March pump #893-07 brushless air cooled motor
spendy, but quiet and dependable. The one I used was the same pump, but it had a brush motor
. They wore out after a couple of years. Brushless is a big improvement, I'm sure. tinyurl.com/wjtox
The differential controller needs to operate from 12 volts. I don't have a link to the one I used as it was 13 years ago, but I'm sure you can google
for something. The pump power demand is only about an amp@ 12 volts.
I used flexible plastic hose in insulated foam between the solar panel and the tank. Once it was in place, it only needed burping out the air. I had a nice hot shower
whenever I wanted it, even the next morning the water was warm enough, although not really hot.
This was used in Mexico
and the new owner of the boat is still raving about it. Richard Spindler of Latitude 38 Magazine saw the hot water system and made some comments in last March's "letters" column about it.