The word “geo” means earth, and “thermal” means heat. So, geothermal means heat from the earth. If you were to dig ten feet below ground level, almost anywhere in the world, you would find the temperature to be between 50° and 60°F (10° and 16°C). No matter what the temperature outside, the readings ten feet below the earth remain fairly constant. Geothermal heat pump systems use that constant temperature to either heat or cool your home. Using pipes that are buried in the ground near your home, fluid, like antifreeze, is circulated through the heat pump system. In winter, heat from the warmer ground travels through the heat exchanger of the pump and sends warm air into your home. In summer, the cooler temperatures travel through the heat exchanger and cool the air in your home.
To determine whether or not your location has enough sun or wind to supply energy, you can study maps at WindSolarEnergy.org (www.windsolarenergy.org) that show you how much solar or wind power you can expect. In some cases, you might need to use a combination in order to live off-grid.
Geothermal heat pumps use much less energy than conventional heating systems, since they draw heat from the ground and only have to potentially bring the temperature up several degrees. For example, with other heat sources, you have to maintain the fuel source to reach the internal home temperature of your choice. With geothermal, your heat source is already at 60°F and so only has to be heated another ten or so degrees to reach your comfort level. The same is true for air conditioning, where the 60°F temperature can bring your home down to the level you desire without using excess energy. Geothermal heat systems can also heat your home’s hot water.
Since the first geothermally generated electricity in the world was produced at Larderello, Italy, in 1904, the use of geothermal energy for electricity has grown worldwide to about 7,000 megawatts in twenty-one countries around the world. The United States alone produces 2,700 megawatts of electricity from geothermal energy. Using that amount of electricity is comparable to burning 60 million barrels of oil each year. Source: http://geothermal.marin.org/pwrheat.html.