About Geothermal Energy
Geothermal energy is basically the generation of electricity or heating/cooling systems that make use of temperatures in the earth itself. The Earth's core lies approximately 6000 km below the surface and reaches temperatures that near 5000ºC (9000ºF). These extreme temperatures are sufficient to heat the rock that surrounds the core (the mantle) causing it to melt. Melted rock in the mantle is known as magma, as often pictured spewing from an active volcano. Liquid magma has a lower density than the solid rock around it, so it tends to move upwards towards the earth's surface. The majority of the time magma stays below the earth's surface and heats up the surrounding rock and any pockets of water that come in contact with it. Geothermal systems typically take advantage of water tables that are heated by the magma.
There are two types of energy that can be obtained from the earth: earth energy and geothermal energy. It is important to note, however, that in many cases Geothermal Energy is the term that is generically used for either type of energy and little or no distinction is drawn between Earth and Geothermal Energy. From my investigations the best distinction between earth energy and geothermal energy is the difference between making use of water that is heated by temperatures in the earth (geothermal) vs. using the temperature of the earth or water, to heat/cool water in a closed system using a heat pump (earth energy).