The Basics of Geothermal Power
Using Geothermal Heat to Generate Electricity
Geothermal sources are used worldwide to generate electricity for residential and industrial use.
Geothermal power is electricity that is generated using naturally occurring underground heat sources. Deep beneath the Earth’s surface, energy is stored within the rock as heat. Generally speaking, the greater the depth beneath the surface, the higher the temperature is.
History of Geothermal Power
Naturally occurring hot springs have been used for millennia for bathing. However, geothermal sources were not used for generation of electricity until 1911, when a small generator was built in Italy. Italy was the leader in industrial geothermal power until New Zealand built a power station in 1958. The first geothermal plant in the United States was built in California in 1960. Currently, geothermal power plants exist in over 20 countries.
Converting Geothermal Energy to Create Electricity
There are three types of geothermal power plants:
- Dry Steam Plants – This method consists of pumping water down a borehole deep into the Earth, where the heat turns the water into steam. The steam rises through a second borehole and powers a steam turbine. This method relies on natural seams and fractures in the rock, or completely man-made boreholes to pass the water from the surface to the depths, and back to the surface.
- Flash Steam Power Plants – In this case, the return fluid is in the form of water with a temperature over 360 degrees F. A flash chamber is installed before the steam turbine. The super heated water is sprayed into the flash chamber, which is at a much lower pressure than the water. The water “flashes” into steam, and is then passes to the steam turbine.
- Binary Cycle Power Plants – If the return fluid has temperatures less than 400 degrees F, a binary cycle is used to convert the fluid into steam. A heat exchanger is used to transfer the energy from the hot water to a secondary fluid with a much lower boiling point. The secondary fluid is then used to power the steam turbine, and the water in this case is not directly used in the power generation process.
Benefits of Geothermal Power
Geothermal Power is clean, generating very little in the way of by-products or emissions. The hot water used for injection is reclaimed and reused, resulting in a sustainable system. Unlike solar power, geothermal power can be generated 24 hours a day, and is not dependent on environmental conditions. Geothermal power plants can be scaled to meet local need, and can provide cost-effective energy near natural geothermal sources.
Geothermal Power in Iceland
Today, Iceland is a world leader in geothermal power production. Iceland is located on a geological “hot spot”, where volcanic activity is frequent, and deep depths are not required to tap the geothermal energy. In 2005, Iceland generated over 26% of its electricity from geothermal sources. In addition, the majority of residential housing in Iceland uses geothermal methods to heat their home, rather than relying on electric, gas, or oil heating sources. Iceland also relies heavily on hydroelectric power, making it one of the countries with the least dependence on fossil fuel for electricity.
Geothermal power is a clean, renewable source of energy that is most cost-effective at locations with relatively shallow geothermal sources. Geothermal power is sustainable, and provide energy to local residents and industries for many years.
Sources
US Department of Energy Geothermal Technologies website
Energy Statistics in Iceland, Orkustufnun, 2005.
