth’s heat content is approximately 100 billion times 2010 worldwide annual energy consumption, showcasing the vast reservoir of thermal energy available for sustainable use. Earth’s heat flows are not in equilibrium, indicating a dynamic system that replenishes heat over geological timescales, ensuring the long-term sustainability of geothermal energy. Earth is cooling on geological timescales, but anthropic heat extraction does not accelerate the cooling process, demonstrating the minimal impact of geothermal energy production on Earth’s overall heat balance. Wells can further be considered renewable, as they return the extracted water to the borehole for reheating and re-extraction, demonstrating the cyclic nature of geothermal energy production. Wells return the extracted water at a lower temperature, minimizing the impact on local water temperatures and ensuring the long-term sustainability of geothermal energy production. Replacing material use with energy has reduced the human environmental footprint in many applications, showcasing the potential of energy-efficient solutions for sustainability. Geothermal has the potential to allow further reductions in the human environmental footprint, providing a clean and sustainable energy source for a variety of applications.
Iceland has sufficient geothermal energy to eliminate fossil fuels for electricity production, showcasing the potential for geothermal energy to replace fossil fuels entirely. Iceland has sufficient geothermal energy to heat Reykjavik sidewalks, demonstrating the wide range of applications for geothermal energy, from power generation to infrastructure heating. Iceland has sufficient geothermal energy to eliminate the need for gritting, showcasing the potential for geothermal energy to reduce reliance on traditional infrastructure maintenance methods.
Local effects of heat extraction must be considered, recognizing the potential impact of geothermal energy production on local environments. Individual wells draw down local temperatures and water levels over the course of decades, highlighting the need for careful monitoring and management to minimize the impact of geothermal energy production on local environments.
The three oldest geothermal sites experienced reduced output due to local depletion, highlighting the importance of sustainable practices and careful resource management in geothermal energy production. Heat and water were extracted faster than they were replenished, leading to reduced output at the three oldest geothermal sites, demonstrating the need for balanced extraction and replenishment rates for sustainable geothermal energy production. Reducing production could allow these wells to recover their original capacity, showcasing the potential for managing geothermal resources for long-term sustainability. Injecting additional water could allow these wells to recover their original capacity, demonstrating the potential for enhancing geothermal systems to extend their lifespan and ensure sustainable energy production. Such strategies have been implemented at some sites, allowing them to continue providing significant energy, showcasing the effectiveness of responsible management practices in maintaining geothermal energy production.
The Wairakei power station, commissioned in November 1958, attained its peak generation of 173 MW in 1965, showcasing the early development of geothermal power production. The supply of high-pressure steam was faltering at Wairakei in 1965, reflecting the challenges of managing geothermal resources for long-term sustainability. Wairakei was down-rated to intermediate pressure in 1982, demonstrating the need for adapting geothermal power plants to changing reservoir conditions. Output was down-rated to 157 MW in 1982, highlighting the need for proactive management to maintain geothermal energy production over time. Two 8 MW isopentane systems were added in 2005, boosting output by about 14 MW, showcasing the potential for enhancing geothermal power plants to increase their capacity and efficiency. Detailed data were lost due to re-organisations, highlighting the importance of data management and preservation in ensuring the long-term sustainability of geothermal energy projects.
Fluids drawn from underground carry a mixture of gases, including carbon dioxide (CO2), hydrogen sulfide (H2S), methane (CH4), and ammonia (NH3), highlighting the potential environmental impact of geothermal energy production. These pollutants contribute to global warming, acid rain, and noxious smells if released, showcasing the need for effective mitigation strategies in geothermal energy production. Existing geothermal electric plants emit an average of 122 kilograms (269 lb) of CO2 per megawatt-hour (MW·h) of electricity, demonstrating the significantly lower emissions compared to fossil fuel power plants. Existing geothermal electric plants emit a small fraction of the emission intensity of fossil fuel plants, showcasing their potential to contribute to cleaner energy production. Few plants emit more pollutants than gas-fired power, highlighting the generally low environmental impact of geothermal energy production. Some geothermal power in Turkey emits more pollutants than gas-fired power in the first few years, highlighting the need for careful management and optimization of geothermal operations to minimize emissions. Plants are typically equipped with emission-control systems to reduce the exhaust, showcasing the proactive measures taken to minimize environmental impact. Plants experience high levels of acids and volatile chemicals, showcasing the unique challenges associated with managing geothermal emissions. Emerging closed-loop technologies developed by Eavor™ have the potential to reduce these emissions to zero, showcasing the future potential for emissions-free geothermal energy production.
Water from geothermal sources may hold trace amounts of toxic elements, including mercury, arsenic, boron, and antimony, highlighting a potential environmental concern associated with geothermal energy production. These chemicals precipitate as the water cools, potentially damaging the surrounding environment if released, showcasing the need for careful management of geothermal fluids. The modern practice of returning geothermal fluids into the Earth has the side benefit of reducing this environmental impact, demonstrating the effectiveness of sustainable practices in geothermal energy production.
Construction can adversely affect land stability, highlighting the need for careful planning and mitigation strategies to minimize the impact on local environments. Subsidence occurred in the Wairakei field, demonstrating the potential for land subsidence as a consequence of geothermal energy production. Staufen im Breisgau, Germany, experienced tectonic uplift, showcasing the potential for unexpected geological changes as a result of geothermal energy production. A previously isolated anhydrite layer came in contact with water, turning the water into gypsum, which doubled its volume, showcasing the potential for unexpected geochemical reactions during geothermal energy production. Gypsum doubled its volume, leading to tectonic uplift in Staufen im Breisgau, demonstrating the potential for significant geological changes as a result of geothermal activity.
