williams geosciences department home credits copyright williams college contact
green energy basics local green energy projects special features related websites
geothermal energyhydroelectric energyhydrogen energysolar energywind energybiomass energyocean energy
Geothermal Energy

Geothermal Electricity Production: electricity from the earth’s heat

1. Most power plants use steam to rotate a turbine and activate a generator
2. Fossil fuels used to boil water and produce steam
3. Geothermal energy uses hot water from reservoirs below the earth’s surface
4. Three types: Dry Steam, flash steam, and binary cycle
a. Dry Steam: Steam directly pumped from underground to power plant
b. Flash Steam: Use geothermal reservoirs of water under great pressure and temperature
i. Pressure allows the water to reach high temperature without evaporating
ii. Hot water rises to surface and as pressure decreases steam forms
iii. Stream used to turn turbine and activate generator and water allowed to condense and reinjected into reservoir
c. Binary Cycle: Use warm water to heat another liquid that boils at a lower temperature and the gas is used to turn a turbine and activate a generator
i. Water reinjected into reservoir; geothermal water does not come into contact with power plant
5. NREL Research in geothermal Energy (http://www.nrel.gov/geothermal/)

Geothermal Direct Use: Produce heat from hot water within the earth

1. Well drilled into geothermal reservoir provides a constant stream of warm water
2. Water distributed at the surface for different uses
a. Provide heating for buildings and greenhouses, for pasteurization or to dry crops,
3. Water then returned to geothermal reservoir or disposed of at surface
4. In U.S, most plants located in West, Alaska, and Hawaii

Geothermal Heat Pumps: Use shallow ground to heat and cool buildings

1. Ground temperature ten feet (3 meters) below surface remains fairly constant throughout year
2. During the summer, ground is usually cooler than the air; in winter ground is usually warmer than air
3. Three Parts: Ground Heat Exchanger, Heat Pump System, Air Delivery System
a. Heat Exchanger: System of fluid filled pipes buried in the shallow ground that either absorb or dissipate heat into the ground
b. Heat Pump System: Blows air warmed or cooled by heat exchanger into building
i. In winter, air heated by heat exchanger brought into the building by using the Air Delivery System
ii. In summer, fluid in heat exchanger heated by air in building and then heat dissipated in the ground
iii. This heat from the building can also be used to heat water
Reference: http://www.eere.energy.gov/RE/geothermal.html

Click here to visit geothermal energy photo gallery.