I highly recommend Jack's Solar if you decide to do this. He is used by T&D when they install solar heat for a new pool.
My pool is 16 x 30 x 4 (no deep end), and the solar system has 8 panels. The cost for solar was $4500. We keep the pool at about 88, and it works fine. In the winter months, it doesn't get that warm, and you will need to use the solar cover if you intend on swimming in February.
The system works by circulating hot water from the collectors through the regular pool plumbing. There is a controller with which you set your desired temperature. When the pool water is cooler than your desired temperature and the collector water is warmer than the pool water, the electric valves open to allow hot water into the system.
I'm not sure how you would do this practically with manual valves.
Give Jack a call ... he's very personable and won't pressure you. Feel free to tell him that Steve Nagy sent you ... I'll take any help I can get to "soften him up" when I ask for a quote on solar electric!
