Geothermal energy has been utilized for thousands of years for heating and bathing, but it was not until the early years of the twentieth century that scientists began experimenting with the use of geothermal power for generating electricity. Since the first few light-bulbs were powered by geothermal electricity in 1904 the technology has flourished, becoming an important area of research particularly as we become more aware of our unsustainable reliance on fossil fuels. Because geothermal energy is sustainable if managed properly, many believe that it could be the key to our present energy crisis.
Geothermal energy is a blanket term which includes energy that is generated from heat under the ground and from heat sourced from the air and oceans. Under-ground sources of heat are the most commonly used solely because they are economically and technologically simpler to harvest.
The science is simple - two bore-holes are drilled deep into the Earth's surface where it has been established that there are significantly high temperatures. Down one bore-hole water is pumped at high pressure until it reaches the high-temperature zone, at which point it converts into boiling water and steam and rises back to the surface through the second bore-hole. Upon reaching the surface the water and steam are converted into electricity through the use of a turbine. This technique is known as 'hot dry rock geothermal energy generation'.
Efficient geothermal power plants will recycle the water received on the surface, pumping it back down the first bore-hole to repeat the cycle. In some areas where there is a significant source of heat the ground may prevent the effective transfer of water and heat naturally; if this is the case it has become standard to inject the drilled holes with water laced with chemicals (usually acid) to enhance the ground's permeability. This is known as an Enhanced Geothermal System and there are a number of these plants under construction or already online.
Concerns And Benefits
There are a number of concerns regarding geothermal energy, though unusually for electrical generation techniques none concern carbon emissions. Some scientists believe that the mismanagement of areas utilized for their heat can result in a cooling of the ground which may in turn have implications for the surrounding environment. Though supporters of the technology argue that this would only occur if too much water was pumped into the ground (effectively exhausting the energy potential of the heat source and thus cooling the area, much like putting out a fire), others suggest that this potential issue prevents geothermal energy from being classed as truly 'renewable'.
Another major concern is that the injection of water into the ground can cause instability, as was the case in Basel in Switzerland when water injection was believed to be the cause of an earthquake in December of 2006. These risks are countered by the single biggest benefit of the technology, however - geothermal electricity generation is clean, generating less than one percent of the carbon emissions that fossil fuel power-plants do.