I think you need to qualify that first statement with a timeframe. Otherwise, it is clearly untrue. 100% supply is realistically possible with only renewable energy -- within a few years by investing in storage, local wind power in South Germany where the main demand is etc.
Build enough batteries and hydro to last for a few hours to a few days and use power-to-gas for longer periods of low generation (e.g. winter and no wind). There is already infrastructure in place for strategic gas reserves. We just need to build additional gas plants to meet demand when wind and solar are at production minimums.
But batteries and hydro are extremely expensive at grid-scale. How economically uncompetitive are you willing to make Germany in exchange for not using nuclear?
Nuclear is also extremely expensive. Personally I see opportunities in being an early adopter of technologies that have to become quite popular over the next few years if we want to prevent catastrophic climate change, but I'm not enough of an economist to have a strong opinion.
I would also be okay with building some nuclear, put nuclear and renewables don't go very well together, and I believe it's much harder to build enough nuclear plants quickly enough to replace all fossil energy consumption than it is to build enough wind turbines.
All of those, plus "smart grid" stuff to get better control over demand, plus Power to Gas (electricity to methane) and gas turbines (very inefficient, but existing infrastructure can store huge amounts of energy, and efficiency isn't the primary concern for the exceptional case).