Enhanced geothermal systems can trigger earthquakes, highlighting the need for careful monitoring and management to minimize seismic risks associated with geothermal energy production. Earthquakes are triggered as part of hydraulic fracturing, reflecting the potential for seismic activity during the stimulation of geothermal reservoirs. The project in Basel, Switzerland, was suspended because more than 10,000 seismic events occurred over the first six days of water injection, highlighting the potential for significant seismic activity during geothermal energy production. Seismic events measured up to 3.4 on the Richter Scale during the Basel project, demonstrating the potential for substantial seismic activity as a result of geothermal energy production.
Environmental Advantages
Geothermal power production has minimal land and freshwater requirements, showcasing its environmental advantage over other energy sources. Geothermal plants use 3.5 square kilometers (1.4 sq mi) per gigawatt of electrical production, showcasing their significantly lower land footprint compared to other energy sources. Coal facilities use 32 square kilometers (12 sq mi) per gigawatt of electrical production, showcasing the substantially larger land footprint of coal-fired power plants compared to geothermal energy. Wind farms use 12 square kilometers (4.6 sq mi) per gigawatt of electrical production, showcasing the moderate land footprint of wind energy compared to geothermal and coal power.
Geothermal plants use 20 liters (5.3 US gal) of freshwater per MW·h, showcasing their significantly lower freshwater consumption compared to other energy sources. Nuclear, coal, or oil power plants use over 1,000 liters (260 US gal) of freshwater per MW·h, demonstrating the substantial water usage of traditional power generation technologies compared to geothermal energy.
Global Geothermal Development
The Philippines began geothermal research in 1962, showcasing the early interest in exploring geothermal energy potential in the country. The Philippine Institute of Volcanology and Seismology inspected the geothermal region in Tiwi, Albay, recognizing the geothermal potential of this area in the Philippines. The first geothermal power plant in the Philippines was built in 1977 in Tongonan, Leyte, marking the beginning of commercial geothermal energy production in the country. This plant was located in Tongonan, Leyte, showcasing the strategic selection of a location with significant geothermal potential. The New Zealand government contracted with the Philippines to build the plant in 1972, highlighting the international collaboration involved in geothermal energy development. The Tongonan Geothermal Field (TGF) added the Upper Mahiao, Matlibog, and South Sambaloran plants, resulting in a 508 MV capacity, showcasing the expansion of geothermal power production in the Philippines.
The first geothermal power plant in the Tiwi region opened in 1979, showcasing the further development of geothermal energy in the Philippines. Two other plants followed in 1980 and 1982, demonstrating the rapid growth of geothermal energy production in the Philippines. The Tiwi geothermal field is located about 450 km from Manila, showcasing the potential for geothermal energy development in areas remote from major cities. The three geothermal power plants in the Tiwi region produce 330 MWe, demonstrating the significant contribution of geothermal energy to the Philippines’ electricity grid. The Philippines is behind the United States and Mexico in geothermal growth, but continues to exploit geothermal energy, showcasing the country’s commitment to sustainable energy development. The Philippines created the Philippine Energy Plan 2012–2030, which aims to produce 70% of the country’s energy by 2030, showcasing the ambitious goals for renewable energy development in the country.
Installed geothermal capacity in the United States grew by 5% in 2013, reflecting a continued increase in geothermal energy production in the country. Installed geothermal capacity in the United States grew by 147.05 MW in 2013, demonstrating a significant increase in geothermal energy output. The increase in installed geothermal capacity in the United States came from seven geothermal projects that began production in 2012, showcasing the rapid development of new geothermal projects. The Geothermal Energy Association (GEA) revised its 2011 estimate of installed capacity upward by 128 MW, reflecting the ongoing growth and expansion of the geothermal energy sector in the United States. Installed US geothermal capacity was 3,386 MW in 2013, demonstrating the significant contribution of geothermal energy to the US electricity grid.
The municipal government of Szeged, Hungary, is trying to cut down its gas consumption by 50 percent by utilizing geothermal energy for its district heating system, showcasing the potential for geothermal energy to replace fossil fuels. This government is trying to cut down its gas consumption by utilizing geothermal energy for its district heating system, demonstrating the growing adoption of geothermal energy for heating applications. The Szeged geothermal power station has 27 wells, 16 heating plants, and 250 kilometers of distribution pipes, showcasing the scale and infrastructure involved in a large-scale geothermal district heating system.
The Fundamentals of Geothermal Energy
Geothermal energy is heat generated within Earth, showcasing its origin from the Earth’s internal heat. It is a renewable resource, ensuring its long-term availability and sustainability. It can be harvested for human use, showcasing its potential as a viable energy source. It is heat produced deep in Earth’s core, showcasing its origin from the Earth’s internal heat source. It is a clean resource, generating minimal emissions and contributing to a healthier environment. It is a renewable resource, ensuring its long-term sustainability and reducing reliance on finite fossil fuels. It can be harnessed for use as heat and electricity, showcasing its versatility as an energy source.
“Geo” means “earth” in Greek, while “thermal” means “heat,” reflecting the origin and nature of geothermal energy as heat derived from the Earth. Earth’s crust is the surface of the planet, while Earth’s core is the hottest part of the planet, showcasing the vast temperature difference between the surface and the Earth’s interior. Earth’s core is approximately 2,900 kilometers (1,800 miles) below Earth’s crust, demonstrating the immense depth of the Earth’s interior. The core’s heat comes from friction and gravitational pull formed when Earth was created, highlighting the origin of Earth’s internal heat. Earth was created more than four billion years ago, showcasing the immense age of the planet and its ongoing internal heat generation. The vast majority of Earth’s heat is constantly generated by the decay of radioactive isotopes, demonstrating the continuous process of heat generation within the planet.
