Feature Report: Geothermal Energy, the Earth’s Heat

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High-Temperature Geothermal Energy: Power

Medium and high-temperature geothermal energy harnesses extremely hot water and steam from beneath the Earth to generate electricity in dedicated power plants.

fr - La géothermie haute énergie : l’électricité
The geothermal power plant in Nesjavellir, near the Hengill volcano in Iceland. © WIKICOMMONS

Global Resources

Global high-temperature geothermalDescribes the technology used to tap subsurface heat to produce energy... energy resources used for powerIn physics, power is the amount of energy supplied by a system per unit time. In simpler terms, power can be viewed as energy output... generation are found in a relatively few countries, in areas characterized by volcanic activity. They are mainly located in Asia, the Pacific islands, the African Great Lakes region, North America, the Andean countries of South America, Central America and the Caribbean.  

30%: the share of geothermal power in Iceland

Around 20 countries in the world produce geothermal power, for a total installed capacityThe power generation capacity of a particular plant. It is usually expressed in megawatts (or sometimes even gigawatts)... of 10.93 GW. It plays an essential role in some countries like the Philippines, where it accounts for 17% of electricityForm of energy resulting from the movement of charged particles (electrons) through a conductor... produced, and Iceland, where it represents 30%. Global installed capacity is projected to double by 20201.

Medium-Temperature Geothermal Power Plants

Geothermal water at temperatures of 90 to 160°C can be used in liquid form to generate power; this is called medium-temperature geothermal energy.

This technology involves power plants that harness groundwater via geothermal wells. This type of power plant is built near aquifers located at depths of 2,000 to 4,000 meters. In volcanic areas (“hotspots”), where the subsurface holds more heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... , the water used by the power plants is sometimes found closer to the surface, at depths of less than 1,000 meters.

In these plants, water that has been pressurized to stop it boiling circulates through a heat exchanger. This equipment contains pipes filled with geothermal water that are in contact with pipes filled with another fluid, generally a hydrocarbonOrganic compound consisting of carbon and hydrogen. Hydrocarbons are the principal constituents of crude oil, natural gas and petroleum products. . When it comes into contact with the water-filled pipes, the fluid heats up, boils and vaporizes. The steam obtained drives a turbine that generates power. In the process, the steam cools, returning to its liquid state before being reused in another production cycle.

High-Temperature Geothermal Energy in Volcanic Areas

If the geothermal water is hotter than 160°C, it can be used directly in the form of steam to drive turbines and generate power. This is called high-temperature geothermal energy. This principle was applied as long ago as 1913 in the world’s very first geothermal power plant, in Larderello, Italy.

The very first geothermal power plant in history was built in Larderello, Italy, in 1913.

This type of power plant uses water from water tables in volcanic regions, at depths of 1,500 to 3,000 meters. On very rare occasions, the water is present in the reservoir in the form of steam. In 95% of cases, the water is liquid. The drop in pressure experienced by the liquid in the wells as it flows to the surface causes some of the liquid to become vapor. At the surface, the liquid water is separated from the dry steam in a separator. The dry steam is fed to the turbine, while the liquid water can be vaporized again by reducing its pressure even further. The residual liquid water is injected back into the reservoir.

 

Medium and high-temperature geothermal energy is used in a wide variety of applications. In industry, for example, geothermal water and steam can be used to wash and dry wool. They can also be used to manufacture pulp or treat biomassIn the energy sector, biomass is defined as all organic matter of plant or animal origin...

Source :

(1)  Géothermie Perspectives (in French only)