A tweet from the Department of Energy (DOE) gives a link to a DOE webpage highlighting a graph from, and giving a link to, a study by the American Wind Energy Association.

Skipping the question of how appropriate it is for the DOE to flack for an advocacy organization, we can address the topic: the rapid growth of wind-energy installation.

For years, wind advocates have been bragging about the growth of installed wind-power capacity, which they compare to other energy sources. What they rarely (if ever) talk about is production.

Because windmills cannot be turned on at will—in industry jargon, they are not dispatchable—the power they produce depends on how much the wind blows. At 25 percent, the average capacity factor for wind power is well below those of conventional sources. So a better comparison, rather than the theoretical potential of windmills installed, is the growth in actual electricity produced.

When we compare growth in electric power generation since 2005, we see that the increase in wind power pales in comparison to that of natural-gas-generated electricity. On an annualized basis, natural gas power generation has grown four times as much as wind power—roughly 600 billion kilowatt hours (kW-h) per year for gas versus about 140 billion kW-h per year for wind. Even that comparison is overly kind to wind, because the wind typically blows less when you need it most.

The pattern of generation in 2012 shows why capacity comparisons are nearly useless. From January to July 2012, total power generation in the U.S. rose 22 percent to match the high demand during the hot summer months. However, because wind power is at the mercy of the weather (remember, it is not dispatchable), wind power generation actually dropped 24 percent between January and July. Over the same period, natural gas power jumped 53 percent, and coal-fired power increased 25 percent.

We should also note that the phenomenal growth in natural gas production occurred without anything like the production tax credit that subsidizes wind power by an amount equal or greater than 40 percent of the wholesale price of electricity. As we have shown before, an equivalent subsidy for oil would be about $50 per barrel.