I am from Germany too. Yes, sometimes we have negative prices for electricity. But that does not mean, it pays for investments for facilities, which only make sense with low or negative electricity prices. And it is a rather temporary phenomenon. With the transition from coal to gas, it becomes much more feasible to switch off power generation to avoid surplus electricity.

Long term, with enough battery powered electrical cars on smart grids, charging will be synchronized with the electrical power levels. And then we are back to electrolysis using 3x the electrical power.