Nuclear works
now. A 100% renewable grid will require energy storage. We have small scale options for energy storage, but none of the current energy storage technology we have
now scales large enough to meet the demands of a 100% renewable grid.
Remember that heating in most of Europe is provided by natural gas. The primary need for heat is during the nighttime. Solar works only during the day, wind works great at dawn and dusk but not particularly well at night, and both of these systems have inherent unpredictability. You never know that there isn't some weather pattern that's going to take all your solar/wind down to 30% of its normal capacity for a week. Hydro and geothermal may fit the bill, but AFAIK Germany and Europe in general doesn't have the capacity.
The ultimate goal is a 100% renewable grid consisting of an energy storage system which will work all night, and will be recharged by solar and wind when those systems are operating at peak capacity. Natural gas heating will be replaced by heat pumps with a fallback to electric resistive heating when temperatures drop too low for a heat pump to be effective. Right now, there is no such energy storage system that will scale to meet these needs.
We'll get there one day, but until then, we need an energy generation technology that works all day every day with no dependencies on weather, and scale to the size of a continent. The only -- the only -- technologies that currently exist which do this are coal, natural gas, and nuclear. Pick one. You must pick one -- platitudes about renewable energy and technology which may or may not exist in a decade will not prevent the pipes from freezing tonight.
Right now, Germany has chosen coal and natural gas, and has phased out nuclear. IMHO this was the wrong choice.
(Before anyone says Germany has phased out coal, they have not phased out coal. Germany mines coal, selling coal to Poland, Poland uses coal to produce electricity, Germany buys electricity from Poland.)
> (Now, fission would be a different story. I am all for researching this intensively).
I suspect you meant fusion; I don't normally point out typos, but in this case, I think it's important.