Geothermal Energy

Sources of Geothermal Energy

Grand prismatic hot spring in Yellowstone National Park. Image by US National Park Service.

Less important but still considerable are two other sources of geothermal heat. Friction caused by denser rock that has cooled in the core that sinks creating frictional heat with other rock and radioactive decay of certain elements.

Geothermal Power Plants

Sometimes geothermal energy is used to provide heating and cooling to buildings or homes. This is done simply by using the Earth as a heatsink where heat can be transferred when it’s warmer outside and obtained when it’s colder. However, geothermal power is primarily used to generate electricity using power plants.

Nesjavellir Geothermal Power Plant in Þingvellir, Iceland.

Dry steam geothermal power plants use geothermal vents that release steam to directly turn turbines to generate electricity. Once this steam is used it is condensed back into water and reinjected into the water reservoir.

Flash steam geothermal power plants use geothermal water that is extremely hot and convert the water to steam that powers turbines. When this water reaches the steam vessel some of it instantly becomes steam and some of it remains water that is now colder. This cooled water bypasses the power plant and is reinjected back into the water reservoir along with the condensed steam.

Binary cycle power plants can use either steam or water because they use heat exchangers. Essentially two tubes spiral around each other, one filled with the geothermal water or steam, the other filled with a thermal working fluid (water, oil, etc). Heat from the former is transferred to the later since the two tubes are touching and the working fluid is converted to a gas which turns turbines to generate electricity.

Environmental Impact of Geothermal Energy

Geothermal energy has very minimal environmental impact. There is zero carbon dioxide or other greenhouse gas emissions from operation. The only emissions come from plant material construction like concrete, steel, etc and naturally occurring pollutants that are trapped in the geothermal reservoir which leak out when the well is drilled. Although you might see smoke stacks incorporated in geothermal power plants they are for releasing steam.

Land area used is minimal but there have been reports and studies showing that geothermal power plants can be responsible for Earthquakes and Landslides. This is due to disturbances in the local geology due to drilling of the source and reinjection wells used by geothermal plants. No major incidences have been reported with mainly small tremors being the result.