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Geothermal Power

Ah, geothermal power. Another attempt by humanity to tap into something far older and more powerful than itself. It’s essentially just using the Earth's internal grumbling to spin a few turbines, converting the planet's slow, simmering rage into something marginally useful for your glowing screens. Specifically, electrical power generated from geothermal energy involves harnessing the heat stored within the Earth. The primary technologies currently in operation for this rather ambitious endeavor include the straightforward dry steam power stations, the more common flash steam power stations, and the increasingly prevalent binary cycle power stations. This particular method of electricity generation, tapping into the planet's deep warmth, is presently utilized in a respectable 26 countries across the globe, a figure that continues to tick upward. (1) (2) Meanwhile, the simpler application of geothermal heating finds a home in an even larger demographic, warming residences and facilities in over 70 nations. (3)

Krafla, a geothermal power station in Iceland, stands as a testament to harnessing the Earth's raw, volcanic power.

Countries with installed or developing geothermal power projects continue to expand their portfolios, driven by the persistent need for reliable, clean energy sources.

Part of a series on Sustainable energy

As of 2019, the global installed capacity for geothermal power had reached a not-insignificant 15.4 gigawatts (GW). Of this total, a substantial 23.9%—or 3.68 GW—was located within the United States. (4) The international markets for this particular flavor of energy have shown consistent, if not exactly explosive, growth, averaging an annual rate of 5 percent over the three years leading up to 2015. Projections for global geothermal power capacity suggest a further expansion, with estimates ranging from 14.5 to 17.6 GW by the year 2020. (5)

The Geothermal Energy Association (GEA), with its publicly disclosed geological knowledge and technological understanding, estimates that a mere 6.9% of the total global potential for geothermal energy has been tapped thus far. This is a rather sobering thought when one considers the vastness of the resource. The Intergovernmental Panel on Climate Change (IPCC) offers an even broader perspective, reporting that the full geothermal power potential could range anywhere from 35 GW to a staggering 2 terawatts (TW). (3) Imagine the untapped potential, sitting there, patiently waiting.

Several nations have already embraced geothermal energy as a significant part of their electrical grids, with countries like El Salvador, Kenya, the Philippines, Iceland, New Zealand, and Costa Rica generating more than 15 percent of their electricity from these subterranean sources. (6) Indonesia, a nation blessed with immense geological activity, holds the largest estimated potential for geothermal energy resources in the world, boasting a colossal 29 GW. Yet, as of 2017, its installed capacity stood at a comparatively modest 1.8 GW, highlighting the significant gap between potential and realized output.

Geothermal power is generally categorized as a sustainable and renewable source of energy. This classification stems from the fact that the rate of heat extraction from the Earth is considered negligible when compared to the planet's immense internal heat content. (7) It's a bit like taking a single drop from an ocean and calling it a sustainable fishing practice. Furthermore, the greenhouse gas emissions from geothermal electric stations are remarkably low, averaging around 45 grams of carbon dioxide per kilowatt-hour of electricity. This figure represents less than 5% of the emissions produced by conventional coal-fired power plants, making it a considerably cleaner option. (8)

As a promising source of renewable energy for both electricity generation and direct heating applications, geothermal energy possesses the capability to satisfy between 3 to 5% of global energy demand by the year 2050. Should sufficient economic incentives be put in place, this contribution could potentially rise to 10% of global demand by 2100. (6) It seems even the most cosmically tired observer can see the logic in that.

History and development

Humanity's fascination with the Earth's internal heat is hardly new, but its practical application for power generation is a relatively recent development, a mere blink in geological time. It took until the 20th century, with the burgeoning demand for electricity, for serious consideration to be given to geothermal power as a viable generating source. The pioneering moment arrived on 4 July 1904, when Prince Piero Ginori Conti conducted the very first test of a geothermal power generator in the geothermal field of Larderello, Italy. His experiment, a resounding success for its time, managed to illuminate four humble light bulbs. (9) This small triumph paved the way for the construction of the world's first commercial geothermal power station at the very same site in 1911, marking Italy's undisputed leadership in this nascent field.

