Geothermal energy can be used to heat homes in the winter and cool them in the summer.
[The] ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of this by exchanging heat with the earth through a ground heat exchanger.
As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water.
They do cost considerably more to install, but can pay for themselves in 5-10 years and you then then have no heating and cooling energy expenses except for maintenance on the system.