[AChimp]

As far as I know, geothermal energy can only be harnessed effectively in certain environments (type of ground, etc.)

It's fairly efficient if it will work in your geographical region. I have my doubts about it working as well further north, even here in Winnipeg. We get some cold ass frosts in the winter that go a few feet deep, so I don't know how "warm" the underground could be. :/