I guess I consume most of it. There are 4kWh of batteries connected to the panels. I set my dishwasher and my washing machine to run when production is high.

so you have a ±2k eur battery on top of probably 1.6Kw solar modules costing about 1k eur, attached to balcony and generating about 5kwh/day? And probably with very nice sun conditions because otherwise you'd need more solar.

Now let's take french household prices per kwh of 25ct/kwh. It means at 5kwh/day consumption the bill would be 450eur/y. So a 3k investment in this case would pay for itself in 6-7 years.

For a german household with highest prices in EU payback would be in about 4y assuming 40ct/kwh

But realistically many will not even buy a bess not being able to capture all solar output and many will have worse solar conditions. I'm not sure balcony solar in Germany generates even 1% of total solar production in the country despite streamlined installation process

The batteries where 800€, the panels about 400 and the inverter I think around a hundred (all from Amazon). All the stuff I needed to attach the panels to the balcony and the cables where surprisingly expensive.