Full disclosure: we did not install solar thermal in our home, so I know less about it — but we did consider it, and I used to work for a company that sold these systems, so I know a enough about it to provide a good overview.
Solar thermal basically takes the sun’s heat and transfers it to something in the home to heat domestic hot water and/or to heat the home. To do this, it needs to store the heat – usually in the form of a 50-80 gallon water tank.
Solar thermal systems vary widely in their complexity and construction. In Israel, for example, most residences have black water tanks on the roofs for their domestic hot water – thereby absorbing the sun’s heat for free. These could be considered solar thermal systems, but they are very basic. More complex systems can have vacuum tubes, reflectors, drain-back systems to prevent overheating, anti-freeze liquid to prevent freezing, pumps, and an extra hot water storage tank sitting in the mechanical room.
Solar thermal is one of my favorite technologies because it is so efficient – it simply pulls the sun’s heat in to water. The problem is that it is difficult to store, and many people don’t have room in their mechanical rooms for another large hot water tank.
Swimming pools, however, are built-in storage tanks – the heat goes directly to where you want it: in the pool. Why aren’t there more solar thermally heated swimming pools? At this point, it’s a combination of economics and awareness. According to the Department of Energy, a solar pool heating system usually costs between $3,000 and $4,000 and provides a payback of 1.5-7 years, depending on local fuel costs.
A general problem with solar thermal collectors is that they are much less aesthetically pleasing than solar electric panels. On the financial side, there is still a 30% federal tax credit, and the State of Minnesota introduced a 25% rebate (up to $2,500) in January 2014. In any case, it is worth checking out the costs and benefits of solar thermal, whatever the climate – but particularly if you have a pool!