I live in NM where the temperature gets below freezing in winter and around 100 degrees in summer. In my small mechanical room I have a propane boiler and an indirect-fired WH which I use for my radiant floor and hot water. I also have a heat pump minisplit, and I have PV electricity. Which would be better (more sustainable) for me for heating water--a system such as the Vitosol that works with my boiler but kicks in first; a Vitosol with electric backup; or an hybrid electric heat pump HWH powered by my PV? I notice you also write about the outdoor compressor that goes with the heat pump, the SANCO2, which I'm also considering. Thank you for any advice you can give me.