I suspect your brother-in-law fell for advertising promises, about 5-7 heat pumps on the roof, 6 kWh storage. They have the electricity consumption for heat pump, cooling, house consumption blah blah. The system is already too small on 21.6., autonomy 100% actually runs from March to October. The storage doesn't even cover the night consumption of 8 kWh, I don't even see a washing machine, stove, breakfast peak there.