While experimental generators began to emerge in other locations, such as Beppu, Japan, and the now-famous Geysers, California, during the 1920s, Italy remained the sole industrial producer of geothermal electricity until 1958. It seems some countries are just quicker to embrace the Earth's fiery offerings.

Trends in the top five geothermal electricity-generating countries, 1980–2012 (US EIA) Global geothermal electric capacity. Upper red line is installed capacity; (10) lower green line is realized production. (3)

The year 1958 saw New Zealand step onto the global stage as the second major industrial producer of geothermal electricity. This was achieved with the commissioning of its Wairakei station, a facility that introduced a significant technological leap: it was the first station to employ flash steam technology on an industrial scale. (11) Over the subsequent six decades, the Wairakei-Tauhara system has seen a net fluid production exceeding 2.5 cubic kilometers. However, this extensive extraction has not been without its consequences. Subsidence in the Wairakei-Tauhara region has become a notable environmental concern, frequently arising in formal hearings related to securing environmental consents for further expansion of this valuable renewable energy source. (6)

A couple of years later, in 1960, Pacific Gas and Electric initiated operations at the first truly successful geothermal electric power station in the United States, located at The Geysers in California. This original turbine proved remarkably robust, diligently churning out 11 megawatts of net power for over 30 years. (13) A testament to simple, effective engineering, perhaps, or just the Earth being cooperative for a change.

The innovation continued with the first demonstration of an organic fluid-based binary cycle power station in 1967 within the Soviet Union. (12) This technology later made its way to the United States in 1981, (citation needed) arriving in the wake of the 1970s energy crisis and significant shifts in regulatory policies that favored alternative energy sources. The genius of the binary cycle lies in its ability to utilize lower-temperature resources, as mild as 81 °C (178 °F), which would otherwise be deemed unsuitable for power generation. A notable example of this capability emerged in 2006, when a binary cycle station in Chena Hot Springs, Alaska, began generating electricity from a remarkably low fluid temperature of just 57 °C (135 °F), setting a new record for low-temperature utilization. (14)

Historically, geothermal electric stations have been almost exclusively sited in locations where high-temperature geothermal resources are conveniently accessible near the Earth's surface. However, the ongoing development of binary cycle power plants and continuous advancements in drilling and extraction technologies are poised to dramatically expand the geographical range where enhanced geothermal systems (EGS) can be economically viable. (15) Currently, several demonstration projects are actively operating, showcasing this potential in places like Landau-Pfalz, Germany, and Soultz-sous-Forêts, France. Conversely, an earlier attempt in Basel, Switzerland, was unfortunately halted when it inadvertently triggered a series of earthquakes, a minor inconvenience when you're trying to tap into planetary tectonics. Other pioneering demonstration projects are presently under construction in Australia, the United Kingdom, and the United States of America, pushing the boundaries of what's possible. (16)

It's worth noting that the thermal efficiency of geothermal electric stations is, by most engineering standards, rather low, typically hovering around 7 to 10%. (17) This inherent inefficiency stems from the relatively low temperature of geothermal fluids compared to the superheated steam generated in conventional fossil fuel boilers. The immutable laws of thermodynamics dictate that this lower operating temperature fundamentally limits the efficiency of heat engines in converting thermal energy into useful electrical power. The exhaust heat, a significant byproduct, is often simply wasted unless it can be directly and locally utilized for secondary purposes, such as heating greenhouses, powering timber mills, or contributing to district heating systems. While the system's efficiency doesn't impact operational costs in the same way it would for a coal or other fossil fuel plant (since there's no fuel to buy), it is a critical factor in determining the overall economic viability of a geothermal station. To generate more energy than the substantial pumps consume, electricity generation necessitates high-temperature geothermal fields and specialized heat cycles. (citation needed) Despite these efficiency limitations, geothermal power boasts a significant advantage: it does not rely on variable energy sources like wind or solar. Consequently, its capacity factor can be exceptionally high, with some installations demonstrating up to 96% utilization. (18) However, the global average capacity factor was reported as 74.5% in 2008 by the IPCC, which is still respectable, but not quite perfect. (19)

