I'm totally a green energy freak as well, but don't know much more than the general concept of geothermal. Question: if you're using the temp differential to cool your house, don't you end up heating the soil? By how much? I've read about the effects of global warming temp rises on soil/microbe/plant communities, and of course if the ground in question is under a sidewalk the impact would be minimal, but I'm curious...

BTW I'm TOTALLY doing that NStar thing--thank you for posting about it since I never read the extras they put in with my statement.