Geothermal energy
Geothermal energy is heat within the earth. It is a renewable energy source because heat is continuously produced inside the earth1.
The earth has four layers: the inner core, the outer core, a mantle of magma and rock sorrounding the outer core and a crust of solid rock that forms the continents and ocean floors. Temperatures in the mantle range from 392°F to 7,230°F depending on the closeness to the inner core. The inner core is believed to be about 10,800 degrees Fahrenheit (°F), which is as hot as the sun. Rocks and water absorb heat from magma deep underground2.
Wells, ranging from a few feet to several miles deep, are drilled into underground reservoirs to tap steam and very hot water that can be brought to the surface of the earth to generate electricity3. The method through which electricity is generated depends on the type of geothermal power plant being used. There are three main types: dry steam, flash steam and binary cycle4.
Dry steam power plants directly use steam from geothermal reservoirs to turn turbines, which generate electricity.
Flash steam plants, which are the most common today, bring high-pressure water (over 182°C) from underground into lower-pressure tanks. This makes the water flash into vapor, which turns the turbines to produce electricity. Any remaining liquid in these lower-pressure tanks is flashed into a second tank to extract more energy.
Binary cycle power plants use moderate-temperature geothermal water (below 150°C ) that passes through a heat exchanger. The heat is transferred to a secondary fluid that has a lower boiling point which vaporizes and drives a turbine. This type of power plant is effective in areas that have low temperatures.
In 2023, the 10 leading countries in terms of geothermal installed capacity were United States (3,900 MW), Indonesia (2,418 MW), Philippines (1,952 MW), Turkey(1,691 MW), New Zealand(1,042 MW), Kenya(985 MW), Mexico (976 MW), Italy (916 MW), Iceland (754 MW) and Japan (576 MW)5.
Kenya is currently the leading nation in geothermal energy development in Africa6. Approximately 45 % of total electricity production in the country comes from geothermal energy (Rotich et al., 2024). Kenya is home to the Great Rift Valley which hosts vast geothermal resources, mainly at Olkaria. KenGen7 owns and maintains five geothermal power stations at Olkaria, Olkaria I, Olkaria II, Olkaria IV, Olkaria 1 unit 4 and 5, Olkaria V and Olkara I unit 6. In addition to the power stations, KenGen owns fifteen well heads generation plants in Olkaria and one at Eburru. These geothermal powerplants have a combine capacity of 799MW8.
As of 2022, Turkey was the leading country in geothermal energy installations in Europe, with a capacity of 1,691.29 MW9. The country had 63 plants on 27 geothermal fields, with almost all the power plants being on the south or east of Izmir, which is Turkey’s largest city.
In the article ‘Why can’t we use geothermal everywhere?’10, the secretary general of the European Geothermal Energy Council, Dumas, highlights three barriers to geothermal installation in Europe. The first one is physical space, especially in the urban areas. With residential buildings, schools, parks etc surrounding us, there’s no space to install heat-pumps and larger district-size geothermal heating systems, technologies which are necessary to extract geothermal energy. The second one is investment cost. He notes that even though operational costs in the long run are basically zero, geothermal energy is capital intensive, compared to other sources of energy. The third issue he points out is lack of public awareness of the use of geothermal energy in major European cities.
The Earth’s interior heat is continuously created making geothermal energy a dependable and steady energy source. It produces no greenhouse gases or air pollution, making it a clean and eco-friendly energy source 11.
Next: Biofuel energy
References
Footnotes
Remember a renewable energy source is one that is constantly replenished and can never run out.↩︎
TOP 10 countries with the highest installed geothermal power generation capacity in 2023↩︎
Kenya Electricity Generating Company PLC (KenGen), is a government enterprise in the Republic of Kenya charged with the production of electricity for the country. KenGen is the largest electric power producer in Kenya, generating over 60% of the electricity consumed in the country.↩︎
The potential of geothermal energy in Africa: A sustainable solution for power generation↩︎