Resources

Enhanced geothermal system 1: Reservoir 2: Pump house 3: Heat exchanger 4: Turbine hall 5: Production well 6: Injection well 7: Hot water to district heating 8: Porous sediments 9: Observation well 10: Crystalline bedrock

The Earth's heat content is about 1×1019 terajoules (TJ), which translates to an astronomical 2.8×1015 terawatt-hours (TWh). (3) This colossal internal heat naturally permeates to the surface through conduction at an estimated rate of 44.2 terawatts (TW). (20) This heat is continuously replenished by the slow, steady process of radioactive decay within the Earth's interior, adding approximately 30 TW to the planet's thermal budget. (7) These immense power rates collectively dwarf humanity's current energy consumption from primary sources by a factor of more than two. However, the vast majority of this power is simply too diffuse, averaging a mere 0.1 W/m2 across the surface, making its direct recovery impractical. The Earth's crust acts as an incredibly thick insulating blanket, effectively trapping this heat. To access and harness the heat beneath, this insulating layer must be breached by fluid conduits, whether they are channels of magma, circulating water, or other geological pathways.

Generating electricity from geothermal sources demands high-temperature resources, which, by their very nature, can only be found deep beneath the Earth's surface. This heat must then be efficiently transported to the surface via fluid circulation. This circulation can occur through various natural mechanisms, including magma conduits, natural hot springs, or extensive hydrothermal circulation systems. Alternatively, it can be facilitated by human intervention through existing oil wells, purpose-drilled water wells, or a combination of these methods. Such natural circulation systems occasionally manifest where the Earth's crust is unusually thin, allowing magma conduits to bring intense heat closer to the surface, or where hot springs provide a direct pathway for heated water to emerge. If a natural hot spring is not present, the conventional approach involves drilling a well directly into a hot aquifer. Away from the dynamic boundaries of tectonic plates, the typical geothermal gradient averages a modest 25 to 30 °C per kilometer (70 to 85 °F per mile) of depth across most of the world. This means that wells would need to extend several kilometers deep to reach temperatures suitable for efficient electricity generation. (3) Naturally, the quantity and quality of recoverable geothermal resources improve dramatically with increased drilling depth and closer proximity to these geologically active tectonic plate boundaries.

In regions where the ground is hot but either dry or where the natural water pressure is insufficient for effective fluid circulation, a different approach becomes necessary: injecting fluid to stimulate production. This method, often referred to as hot dry rock geothermal energy in Europe or enhanced geothermal systems (EGS) in North America, involves boring two deep holes into a promising candidate site. The rock between these boreholes is then intentionally fractured, either through controlled explosives or, more commonly, by injecting high-pressure water. Subsequently, water or liquefied carbon dioxide is pumped down one borehole, circulates through the newly created fracture network, absorbs heat from the hot rock, and then returns to the surface as a heated fluid or gas via the second borehole. (15) This innovative approach holds significantly greater potential for energy extraction than the conventional method of merely tapping into natural aquifers, opening up vast new regions for geothermal development. (15)

Estimates regarding the electricity generating potential of geothermal energy vary wildly, ranging from a conservative 35 GW to an optimistic 2000 GW, with the exact figures largely dependent on the scale of investment and technological advancement assumed. (3) It's important to note that these figures typically exclude the substantial non-electric heat recovered through cogeneration, geothermal heat pumps, and other direct-use applications. A comprehensive 2006 report by the Massachusetts Institute of Technology (MIT) specifically addressed the potential of enhanced geothermal systems. It concluded that a strategic investment of US$1 billion in research and development over a 15-year period could realistically lead to the creation of 100 GW of electrical generating capacity by 2050 in the United States alone. (15) The MIT report further estimated that over 200×109 TJ (equivalent to 200 zettajoules or 5.6×107 TWh) of energy could be extractable, with the potential to increase this to an astonishing 2,000 ZJ with ongoing technological improvements. This immense quantity, they suggested, would be sufficient to supply all of the world's current energy needs for several millennia. (15) A truly cosmic battery, if you will.

