Geothermal energy is a consistent and reliable resource that is ideal for replacing baseload power sources such as polluting coal plants. Though initial development of a project can be expensive, long-term costs are extremely low. We should be investing heavily in geothermal development for our energy future.
Geothermal power, like all renewable resources, keeps economic benefits local. The most promising geothermal project sites are in rural areas. Geothermal power provides local jobs, retains dollars locally, pays local property taxes, and contributes royalties to the local county to support services. A study by the Oregon Department of Energy found that a 100 MW project in Eastern Oregon could create over a million dollars of additional local income each year, and would pay $4–6 million in local and state fees, royalties and taxes. In contrast, a similarly sized natural gas project sends $20-35 million out of the region every year for fuel costs alone.
How It Works
There are several types of geothermal power technologies. Most of the installed geothermal electrical generating plants use either flash or binary technologies. Generally, flash technologies are used when the geothermal resource has temperatures of 350°F and higher, and binary technologies are used with temperatures below 350°F. In both technologies, the geothermal fluids are returned to the underground reservoirs and naturally reheated for reuse.
In a flash steam process, (see diagram) water from underground wells is separated (flashed) into steam and water. The water is directly returned to the geothermal reservoir by injection wells, or cycled for other process or agricultural uses before re-injection. The steam is used to drive a turbine and generate electricity. Any gases in the steam are removed and, if necessary, treated to remove dissolved pollutants. The steam is cooled to liquid form and then also reinjected into the geothermal reservoir. For very high temperature resources, the water can be controlled to flash more than once to recover even more energy from the same resource.
A binary power plant is used for moderate-temperature resources. The hot water from a geothermal source is used to heat a secondary working fluid, such as ammonia or isobutane, in a closed-loop system. The working fluid is vaporized in a heat exchanger and is then used to drive a turbine-generator. A cooling system is used to condense the vaporized working fluid back into liquid form to begin the process again. The hot water from the geothermal resource is injected back into the reservoir. The hot water and the working fluid are kept separate, so that environmental issues are minimal.
Underground Natural Energy