From the Institute for Energy Research:
CLAIM: Already, Iowa and South Dakota produce enough wind energy to meet more than 20 percent of their electricity needs, and wind energy now produces more than 10 percent of the electricity in nine states.
FACT: Iowa and South Dakota may produce enough wind each year to equal 20 percent of their annual electricity consumption, but this does not mean that the electricity was actually needed and used when it was produced.
According to a 2012 study, the greatest amounts of wind generation occur when electricity demand is lowest—during the spring and fall and during the late evening and early morning hours—and coupled with the absence of storage, this means that wind generation cannot follow electricity demand. The same study’s analysis of wind availability across three key electricity markets showed that wind generation on the 10 highest demand days ranged from only 1.8 percent to 15.9 percent of total generation.[iv] As such, stating that gross wind production for 2012 was great enough to satisfy 20 percent of a state’s electricity needs is a less meaningful statistic for intermittent power than for traditional sources.