The 2011 Technology Roadmap Geothermal Heat and Power shows that there is potential to achieve at least a tenfold increase in the global production of heat and electricity from geothermal energy - heat emitted from within the earth's crust - between now and 2050. More »»
Geothermal power comprises mature renewable technology options that can provide base-load power from energy stored in trapped vapour and liquids. Enhanced geothermal technologies are under devlopment that would allow to greatly expand the use of this technology family beyond countries that have resources suitable for established technologies.
About geothermal energy
Geothermal energy can provide low-carbon base-load power, heat (and cooling) from high-temperature hydrothermal resources, deep aquifer systems with low and medium temperatures, and hot rock resources.
Although the use of geothermal hot springs has been known since ancient times, active geothermal exploration for industrial purposes started at the beginning of the 19th century in Italy. At the end of the 19th century, the first geothermal district heating system began operating in the US, with Iceland following in the 1920s. At the start of the 20th century, the first successful attempt to produce electricity from geothermal source was achieved. Since then, the production of electricity from geothermal has increased steadily reaching over 75 TWh in 2013.
Geothermal typically provides base-load generation, since it is generally immune from weather effects and does not show seasonal variation. Capacity factors of new geothermal power plants can reach up to 95%. The base-load characteristic of geothermal power distinguishes it from several other renewable technologies that produce variable power.
In 2012, global geothermal power capacity was 11.4 GW and generated around 72 TWh of electricity. Geothermal electricity provides a significant share of total electricity demand in Iceland (25%), El Salvador (22%), Kenya and the Philippines (17% each), and Costa Rica (13%).
For heating, geothermal resources spanning a wider range of temperatures can be used in applications such as space and district heating, spa and swimming pool heating, greenhouse and soil heating, aquaculture pond heating, industrial process heating and snow melting.
Geothermal generation and projection by region
Geothermal technologies differ in the type of resource that they use for power or heat generation. Three types of resources are: high-temperature hydrothermal resources (volcanic resources), low and medium-temperature hydrothermal resources, and hot rock.
Flash steam plants, which make up about two-thirds of geothermal installed capacity today, are used where water-dominated reservoirs have temperatures above 180°C. In these high-temperature reservoirs, the liquid water component boils, or “flashes,” as pressure drops. Separated steam is piped to a turbine to generate electricity and the remaining hot water may be flashed again twice (double flash plant) or three times (triple flash) at progressively lower pressures and temperatures, to obtain more steam.
Dry steam plants, which make up about a quarter of geothermal capacity today, directly utilise dry steam that is piped from production wells to the plant and then to the turbine. Control of steam flow to meet electricity demand fluctuations is easier than in flash steam plants, where continuous up-flow in the wells is required to avoid gravity collapse of the liquid phase.
Binary plants constitute the fastest-growing group of geothermal plants, because they are able to also use the low- to medium-temperature resources, which are more prevalent. Binary plants, using an organic Rankine cycle (ORC) or a Kalina cycle, typically operate with temperatures varying from as low as 73°C (at Chena Hot Springs, Alaska) to 180°C. In these plants, heat is recovered from the geothermal fluid using heat exchangers to vaporise an organic fluid with a low boiling point (e.g. butane or pentane in the ORC cycle and an ammonia-water mixture in the Kalina cycle), and drive a turbine. Today, binary plants have an 11% share of the installed global generating capacity and a 44% share in terms of the number of plants.
Geothermal energy can also provide heat. Even geothermal resources at temperatures of 20°C to 30°C (e.g. flood water in abandoned mines) may be useful to meet space heating demand or other low-temperature applications. Geothermal “heat-only” plants can feed a district heating system, as can the hot water remaining from electricity generation, which can also be used in applications demanding successively lower temperatures. Because transport of heat has limitations, geothermal heat can only be used where a demand exists in the vicinity of the resource
Geothermal technologies using hot rock resources could potentially enable geothermal energy to make a much larger contribution to world energy supply. Technologies that utilize hot rock resources are also known as enhanced or engineered geothermal systems (EGS). These systems aim at using the earth’s heat where no or insufficient steam/hot water is available or where permeability is low. EGS plants differ from conventional plants only as far as heat/steam extraction is concerned. EGS technology, therefore, is centred on engineering and creating large heat exchange areas in hot rock. The process involves enhancing permeability by opening pre-existing fractures and/or creating new fractures.
Conventional geothermal is a mature technology that can provide baseload power or year-round supply of heat. The resource can be exploited only in favourable regions (a constraint that can be relaxed when EGS systems are ready to be commercialised). Matching heat demand to resource availability can be difficult given the costs and difficulty of transporting heat long distances.
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