USA windpower now producing over 43,000 megawatts

Let us note that, from the article, this translates into only 3 percent of total electricity generated nationwide. This is in large part due to the inability for wind power to generate a constant power load. From what I recall the nuclear power plants can produce a load of about 100 x 1400 MW = 140,000 MW and this is estimated to be about 20 percent of the elctricity produced nationwide.

Roughly speaking it looks like the nuclear power plants have three times as much installed capacity than solar and produce 6 times as much power to the grid. Since the nuclear power plants are near 100 percent capacity, I wonder what is the reason why wind has roughly a 50 percent production capability: is it maintenance or wind availability ?