We are in a similar situation in that we use a LOT of power.......well pump, hot water heater, forced hot air heating, centra A/C, mini-splits for the basement, hot tub, etc. add in some of the nation's highest electrical rates and our electric bill is between $350 and 650/month so the payoff timeline for us on this is only in the 8-9 year range.
This is a retirement play for us (we 48 and 49).......I can't control property taxes or healthcare costs we will face in retirement but I can do this and eliminate the bulk if not all our power expense and if we eventually move to at least one vehicle being an EV we are controlling even more of our expenses as a hedge against energy costs.
39 panels for us feels like a small substation but we clearly need it.