Geothermal Energy is thermal energy that comes directly from the heat of the earth. The word geothermal comes from the Greek word “γη”, which means earth and from the Greek word “θερμός”, which means hot. The heat from the earth is then used in the form of steam or hot water to heat buildings or produce electricity. Geothermal energy is considered a renewable green source of energy because the ‘fuel’ (i.e. the heat of the earth) that is used is practically unlimited.
For the commercial production of electricity from geothermal energy a geothermal reservoir is necessary that will provide hot water and steam resources that is required for the production of electricity. A geothermal reservoir is a large area where natural geothermal resources are found. For the commercial production of electricity high temperature reservoirs (with temperatures above 302oF/150oC) that are located close to the surface (1 – 2 miles from the surface) are more suitable. These places are usually found in areas near the tectonic places where there is also high volcano activity.
There are three different types of geothermal power plants commonly used for the commercial generation of electricity:
- The dry steam systems use the steam from a geothermal reservoir in order to turn the turbines that generate electricity.
- The flash steam systems are the most common type of geothermal power systems. They use the high pressure hot water from a geothermal reservoir and convert it to steam in order to turn turbines that generate electricity. When the steam used to generate electricity cools down it turns into water. The water is then sent back to the earth in order to be reused.
- The binary cycle systems transfer the heat from the reservoirs hot water to another liquid. This other liquid is then turned into steam which in turn is used to turn the turbines that generate electricity.
Geothermal energy can also be used for home use and particularly for heating purposes. In this case Geothermal Heat Pumps are used in order to extract the heat out from the earth and into the house. In order to heat a house, the heat pump pipes are inserted into the ground taking advantage of the ground’s constant temperature throughout the year. Then the special liquid that flows through the pipes is warmed up, thus taking the warmer temperature into the house. The heat pump extracts the heat which is then used to warm the house. The colder liquid then flows down to the ground through the closed circulation pipes in order to be warmed again. Geothermal energy systems for home use can be used in most regions of the earth since they do not require the high temperatures required for the commercial use. It is estimated that they can save up to 70% of the heating costs of a house.