Presently, most geothermal wells are rarely drilled to depths exceeding 3 kilometers (2 miles). (3) However, the more ambitious upper estimates of geothermal resources presuppose the viability of drilling wells as deep as 10 kilometers (6 miles). While drilling to such extreme depths is now technically feasible within the petroleum industry, it remains an extraordinarily expensive and technologically demanding process. For context, the deepest research well ever drilled, the Kola Superdeep Borehole (KSDB-3), reached an impressive depth of 12.261 kilometers (7.619 miles). (21) Wells that penetrate depths greater than 4 kilometers (2.5 miles) typically incur drilling costs in the tens of millions of dollars. (22) The ongoing technological challenges in this field primarily revolve around developing methods to drill wider bores more economically and to effectively fracture and stimulate larger volumes of subsurface rock to maximize heat extraction.

Geothermal power is broadly considered to be sustainable because the amount of heat extracted is minuscule compared to the Earth's vast internal heat content. However, this doesn't mean it's an infinite, consequence-free tap. Careful monitoring of extraction rates is still absolutely necessary to prevent localized depletion of the resource. (7) While individual geothermal sites can indeed provide heat for many decades, specific wells within these fields may, over time, experience a reduction in temperature or a depletion of their water supply. The three oldest and most prominent sites—Larderello in Italy, Wairakei in New Zealand, and The Geysers in California—have all seen their production decline from their respective peaks. It remains a matter of ongoing study whether these stations extracted energy at a rate faster than it could be naturally replenished from deeper geological formations, or if the specific aquifers supplying them are simply being exhausted. If production does indeed diminish, and if water is reinjected into the reservoir, these wells theoretically possess the potential to recover their full capacity. Such mitigation strategies, involving the reinjection of spent geothermal fluids, have already been successfully implemented at several sites, demonstrating a proactive approach to resource management. The long-term sustainability of geothermal energy, when managed correctly, has been amply demonstrated by the continuous operation of the Larderello field in Italy since 1913, the Wairakei field in New Zealand since 1958, (23) and The Geysers field in California since 1960. (24)

Power station types

  • Dry steam (left), flash steam (centre), and binary cycle (right) power stations.

Geothermal power stations share a fundamental similarity with other steam turbine thermal power stations: they all utilize heat from a primary fuel source to heat a working fluid, which then drives a turbine connected to a generator to produce electricity. In the unique case of geothermal, the "fuel source" is, of course, the Earth's core itself – a rather impressive, if somewhat inaccessible, furnace. After the working fluid has done its job spinning the turbine, it is cooled and returned to the heat source, completing the cycle.

Dry steam power stations

Dry steam stations represent the simplest and, historically, the oldest design among geothermal power plants. There are relatively few power stations of this type in operation today, primarily because they demand a very specific resource: a geological reservoir that naturally produces dry steam. Despite their rarity, these stations are recognized for their high efficiency and the relative simplicity of their operational facilities. (25) At such sites, while liquid water might indeed be present within the deep reservoir, only steam, not water, is drawn to the surface for power generation. (25)

Dry steam power plants directly harness geothermal steam, typically at temperatures of 150 °C (300 °F) or higher, to rotate turbines. (3) As these turbines spin, they drive a generator, thereby producing electricity and contributing to the overall power grid. (26) Following its passage through the turbine, the steam is directed into a condenser, where it undergoes a phase change, reverting back into a liquid state. This condensed water is then cooled, often by external means, before being reinjected down a pipe into deep wells. There, it can be reheated by the Earth's natural processes and potentially produced again, forming a closed loop. A classic example of this type is The Geysers in California. However, after the initial three decades of continuous power production, the natural steam supply at The Geysers began to deplete, leading to a substantial reduction in electricity generation. To address this, a supplemental water injection program was developed and implemented throughout the 1990s and 2000s, ingeniously utilizing treated effluent from nearby municipal sewage treatment facilities to replenish the reservoir and restore some of its former capacity. (28) It seems even the Earth appreciates a good recycling program.

