Just to clarify, the German electricity grid doesn’t stop functioning when renewable production drops because Germany imports power from neighboring countries to make up the demand and massively overbuilt its renewable sector compared to what would be required if renewables weren’t variable.
Its also important to point out that a large fraction of renewables used by Germany are biofuels that are significantly more reliable than wind and solar but are not what people here think of when they talk about renewable energy.
In reality, Germany is so “successful” investing in renewable energy because it is a rich country willing to spend significant amounts surrounded by neighboring states willing to provide electricity. In reality, renewable energy is still significantly more expensive at he moment and adding storage into the mix just increases the cost.