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.
