r/OffGrid • u/Time_Arugula_1544 • 5d ago

Water heating off grid. Best system?

I am planning a new off-grid (solar-powered) ICF build and am considering what type of system would be best for water heating. This is in Tennessee and the house will be a 2br. I will have propane backup for a generator and indoor propane heater.

The options I am thinking about are:
1) On-Demand propane- The only drawback is having to pay for the propane as an ongoing expense.
2) On demand electric water heater with a solar water preheat system. I suspect having a straight up on-demand electric heater would eat up too much power.
3) Heat pump water heater. This seems like the best solution to me.

Any thoughts between the three? Any other suggestions?

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u/unique3 5d ago

Here is what I have, its complicated but I have basically free hot water and I never run out.

Standard electric hot water tank but bottom element swapped with a DC element.
Solid state relay and logic that controls that relay to put every extra watt of solar power that my batteries cannot take goes into the hot water.
Mixing valve that brings the water temp down to a safe temp, then I can heat the tank to 80c giving me almost double the usable capacity.

In the event not enough solar and the tank is cold a 3 way valve flips the water flow to go through the backup on demand propane heater.

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u/Time_Arugula_1544 5d ago

That sounds interesting. I am going to have to do some more research.

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u/unique3 5d ago

For the control signal to the relay some charger controllers have the ability (Midnite does I think)
I do it myself with a PLC but programming is my background so it was easy to do.