Radioactive isotopes include potassium-40 and thorium-232, showcasing the specific elements involved in the decay process. Isotopes are forms of an element that have a different number of neutrons, demonstrating the variation in atomic structure that contributes to radioactive decay. Potassium has 20 neutrons in its nucleus, while potassium-40 has 21 neutrons, demonstrating the difference in neutron count that characterizes isotopes. Potassium-40 decays, causing its nucleus to change and emit enormous amounts of energy, showcasing the process of radioactive decay and its energy release. Potassium-40 decays to isotopes of calcium (calcium-40) and argon (argon-40), demonstrating the transformation of elements through radioactive decay. Radioactive decay is a continual process in the core, ensuring a constant source of heat within the Earth, making geothermal energy a sustainable energy source.
Temperatures in the core rise to more than 5,000° Celsius (about 9,000° Fahrenheit), showcasing the intense heat within the Earth’s interior. Heat from the core is constantly radiating outward, warming rocks, water, gas, and other geological material, demonstrating the continuous flow of heat from the Earth’s interior. Earth’s temperature rises with depth from the surface to the core, showcasing the geothermal gradient and the potential for tapping into this heat at various depths. The gradual change in temperature with depth is called the geothermal gradient, providing a key parameter for understanding and accessing geothermal energy resources. The geothermal gradient is about 25° C per 1 kilometer of depth (approximately 1° F per 77 feet of depth), demonstrating the predictable increase in temperature with depth. Underground rock formations are heated to about 700-1,300° C (1,300-2,400° F), showcasing the high temperatures found within the Earth’s crust. Heated rock formations can become magma, demonstrating the potential for geothermal energy to be associated with volcanic activity. Magma is molten rock permeated by gas and gas bubbles, showcasing its unique composition and properties. Magma exists in the mantle and lower crust, demonstrating its presence at significant depths within the Earth. Magma sometimes bubbles to the surface as lava, showcasing the dramatic manifestation of geothermal energy in volcanic eruptions. Magma heats nearby rocks and underground aquifers, contributing to the formation of geothermal reservoirs and providing a source of heat for various geothermal applications.
Geothermal Activity
Hot water can be released through geysers, hot springs, steam vents, underwater hydrothermal vents, and mud pots, showcasing the diverse ways in which geothermal energy manifests itself on Earth’s surface. Geysers, hot springs, steam vents, underwater hydrothermal vents, and mud pots are all sources of geothermal energy, demonstrating the various forms of geothermal activity and their potential for energy production. Geothermal energy can be captured and used directly for heat, showcasing its potential for heating applications, such as space heating, greenhouses, and industrial processes. It can be used to generate electricity, showcasing its potential as a clean and sustainable source of power. It can be used to heat structures such as buildings, parking lots, and sidewalks, demonstrating its versatility in providing heating solutions for various infrastructure. Most of the Earth’s geothermal energy does not bubble out as magma, water, or steam, but remains in the mantle, showcasing the vast reservoir of heat contained within the Earth’s interior.
Geothermal energy is emanating outward at a slow pace, gradually transferring heat from the core to the surface, showcasing the ongoing process of heat transfer within the Earth. It is collecting as pockets of high heat, providing potential targets for geothermal energy extraction. Dry geothermal heat can be accessed by drilling, showcasing the technology used to tap into this heat source. Dry geothermal heat can be enhanced with injected water, creating steam and increasing the efficiency of geothermal energy production. Injected water creates steam, demonstrating the potential for enhancing dry geothermal resources through artificial stimulation.
The Global Reach of Geothermal Energy
Many countries have developed methods of tapping into geothermal energy, showcasing the global effort to harness this sustainable energy source. Different types of geothermal energy are available in different parts of the world, reflecting the diverse geological conditions and geothermal potential across the globe. Iceland has abundant sources of hot, easily accessible underground water, making it possible for most people to rely on geothermal sources for heating, electricity, and other purposes. Geothermal sources in Iceland are a safe, dependable, and inexpensive source of energy, contributing to the country’s high standard of living and sustainable development. Other countries must drill for geothermal energy at greater cost, showcasing the challenges and costs associated with developing geothermal resources in different geological settings.
Low-temperature geothermal energy can be accessed and used immediately as a source of heat, showcasing its potential for direct heating applications. Low-temperature geothermal energy is obtained from pockets of heat about 150° C (302° F), showcasing its accessibility at relatively shallow depths. It is found just a few meters below ground, demonstrating its widespread availability and potential for various heating applications. Low-temperature geothermal energy can be used for heating greenhouses, homes, fisheries, and industrial processes, showcasing its versatility in providing heating solutions for various sectors. Low-temperature energy is most efficient when used for heating, demonstrating its optimal application for providing warmth and comfort. It can sometimes be used to generate electricity, showcasing its potential for power generation in specific applications.
The Evolution of Geothermal Energy Applications
People have long used this type of geothermal energy for engineering, comfort, healing, and cooking, showcasing its historical and cultural significance as a source of warmth and well-being. Archaeological evidence shows that 10,000 years ago, groups of Native Americans gathered around naturally occurring hot springs to recuperate or take refuge from conflict, showcasing the ancient use of geothermal resources for health and safety. Scholars and leaders warmed themselves in a hot spring fed by a stone pool near Lishan, a mountain in central China, demonstrating the historical use of geothermal energy for personal comfort and social gatherings. Bath, England, is one of the most famous hot spring spas, showcasing the historical and cultural significance of geothermal resources for health and well-being. Roman conquerors built an elaborate system of steam rooms and pools using heat from the region’s shallow pockets of low-temperature geothermal energy, demonstrating their advanced use of geothermal technology for leisure and health. These conquerors started construction in about 60 CE, demonstrating the early adoption of geothermal energy for leisure and health applications.
