Geothermal energy is a very efficient resource for heating and cooling buildings, drying agricultural products, and processing heating for industry. However, according to the Encyclopedia Britannica, one of the biggest problems in using geothermal energy is extracting it. To obtain geothermal power efficiently, heat energy must be concentrated in a small area. This may be done by underground reservoirs of hot water or steam that can be funneled into a drill hole. The mass transfer of heat from deeper levels to the near surface by volcanism is the most effective way to achieve this concentration.
Geothermal energy is used best in the generation of electricity.
In geothermal power plants, hot water is turned into steam, which is then used to power a turbine. The mechanical energy from the turbine is then converted to electricity by a generator. Another source of geothermal energy is hot and dry, sub-surface rocks. This may only be used when the problems of circulating water through them for heating and conversion to steam are resolved. The U.S. Department of Energy has a Geothermal Energy Technical Site that goes into great detail on the growth of the Geothermal industry.