Flash steam power stations

Flash steam stations are significantly more common and represent a technological step up from dry steam designs. These plants operate by drawing deep, high-pressure hot water from geothermal reservoirs into lower-pressure tanks, a process that causes a portion of the hot water to "flash" or rapidly vaporize into steam. This resulting flashed steam is then channeled to drive turbines. Such systems typically require fluid temperatures of at least 180 °C (360 °F), and often substantially higher, to operate efficiently. As of 2022, flash steam stations constitute a substantial 36.7% of all geothermal power plants globally and account for an even larger share, 52.7%, of the world's total installed geothermal capacity. (29)

These plants specifically target geothermal reservoirs containing water at temperatures exceeding 180 °C. The superheated water naturally flows upwards through production wells drilled into the ground, propelled by its own immense pressure. As this water ascends, the pressure exerted upon it diminishes, causing a fraction of the hot water to instantaneously transform into steam. This steam is then mechanically separated from the remaining liquid water and directed to power a turbine/generator assembly, which then produces electricity. Any residual water and the condensed steam are typically reinjected back into the geothermal reservoir, a critical step that helps maintain reservoir pressure and makes this method a potentially sustainable resource. (30) (31) It’s a rather elegant ballet of pressure and phase change, if you’re into that sort of thing.

Binary cycle power stations

Main article: Binary cycle

Binary cycle power stations represent the most recent and, arguably, the most versatile development in geothermal electricity generation. Their key advantage lies in their ability to operate with much lower fluid temperatures, some as low as 57 °C (135 °F). (14) The operational principle is quite clever: moderately hot geothermal water is passed through a heat exchanger, where it transfers its thermal energy to a secondary working fluid. This secondary fluid is carefully chosen for its much lower boiling point than water, often an organic compound like isobutane or isopentane. The heat from the geothermal water causes this secondary fluid to rapidly vaporize, or "flash," into a high-pressure vapor, which then drives the turbines.

This innovative design ensures that the geothermal water itself never comes into direct contact with the turbine, preventing corrosive elements found in some geothermal brines from damaging machinery. This also means that binary cycle plants typically have zero emissions to the atmosphere, as the geothermal fluid is reinjected entirely back into the Earth. Consequently, this is the most common type of geothermal electricity station being constructed globally today, favored for its environmental benefits and its ability to unlock previously unexploitable lower-temperature resources. (32) Both Organic Rankine and Kalina cycles are commonly employed in these systems, each with its own thermodynamic advantages. The thermal efficiency of binary cycle stations typically ranges from about 10–13%, a modest figure but acceptable given the "free" nature of the heat source. (33) In terms of scale, binary cycle power plants exhibit an average unit capacity of 6.3 MW, considerably smaller than the 30.4 MW average for single-flash power plants, 37.4 MW for double-flash plants, and 45.4 MW for power plants operating on superheated steam. (34) This smaller average unit capacity reflects their adaptability to less intense geothermal resources, making them ideal for a broader range of geological settings.

Worldwide production

Cracks at the historic Town Hall of Staufen im Breisgau presumed due to damage from geothermal drilling A geothermal power station in Negros Oriental, Philippines Geothermal power center in the Usulután Department, El Salvador

The International Renewable Energy Agency (IRENA) has meticulously reported that a total of 14,438 megawatts (MW) of geothermal power capacity was operational worldwide by the close of 2020. This installed capacity collectively generated an impressive 94,949 gigawatt-hours (GWh) of electricity during that year. (35) In theory, the Earth's geothermal resources are so vast they could easily meet humanity's entire energy demands. However, the cold, hard truth is that only a minuscule fraction of these global geothermal resources can currently be economically exploited on a profitable basis. (36) The planet has plenty to offer; we just haven't figured out how to politely ask for it, or rather, efficiently extract it, without breaking the bank or the ground beneath our feet.