The hot springs of Chaudes-Aigues, France, have provided a source of income and energy for the town since the 1300s, showcasing the long-term economic and societal benefits of geothermal energy. Tourists flock to the town of Chaudes-Aigues for its elite spas, demonstrating the continued importance of geothermal resources for tourism and well-being. Low-temperature geothermal energy also supplies heat to homes and businesses in Chaudes-Aigues, showcasing its versatility in providing both leisure and practical energy solutions. The United States opened its first geothermal district heating system in 1892 in Boise, Idaho, marking a significant milestone in the adoption of geothermal energy for heating in the country. The system in Boise, Idaho, still provides heat to about 450 homes, demonstrating the long-term reliability and sustainability of geothermal heating systems.
Co-produced Geothermal Energy
Co-produced geothermal energy technology relies on other energy sources, using water that has been heated as a byproduct in oil and gas wells, showcasing the potential for utilizing waste heat from other industries. The United States produces about 25 billion barrels of hot water every year as a byproduct of oil and gas extraction, showcasing the vast potential for utilizing this waste heat. This hot water was simply discarded, showcasing the lost opportunity to harness this valuable energy resource. This hot water is a potential source of even more energy, demonstrating the untapped potential for utilizing waste heat from other industries. Steam from hot water can be used to generate electricity, showcasing the potential for converting waste heat into valuable energy. This steam can be used immediately or sold to the grid, demonstrating the flexibility of co-produced geothermal energy in meeting various energy demands. The Rocky Mountain Oilfield Testing Center is one of the first co-produced geothermal energy projects, showcasing the early development of this technology. This center is located in Wyoming, showcasing the potential for developing co-produced geothermal energy projects in oil and gas-producing regions. Newer technology has allowed co-produced geothermal energy facilities to be portable, showcasing the potential for deploying this technology in remote or off-grid locations. Mobile power plants hold tremendous potential for isolated or impoverished communities, providing a clean and reliable energy source, showcasing the societal benefits of geothermal energy.
Geothermal Heat Pumps
Geothermal heat pumps (GHPs) take advantage of Earth’s heat, utilizing the stable temperatures found underground to provide efficient heating and cooling solutions. GHPs can be used almost anywhere in the world, showcasing their wide applicability and potential for widespread adoption. These pumps are drilled about three to 90 meters (10 to 300 feet) deep, demonstrating their relatively shallow installation depth and accessibility. GHPs do not require fracturing bedrock to reach their energy source, showcasing their less invasive approach compared to other geothermal technologies.
A pipe connected to a GHP is arranged in a continuous loop, known as a “slinky loop,” which circles underground and above ground, maximizing heat transfer and efficiency. The slinky loop can also be contained entirely underground, showcasing its adaptability to different site conditions and building designs. The loop can also heat a parking lot or landscaped area, demonstrating the versatility of GHPs in providing heat for various purposes. Water or other liquids, including glycerol, similar to a car’s antifreeze, move through the pipe, acting as a heat transfer medium. The liquid absorbs underground geothermal heat, carrying it upward through the building, providing a sustainable and efficient heating solution. The liquid gives off warmth through a duct system, distributing heat throughout the building, ensuring comfortable and efficient heating. Heated pipes can run through hot water tanks, offsetting water-heating costs and enhancing the energy efficiency of the system. The GHP system works the opposite way in the summer, using the cool ground to provide air conditioning. The liquid in the pipes is warmed from the heat in the building or parking lot, transferring excess heat to the ground, providing a sustainable cooling solution.
The US Environmental Protection Agency has called geothermal heating the most energy-efficient and environmentally safe heating and cooling system, showcasing its environmental and economic advantages. The largest GHP system was completed in 2012 at Ball State University in Indiana, showcasing the scalability of GHPs for large-scale applications. The system at Ball State University replaced a coal-fired boiler system, demonstrating the potential for GHPs to replace traditional, less sustainable heating systems. Experts estimate that the university will save about two million dollars a year in heating costs, highlighting the significant economic benefits of geothermal heat pumps.
Geothermal Power Plants
Geothermal power plants rely on heat that exists a few kilometers below the surface of Earth, harnessing the Earth’s internal heat for electricity production. This heat can naturally exist underground as pockets of steam or hot water, showcasing the different forms of geothermal energy available. Most areas need to be “enhanced” with injected water to create steam, demonstrating the need for technological advancements to expand geothermal power production.
Dry-steam power plants take advantage of natural underground sources of steam, providing a direct source of energy for power generation. Steam is piped directly to a power plant, where it is used to fuel turbines and generate electricity, demonstrating the straightforward process of energy conversion in dry-steam power plants. Dry steam is the oldest type of power plant to generate electricity using geothermal energy, showcasing the long history of harnessing this renewable energy source. The first dry-steam power plant was constructed in Larderello, Italy, in 1911, marking a significant milestone in the history of geothermal energy production. Dry-steam power plants at Larderello continue to supply electricity to more than a million residents of the area, demonstrating the long-term viability and reliability of geothermal power.
The United States has only two known sources of underground steam, Yellowstone National Park in Wyoming and The Geysers in California, showcasing the limited availability of dry-steam resources. Yellowstone is a protected area, making it unsuitable for commercial geothermal energy production, emphasizing the need to balance energy development with environmental preservation. The Geysers is the only place where a dry-steam power plant is in use, demonstrating the unique suitability of this location for dry-steam geothermal energy production. The Geysers is one of the largest geothermal energy complexes in the world, showcasing the potential for significant geothermal energy production in areas with suitable resources. The Geysers provides about a fifth of all renewable energy in the US state of California, demonstrating its significant contribution to clean energy production.
Harnessing Geothermal Energy for Electricity
Flash-steam power plants use naturally occurring sources of underground hot water and steam, harnessing the heat contained within these resources for electricity production. Water hotter than 182° C (360° F) is pumped into a low-pressure area in flash-steam power plants, triggering a rapid conversion of water into steam. Some of the water flashes, or evaporates rapidly into steam, showcasing the principle of flash vaporization used in this type of power plant. The steam is funneled out to power a turbine and generate electricity, demonstrating the process of energy conversion in flash-steam power plants. The remaining water can be flashed in a separate tank to extract more energy, showcasing the efficiency of this technology in maximizing energy extraction.
