First, we must understand why wind is curtailed:
Wind energy is variable, and to some extent unreliable. Due to the extreme ramp times involved in the baseload coal plants, most power companies will not operate wind energy that is greatly in excess of their spare natural gas capacity. If the wind drops, then there has to be enough dispatchable power to cover the load, or you get a brownout or a blackout. This is mitigated somewhat by the distribution of dispatchable loads throughout a region, and certainly throughout a hub on an ISO… but as a region builds out wind power then this will eventually become a concern, and curtailment occurs.
Furthermore, a power company has to make a call in anticipation of a windy night as to exactly how much they choose to tamp back their coal plants. If the wind is sustained and provides constant power throughout the night, they get very high profits on selling a product that has near zero marginal cost... But if the wind rises and falls, they have to constantly ramp up their peakers near max then tamp them back only to ramp them back up again... All while ramping and tamping their larger CCGT plants as quickly as they can - making the night FAR more expensive than it would have been had they just tamped down the coal plant a little less and pitched the blades on the wind turbines.
The much lower price of gas has dramatically reduced the instance of nightly curtailment - because they can now plan to have a natural gas power plant running at moderate capacity through the night which can more adequately ramp up or down while leaving the minute-to-minute changes to the peakers.
In 2012, it's likely that less than 3% of the potential wind energy generation will be curtailed, though as natural gas prices rebound the instance of curtailment is certain to rise again, possibly back into the 10-15% curtailment range.
But even with today's low NG prices the power companies will pitch the blades and let the energy go in response to minor but rapid changes in wind speed, because it's too much of a headache to try to slam the peakers that rapidly up and down... so they'll use blade pitching to try to get a reasonably constant energy level from the wind turbines once their battery reserves are full.
This complexity also causes a great deal of daytime curtailment. Since the baseload capacity is typically ramped up near maximum, there again is a narrow range of operational flexibility from the peakers and the natural gas plants… so again there will be some energy discarded by pitching the blades. For instance: in 2010 throughout MISO, nearly 40% of the wind curtailment occurred during peak hours. In 2011, ~58.9% of the wind curtailment occurred during peak hours.
Another reason for curtailment comes with wind farm design itself: If a power plant builds out a 100 MW wind farm, it's not uncommon for them to only build an ~80 MW (or less) capacity transmission line connecting that wind farm to the grid. The major transmission lines are expensive enough that it isn't cost effective for transmission to be built out with sufficient capacity to handle rare 100% loads. Obviously, during extremely strong winds the blades will have to be pitched back or locked down because the transmission lines wouldn't handle the full load. Due to the very low price of natural gas, this is probably the majority of the issue surrounding wind curtailment today, though as we've discussed before the price of natural gas will not hold, and as the price of natural gas rises, the night-time curtailment of wind will once again occur nightly throughout the wind belt.
All of the above actions of the power companies are, of course, dictated by the minute-by-minute variation in RT price on the ISO hubs... which is another layer of complexity that I chose to avoid by replacing the ISO hub by a purely rational decision maker - which is fair enough for this post.
Finally, blades are locked down in winds that exceed the maximum rated wind for that particular turbine, but this represents a very small percentage of current wind curtailment.
None of this is intended to disparage wind power. As a renewable generation technology that is truly cost competitive with coal on a $/MWh basis, wind has expanded at a tremendous rate and is now generating over 4% of the nation's electricity, and will eventually exceed 20%. But there are complications with wind, and those complications cause curtailments. The higher the penetration of wind, the greater the amount of curtailments that will be required. Understanding why wind is curtailed will help resolve these issues and avoid distractions or fantasies - such as the notion that charging EV's overnight will reduce wind curtailments. They won't. What is needed to reduce wind curtailment is a fast-response demand response. This is often envisioned as some form of grid-to-grid storage, but that narrowing of focus is a distraction. What is critical, however, to reducing curtailment is to have some rapid flexibility of demand that can accommodate a rapidly changing supply.
The EV charging cycle:
Plugging in an EV represents an absolutely constant demand increase from ~7:00 pm until ~5:00 am. There's no demand response enabled here... there's just a dependable higher baseload demand. The most profitable response for this will - in all cases - be for the power company to just tamp down their baseload power a little less each night to accommodate a higher baseload demand. (for more on this, see: http://seekingalpha.com/instablog/1005406-glenn-doty/702131-recent-analysis-from-the-union-of-concerned-scientist-is-garbage).
EV Potential vs Reality:
If an EV owner had a 3-phase ultra-fast-charger hooked up to a smartgrid controller which could immediately ramp-up or tamp-down the charging rate based on 5-second pricing signals from the local ISO... then you would have an option that would clearly take advantage of the variable energy bursts from the wind and you would directly reduce wind curtailment. But that type of set-up would add ~$5,000-$10,000 to the price of owning an EV, and would still only function during the times in which your EV was hooked up to such a system.
No current EV owners have such a thing. For current EV owners, and those unwilling to invest another ~$5,000-$10,000 in making them clean, the energy they are powering their cars with is almost certainly coal-sourced.
Without some kind of ultra-fast charger (which would experience EXTREMELY high charging losses) hooked up to a rapid response smartgrid controller, then an EV is going to be consuming baseload power with absolutely no impact on the rate of wind curtailment, minimization of load following, peaker utilization, optimal capacity utilization, or any other system management concerns or system carbon intensity reduction concerns.