The energy on earth is a direct result of the sun. Geothermal harvests the earth from the sun to make it productive for mankind. The earth acts as a large blast to heat, and cool your building. The earth has seasonal changes which of course affect the weather; however below the ground there is very little temperature change through the year. The sun warms the ground in the summer and snow cools it in the winter but there is little change in the grounds temperature a few feet below the ground.
Using geothermal is having a fuel well in your own back yard. During the winter a heat pump takes the heat out of your ground and puts the heat in your building. In the summer that same heat pump takes the heat out of your building and puts it back in the ground. This is accomplished through pipes buried in the ground