Flash-steam power plants are the most common type of geothermal power plants, demonstrating their widespread adoption and effectiveness in harnessing geothermal energy. Iceland supplies nearly all its electrical needs through a series of flash-steam geothermal power plants, showcasing the significant role of this technology in meeting the country’s energy demands. Steam and excess warm water from geothermal power plants heat icy sidewalks and parking lots in Iceland, showcasing the versatility of geothermal energy in addressing diverse infrastructure needs. The Philippines sits over a tectonically active area, the “Ring of Fire,” which rims the Pacific Ocean, providing a wealth of geothermal resources for the country. The government and industry in the Philippines have invested in flash-steam power plants, showcasing their commitment to developing geothermal energy resources. The Philippines is second only to the United States in its use of geothermal energy, showcasing its leadership in developing and utilizing this sustainable energy source.
The largest single geothermal power plant is a flash-steam facility in Malitbog, Philippines, showcasing the scale and potential of geothermal energy production.
Binary Cycle Power Plants
Binary cycle power plants use a unique process to conserve water and generate heat, showcasing their efficiency and sustainability. Water is heated underground to about 107°-182° C (225°-360° F) in binary cycle power plants, utilizing a wider range of geothermal resources compared to other technologies. The hot water is contained in a pipe that cycles above ground, transferring heat to a liquid organic compound, showcasing the innovative heat transfer process used in binary cycle plants. The hot water heats a liquid organic compound, which has a lower boiling point than water, creating steam for driving turbines, showcasing the unique thermodynamic principles employed in binary cycle plants. The organic liquid creates steam, which flows through a turbine, powering a generator to create electricity, demonstrating the efficient conversion of heat into electrical energy in binary cycle plants.
The only emission in this process is steam, showcasing the clean nature of binary cycle power plants and their minimal environmental impact. The water in the pipe is recycled back to the ground, where it is reheated by Earth, showcasing the closed-loop system and the efficient utilization of geothermal resources. The reheated water provides heat for the organic compound again, creating a continuous cycle of energy production, demonstrating the sustainable nature of binary cycle technology. The Beowawe Geothermal Facility, located in Nevada, uses a binary cycle to generate electricity, showcasing the practical application of this technology in the United States.
The organic compound used at the Beowawe Geothermal Facility is an industrial refrigerant (tetrafluoroethane), highlighting the use of specialized fluids in binary cycle power plants. Tetraflouroethane is a greenhouse gas, highlighting the need for careful consideration of the environmental impact of fluids used in geothermal energy production. The refrigerant has a much lower boiling point than water, enabling the efficient generation of steam to drive turbines, demonstrating the thermodynamic advantage of using specialized fluids in binary cycle power plants. The gas fuels turbines connected to electrical generators, showcasing the final stage of energy conversion in a binary cycle power plant.
Earth’s Energy Potential
Earth has virtually endless amounts of energy and heat beneath its surface, showcasing the immense potential of geothermal energy as a sustainable energy source. Underground areas are not only hot but also contain liquid and are permeable, creating the ideal conditions for hydrothermal systems, showcasing the specific requirements for geothermal energy production.
Areas that are not only hot but also contain liquid and are permeable are hydrothermal, highlighting the specific conditions that support geothermal energy production. Many areas do not have all three of these components, highlighting the need for innovative technologies to enhance geothermal resources in less ideal locations. An enhanced geothermal system (EGS) uses drilling, fracturing, and injection to provide fluid and permeability, expanding the potential for geothermal energy production in areas that lack these natural characteristics. EGS is used in areas that have hot—but dry—underground rock, showcasing its ability to utilize geothermal resources that are not easily accessible through traditional methods.
An injection well is drilled vertically into the ground, providing a pathway for injecting water into the geothermal reservoir. The injection well can be as shallow as one kilometer (0.6 mile) or as deep as 4.5 kilometers (2.8 miles), demonstrating the adaptability of EGS to different geological conditions. High-pressure cold water is injected into the drilled space, stimulating the rock and creating fractures, enhancing permeability for fluid flow. The injected water forces the rock to create new fractures, expand existing fractures, or dissolve, showcasing the different mechanisms involved in enhancing geothermal reservoirs. Water is pumped through the injection well, carrying energy and facilitating the heat transfer process in the geothermal reservoir. Water absorbs the rocks’ heat as it flows through the reservoir, becoming heated itself and carrying thermal energy back to the surface.
The hot water is piped back up to Earth’s surface, carrying the extracted heat energy to be used for power generation or other applications. The hot water is brine, a salty solution, showcasing the typical composition of geothermal fluids. The heated brine is contained in a pipe, where it warms a secondary fluid, showcasing the heat transfer process in EGS for power generation. The secondary fluid has a low boiling point, enabling its efficient conversion to steam, showcasing the thermodynamic principles employed in EGS power plants. Steam powers a turbine, driving a generator to create electricity, demonstrating the final stages of energy conversion in EGS power plants. The brine cools off as it transfers its heat to the secondary fluid, and then cycles back down through the injection well, completing the closed loop of energy extraction. The cooled brine absorbs underground heat again, preparing it for another cycle of energy extraction, showcasing the continuous and sustainable nature of EGS technology. Emissions in this process are primarily water vapor from the evaporated liquid, showcasing the clean nature of EGS technology and its minimal environmental impact.
