Geothermal - How It Works
Geothermal energy involves the exploitation of different grades of thermal energy stored within the earth.
In certain geological areas, heat from deep within the earth’s interior can rise up to the surface. Whenever water enters fissures in this hot rock, it can become heated and can emerge on the surface as hot springs, or even as steam, creating features such as steam vents, geysers and hot mud springs. Alternatively, heated water can be trapped below the earth’s surface as a geothermal reservoir. This heat can reach temperatures of 400°C. It can be accessed by drilling to depths of over two miles.
Ground-source heat is a different form of geothermal energy. It is extracted from the low-temperature heat (10–20°C) that is found at relatively shallow depths within the earth’s crust. This source of heat remains at a relatively constant temperature all year and can be taken from the ground itself or from groundwater. Heat pumps can increase the temperature to provide a more useful output temperature of around 40–50°C, ideal for low-temperature heating systems like under floor systems and radiant panels.
How it Works
Geothermal energy can be used directly to provide heating. Alternatively, geothermal power plants can access steam, heat or hot water from geothermal reservoirs, which can be used to turn generators and produce electricity. After the geothermal energy has been extracted from the water, the water is returned down the well into the reservoir and reheated. There are several types of geothermal power plant available, depending on the temperature and pressure of the geothermal source.
Ground-source heat pumps are not strictly a renewable source of energy, because they require electricity to extract and make use of low-grade heat. However, there is no reason why this electricity could not be generated by another form of renewable energy. Heat pumps can be very energy efficient, producing four or five times the amount of heat energy for every unit of electrical energy needed. A heat pump takes the heat from a refrigerant fluid (or water) that is in contact with the ground, extracts the heat from this source and transfers it to a heat sink where it can then be circulated through a heating system. Although the refrigerant fluid is cooled by this process, it can be re-circulated back through the ground where it will absorb more heat before being passed through the heat pump again.
Heat pumps do not produce electricity; however, they can provide heating and can be operated in reverse to provide cooling. They can be used in most kinds of building and have both domestic and commercial applications.