I am going to bid the electric on a new bathroom in one of the town parks. It will be design build so there might not be any plans. We have long cold winters here, so the plan is to shut one stall down in the winter, and leave the other open. In that stall the town engineer wants to see some input on "solar assisted heating". There will be some kind of conventional heat in there also. What might solar assisted heating consist of? What manufacturer makes anything like this? Thanks