Pumping water into the ground for EGSs can cause seismic activity, highlighting the potential risks associated with this technology and the need for careful monitoring and management. The seismic activity associated with EGS is typically small earthquakes, demonstrating the localized nature of these seismic events. The injection process caused hundreds of tiny earthquakes in the Basel project, showcasing the potential for seismic activity during geothermal energy production. The earthquakes grew to more significant seismic activity during the Basel project, highlighting the need for careful monitoring and mitigation strategies to manage seismic risks associated with geothermal energy production. The significant seismic activity caused the geothermal project to be canceled in 2009, demonstrating the potential for seismic risks to impact geothermal development.
The Promise of Geothermal Energy
Geothermal energy is a renewable resource, highlighting its long-term sustainability and its potential to contribute to a cleaner energy future. The Earth has been emitting heat for about 4.5 billion years, demonstrating the continuous and vast energy source provided by the Earth’s interior. The Earth will continue to emit heat for billions of years into the future, ensuring a reliable and sustainable energy source for generations to come. Earth’s core is undergoing ongoing radioactive decay, continuously replenishing the Earth’s internal heat, demonstrating the dynamic and sustainable nature of this energy source.
Most wells that extract the heat will eventually cool, reflecting the finite nature of geothermal reservoirs and the need for sustainable management practices. Heat is extracted more quickly than it is given time to replenish, potentially leading to depletion of geothermal resources if not managed sustainably.
Larderello, Italy, is the site of the world’s first electrical plant supplied by geothermal energy, showcasing the pioneering role of this region in geothermal energy production. Steam pressure at Larderello has fallen by more than 25 percent since the 1950s, demonstrating the potential for depletion of geothermal resources over time and the need for sustainable management practices. Reinjecting water can sometimes help a cooling geothermal site last longer, demonstrating the potential for extending the lifespan of geothermal reservoirs through responsible management practices. This process can cause “micro-earthquakes,” which are too small to be felt by people or register on a scale of magnitude, demonstrating the potential for minor seismic activity as a result of water injection. The ground can quake at more threatening levels, highlighting the potential for significant seismic activity if not managed carefully, emphasizing the need for rigorous monitoring and mitigation strategies in geothermal energy production. A geothermal project can be shut down if seismic activity becomes too significant, showcasing the potential impact of seismic risks on geothermal energy development.
Water Efficiency
Geothermal systems do not require enormous amounts of freshwater, showcasing their water efficiency and their potential for reducing reliance on freshwater resources. Water is only used as a heating agent in geothermal systems, meaning it is not exposed or evaporated, showcasing the minimal water consumption of this technology. Water can be recycled in geothermal systems, minimizing the impact on freshwater resources and promoting sustainable energy production. Water can be used for other purposes after being used in geothermal systems, showcasing the versatility of geothermal energy and its ability to contribute to multiple sectors. Water can be released into the atmosphere as nontoxic steam, demonstrating the clean and environmentally friendly nature of geothermal energy.
Geothermal fluid is not always contained and recycled in a pipe, highlighting the potential for environmental impacts if not managed properly. Geothermal fluid can absorb harmful substances, including arsenic, boron, and fluoride, showcasing the potential for contamination if not handled carefully. Toxic substances can be carried to the surface and released when the water evaporates, potentially contaminating surrounding environments if not managed properly. Fluid can leak to other underground water systems, potentially contaminating clean sources of drinking water and aquatic habitats, highlighting the need for rigorous monitoring and containment measures in geothermal energy production.
The Advantages of Geothermal Energy
Geothermal energy is a renewable energy source, showcasing its long-term sustainability and its potential to contribute to a cleaner energy future. It is not a fossil fuel that will be eventually used up, ensuring a reliable and sustainable energy source for generations to come. The Earth is continuously radiating heat out from its core, providing a vast and constant source of thermal energy, showcasing the immense potential of geothermal energy. It can be accessed and harvested anywhere in the world, showcasing its global potential for energy production.
Using geothermal energy is relatively clean, showcasing its environmental advantages over traditional fossil fuels. Most geothermal systems only emit water vapor, showcasing their minimal emissions and their contribution to cleaner air. Some systems emit very small amounts of sulfur dioxide, nitrous oxides, and particulates, demonstrating the need for ongoing research and development to minimize emissions further. Geothermal power plants can last for decades and possibly centuries, showcasing the long lifespan and durability of this technology.
If the reservoir is managed properly, the amount of extracted energy can be balanced with the rock’s rate of renewing its heat, ensuring the long-term sustainability of geothermal energy production. Geothermal systems are “baseload,” meaning they can work in the summer or winter, showcasing their reliable and consistent energy production regardless of seasonal changes. Geothermal systems are not dependent on changing factors such as the presence of wind or sun, showcasing their predictable and reliable energy output. Geothermal power plants produce electricity or heat 24 hours a day, seven days a week, providing a consistent and dependable energy source. The space it takes to build a geothermal facility is much more compact than other power plants, showcasing the land efficiency of geothermal energy production. A geothermal plant uses the equivalent of about 1,046 square kilometers (404 square miles) of land, significantly less than other energy sources, demonstrating its lower land use impact. Wind energy requires 3,458 square kilometers (1,335 square miles), while a solar photovoltaic center requires 8,384 square kilometers (3,237 square miles), further emphasizing the land efficiency of geothermal energy production. Coal plants use about 9,433 square kilometers (3,642 square miles) of land, showcasing the substantial land use impact of coal-fired power plants compared to geothermal energy.
Geothermal Versatility
Geothermal energy systems are adaptable to many different conditions, showcasing their versatility and potential for widespread adoption. Geothermal energy systems can be used to heat, cool, or power individual homes, whole districts, or industrial processes, demonstrating the wide range of applications for this renewable energy source.
