Heating a pool or a spa is a task that can be accomplished with quite low temperature solar fluid. Often this application can be carried out with low grade solar availability that is not useful for anything else. Mechanically, it is just another radiant heating zone that is controlled manually with a simple ball valve. It is a good example of an application that is quite reasonable to accomplish with solar energy that would be somewhat wasteful to accomplish with fossil fuels.

This is a good use for excess solar energy during the summer. It will extend the season for the pool and keep the solar panels cool. Your roof will be cooler and your air conditioning needs may be lower as a result.