12V heater from solar water pump panels
I have a design in mind that I would like to get some feedback on. I have an existing well at my off-grid cabin, and I'm preparing to install a Grundfos SQFlex solar pump in the well (I currently have a 110V pump in the well that runs off my generator). To run the pump, I'll use (3) 175W panels wired to get a combined ~100V to run the pump (via a Grundfos control box). However, I'll only need to pump water Mar-Nov, so I'm looking for a way to utilize the solar panels during the winter (when not needed for pumping water). My plan is to have the panels operate a small 12V heater to leave in the cabin, just to help keep the temperature from freezing inside the cabin during the weeks between visits. My thought is that I would run a line from the panel combiner box to both the pump control box as well as to the cabin for the 12V heater. The DC wiring from the combiner box to the 12V heater in the cabin would run through a MPPT charge controller (to step down to 12V). The heater would be then connected to the charge controller via the load control "out" terminals on the charge regulator. My plan would be that the heater would be always on, but would only run when the panels are putting out enough power to turn it on and run it. It wouldn't put out much heat, but it's a small cabin (~1000 sq ft) so my hope is that it would be enough to help keep the cabin above freezing. I've attached a schematic of the proposed system and wiring. Can any of you see any flaws in my logic or proposed set up? Thanks.
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