And yes, 1% of German energy is a ton of energy; but that is an incredibly optimistic forecast of if _every_ German did this. There are 85 million Germans; they could do a lot of things with their combined efforts. Backyard furnaces produced millions of tons of steel; seems like a very apt comparison.
I actually have solar of my own. It powered my entire life (off grid!) for years. That still doesn't mean I think individual small-scale solar is a meaningful solution to the climate crisis.
The biggest risk around climate, in my opinion, is the risk that people and governments think "we're doing something" when they are not. In this case, balcony solar has a very short payback time (a claimed 5 years for one guy's install! That is preposterously short for any investment!) because of the strange way that residential power is priced. If people really paid for the power and the grid infrastructure in relation to the real costs, balcony solar would never pay itself back, but essentially nobody understands that. Instead, they see the large amount they're saving and mentally that magnifies the impact of what they're doing. From the various posts I found, an ideal, un-shaded install produces between 200 and 500 kWh per year, depending on orientation and size. Obviously any sort of shading would drop that off a cliff. Compare that with the 38 MWh (38,000 kWh) per year of primary energy that the average German consumes...
