These plants generate electrical power using geothermal energy. The plant types include; Dry steam power stations, flash steam power stations and binary cycle power stations. This electric generation type is currently used in 26 countries. Statistics show that worldwide generation capacity of geothermal plants amount to 12.8 gigawatts and projected to reach 18 gigawatts by 2020. Geothermal power is considered to be sustainable and renewable source of energy because the heat extraction is small compared to the heat’s content. The amount of greenhouse emissions is small compared to coal fired and other power plants.
Geothermal power stations are similar to other steam turbine thermal power stations in that heat from a fuel source(in this case the Earth’s core) is used to heat water or other working fluid. The working fluid is then used to turn a turbine of a generator producing electricity.
Types of Geothermal plants
1. Dry Steam Power Stations
They are the simplest and oldest design. This type is not often found, but is the most efficient. This system may have a liquid reservoir but steam is used as the working fluid. This plant uses dry steam of 150 deg Celsius to turn the turbines connected to a generator. As the turbines rotate, electricity is generated. The steam then moves to a condenser where it is cooled to liquid form and recirculated back into the system to continue the process.
Flash Steam Power Stations.
These stations move deep high pressure hot water into low pressure tanks and use the resulting flashed steam to drive turbines. They require temperatures of at least 180 degree Celsius or more. This type is most commonly used today. In this power plant the hot water flows up through wells in the ground under its own pressure. As it flows upward the pressure decreases and some of the hot water boils into steam. The steam then separates from the water and is used to drive the turbine which causes the generator to produce electricity.
Binary Cycle Power Stations
These power station types are the most recent technology. They can accept fluid temperatures as low as 57degree Celsius. The hot geothermal water is passed by a secondary fluid with a much lower boiling point then water. This causes the secondary fluid to flash vapourize and drive the turbine. This is the most common type being constructed today and has a thermal efficiency of 10-13%.