In order to understand why geothermal energy is considered an environment friendly alternative to fossil fuel, you must first be familiar with the basic workings of this technology. So how does geothermal energy work?
First of all, geothermal energy can be used in a variety of ways. There are those who utilize the heat directly for home heating (and even cooling) systems. Others use them in greenhouses, fish farms, and spas. Of course, I haven’t forgotten its most celebrated application – to produce electricity.
Thus, in answering the question, “How does geothermal energy work?”, one must first specify the specific application of the energy.
For those applications which utilize geothermal energy directly like those in fish farms, spas, and greenhouses, hot spring water is simply tapped from underneath the ground surface and redirected into these facilities.
The hot water may get its heat from magma that is able to creep upward and heat its surroundings, including the groundwater there. Magma doesn’t have to contribute heat directly though, as this melted mantle material can be found very deep underground and hence difficult to gain access to.
In some cases, where magma isn’t found in the direct vicinity, you can still obtain hot water by simply drilling deep in the ground. Always remember that the deeper you drill, the hotter the temperature gets.
Geothermal energy used to power household room heaters are extracted from the ground (not through water). During winter, ground underneath the surface is warmer than the temperature above. Heat is then extracted by using geothermal heat pumps. A typical geothermal heat pump extracts heat through a series of pipes containing either circulating water or an antifreeze solution, just like a refrigerator or an air conditioning unit.
Now for the last application mentioned earlier. How does geothermal energy work in the case of geothermal power plants?
Just like most power plants (e.g. hydro and wind power), energy is converted to electricity through the use of turbines. There are three ways of doing this.
One method directs hot steam drawn from underground into the turbine. Another draws extremely hot water from underneath, flashes it into steam, which is then directed to the turbine. The third method makes use of a heat exchanger to transfer heat from hot water drawn from underground unto a fluid (isobutane is commonly used) that is directed to the turbine.
In all three methods, the turbine is responsible for converting the kinetic energy of the directed fluid (which makes it turn) into electricity.
Universe Today has some interesting topics related to geothermal energy which you might be interested in. Here are two of them:
Geothermal Heat
Geothermal Heating
You can find more information about geothermal heat pumps from the US Department of Energy as well on the Energy Star website.
Tired eyes? Perhaps you’d like to listen to some Astronomy Cast episodes instead:
Volcanoes, Hot and Cold
Space Elevators
Sources:
http://www.ucsusa.org/clean_energy/technology_and_impacts/energy_technologies/how-geothermal-energy-works.html
http://science.howstuffworks.com/environmental/energy/geothermal-energy.htm
http://en.wikipedia.org/wiki/Geothermal_energy
http://www.eia.gov/kids/energy.cfm?page=geothermal_home-basics