At my old house in Maine, we used to have a solar hot water heater. Basically it was a big solar panel and an electric pump that would pump this oil-like substance through the panels. The sun would heat the oil in the panels, and the pump would circulate the oil down to the tank around the water. The tank was super-insulated, and it was pretty efficient, even in the cold winters in northern Maine. IIRC, the unit was pretty expensive at retail, but we bought it at auction for under $500. I think that it would do okay in Pittsburgh, but you could probably ask around to be sure. It would have to be fairly cheap to really save a lot on hot water bills, unless you had hot water heat in your house.

I haven't had any experiance with a ground source heat pump, but I have heard they are pretty efficient.