How does it work?
1. The heat from the earth's core continuously flows outward toward the surface of the earth. It transfers heat to the surrounding layer of rock, the mantle.
2. When temperatures and pressures become hot enough, some mantle rock melts, becoming magma.
3. Then, because it is lighter (less dense) than the surrounding rock, the magma rises (convects), moving slowly up toward the earth's crust, carrying the heat from below.
4. Sometimes the hot magma reaches all the way to the surface, where we it known as lava. But most often the magma remains below earth's crust, heating nearby rock and water sometimes as hot as 700 degrees F. This natural collection of hot water is called a geothermal reservoir.
How is it used as a power source?
In geothermal power plants steam, heat or hot water from geothermal reservoirs provides the force that spins the turbine generators and produces electricity. The used geothermal water is then returned down an injection well into the reservoir to be reheated, to maintain pressure, and to sustain the reservoir.
PRO
1. Clean. Geothermal plants produce no greenhouse gas emission
2. Easy on the land. The land area required for geothermal power plants is smaller per megawatt than for almost every other type of power plant. Geothermal installations don't require damming of rivers or harvesting of forests -- and there are no mine shafts, tunnels, open pits, waste heaps or oil spills.
3. Reliable. Geothermal power plants are designed to run 24 hours a day, all year. A geothermal power plant sits right on top of its fuel source. It is resistant to interruptions of power generation due to weather, natural disasters or political rifts that can interrupt transportation of fuels.
4. Flexible. Geothermal power plants can have modular designs, with additional units installed in increments when needed to fit growing demand for electricity.