Total US consumption is was 4,119 TWh in 2008. (Wind was 55.4 TWh.) Last year 10 GW were added, if we can assume an average capacity factor of 30% (this being the US), they should be good for 26.3 TWh, or an annual increase of market share by around 0.66 percentage points. 48.7/0.66 = 73.8.

_{*Lunatic*, n.
One whose delusions are out of fashion.}