Geothermal energy is one of the oldest sources of energy. It is simply using and reusing (reusable energy) heat from the inside of the earth. Most of the geothermal energy comes from magma, molten or partially molten rock. Which is why most geothermal resources come from regions where there are active volcanoes. Hot springs, geysers, pools of boiling mud, and fumaroles are the most easily exploited sources. The ancient Romans used hot springs to heat baths and homes, and similar uses are still found in Iceland, Turkey, and Japan.
The true source of geothermal energy is believed to come from radioactive decay occurring deep within the earth. Electricity is one of the biggest outputs of geothermal energy. It was first recorded to produce electricity in 1904 in Italy. There are now geothermal power plants in operation in New Zealand, Japan, Iceland, the US and elsewhere. For the generation of electricity, hot water, at temperatures ranging from about 700 degrees F, is brought from the underground reservoir to the surface through production wells, and is flashed to steam in special vessels by release of pressure.
The steam is separated from the liquid and fed to a turbine engine, which turns a generator. In turn, the generator produces electricity. Spent geothermal fluid is injected back into peripheral parts of the reservoir to help maintain reservoir pressure. If the reservoir is to be used for direct-heat application, the geothermal water is usually fed to a heat exchanger before being injected back into the earth. Heated domestic water from the output side of the heat exchanger is used for home heating, greenhouse heating, vegetable drying and a wide variety of other uses.
Hot water and steam exist at many subsurface locations in the western U. S. These resources can be classified as low temperature (less than 194 degrees F), moderate temperature (194 302 degrees F), and also high temperature (greater than 302 degrees F). The uses to which these resources are applied are also influenced by temperature. If the reservoir is to be used for direct-heat application, the geothermal water is usually fed to a heat exchanger before being injected back into the earth.
Heated domestic water from the output side of the heat exchanger is used for home heating, greenhouse heating, vegetable drying and a wide variety of other uses. Hot water and steam exist at many subsurface locations in the western U. S. The highest temperature resources are generally used only for electric power generation. Current U. S. geothermal electric power generation totals approximately 2200 MW or about the same as four large nuclear power plants.
Uses for low and moderate temperature resources can be divided into two categories: direct use and ground source heat pumps. Direct use, as the name implies, involves using the heat in the water directly. This is done without a heat pump or power plant. Direct use can be used for such things as heating buildings, industrial processes, greenhouses, aquaculture (growing of fish), and resorts. Direct use projects generally use resource temperatures between 100 300 degrees F. Current U. S. stalled capacity of direct use systems totals 470 MW or enough to heat 40,000 average sized houses.
Ground-source heat pumps use the earth or groundwater as a heat source in winter and a heat sink in summer. Using resource temperatures of 40-100 degrees F, the heat pump, a device that moves heat from one place to another, transfers heat from the soil to the house in winter and from the house to soil in summer. Accurate data is not available on the current number of these systems; however, the rate of installation is thought to be between 10,000 and 40,000 per year.
Even though geothermal energy is a highly productive reusable energy source, is it not being taken advantage of nearly enough today. It ranks third on the reusable energy list behind hydroelectricity and biomass and ahead of solar and wind. Despite these impressive statistics, the current level of geothermal use pales in comparison to its potential. The key to wider geothermal use is greater public awareness, technical support, and more research and development to make geothermal energy easier to install and become a modern and widely use source of energy.
