In the 70s we designed systems not only to heat the water but the home too. Now you can find dual purpose solar panels with PV on top and passive on the bottom. Some even use a heater element powered by the excess from the PV to do it but they all have the same issue of providing hot water early on.
I thought about doing the diversified load but in the end it would cost a lot to run the wires, fuses and get the 12v element for hot water when I didn't need it. The same money will fill the propane tanks many times and we have hot water when we want it.