The zombies have taken over, the ice age occurred, and everyone decided to cut loose with the nukes. How much time do you have to set up the solar panels and wind turbines before the electrical grid fail? The Straight Dope takes a look…
Bottom line? My guess is that within 4-6 hours there would be scattered blackouts and brownouts in numerous areas, within 12 hours much of the system would be unstable, and within 24 hours most portions of the United States and Canada, aside from a rare island of service in a rural area near a hydroelectric source, would be without power. Some installations served by wind farms and solar might continue, but they would be very small. By the end of a week, I’d be surprised if more than a few abandoned sites were still supplying power.