A friend of mine has a great DIY solar system that I'm going to try to duplicate on my pool over the winter. He bought about 150' of black plastic irrigation tubing (about 1/2" or 3/4" dia.), tapped it into his return plumbing, and added a valve to open and close the flow. He cut a hole in the wall to run the tubing outside and the 150' or so lays on the roof above, picking up heat. It then runs back through the wall and into a return pipe. He says it easily lengthens his swimming season and in the summer, it dissipates heat when he runs the pumps at night. I've been running my system at night for 2 weeks and still have 90 deg. water. His pool's at 83! I know I won't have to spend $300 to do this. I only have a small roof area to work with but I can run the tubing in a big spiral to maximize efficiency. I don't have a place to set up 10' or 20' solar panels. I'll post results next spring.
Hal