Wind energy advocates often point out that a State, the U.S., or the entire world has enough wind energy to supply all of its electricity needs many times over. Writing in Scientific American, for example, Mark Jacobson and Mark Delucchi note that the world in 2030 is projected to consume 16.9 trillion watts (terawatts, or TW) of power, with about 2.8 TW consumed in the U.S. Total wind flows worldwide generate about 1,700 TW, and accessible wind resources total an estimated 40-85 TW.
Based on such math, the American Wind Energy Association (AWEA) argues, for instance, that Arizona has enough wind to meet 40% of its electricity needs, Michigan wind resources could meet 160% of the State’s electricity needs, and wind in Oklahoma could provide nearly 31 times the State’s electricity needs. Yet despite ratepayer subsidies, special tax breaks, and renewable energy mandates and goals in 37 States, wind supplied 2.2% of total U.S. electric generation in 2010. Why don’t we get lots more of our electricity from this ‘free,’ ‘non-polluting’ ‘renewable’ source?
The chief impediments are wind energy’s inherent drawbacks. First, wind energy is intermittent — at any given time the wind may blow too hard or too soft or not blow at all. Second, wind is non-dispatchable. When Shakespeare’s Owen Glendower boasted, “I can call spirits from the vasty deep,” Henry Hotspur replied: “Why, so can I, or so can any man; but will they come when you do call for them?” Like Glendower’s spirits, the winds answer to no man. The wind is not ours to ‘dispatch’ as electricity demand rises or falls.
There are three main ways of compensating for wind’s intermittency and non-dispatchability — pumped storage (pump water uphill when there’s too much wind relative to demand; let it run downhill and drive turbines when there’s too little wind), natural gas backup generation, and wind dumping (idle the turbines when demand is low). Incorporating those techniques to keep supply in balance with demand adds to the cost of wind electricity, which is typically more costly than coal- and gas-generated electricity even without storage and backup.
What’s more, according to a new Reason Foundation/Independence Institute report, the storage, backup, and idling costs become prohibitive as wind’s share of total generation increases beyond 10-20%.
The report, The Limits of Wind Power by William Korchinski, contains several sobering graphics. Figure 6 from the study shows how variable (intermittent) the wind can be, reducing output as much as 16 MW per minute.
The report quotes E.ON, the German power producer that experienced this sudden decline in wind energy during Christmas in 2004:
Whilst wind power feed-in at 9.15 am on Christmas Eve reached its maximum for the year at 6,024MW, it fell to below 2,000MW within only 10 hours, a difference of over 4,000MW. This corresponds to the capacity of 8 x 500MW coal fired power station blocks. On Boxing Day, wind power feed-in in the E.ON grid fell to below 40MW. Handling such significant differences in feed-in levels poses a major challenge to grid operators.
Let’s suppose that some States actually take AWEA’s message to heart and build enough wind capacity to meet 100% of their power needs. To what extent would actual wind generation match electric demand throughout the year? Figure 11 of the study illustrates the results for the PMJ Interconnection region comprising all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and the District of Columbia.
As the figure shows, on hundreds of days the PJM region’s turbines would produce either significantly more or significantly less power than customers consume.
As noted above, there are three main ways of dealing with wind’s intermittency and non-dispatchability. One technique is pumped storage: “pumping water uphill when there is excess wind energy, and then running the water downhill through a turbine when wind energy is limited.” The PJM pumped storage capacity for 2010 was about 5,000 MW, compared to the area’s average hourly electric demand of 77,800 MW. In other words, PJM currently has about two hours worth of stored power. That’s okay because the overwhelming lion’s share of the region’s electricity does not come from wind.
But suppose PJM got all of its electricity from wind — what would it take to have enough pumped storage in case the wind doesn’t blow? Korchinski calculates that PJM would need to be able to pump uphill “a body of water that is about 2,000 square miles by 100 feet deep” — the dimensions of Lake of the Woods in Canada.
Since constructing artificial lakes of that size is impractical (and would have significant ecological impacts as well), pumped storage is typically combined with natural gas backup generation and wind dumping. Turbines left idle (dumping) do not generate income. Gas backup means running gas turbines inefficiently, in “spinning reserve” mode, so they are “ready to increase or decrease power on short notice.” The greater the penetration of wind in the electricity fuel mix, the greater the reliance on wind dumping and gas backup.
As wind penetrations increase, the grid requires increasing amounts of spinning reserves to maintain reliability. At high wind penetrations, even large amounts of power storage cannot prevent significant (and expensive) wind dumping. The already high cost of wind power increases with the construction of storage facilities, and the cost to construct extra wind turbines, which will be dormant during periods of wind dumping.
The takeaway message for policymakers and a public bombarded with propaganda about obtaining 40%, 160%, or even 3100% of a State’s electricity from wind?
Very high wind penetrations are not achievable in practice due to the increased need for power storage, the decrease in grid reliability, and the increased operating costs. Given these constraints, this study concludes that a more practical upper limit for wind penetration is 10%.