Geothermal energy

Geothermal energy is thermal energy extracted from the Earth's crust. The name comes from Greek roots meaning "hot Earth."

This energy is a vital resource for heating and electricity. It is considered renewable because the heat extraction rates are insignificant compared to the Earth's total heat content. Unlike solar or wind power, geothermal plants produce power at a constant rate. They do not depend on changing weather conditions. This makes geothermal energy a very reliable source of power for the planet.

The heat inside our planet comes from two main sources. About 20% of this is residual heat from planetary accretion, which is the process of the planet's formation. The remaining heat comes from the radioactive decay of naturally occurring isotopes. For example, granite with high thorium content can power the high temperature of rock through decay.

The Earth's internal thermal energy flows to the surface by conduction. This happens at a rate of 44.2 terawatts (TW). Meanwhile, radioactive decay replenishes this heat at a rate of 30 TW. These rates are more than double humanity's current total energy consumption.

There are several ways to capture this energy. Hydrothermal systems use naturally occurring reservoirs of hot water or steam. Vapor-dominated plants, like those at Larderello, use superheated steam from temperatures between 240 and 300 °C. Liquid-dominated reservoirs (LDRs) are more common near volcanoes. Flash plants are often used with these liquid sources. In a flash plant, steam is separated from liquid via cyclone separators to drive generators.

Another method is the binary cycle power station. This uses an organic fluid to capture energy from lower temperatures. In 2006, a plant in Alaska used this to produce electricity from a record low temperature of 57 °C.

When natural water is not available, engineers use enhanced geothermal systems (EGS). This process involves injecting water to hydraulically fracture bedrock. This creates an artificial hot water reservoir.

This technology allows us to access heat in a greater geographical range. Most traditional plants are built near tectonic plate boundaries. At these boundaries, the crust is thinner and the heat is closer to the surface. This makes it easier and more efficient to extract the energy.

Humans have used geothermal heat for millennia. People used hot springs for bathing during the Paleolithic era. In the first century CE, Romans used hot springs for public baths and underfloor heating. The world's oldest geothermal district heating system has operated in France since the 15th century. Industrial use began in 1827 in Larderello, Italy, to extract boric acid. In 1904, Prince Piero Ginori Conti tested the first geothermal power generator.

It successfully lit four light bulbs. The first commercial plant followed in 1911.

The geothermal industry is a significant global economic force. As of 2019, 13,900 megawatts (MW) of geothermal power was available worldwide. The industry employed about 100,000 people in 2019. The cost of generating this power has decreased significantly. During the 1980s and 1990s, costs fell by 25%. By 2021, the US Department of Energy estimated that a new plant costs about $0.05/kWh.

This makes it an increasingly competitive energy source.

Geothermal energy provides a cleaner alternative to fossil fuels. Geothermal electric stations emit an average of 45 grams of carbon dioxide per kilowatt-hour. This is less than 5% of the emissions produced by coal-fired plants. Many countries rely heavily on this resource. Iceland, El Salvador, Kenya, the Philippines, and New Zealand all use geothermal energy for a significant share of their power. As of 2024, countries like Costa Rica and El Salvador use it to provide a large percentage of their national electricity.