Geothermal power

In the 20th century, demand for electricity led to the consideration of geothermal power as a generating source. Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904 in Larderello, Italy. It successfully lit four light bulbs. Later, in 1911, the world's first commercial geothermal power station was built there. Experimental generators were built in Beppu, Japan and the Geysers, California, in the 1920s, but Italy was the world's only industrial producer of geothermal electricity until 1958. at Wairakei-Tauhara has been an issue in a number of formal hearings related to environmental consents for expanded development of the system as a source of renewable energy. The original turbine lasted for more than 30 years and produced 11 MW net power. An organic fluid based binary cycle power station was first demonstrated in 1967 in the Soviet Union Demonstration projects are operational in Landau-Pfalz, Germany, and Soultz-sous-Forêts, France, while an earlier effort in Basel, Switzerland was shut down after it triggered earthquakes. Other demonstration projects are under construction in Australia, the United Kingdom, and the United States of America. The thermal efficiency of geothermal electric stations is low, around 7 to 10%, because geothermal fluids are at a low temperature compared with steam from boilers. By the laws of thermodynamics this low temperature limits the efficiency of heat engines in extracting useful energy during the generation of electricity. Exhaust heat is wasted, unless it can be used directly and locally, for example in greenhouses, timber mills, and district heating. The efficiency of the system does not affect operational costs as it would for a coal or other fossil fuel plant, but it does factor into the viability of the station. In order to produce more energy than the pumps consume, electricity generation requires high-temperature geothermal fields and specialized heat cycles. Because geothermal power does not rely on variable sources of energy, unlike, for example, wind or solar, its capacity factor can be quite large – up to 96% has been demonstrated. However the global average capacity factor was 74.5% in 2008, according to the IPCC. ==Resources==

The Earth's heat content is about 1 E31 J|. and is replenished by radioactive decay at a rate of 30 TW. These power rates are more than double humanity's current energy consumption from primary sources, but most of this power is too diffuse (approximately 0.1 W/m2 on average) to be recoverable. The Earth's crust effectively acts as a thick insulating blanket which must be pierced by fluid conduits (of magma, water or other) to release the heat underneath. Electricity generation requires high-temperature resources that can only come from deep underground. The heat must be carried to the surface by fluid circulation, either through magma conduits, hot springs, hydrothermal circulation, oil wells, drilled water wells, or a combination of these. This circulation sometimes exists naturally where the crust is thin: magma conduits bring heat close to the surface, and hot springs bring the heat to the surface. If a hot spring is not available, a well must be drilled into a hot aquifer. Away from tectonic plate boundaries the geothermal gradient is 25 to 30 °C per kilometre (70 to 85 °F per mile) of depth in most of the world, so wells would have to be several kilometres deep to permit electricity generation. Wells drilled to depths greater than generally incur drilling costs in the tens of millions of dollars. and at the Geysers field in California since 1960. ==Power station types==

Geothermal power stations are similar to other steam turbine thermal power stations in that heat from a fuel source (in geothermal's case, the Earth's core) is used to heat water or another working fluid. The working fluid is then used to turn a turbine of a generator, thereby producing electricity. The fluid is then cooled and returned to the heat source. Dry steam power stations Dry steam stations are the simplest and oldest design. There are few power stations of this type, because they require a resource that produces dry steam, but they are the most efficient, with the simplest facilities. At these sites, there may be liquid water present in the reservoir, but only steam, not water, is produced to the surface. As the turbine rotates it powers a generator that produces electricity and adds to the power field. Then, the steam is emitted to a condenser, where it turns back into a liquid, which then cools the water. After the water is cooled it flows down a pipe that conducts the condensate back into deep wells, where it can be reheated and produced again. At The Geysers in California, after the first 30 years of power production, the steam supply had depleted and generation was substantially reduced. To restore some of the former capacity, supplemental water injection was developed during the 1990s and 2000s, including utilization of effluent from nearby municipal sewage treatment facilities. Flash steam power stations Flash steam stations pull deep, high-pressure hot water into lower-pressure tanks and use the resulting flashed steam to drive turbines. They require fluid temperatures of at least , usually more. As of 2022, flash steam stations account for 36.7% of all geothermal power plants and 52.7% of the installed capacity in the world. Flash steam plants use geothermal reservoirs of water with temperatures greater than 180 °C. The hot water flows up through wells in the ground under its own pressure. As it flows upward, the pressure decreases and some of the hot water is transformed into steam. The steam is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam may be injected back into the reservoir, making this a potentially sustainable resource. Binary cycle power stations Binary cycle power stations are the most recent development, and can accept fluid temperatures as low as . The moderately hot geothermal water is passed by a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to flash vaporize, which then drives the turbines. This is the most common type of geothermal electricity station being constructed today. Both Organic Rankine and Kalina cycles are used. The thermal efficiency of this type of station is typically about 10–13%. Binary cycle power plants have an average unit capacity of 6.3 MW, 30.4 MW at single-flash power plants, 37.4 MW at double-flash plants, and 45.4 MW at power plants working on superheated steam. ==Worldwide production==