Al Gore, during his address at The Climate Project Asia Pacific Summit, famously suggested that Indonesia, with its extraordinary geological endowments, possesses the potential to become a true superpower in the realm of electricity production from geothermal energy. (37) This is hardly surprising, given its position on the highly active Pacific Ring of Fire. Following this optimistic outlook, in 2013, the publicly owned electricity sector in India announced an ambitious plan to develop the country's very first geothermal power facility. This pioneering project is slated for the landlocked state of Chhattisgarh, marking a significant step for India into the geothermal landscape. (38)

Geothermal power in Canada also holds considerable promise, primarily due to its strategic location along the aforementioned Pacific Ring of Fire. The region exhibiting the greatest potential within Canada is identified as the Canadian Cordillera, a vast mountain range stretching from British Columbia all the way into the Yukon territory. Estimates for the generating output from this region have ranged widely, from a conservative 1,550 MW to a more optimistic 5,000 MW, underscoring the significant, yet largely untapped, resource. (39)

The geography of Japan is, by nature, exceptionally advantageous for geothermal power production. The archipelago is dotted with numerous hot springs and volcanic activity, which could readily supply the necessary heat for geothermal power plants. However, despite this natural abundance, a monumental investment in Japan's existing infrastructure would be absolutely essential to fully realize and exploit this potential on a large scale. (40) It seems even the most obvious solutions require significant upfront effort and capital.

Utility-grade stations

Yearly geothermal generation by continent (41) Geothermal generation by country, 2021 (41)

The largest concentration of geothermal power plants in the world is found at The Geysers, a sprawling geothermal field nestled in California, United States. (42) This single complex has been a cornerstone of American geothermal energy for decades. As of 2021, a select group of five countries—Kenya, Iceland, El Salvador, New Zealand, and Nicaragua—distinguish themselves by generating more than 15% of their total electricity from geothermal sources. (41) These nations are, in essence, leading the charge in truly integrating Earth's internal furnace into their national grids.

The following table provides a detailed breakdown of geothermal energy production and capacity for various countries, utilizing data from the year 2021. This data, thoughtfully compiled by the Energy Information Administration (EIA), (41) includes several key metrics for each listed nation:

  • Gen (TWh): The total electricity generated from geothermal sources, measured in terawatt-hours.
  • % gen.: The percentage of that country's total electricity generation that was derived from geothermal energy, offering insight into its relative importance in the national energy mix.
  • Cap. (GW): The total installed geothermal capacity, expressed in gigawatts.
  • % cap. growth: The percentage growth in geothermal capacity, indicating recent expansion efforts.
  • Cap. fac.: The geothermal capacity factor for that year, a measure of how often the plants were actually operating at their maximum potential.

Only countries with more than 0.01 TWh of generation are included, ensuring a focus on significant contributors. Links for each location direct to their respective geothermal power pages, where available, for deeper exploration.

Country Gen (TWh) % gen. Cap. (GW) % cap. growth Cap. fac.
World 91.80 0.3% 14.67 1.7 71%
United States 16.24 0.4% 2.60 1.0 71%
Indonesia 15.90 5.2% 2.28 6.9 80%
Philippines 10.89 10.1% 1.93 0 64%
Turkey 10.77 3.4% 1.68 3.9 73%
New Zealand 7.82 18.0% 1.27 0 70%
Iceland 5.68 29.4% 0.76 0 86%
Italy 5.53 2.0% 0.77 0 82%
Kenya 5.12 43.4% 0.86 0 68%
Mexico 4.28 1.3% 1.03 0 47%
Japan 3.02 0.3% 0.48 0 72%
Costa Rica 1.60 12.6% 0.26 0 70%
El Salvador 1.58 23.9% 0.20 0 88%
Nicaragua 0.78 16.9% 0.15 0 58%
Russia 0.45 0.04% 0.07 0 69%
Papua New Guinea 0.40 8.2% 0.06 0 82%
Chile 0.33 0.4% 0.04 0 94%
Guatemala 0.32 2.2% 0.05 0 73%
Honduras 0.31 2.6% 0.04 0 91%
Germany 0.25 0.04% 0.05 15.0 62%
Portugal 0.18 0.4% 0.03 0 70%
France 0.13 0.03% 0.02 0 95%
China 0.13 0.002% 0.03 0 55%
Croatia 0.07 0.5% 0.01 0 85%

