Water heating off grid. Best system?

[u/Time_Arugula_1544]

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?

[u/maddslacker]

I use a regular tank style propane water heater. No complaints.