Yes you can heat water or heat living place in winter as I do, if you install a heat pump you can do it better.
Diverter may be built in different ways i built it as a dc/dc that clamp battery bus at a preset voltage or pv array 1-2 precent above MPP voltage and divert power to dump resistors, as radiant heaters and water tanks, i presented it in this forum, but schematic has an error presented in that thread, probably i will reedit it.
This diverter no need any relay and can operate stand alone only with the solar array, it can operate both ongrid even during grid blackouts and offgrid.
If you need to adapt other voltage to your resistors diverter need two stages, buck converter to control and foreward open loop to adapt voltages, may be only a foreward pwm controlled, but my experience shows that tho stages is more robust, and stable, you need use use a single full protected stage (buck stage), is more simple and effective to protect it in compare with a pushpull or bridge foreward converter.
If you use a heat pump inverter driven motor you need an application to control that inverter to maintain a preset input voltage, if your battery or pv array meets with input voltage range o that inverter you need no other device, if not, the simplest is an open loop foreward converter that acts as a transformer
(dc).