If you want to use solar power for heat why would you use PV panels?
In the late 70's I built a very low tech solar water heater out of scavenged materials. It was about 4" by 16' and provided about 40 gallons of very hot water any day the sun shined.
OTOH, once you had all the hot water you wanted and the floor was warm or in summer the system would not be as handy as PV.
Another thought might be to use a heat pump water heater. ?????