Using electricity to heat water is wasteful. A solar water heater provides one of the best returns of any home energy project.
We got a free heat exchanger tank, free panel, and then bought smaller parts like the circulation pump, controller and plumbing. The incoming cold water from the well is heated in the solar tank, which holds 50 gallons. The solar tank temperature has reached 160F, but in the picture here it’s just 132F. Then, water flows into the electric 40 gallon tank. Mostly the electric heater doesn’t run any more, but if it is a cloudy day it will, so we always have hot water. We’ve had it running for two billing cycles, and it is saving us about $20/month, or about 200 kWh. Last month our total was 450 kWh to run the house, well, home office, electric mower, etc.
To prevent freezing, it is a drainback system. There is air in the outer heat exchanger of the tank. When the pump stops running, the water in the panel drains back into the tank, and the air flows up into the panel. For extra protection, the solar-loop water is mixed with propylene glycol (nontoxic antifreeze).