presumed due to damage from geothermal drilling , Philippines , El Salvador The International Renewable Energy Agency has reported that 14,438 MW of geothermal power was online worldwide at the end of 2020, generating 94,949 GWh of electricity. In theory, the world's geothermal resources are sufficient to supply humans with energy. However, only a tiny fraction of the world's geothermal resources can at present be explored on a profitable basis. Al Gore said in The Climate Project Asia Pacific Summit that Indonesia could become a super power country in electricity production from geothermal energy. In 2013 the publicly owned electricity sector in India announced a plan to develop the country's first geothermal power facility in the landlocked state of Chhattisgarh. Geothermal power in Canada has high potential due to its position on the Pacific Ring of Fire. The region of greatest potential is the Canadian Cordillera, stretching from British Columbia to the Yukon, where estimates of generating output have ranged from 1,550 MW to 5,000 MW. The geography of Japan is advantageous for geothermal power production. Japan has numerous hot springs that could provide fuel for geothermal power plants, but a massive investment in Japan's infrastructure would be necessary. Utility-grade stations , Iceland, El Salvador, New Zealand, and Nicaragua) generate more than 15% of their electricity from geothermal sources. Only includes countries with more than 0.01 TWh of generation. Links for each location go to the relevant geothermal power page, when available. ==Environmental impact==

Nesjavellir power station in southwest Iceland Existing geothermal electric stations that fall within the 50th percentile of all total life cycle emissions studies reviewed by the IPCC produce on average 45 kg of equivalent emissions per megawatt-hour of generated electricity (kg eq/MWh). For comparison, a coal-fired power plant emits 1,001 kg of equivalent per megawatt-hour when not coupled with carbon capture and storage (CCS). Stations that experience high levels of acids and volatile chemicals are usually equipped with emission-control systems to reduce the exhaust. Geothermal stations can also inject these gases back into the earth as a form of carbon capture and storage, such as in New Zealand In addition to dissolved gases, hot water from geothermal sources may hold in solution trace amounts of toxic chemicals, such as mercury, arsenic, boron, antimony, and salt. These chemicals come out of solution as the water cools, and can cause environmental damage if released. The modern practice of injecting geothermal fluids back into the Earth to stimulate production has the side benefit of reducing this environmental risk. Station construction can adversely affect land stability. Subsidence has occurred in the Wairakei field in New Zealand. Enhanced geothermal systems can trigger earthquakes due to water injection. The project in Basel, Switzerland was suspended because more than 10,000 seismic events measuring up to 3.4 on the Richter Scale occurred over the first 6 days of water injection. The risk of geothermal drilling leading to uplift has been experienced in Staufen im Breisgau. Geothermal has minimal land and freshwater requirements. Geothermal stations use 404 square meters per GWh versus 3,632 and 1,335 square meters for coal facilities and wind farms respectively. While volcanic activity produces geothermal energy, it is also risky. the Puna Geothermal Venture has still not returned to full capacity after the 2018 lower Puna eruption. ==Economics==

Geothermal power requires no fuel; it is therefore immune to fuel cost fluctuations. However, capital costs tend to be high. Drilling accounts for over half the costs, and exploration of deep resources entails significant risks. A typical well doublet in Nevada can support 4.5 MW of electricity generation and costs about $10 million to drill, with a 20% failure rate. In total, electrical station construction and well drilling costs about 2–5 million € per MW of electrical capacity, while the levelised energy cost is 0.04–0.10 € per kWh. Research suggests in-reservoir storage could increase the economic viability of enhanced geothermal systems in energy systems with a large share of variable renewable energy sources. Geothermal power is highly scalable: a small power station can supply a rural village, though initial capital costs can be high. The most developed geothermal field is the Geysers in California. In 2008, this field supported 15 stations, all owned by Calpine, with a total generating capacity of 725 MW. ==See also==