Environmental impact

The 120- MW e Nesjavellir power station in southwest Iceland

Even when you're trying to be "sustainable," there are always caveats, aren't there? Existing geothermal electric stations, particularly those that fall within the 50th percentile of all total life cycle emissions studies reviewed by the IPCC, produce a relatively low average of 45 kilograms of CO2 equivalent emissions per megawatt-hour (kg CO2 eq/MWh) of generated electricity. (43) For a stark comparison, a typical coal-fired power plant, without the benefit of carbon capture and storage (CCS), belches out a staggering 1,001 kg of CO2 equivalent per megawatt-hour. (8) (43) This makes geothermal a significantly cleaner option, though not entirely emission-free. It's also an intriguing hypothesis that since many geothermal projects are located in volcanically active areas that naturally emit greenhouse gases, these geothermal plants might actually decrease the overall rate of natural de-gassing by reducing the pressure on underground reservoirs. (44) A pleasant thought, that humanity might accidentally do something beneficial for the planet.

Stations that encounter high levels of acids and volatile chemical compounds within their geothermal fluids are typically outfitted with advanced emission-control systems. These systems are designed to meticulously scrub and reduce the release of harmful substances into the atmosphere. Furthermore, a highly effective and increasingly common practice involves injecting these non-condensable gases back into the Earth, essentially performing a form of carbon capture and storage. This method is actively employed in places like New Zealand (44) and within the innovative CarbFix project in Iceland, demonstrating a proactive approach to minimizing environmental impact.

Other geothermal facilities, such as the Kızıldere geothermal power plant in Turkey, showcase an even more impressive capability. This plant has demonstrated the ability to utilize its geothermal fluids to process captured carbon dioxide gas into dry ice at two adjacent industrial plants. This ingenious integrated process results in an extremely minimal environmental footprint, transforming a potential waste product into a valuable commercial commodity. (45)

Beyond dissolved gases, the hot water extracted from geothermal sources can also carry trace amounts of various toxic chemicals in solution. These often include elements like mercury, arsenic, boron, antimony, and various salts. (46) As the geothermal fluid cools during the energy extraction process, these chemicals can precipitate out of solution. If these substances were simply released into the environment, they could undoubtedly cause considerable ecological damage. However, the modern and widely adopted practice of reinjecting spent geothermal fluids back into the Earth, primarily to stimulate and maintain reservoir production, has the significant added benefit of mitigating this environmental risk by keeping these potentially harmful chemicals safely underground.

The sheer act of station construction and, more specifically, the extensive drilling required for geothermal projects can, at times, adversely affect local land stability. A notable instance of this occurred in the Wairakei field in New Zealand, where measurable subsidence of the land surface has been observed due to fluid extraction. (47) More dramatically, enhanced geothermal systems (EGS), which rely on injecting water at high pressure to fracture deep rock formations, have been known to trigger earthquakes. The project in Basel, Switzerland, for example, was controversially suspended after more than 10,000 seismic events, some measuring up to 3.4 on the Richter Scale, occurred within the first six days of water injection. (48) The risk of geothermal drilling leading to uplift of the ground, rather than subsidence, has also been documented, notably in Staufen im Breisgau, Germany, where significant structural damage to buildings occurred. It seems the Earth objects to being prodded too aggressively, and it makes its displeasure known.

