Two of the most important geothermal energy advantages are that this source of energy is both extremely clean and sustainable. Geothermal energy is natural heat from within the earth. Heat is constantly produced in the "magma" layer beneath the earth's crust, which consists of hot molten rock. Tapping into this natural, permanently available source of heat is a sustainable alternative to generating heat and energy by burning coal and other fossil fuel energy sources.
The key geothermal energy advantage of cleanliness depends on how the geothermal energy is tapped. To maximize the environmental friendliness of the energy source, it is important for the geothermal energy system to be built with care, as some systems do leak out air borne pollutants, in particular hydrogen sulfide. In the "cleanest" geothermal systems, all the steam, air, and gases that are used are subsequently returned to the underground vent that they came from.
The scale of advantages of geothermal energy depends on geographical location. While geothermal heat that can be used as a power source exists everywhere under the surface of the earth, there are relatively few locations or areas where geothermally heated water, generally the easiest and most profitable type of geothermal energy to tap, come close to the surface of the earth. Iceland is one good example, where nearly all residential and commercial buildings are heated by means of hot geothermal water.
Given the powerful geothermal energy advantages, it is not as widely employed as one might expect. In many locations or countries, this is often due to the high setup cost of building the initial geothermal power system. Other disadvantages of geothermal energy include the potential leakage of poisonous gases into the atmosphere, the risk that after considerable investment a site may cease to produce the same levels of heat a few years later, and the difficulty that may be experienced in many countries of finding a suitable location. Exploratory drilling to identify a suitable site may be extremely costly, with no guarantee of success.
In spite of these disadvantages, if a long term view is taken, then the overall geothermal energy advantages can be compelling. As stocks of fossil fuels diminish, tapping into sustainable energy sources is considered a priority by many. If a country or corporation can withstand the high capital expenditure that may be needed to start up a geothermal power station, then the geothermal energy advantages in the long term may pay off handsomely.