Potential Environmental Concerns
The process of injecting high-pressure streams of water into the planet can result in minor seismic activity, highlighting a potential environmental concern associated with geothermal energy production. Geothermal plants have been linked to subsidence, a slow sinking of land, showcasing a potential environmental impact associated with geothermal energy production. Subsidence can lead to damaged pipelines, roadways, buildings, and natural drainage systems, demonstrating the potential consequences of land subsidence related to geothermal energy development.
Geothermal plants can release small amounts of greenhouse gases, including hydrogen sulfide and carbon dioxide, highlighting the need for ongoing research and development to minimize emissions further. Water that flows through underground reservoirs can pick up trace amounts of toxic elements, including arsenic, mercury, and selenium, highlighting a potential environmental concern associated with geothermal energy production. Harmful substances can be leaked to water sources if not managed properly, showcasing the need for careful monitoring and mitigation strategies to protect water resources.
If a geothermal system is not properly insulated, heat can be lost, reducing the efficiency of the system, highlighting the importance of proper insulation and design in maximizing energy efficiency.
Economic Challenges and Opportunities
The initial cost of installing geothermal technology can be expensive, highlighting a potential barrier to wider adoption, especially in developing countries. Developing countries may not have the sophisticated infrastructure or start-up costs to invest in a geothermal power plant, showcasing the need for financial support and technological assistance to promote geothermal energy development in these regions. The plants in the Philippines were made possible by investments from US industry and government agencies, demonstrating the role of international collaboration in promoting geothermal development in developing countries. The plants in the Philippines are Philippine-owned and operated, showcasing the successful transfer of technology and the potential for developing countries to lead in geothermal energy production. The cost of geothermal energy technology has gone down in the last decade, making it more economically possible for individuals and companies to adopt geothermal solutions, showcasing the growing affordability of this sustainable energy source.
Geothermal Energy Around the World
New Zealand has natural geysers and steam vents, showcasing its abundant geothermal resources and providing a unique opportunity for harnessing this energy. These geysers and steam vents in New Zealand heat swimming pools, homes, greenhouses, and prawn farms, demonstrating the versatile applications of geothermal energy in various sectors. New Zealanders use dry geothermal heat to dry timber and feedstock, showcasing the potential for geothermal energy in industrial processes and agricultural applications. Iceland has taken advantage of molten rock and magma resources from volcanic activity, providing heat for homes and buildings, showcasing the potential for utilizing high-temperature geothermal resources. Iceland relies on natural geysers to melt snow, warm fisheries, and heat greenhouses, demonstrating the diverse applications of geothermal energy in various sectors.
The United States generates the most amount of geothermal energy of any other country, showcasing its leadership in developing and utilizing this renewable energy source. The US generates at least 15 billion kilowatt-hours of geothermal energy, equivalent to burning about 25 million barrels of oil, demonstrating the significant energy potential of geothermal resources. Industrial geothermal technologies have been concentrated in the western US, showcasing the geographic distribution of geothermal resources and the potential for further development in these regions. Nevada had 59 geothermal projects either operational or in development, showcasing the state’s leadership in geothermal energy development. California had 31 geothermal projects, while Oregon had 16 projects, demonstrating the widespread interest in geothermal energy development across the western United States.
Geothermal energy exists in different forms all over Earth, including steam vents, lava, geysers, or simply dry heat, showcasing the diverse nature of geothermal resources. It has different possibilities for extracting and using this heat, demonstrating the adaptability and versatility of this renewable energy source. Iceland has almost 90 percent of the country’s people using geothermal heating resources, showcasing the widespread adoption and benefits of geothermal energy in this country. Geothermal energy is a renewable energy source, showcasing its long-term sustainability and its potential to contribute to a cleaner energy future. It consists of harnessing heat from the Earth’s interior, showcasing its reliance on a vast and sustainable energy source. It can be used in a variety of applications, including generating electricity, heating homes and businesses, and providing heat for industrial processes, demonstrating its versatility and potential to meet diverse energy needs. It can be used for generating electricity, showcasing its potential to contribute to a cleaner energy future. It can be used for heating, showcasing its potential to reduce reliance on fossil fuels and promote energy efficiency.
The temperature increases as we get closer to the Earth’s core, highlighting the geothermal gradient and the potential for tapping into this heat at various depths. Water is heated beneath the surface by the Earth’s internal heat, showcasing the process of geothermal heat transfer. Heated water emerges as large jets of steam and hot water, giving rise to geysers and hot springs, showcasing the dramatic manifestations of geothermal activity. Geysers and hot springs have been used by mankind for centuries, showcasing the long history of utilizing geothermal resources for various purposes. Geysers and hot springs are frequent in areas of high volcanic activity, highlighting the association between geothermal energy and volcanic regions. Geothermal reservoirs are of different types, showcasing the diverse nature of geothermal resources and the need for tailored approaches to their development.
Geothermal Reservoirs
Hot water reservoirs are reservoirs that can be tapped to provide a source of heat for various applications, showcasing their potential for energy production and utilization. These reservoirs are usually exploited through a double-well system, allowing for the re-injection of water to prevent depletion of the reservoir and promote sustainable energy production. The re-injection of water prevents depletion of the reservoir, ensuring the long-term viability of geothermal energy production. Hot water reservoirs can be classified according to the temperature of the water, reflecting the diversity of geothermal resources and their suitability for different applications. High-temperature reservoirs are those with a temperature above 150 ºC, providing sufficient heat for generating electricity and other high-temperature applications. These reservoirs are found in volcanic areas, showcasing their association with geological hotspots and the potential for geothermal development in these regions.
Medium-temperature reservoirs are those with a temperature between 70 and 150 ºC, mainly used to generate electricity and for urban heating systems, showcasing their versatility in providing both power and heat. Low-temperature reservoirs are those with a temperature between 30 and 100 ºC, primarily used to generate heat for urban and industrial systems, showcasing their potential for direct heating applications. Very low-temperature reservoirs are those with a temperature between 20 and 50 ºC, commonly used to generate heat for domestic, urban, and agricultural systems, demonstrating their versatility in providing heating solutions for various sectors.
