Geothermal power plants use naturally heated water from the earth to create electricity. There are three types: dry steam, flash steam, and binary cycle. Each type uses geothermal water to spin turbine blades, but in different ways. Hot dry rock thermal energy may be used in areas with hot dry rocks or low water pressure.
There are three different types of geothermal power plants: dry steam plants, flash steam plants and binary cycle plants. Geothermal power plants use naturally heated water from the earth to create electricity. This is called geothermal water. The plants use this geothermal water to spin the plant’s turbine blades. Each type of power plant accomplishes this feat in a slightly different way.
When a geothermal power plant uses steam in the same form it comes from the ground, the plant is called a dry steam plant. In dry steam geothermal power plants, wells are drilled into the rock until the reservoir is reached. Steam that reaches temperatures of 302°F (150°C) or more is then brought to the surface. Once the steam reaches the turbines, it spins the turbine blades. This generates electricity.
In flash steam geothermal power plants, water is pumped from the high pressure tank. The pressure keeps the water in a liquid state even if the temperature of the water is well above the boiling point. Once it reaches the surface, the pressure is reduced and water above 360°F (182°C) turns to steam. The steam is then used to spin the turbine blades. Water that does not turn into steam, as well as water that condenses after turning into steam, is pumped back into the tank.
Binary cycle geothermal power plants do not use water to turn the turbine blades. Rather, water with temperatures between 225-360°F (about 107.2-182.2°C) is used to heat a separate fluid that has a boiling point well below that of water. When this fluid is vaporized, the steam is used to spin the turbine blades. In this system, the water and the fluid never combine. Because these plants can use fluids with lower boiling points than water, they can make use of lower temperature geothermal water.
In areas where there are hot dry rocks or where there is not enough water pressure, a system called hot dry rock thermal energy, called enhanced energy systems in North America, may be used. In this system, two holes are drilled into the rock. The water is then pumped into the rock through a hole. The heat from the rock heats the water which is then pumped down the second hole and is used to generate electricity. The water is then pumped back into the first hole to restart the cycle.
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