This is doing it the hard way. Finally got around to plumbing the water heater so we can use excess solar power to heat water. We both had a hot shower last night with some to spare and the next day she had enough hot water at 2pm to do the dishes running out near the end. I was given this 10 gallon 2000W 120V 7.2 ohm heater and will use it to dump excess power from the 810W of panels I use to run the chest fridge. Yesterday was the proof of concept run. I have three groups of panels. The one for the test was 345W total. From that 140W at 32V actually goes to the water heater. Quite pleased that from 10am to 5:30pm was enough time at that power level to heat the water. The fridge typically runs from 100-220 minutes a day and durring that time I don't heat water. If you have followed my UNO fridge project, that program is actually called waterheater. The fridge uses only a car battery to provide surge at startup. The fridge only runs durring the day when the panels are active. I store cold in liquid mass instead of power in a battery bank. Panels are sized so the system can run on a really cloudy rainy day. That means most days I have power to spare. When I finish the power controller, voltage to the water heater element should be around 40V to give me about 220W. Once I super insulate this water heater that should be enough for normal use. Next will be another water heater for the laundry. Having a micro controller makes diverting loads easy.
Plumbing is a little interesting. I have an under 10 gal propane water heater that I only run when needed. The solar water heater is plumbed into the cold water line of the shower. That allows me to use either heater.