51
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.
For what it is worth, utility-scale batteries have been the next step in added storage capacity after pumped hydroelectric is built out