The graph and the first few words of the article tell the story best.
Even though the production tax credit began in 1992, windpower didn't take off until 2001. So something is in play besides the tax credit. What is it?
The price of natural gas. Look at the graph.
The first natural gas shortages in 2000-2001 and the spike in nat gas prices at that time set off the first segment rise of the graph. Until 2005.
In 2005 the graph line(capacity) gets steeper which reflects the shortages and price rise of gas caused by Katrina. Until 2007.
In 2007 the graph line increases gets steeper again to reflect that the price of natural gas had started following the price of oil(going up).
The author is not well informed when he speaks about nighttime wind power in Texas. Because Texas generates more power from nat gas than from coal, wind is substituted for nat gas at night.
My point was that a glance at the graph makes it seem that there’s a close match between capacity and production of wind power. A more honest graph would have shown that, while there’s a very strong corelation between capacity and production, in fact actual production is only 1/5 th of the potential production implied in the capacity figures.
You make good points about there being other factors involved — there always are. Grid management measures, such as the substitution of wind for natural gas that you mention, would certainly make things less bad, in practice. However, the fact remains: production is only 1/5 of potential production. The graph does not show that discrepency graphically (you can figure it out, but the graphics do not reflect reality). It’s not an honest graph.