Geothermal Energy
Example of Geothermal Energy
When you see a hot springs or a geyser, you are witnessing hot geothermal water which has absorbed heat from the rocks and come up through the faults and cracks to reach the earth's surface. When the water remains under the earth's surface, it is called a geothermal reservoir. Geologists, geochemists, drillers, and engineers often explore to find underground areas that have these reservoirs. Wells can be drilled into the reservoirs and carry the water to the surface. This water can be used to generate electricity in geothermal power plants.
How Does it Work?
A geothermal power plant is a facility where the steam, heat, or hot water from the reservoir is the energy to spin a turbine which generates and produces electricity. When the plant is finished with this gift of heat from the underground, it returns the geothermal water to the reservoir through an injection well.
There are three types of geothermal power plants: dry, hot and binary.
A dry steam reservoir is a source of steam but very little water.
A hot water reservoir generates mostly hot water. The hot water is between 300-700 degrees F. It arrives at the surface through a production well. At the time of the water's release from the pressure of the reservoir below and from the well, some of the water "flashes" into steam in a separator. The steam released then drives the turbines.
A binary power plant passes the geothermal water through a heat exchanger. In the exchanger, the heat is transferred into a second (binary) liquid which is then heated and it flashes into vapor. The vapor is changed back into a liquid and used to flash into vapor again and again.
Iceland, which sits above a rift in the earth's crust, is a good example of a country that has exploited the vast geothermal reservoirs beneath it. The country gets much of its energy from the reservoirs and its geothermal power plants.
In certain western states such as New Mexico and Arizona, natural hot springs are tapped for their medicinal and therapeutic value (and for the tourism dollar!)
Does it Make Sense For the Average Homeowner?
Even if the geothermal water you are above is not as hot as it needs to be to generate electricity, geothermal waters that range from 50 degrees F to over 300 degrees F can be used directly to make our lives better and more energy efficient. These waters are being tapped for the following purposes:
- Help grow flowers, vegetables, and other crops in greenhouses
- Shorten the time to grow fish, shrimp, abalone, and alligators to maturity in aquaculture
- Heat and cool home and businesses when combined with Geothermal heat pumps
Geothermal Energy as an Alternative Home Energy Source
Not all of us are located above a fault or rift in the earth's crust, where the geothermal activity is very accessible. We are, however, able to access the ground temperature (just under the earth's surface) wherever we are, employ a geothermal heat pump, and heat and cool buildings. Geothermal heat pumps take advantage of the fact that ground temperatures everywhere are fairly constant. They range from 45 degrees F to 75 degrees F, and stay at that temperature throughout the year. Therefore, the temperature just below the earth's surface is warmer than the air above it during the winter and cooler than the air above it in the summer.
Geothermal heat pumps let us exchange the heat that is just below the ground's surface through a heat exchanger. These are also called geoexchange systems. The exchanger employs a continuous loop of water (or other liquid) circulating in pipes buried underground. The pipes are located next to the building or house which we want to heat or cool. The heat exchanger transfers the ground's temperature to the circulating water in the loop and carries it to the house. An indoor geoexchange system then uses electrically-driven compressors and heat exchangers in a vapor compression cycle to integrate this heat/cool into the building's heating/cooling systems.
Geothermal heat pumps are economical
Consumers give geothermal heat pumps rave reviews. They produce comfortably warm air, even when it is a bitterly cold winter day. Operating costs are very low. Early users were the more affluent, but geothermal heat pump use is widespread now. Low operating costs make up for the cost of installation within a few years. Estimations are that you can save 30-70 percent in heating costs and 20-50 percent in cooling costs by the use of a geothermal heat pump.
More than 300,000 homes, schools, and offices in the U.S. are using geothermal heat pumps (GHPs). Some models of geothermal heat pumps come with two-speed compressors and variable fans for more comfort and energy savings.
Pros and Cons
As in any alternative energy source, there are pros and cons to geothermal energy.
Pros: Geothermal systems do double duty. They can do the work of a furnace and an air conditioner. Since you can place the heat exchangers indoors (because outside air is not what is exchanged) they can be installed in a basement or attic. They are so compact that some fit on a top closet shelf. Geoexchange systems are quiet and economical. They are increasingly popular as a heating or cooling system.
Because geoexchange systems do not need to create heat, they use no natural gas, propane, or fuel oil. Thus, they provide clean energy.
Installation of the system is an initial significant expense, but this will be made up eventually in low operating costs.
Cons: Installation costs are high.
The system requires some land, especially if you are considering a horizontal loop.
Geoexchange systems that are too large waste energy. The actual system must be built to generate within 15& of the calculated load.
To learn more about geothermal heat pumps, visit eere.energy.gov
