Good question. In my case we're spending an inordinate amount on power currently, because we're using upwards of 20kW / day. Part of that is a horribly ineffi

Good question. In my case we're spending an inordinate amount on power currently, because we're using upwards of 20kW / day. Part of that is a horribly inefficient hot water system, part of it is needing an air conditioner this time of year (here in Australia). The new system will include a smart meter changeover, which means hot water can be off-peak, and time-constrained, and air-conditioner will be used primarily during the times that we're generating power. Combined with some other plans - adding a shade-roof over one of the existing poorly insulated structures, replacing the HWS with a heat pump, etc - I expect that we'll be close to power-positive most sunny summer days when we're on-site, and every non-cloudy day that we're not. Payback for my neighbour was ~ 3 years, though he was more extravagant with his air conditioner because it wasn't costing him anything to put it on. I expect a similar or slightly faster payback period. In which case - it makes more sense for me to do this immediately. Whether it would have been the case 3 years ago, I'm not so sure.