Despite these localized issues, geothermal energy generally boasts minimal land and freshwater requirements compared to many other energy sources. Geothermal stations typically utilize only 404 square meters per gigawatt-hour (GWh) of electricity produced. In stark contrast, coal facilities demand a sprawling 3,632 square meters per GWh, and even wind farms, often lauded for their green credentials, require 1,335 square meters per GWh. (47) Furthermore, geothermal operations are remarkably parsimonious with water, consuming a mere 20 liters of freshwater per MWh. This is a fraction of the over 1000 liters per MWh typically required by nuclear, coal, or oil-fired power plants, making geothermal an attractive option in water-stressed regions. (47)

While large-scale geothermal circulation systems inherently involve the removal of heat from the Earth, leading to a theoretical local climate cooling, an estimation provided by the Leningrad Mining Institute in the 1980s concluded that any possible cool-down effect would be negligible when compared to natural climate fluctuations. (49) So, don't expect geothermal plants to solve global warming by making the planet noticeably colder.

Finally, while volcanic activity is the very source of geothermal energy, it also brings with it inherent risks. As of 2022, the Puna Geothermal Venture in Hawaii had still not fully returned to its maximum operational capacity following the devastating 2018 lower Puna eruption. (50) It's a stark reminder that even when harnessing the Earth's power, the Earth always has the last word.

Economics

One of the most compelling economic advantages of geothermal power is its independence from fuel. Unlike fossil fuel plants, which are constantly at the mercy of volatile global commodity markets, geothermal operations require no fuel purchases. This immunity to fuel cost fluctuations provides a remarkable degree of price stability and predictability, a rare luxury in the energy sector. However, this significant operational advantage is balanced by the fact that capital costs for geothermal projects tend to be notably high. A substantial portion of these initial costs, often exceeding half of the total investment, is attributed to drilling. Furthermore, the exploration for and development of deep geothermal resources inherently entails significant geological and financial risks, as successful drilling is not always guaranteed.

Consider a typical well doublet in Nevada, designed to support approximately 4.5 MW of electricity generation. The cost to drill such a system alone can reach around 10million,anditcomeswitharatherunsettling2010 million, and it comes with a rather unsettling 20% failure rate. ([22](/Geothermal_power#cite_note-22)) This means one in five expensive holes might yield nothing. In total, the combined costs for electrical station construction and the necessary well drilling typically range from 2 to 5 million euros per MW of electrical capacity. When these costs are amortized over the lifetime of the project, the [levelized energy cost](/Levelised_energy_cost) (LCOE) for geothermal electricity generally falls between 0.04 and 0.10 euros per kWh. ([10](/Geothermal_power#cite_note-10)) [Enhanced geothermal systems](/Enhanced_geothermal_system) (EGS), being at the cutting edge of technology and often targeting more challenging geological formations, tend to fall on the higher end of these ranges. In 2007, EGS projects were reporting capital costs exceeding 4 million per MW and levelized costs above $0.054 per kWh. (51) The upfront investment is steep, but the long-term benefits of a stable, domestically sourced power supply are often deemed worth the gamble.

Recent research has begun to explore the concept of in-reservoir energy storage, a fascinating development that could significantly increase the economic viability of enhanced geothermal systems. This approach is particularly relevant in modern energy systems that are increasingly integrating a large share of variable renewable energy sources like solar and wind, which fluctuate with weather conditions. (52) (53) By leveraging the thermal mass of the Earth, geothermal systems could potentially store excess energy during periods of high renewable generation and release it when demand is high or other renewable sources are unavailable. (54) This flexibility could turn geothermal plants into dispatchable power sources, providing crucial grid stability.

Geothermal power is also highly scalable, a characteristic that makes it adaptable to diverse energy needs. A relatively small geothermal power station, for instance, can be designed to reliably supply electricity to a rural village, thereby fostering local energy independence. However, it's important to remember that even for these smaller projects, the initial capital costs can still be substantial, posing a barrier to entry for communities with limited financial resources. (55)

The most extensively developed and commercially successful geothermal field globally remains The Geysers in California. As of 2008, this remarkable field was home to 15 operational power stations, all under the ownership of Calpine Corporation, collectively boasting a total generating capacity of 725 MW. (56) It stands as a testament to the enduring potential and economic viability of this ancient energy source, even if it took humanity a while to figure out how to properly tap it.

See also