Renewable Energy - Geothermal Energy

Geothermal energy, or heat from the earth, represents an enormous, underused heat and power resource that is clean, reliable, renewable and homegrown (less dependent on foreign oil and transportation).

Geothermal resources range from shallow ground, hot water and rock several miles below the Earth's surface, to the extremely hot molten rock called magma. Deep wells can be drilled into underground reservoirs to tap steam and very hot water that can be brought to the surface for use. In the U.S., most geothermal reservoirs are located in the western states.

Below the earth's crust, the top layer of the mantle is a hot liquid rock called magma. The crust of the earth floats on this liquid magma mantle. For every 100 m below the earth's surface, the temperature of the rock increases about 3^oC.
The heat, termed geothermal energy, can now be accessed by drilling water or steam wells in a process similar to drilling for oil.

Almost everywhere, the shallow ground or upper 10 feet of the Earth's surface maintains a nearly constant temperature between 50° and 60°F (10° and 16°C).

A geothermal or ground source heat pump system can use that constant temperature to heat or cool a building. Pipes are buried in the ground near the building. Inside these pipes a fluid, like the antifreeze in a car radiator, is circulated.

In winter, the heat pump removes heat from the heat exchanger and delivers it indoor.

In summer, the process is reversed, and heat is removed from the indoor into the heat exchanger. This heat can be used to heat household water system, swimming pools or spas.
(Pic.: Mcquay.com)

Deep under the surface, water sometimes makes its way close to the hot rock and turns into boiling hot water or into steam. The hot water can reach temperatures of more than 148^oC. It does not boil under pressure beneath the surface. (It is called a hot spring when it break through the earth surface. With volcanic eruption, magma breaks through the surface of the earth and is called lava.)

The most common utilization of geothermal energy is through hydrothermal means. In S. California, hydrothermal water is used to heat buildings during the winter. The hot water runs through miles of insulated pipes to dozens of public buildings. Use is made of for plant growth in greenhouses, for dehydrating foodstuffs, for snow melting on sidewalks in winter.

Geothermal Electricity
On a bigger scale in geothermal power plants, the steam generated by heated water is used to rotate the turbines of the generators.
California's geothermal power plants produce about 50% of the world's geothermally generated electricity. The geothermal power plants produce enough electricity for about two million homes.

California contains the largest amount of geothermal generating capacity in the US due to its geological location. In 2007, geothermal energy produced 4.5% of the state's total system power. It has 43 operating geothermal plants with capacity near 1,800 MW, about 67% of the total United States' geothermal generation.
(Photo: Energy.ca.gov)

The largest concentration of geothermal plants is located north of San Francisco in the Geysers Geothermal Resource Area in Napa and Sonoma Counties. This location has been producing electricity since the 1960s. It uses dry steam; one of only two places in the world for this resource (the other being in Larderello, Italy).

As of 2008, geothermal power supplies less than 1% of the global energy. The US has the greatest amount of geothermal energy production in the world. Geothermal systems have been in use since the late 1940s, but it wasn't till the 1970s that they became more popular as a renewable source of energy.

References and related news:

Geothermal Energy: Energyquest.ca.gov
Geothermal Basics: Eere.energy.gov
Ball State to go geothermal EnergyCurrent
Geothermal Energy in California: Energy.ca.gov

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