There’s plenty of fixed fees in German electricity bills, on top of that the Wh price contains infrastructure levies. As the network changes so will the mix between fixed and consumption-based prices.
That said yes the Green party and its core voting demographic are notoriously bourgeois. “Let them install heat pumps” they said, caressing the one they installed, completely ignoring that at scale district heating is much more sensible. Their non-bourgeois core voters (the ones with a permaculture garden in the countryside) will then defend that by “but we don’t want centralisation” MFs municipality-level is not centralised.
If your balcony collapses due to 800W worth of solar it’d also collapse due to a couple of planters or a fat friend coming over so I guess you should take such worries as an admission on their part and withhold rent until they prove that the balcony is safe to use.