When we were in Florida for the winters I fooled around with a
homemade solar heater for the pool. I got a 4x8 sheet of plywood,
cut it in half for two, 4x4 pieces and painted on side black.
Then I got some black PVC tubing and coiled as much as I could
of it on each of the pieces of plywood, attaching the coils with
plastic retainers. Connected the two coils in series and mounted
them so they faced the sun directly. I used a submersible pump to
run water from the pool, through the coils and then back to the pool.
Thermocouples were attached in the "send" and "return" lines.
During the day I'd measure about a 4-6 degree delta between the pump
side and the return side. It worked pretty good but it would take quite
a while to raise the pool water temp significantly and the losses at
night would wipe out any gain made during the day. Junked it.
When I had 240 sq/ft of collector it would make a dent in a 500 sq/ft
pool but when I cut that back to 160 sq/ft it wasn't worth doing most
of the time so I put in the plumbing to switch it to the spa.
It is a flip of a switch either way and it was good today on the spa.
I ended up with 99 degree water and that was about 20 over ambient.
Without glazed collectors and a better cover I doubt I can do better.
