You can get DC SSR that have mosfets in them, they still use the opto isolator and are specifically designed to switch DC sourced loads on and off, readily available on aliexpress for similar prices to the AC versions.
I have a similar situation, I am have recently installed a 12 volt 400AH Lifepo4 battery (4 x 3.3v 400 AH cells), these are charged by a 60amp mppt charge controller, powered by 6 x 140 watt panels mounted on a frame above the porch leading into the house.
The battery powers a 1500 watt sine wave inverter, that runs everything in my home office, 3 pcs, stereo, lights etc. If Im not using the office much, then the battery is full and the sun is shining; the controller just sits drawing zero current from the panels. I thought about switching the panel outputs direct to an extra low voltage HWC element fitted in the bottom of the cylinder and using the DC SSR to do the switching. A voltage sensor can turn this off when the battery voltage drops back with load, although this is a bit tricky with lifepo4 cells as the voltage curve is virtually flat for all loads, perhaps a current sensor would be more appropriate.
Cheers
Mike
NZ
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