Geothermal Energy

What is geothermal energy?

Geothermal energy is heat that comes from inside the earth. Geo means earth in Greek and therme means heat. Leveraging this geothermal energy, we can heat buildings and produce electricity using the heat, hot water and steam from inside the earth. Geothermal is a renewable energy source because the water is replenished by rainfall and the heat is continuously produced inside the earth.

How does geothermal energy get up to the earth’s surface?

Far below the earth’s surface (4,000 miles) in the earth’s rocky core, geothermal heat is continuously produced. This heat transfers though rocky layers and when temperatures and pressures rise enough, rock actually melts and becomes magma. The magma is lighter than the rock around it so it rises, moving gradually to the earth’s surface, bringing the heat up from below.

If the hot magma reaches all the way to the earth’s surface it emerges as lava. Usually the magma stays below the earth’s surface and heats rocks and water (rainwater that has seeped deep into the earth) that are close by. Rock and water temperatures can reach more than 700 degrees Fahrenheit. The very hot water sometimes expands and rises up through the earth via fissures. This geothermal energy reaches the earth’s surface as hot springs or geysers. Most of the water stays far below the earth’s surface trapped in subterranean layers of porous rock. These naturally occurring pools of water are called geothermal reservoirs.

How is geothermal energy used?

Geothermal energy can be tapped both near the earth’s surface and far below. Three ways this energy is harnessed are through:

1. Geothermal heat pumps, which utilize the earth’s ability to store heat in the shallow ground or water to control building temperatures above ground.  Residential geothermal energy systems
2. Electricity generation in a power plant. In order for electricity to be generated, water or steam must be very hot (300 to 700 degrees Fahrenheit) in order to power turbines. Geothermal power plants are constructed where reservoirs are close to the surface -- less than two miles below.
3. Direct Use and District Heating Systems -- Direct use means directly using the warm water, for relaxing and soothing muscles in hot springs or health spas. District heating systems pump geothermal water through a heat exchanger, where it transfers its heat to clean city water that is piped to buildings in the district. There, a second heat exchanger transfers the heat to the building’s heating system.

What are the three types of geothermal power plants?

1. Dry steam plants power generator turbines by utilizing steam coming directly from geothermal reservoirs.
2. Flash steam plants power generator turbines fueled by steam produced from high-pressure hot water found far below the earth’s surface. The steam is recycled -- once it cools and becomes water, it is put back into the ground to be reused. Flash plants are the most common geothermal power plants.
3. Binary power plants move heat from geothermal hot water to a different liquid. The heat causes the second liquid to change to steam, which powers a generator turbine.

What are the benefits of geothermal energy?

1. Geothermal energy is available all day and night, every day of the year. Geothermal power plants are ready for use more than 90% of the time where as coal plants are available only about 75% of the time.
2. It’s clean. Geothermal energy can be taken from the earth without burning fossil fuels such as gas, coal, or oil.
3. It is flexible. Geothermal power plants are modular. This makes is easy to adapt them for growth.

Is geothermal energy a renewable resource?

Geothermal energy is a renewable resource because heat is continuously produced inside the earth. If hot water is taken out of the earth’s underground reservoirs, it can be put back, making geothermal a sustainable energy source.

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