About six months ago we did the start up of a solar thermal system to heat our indoor lap pool, leisure pool, and domestic hot water for showers. The solar system is in addition to natural gas boilers. The system is very sophisticated, has 100 4'x10' panels, and its own website for monitoring energy usage and controlling the system. The reason for getting the system was to cut down on our monthly gas bills and was to be mostly paid for by grants. During the initial planning it was determined that the return on investment (from our organization) would be shorter than the warranty period of the panels, therefore the investment made sense.
The system has been operational for about 6 months now. In those 6 months the system has not been perfect as there have been a variety of small changes to add more efficieny. Most of the kinks are ironned out and we will likely see more efficiency out of the system when the weather outside is colder.
When I last did the math, the initial investment will be cutting it close to the warranty period of the panels. That will be about 15 years. For a full payback, including the money from the grants,assuming natural gas prices stay the same (which they won't), then we will have to wait over 80 years.
It is a very neat system and it does what it is supposed to do, but it is not financially feasible. If you want to spend more money for state of the art technology for pool heating or you want a LEED Platinum certfication then it will be a good investment for you. However, if you are trying to cut costs during difficult financial times, this is not the answer.