Approximately 25 TWh (yes, 25 terawatt-hours) of wind energy was curtailed (idled) in the U.S. last year to keep the off-peak grid energy price from frequently going negative. That is about equal to the energy in 700 million gallons of gasoline just being thrown away. Curtailed wind energy in the U.S. appears likely to exceed 40 TWh in 2011.
Seems way higher than I'd expect, but it certainly emphasizes that we should be charging during off-peak whenever possible. I know that here in CA minimum grid demand is typically around 3-4 am, though most of my charging tends to occur between 1am-3am.
Makes me wish I could set a charge timer that centered the charge around the middle of the off-peak time period of 12am-5am - so if the car knows it has to charge for 2 hours, it'd charge from 1:30am-3:30am - or if it knew it had to charge for 4 hours it'd charge from 12:30am-4:30am. This would also have the benefit of automatically distributing the start / end times which avoids the spike in demand when the off-peak TOU period starts.