- Solar powered hot water systems are a pain in the ass complicated.
- Solar electric panels are stupid simple, either they work, or they don't.
- Heatpump water heaters are more efficient then even gas fired water heaters.
You put this all together, and if you are paying money for all the parts, then the heatpump water heater and solar panels are cheaper and easier to run.
That said, if the shit hits the fan, I can build a solar powered hot water heater with any metal I find lying around. You build a tank (out of anything that won't melt at 212F) then you have some tubing (black plastic tubing works all by itself in SW USA) and you place it on a heat absorbing surface in a box with a glass cover to keep heat from escaping.
They problems come when you try to add it to a pressurized system. Everything becomes a lot more complicated. And everything has to withstand the pressure and added pressure caused by any trapped steam.
I like the drain back solar hot water heater systems. But those require two pumps and controlling electronics.
What a great comment! Thanks for the insight.