[myself248]

I wonder how it would pencil out if you just pumped groundwater through them and returned it to an adjacent well, without even trying to harvest the heat. It cools the panels in summer, and warms them in winter when snow coverage might otherwise be an issue. Melting the snow off can turn an otherwise-nearly-zero period into a productive one.

But this is way simpler than domestic water heating. You don't care about thermostats and storage tanks, you don't worry about overheating, you don't even necessarily have to care about leaks since it's all going the same place anyway. There's only one pump and no valves. The panels themselves could be made to a lower standard since the whole thing could run at nearly-zero pressure.