Dan5, while I agree with you generally, I just can't let two misconceptions pass by.
1. The US power grid never "vents ... excess energy." Generating units are ramped up or down to exactly match supply and demand; even nuclear units can be ramped, but they rarely are because, almost always, there are other units to do so (see point 2 below). Your grid operator,
PJM, does have the ability to store a goodly amount of power in a massive pumped storage facility,
Dominion's Bath County facility (3,003 MW peak output).
2. Nor does the
marginal power in your area (New Jersey) come from nuclear, even overnight. According to two studies (
HERE and
HERE) by PJM's market monitor, eastern PJM (NJ, Delaware, and eastern PA) have natural gas on the margin 45%, coal 41%, and oil 14%. "Marginal" here tells you what kind of unit will make an extra MWh of power demanded. That info's a little dated; the mix will have shifted oil downward (a lot, especially overnight), coal downward, and natural gas upward.
Bottom line: except in very rare conditions, in the U.S. your utility will be burning more of some fossil fuel to charge your car. All the renewable and nuclear is always used all the time anyway. (footnote: very rarely, in the Pacific Northwest, the Bonneville Power Authority curtails wind, so greater load in the northern Oregon region could be serviced entirely by incremental wind. As more wind comes into service, this situation will spread.)