You also must add in the cost of propane for heating the house during the winter for 3 - 5 months. (and a big tank) If I was off grid, in a rural area where th

You also must add in the cost of propane for heating the house during the winter for 3 - 5 months. (and a big tank) If I was off grid, in a rural area where the winters can get severe, I would want a big diesel generator as a backup. A lot of things can happen during a proper winter: roads close, heavy snow, supplies can get hard to get some short periods, you can get cold front that bring the temperature down below 20C. One of the things that sucks about diesel generators are the noise, and the pollution and the maintenance. You also have to run it for a while every now and again and make sure you test everything regularly. He could heat the house electrically with power off the generator and that would integrate nicely with solar and wind power. Oh you can get propane generators as well, I was not familiar with that. That would be more convenient since he already has a propane tank. Just build a bigger one.