The purpose of this article is to establish a broad working definition of geothermal energy. Geothermal energy is exploited from the heat within the earth, from just below the surface, to all the way deep into to the earth’s core. We can determine the measure of heat content by traveling down into the earth. If we go down about 3 and ½ km the temperature of the earth is about 50 - 60 *C. But if we go down about 10 km, the temperature increases to about 300*C. This depicts how heat is brought to the surface of the earth.
The tectonic line, known also as the ring of fire is the place on earth that has the most magma activity. Magma is created through a scientific process known as convection. Beneath the earth there is a lot of activity with plates and the movement of these tectonic plates causes the heat to circulate, creating more hot air, and the air is hotter and less dense and so it rises, upward. The temperature from the risen air literally melts the rocks, which escapes through fissures in the earth's crust creating magma or molten rock. It is the cracks in the earth’s crust, where wells can go down to harness energy from just beneath the earth’s surface. This is what a geothermal reservoir does. It taps into the earth’s crust, and drills to extract energy from the earth’s heated rocks, hundreds of feet below us.
So, how do we capture the heat that is trapped in the rocks? We use rain water to pick up the heat from the rocks in the crust, just below the surface. The space between the rocks become air pockets where the rain water can move through. The air pockets are essential to this process as they allow the hot water to move past the air pockets upward as it is extracted from the magma.
So a geothermal drill for the purpose of harnessing energy to be generated into electricity, would capture heat and draw the hot water up into the well, use it to create electricity; and another well would be drilled to inject the water back into the earth to replace it. In this way we have refilled the reservoir of water, extracted the hot vaporized water we need to create energy, replenished the earth’s stores and given ourselves renewable energy.