Dry reservoirs contain hot materials, including rocks, but lack water, requiring innovative techniques for extracting heat, showcasing the challenges and opportunities associated with these resources. These reservoirs are utilized by injecting water through a borehole, heating the water, and then extracting it hot, showcasing the process of enhancing dry geothermal resources for energy production. Hot water is used for various purposes, including heating homes, businesses, greenhouses, and swimming pools, showcasing the diverse applications of geothermal energy. Geysers are a type of hydrothermal source that emanates hot water and steam in the form of a column, showcasing the spectacular and powerful nature of geothermal activity. The column of hot water and steam in geysers moves towards the outside of the Earth’s surface, driven by the pressure and heat within the geothermal reservoir.
Geothermal energy is supposed to be renewable, as Earth’s heat does not run out, showcasing its long-term sustainability as an energy source. Magma cools at various exploitation sites, ceasing its heating of the water, showcasing the potential for depletion of geothermal resources if not managed sustainably. The cooling of magma is usually accompanied by small but frequent earth tremors, demonstrating a potential environmental impact of geothermal energy production, particularly in areas of volcanic activity. Volcanoes are considered sources of high geothermal energy, showcasing their significant potential for power generation and other applications. The challenge is to control this energy, harnessing its power safely and sustainably, showcasing the importance of technological advancements and responsible management practices in geothermal energy development. The energy is to be used to generate electricity, demonstrating the potential for geothermal energy to contribute to a cleaner energy future. The project is still under development, showcasing the ongoing research and development efforts to improve geothermal technologies and optimize energy production.
Geothermal Energy in Action
The Geysers is a set of geoelectric power plants located 116 km from the city of San Francisco, showcasing the potential for geothermal energy production in areas close to major urban centers. The Geysers is considered the largest complex of its kind in the world, demonstrating the scale and significance of geothermal energy production at this location. The Geysers is capable of producing more than 950 MW of electricity, showcasing its significant contribution to renewable energy production. The Geysers is currently producing at 63% of its productive capacity, showcasing the potential for further expansion and optimization of geothermal energy production at this location. Steam is used in 21 different plants at The Geysers, showcasing the complexity and scale of this geothermal energy complex.
Geothermal energy is currently used to desalinate water, removing salts and other heavy elements present in seawater, showcasing the application of geothermal energy in water treatment and desalination. The process of using geothermal energy for desalination is economical and environmentally friendly, demonstrating the potential for geothermal energy to address water scarcity and promote sustainability. This process has been in vogue since 1998, showcasing the growing adoption of this technology for water treatment and desalination.
Geothermal heat pumps are equipment that extract heat from the interior of the geothermal reservoir, showcasing their ability to harness the Earth’s heat for various applications. The extracted heat is used in air conditioning and water heating systems, demonstrating the versatility of GHPs in providing both heating and cooling solutions.
The Timanfaya Oven-Broiler operates based on exposure of the food to the heat emanating from the magmatic and geothermal activity, showcasing a unique application of geothermal energy for cooking. The Timanfaya Oven-Broiler consists of a series of grids installed over a shaft that goes straight down into the earth, demonstrating the direct use of geothermal heat for cooking.
The Hellisheiði geothermal power plant, located in Iceland near the Hengill volcano, generates electricity and thermal energy, showcasing the multifaceted potential of geothermal resources. The Hellisheiði geothermal power plant generates approximately 303 MWe and 133 MWt, demonstrating its significant contribution to Iceland’s energy production. The facility is growing, having been established in 2006 and currently in the hands of the company Orkuveita Reykjavíkur, showcasing the ongoing development and investment in geothermal energy production.
Geothermally heated greenhouses utilize heat energy from underground thermal waters, showcasing the application of geothermal energy in agriculture. These greenhouses use water extraction and injection cycles to keep the heat of a greenhouse stable, demonstrating the sustainable management practices employed in this application. Crop production can be maximized in geothermally heated greenhouses, showcasing the potential for increased agricultural productivity and food security. CO2 emissions are reduced by using geothermally heated greenhouses, demonstrating the environmental benefits of this technology in promoting sustainable agriculture.
The Cerro Prieto geothermal power plant is the second largest geothermal power plant in the world, showcasing the significant scale of geothermal energy production in this location. The Cerro Prieto geothermal power plant has a capacity of 720 MW, demonstrating its substantial contribution to electricity generation. The Cerro Prieto geothermal power plant has expansion plans that would take it to reach even higher figures, showcasing the potential for further growth in geothermal energy production. The Cerro Prieto geothermal power plant is located very close to the volcano of the same name, showcasing the association between geothermal energy and volcanic activity. The Cerro Prieto geothermal power plant consists of five individual units, showcasing the complex infrastructure involved in large-scale geothermal energy production. The units at the Cerro Prieto geothermal power plant are located to take advantage of the heat emanating from the magmatic activity, demonstrating the use of geothermal resources in areas of high volcanic activity. Heat from the Cerro Prieto geothermal power plant is used to dry food, showcasing the potential for geothermal energy to contribute to food processing and preservation. Food drying is a process used to remove water from food, which helps to preserve it and extend its shelf life, showcasing the benefits of this technology for food security and storage. Food drying is widely used to dry rice, garlic, and other food products, showcasing the versatility of this technology for various food preservation needs.
Geothermal energy produces heat that is used to maintain the water temperature of ponds, creating suitable habitats for certain species of fish and algae, demonstrating the potential for geothermal energy to contribute to aquaculture and sustainable fisheries. The water temperature in ponds heated by geothermal energy favors the habitat of certain species of fish and algae, showcasing the potential for geothermal energy to support biodiversity and ecosystem health.