Much like solar energy, geothermal energy is sustainable, non-polluting, and available all over the world. Geothermal energy comes from the heat stored within the Earth's mantle. This is a layer of superheated rock nearly 2,000 miles thick. The heat from this mantle radiates outward through the planet's thin crust, and is most obvious in volcanic regions or where thermal springs are found. Geothermal energy has advantages over other green solutions like solar and wind power, though, because the energy is 'direct-use'. Since the energy doesn't have to be converted to some other form, like electricity, the usage is more efficient, sustainable and eco-friendly.
Geothermal heating can be and often is completely passive, although users in some more extreme climates or applications may choose to use electricity-based equipment to move or concentrate heat from underground. In these cases, fans, electronic thermostats, residential heat pumps, geothermal heat pumps, and various other equipment may be used. Nonetheless, it is absolutely possible to operate a geothermal heating system off the grid. The specific choice depends on your goals, your climate, and the design of your system.
