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On May 1, Germany ran almost entirely on renewables energy during the day
(transparency.entsoe.eu)
Some fossil-fuel-burning power plants were kept on at minimum operating levels (they're likely not designed for daily restarts) but provided less power than was used to pump water uphill in hydoelectric storage facilities.
And that's how it starts. You add enough wind and solar that they can sometimes provide more electricity than people use. Curtailment orders keep them from causing a problem, but that means wasting otherwise free electricity. So people start installing utility-scale batteries, which soak up that excess, and release it during the morning and evening peaks in net demand. You install even more wind and solar, and people do even more batteries, displacing routine overnight fossil fuel use. Even more wind and solar, and it starts making sense to install low-efficiency long-duration storage, and fossil fuel use disappears completely and permanently.