I don't think most people buy balcony solar in Germany to save money. The eletricity you generate is very little, and it takes years before you even break even, and then you maybe save a couple of dozen euros a year. No, I think it's more about the feeling of independence and sustainability.
A 500W kit costs around 500€. With good orientation you break even in 3.5 years (2kWh per day at 20c the kWh). Very few investments would give you such 25-30% yearly ROI.
They are getting even cheaper. I have four modules with a total capacity of about 1800W (the inverter has a limit of 800W to comply with the regulations). Cost was about 370€ including delivery.
after around 5-7 years you break even, and solar panels can last for 2-4 decades. Most panels you can buy in germany have a warranty of around 25 years. So yeah, you buy them to save money since electricity is hugely expensive in germany.
In the usual contract, you pay an price of 40 cent per kWh, no matter when you use it. But that price is based on a year-round average. Actually, sometimes electricity is super cheap for the utility company, like when the sun is shining in summer and electricity prices go negative. And sometimes it is very expensive, like on dark winter days without sun and wind, when prices are >1 EUR/kWh.
What you can do with balcony solar is skip the cheap summer sun prices (which cost the utility nothing, but they still charge you 40ct), and you still buy at expensive times for 40ct, when it's actually worth much more.
In short term I think it is workable strategy. But in long term I expect the pricing to move more towards market price direction. Either by purely market or some strange adjustments based on consumption timing. And ofc transfer will go up...
I've heard so many lies in support of "cheap solar" that I've lost count. Environmentalists may be the least honest political cohort in existence, which is saying something.
Subsidies.