Geothermal Energy – How a Power Plant Works

Generating electricity through the use of geothermal heat is called geothermal power. Geothermal energy is captured by tapping into sources where cooler water from the surface has seeped down into Earth’s crust.

As the water goes deeper it heats up because the Earth’s center is very hot. As the water heats up it becomes hot enough to start rising to the surface. By drilling into these sources, it opens a route to the surface for the pressurized water. The geothermal power plants are built over these areas so that they can use the heated water rising to the surface.
Today, there are three types of methods to utilize the heated water. All methods use the heated water drawn from the surface. The water is then forced back down into the Earth to prolong the life of the heat source. Geothermal power is generally thought of as a renewable resource. If the water wasn’t forced back down into the Earth then the source would eventually be depleted. In the “dry steam” method, where steam is rising to the surface, the rising steam simply goes directly through a turbine and then into an area where the steam is condensed back to liquid water. In the “flash steam” method, where hot water is rising to the surface, extra machinery depressurizes or “flashes” the water into steam, which is then used to drive a turbine. The last method, the “binary” method, the hot water passes through a device called a heat exchanger. The heat from the water is transferred to a liquid that usually has a lower boiling temperature than water. The other liquid boils at a lower temperature than water, so it is easier to convert into steam to drive the turbine. This other liquid is kept in a closed loop, so it is not lost.

Geothermal power plants use the steam to drive turbines. As the steam is turning the turbine, the steam is doing work. The mechanical energy of the working steam is transferred into the rotation of the turbine. An electric generator converts the mechanical rotational energy of the turbine into electricity. The resulting electric current then runs into the power grid and is part of the electricity sent to power homes, etc. There are currently not enough geothermal power plants to provide the energy need to power a city like Las Vegas, but the plants spread across our country contribute to the powering nearly three million homes.

In the process of drawing the steam or hot water to the surface, geothermal heat is lost to the surrounding material, though not in big enough amounts to heavily effect the operation. Throughout the entire process heat is lost to the air and to the materials enclosing the liquids and the steam. The turbine is not 100% efficient at capturing and transferring energy to the electricity generator. Over all, the plant may lose potential energy because the source of heat may cool. This can be a result of the cooler water that’s being injected back into the Earth. The cooler water may reduce the temperature of the source over time. But, not injecting water back into the source would lose more potential energy because the source’s supply of water would run out. So the good and bad of injecting the water back into the water may offset each other.

Building and using geothermal power plants is very low impact. A few acres of land may be used, with some minor industrial looking buildings built on the area. Geothermal power plants generally do not expel pollutants into the air and they don’t dump the extracted water somewhere on the surface. Only “open” systems expel gases into the air and these include Hydrogen sulfide, trace amounts of arsenic and other minerals. Hydrogen sulfide is toxic and is recognizable by its rotten egg smell. This would be bad if it was expelled from all of our cars, but the amount is very little and is not a major concern. This is only a concern with a part of the geothermal power plants, not the plants using “closed” systems.
Generally the water drawn from the Earth is injected back down to resupply the source. The water usually consists of salts and minerals that would possibly interfere with the ecosystem of the surrounding area, but the water is usually injected back down. If it’s not injected, then the water wouldn’t be harmful the environment. Geothermal power plants are very low impact compared to the other forms of power production. The plants do however, cost around $100 million dollars to build, so companies don’t usually want to invest unless it’s clear that the plant will produce enough energy to be a profit. Plants that are built can produce electricity for between 4.5 and 7.3 cents per kilowatt-hour, putting them on a level of production close to that of new conventional fossil fuel power plants. Geothermal power plants are efficient and have a low environmental impact, making them good investments in the long run. Powering the entire world with geothermal power plants would greatly cut down on the production of green house gases and waste products. The planet Earth has enough geothermal sources that if tapped into with advanced technologies, we really could power the world.

Works Cited Page
• Brown, Warren (1994). Alternate Sources of Energy.
U.S.: Chelsea House Publishers

• (2007). Wikipedia:Geothermal Power. Retrieved March 1, 2007, from Wikipedia
Web site:

• Herda, D.J., & Madden, M. (1991). Energy Resources:Towards a renewable
future.U.S.: D.J. Herda and Margaret L. Madden.

• (2006). How Geothermal Energy Works. Retrieved March 1, 2007, from Union
of Concerned Scientists Web site:

• (2006). Geothermal Power. Retrieved March 1, 2007, from ArticleWorld Web