So you are running the refrigerant through a brazed plate heat exchanger? I’ve used them on boiler systems, I guess that will work.
To me the holly grail of off grid, would be to drive a mini split heat pump directly from the solar panels. Make hay (heat) when the sun is shining, and the COP is the highest (for the day). Then store the heat in water. Which is 100% efficient in season. (All leaks in storage or transfer are just needed heat for the house.)
Would like to know how you did with this.
I,m headed down the same path.