At 10 p.m. on Saturday, the Isar-2 nuclear plant near Munich will begin winding down its power generation in steps of 10 megawatts per minute.

After about 45 minutes, it will drop to 30% capacity and automatically sever from the national electricity grid. The other two plants still in operation, Neckarwestheim-2 and Emsland, will by then be in the midst of a similar process. By midnight, all three will be offline, ending Germany’s tumultuous six-decade reliance on nuclear energy.

When the three plants, which collectively provided Germany with 6% of its power last year, finally shut off, Europe’s largest economy will face an unprecedented challenge: securing its energy supply without nuclear or Russian natural gas, and with renewables expanding at a slower pace than needed.