Geothermal Energy - Power Source that is Clean, Reliable and Homegrown

Types of Geothermal Power Plants
Dry Steam Geothermal Power Plants
Flash Steam Geothermal Power Plants
Binary-Cycle Geothermal Power Plants
The Direct Use of Geothermal Energy
Geothermal Heat Pumps

The core of the Earth which is 4,000 miles below the surface, can reach temperatures of 9000°F. This generated heat is known as geothermal energy. Geothermal energy radiates outwards from the core and heats the surrounding areas. The potential of geothermal energy in the uppermost 6 miles of the Earth's crust amounts to 50,000 times the energy of all oil and gas resources in the world.

Types of Geothermal Power Plants

Geothermal power plants convert hydrothermal fluids to electricity. Three geothermal power plant technologies are used to convert hydrothermal fluid to electricity. The type of conversions used is dependent on the state and temperature of the fluid. The conversion technologies are binary cycle, dry steam and flash steam.

Dry Steam Geothermal Power Plants

Dry steam geothermal power plants are considered to be the oldest type of geothermal power plants. Dry steam geothermal power plants use steam that enters directly to a turbine from a geothermal reservoir. The steam then drives a generator and electricity is produced. Excess steam and very small amount of gases are released by dry steam geothermal power plants.

Figure 1. Illustration of a dry steam geothermal power plant. (Source: Dept. of Energy)

Flash Steam Geothermal Power Plants

The most common type of geothermal power plants is flash steam geothermal power plants. Flash steam geothermal power plants use hydrothermal fluids at temperatures above 182°C to generate electricity. Hydrothermal fluid is sprayed into a tank which is held at a much lower pressure than the hydrothermal fluid. This pressure difference causes some of the hydrothermal fluid to flash or rapidly vaporize. Electricity is produced by the vapors driving a turbine, which in turn drives a generator. More energy can be extracted if any hydrothermal fluid remains as it can be flashed again in a second tank.

Figure 2. Illustration of a flash steam geothermal power plant. (Source: Dept. of Energy)

Binary-Cycle Geothermal Power Plants

Binary-cycle geothermal power plants are different to dry steam and flash steam geothermal power plant in that steam from a geothermal reservoir never comes into contact with the turbine or generator.

Binary-cycle geothermal power plants extract energy from moderate-temperature fluids that can be found in most geothermal areas. Hot geothermal fluid together with a secondary fluid is passed through a heat exchanger. Any fluid with a boiling point lower than water can be used as the secondary fluid. Heat from the geothermal fluid causes the secondary fluid to flash and turns into vapor, which then drives the turbines to produce electricity. Since the binary-cycle geothermal power plant is a closed-loop system, nothing is emitted to the atmosphere. Moderate-temperature water is the more common geothermal resource, and future geothermal power plants will employ the binary-cycle system.

Figure 3. Illustration of a binary-cycle geothermal power plant. (Source: Dept. of Energy)

The Direct Use of Geothermal Energy

Direct heat for commercial, industrial and residential can be provided by geothermal reservoirs of low to moderate temperature water. Substantial savings can be achieved in homes and businesses through the direct use of geothermal energy. Direct use of geothermal energy is also very clean and produces a very small percentage of the air pollutants emitted by burning fossil fuels.

Geothermal Heat Pumps

Also known as the ground source heat pump, geothermal heat pump can be considered as a highly efficient renewable energy technology. Geothermal heat pump is gaining wide acceptance for both commercial and residential buildings. Geothermal heat pumps are used for space heating and cooling, and for water heating. One of the biggest advantages of geothermal heat pump is that it works by concentrating naturally existing heat, instead of producing heat through the burning of fossil fuels.

Source: AZoCleantech
Last update 20th April 2008

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