I am really surprised you don't have solar heated hot tubs. I used mine pretty much for free, (at leas the heat), most of this year. Now it is so warm we won't be using it again until fall. My solar collectors could boil lobsters in it tho.
Tesla, I've been all over your part of California - and your roofs are infested with home-made solar collectors. Folks have been running pool and spa water through coils of black irrigation tubing since at least the early 80's. It doesn't take much power to run a 1/20hp Grundfos pump.
Those who don't use solar heat with gas- at a fraction of the price of electric heat.
