Yesterday I went back to the Bay Area (specifically, Fremont) to visit a friend, and meet his wife and baby, before they move back to Washington State. I took the Central Valley route, south on I-5 and west on I-580 over the Altamont Pass. No, I had no Rolling Stones playing at the time.
On the crests of the foothills at Altamont are almost 5000 wind turbines. Not one of them was turning that I could see. It was a semi-cloudy November day in the Bay Area and even if the wind was light, not one windmill was turning.
How reliable is that?