It's all about transmission lines. From Reuters:
Texas regulators are leaning toward a plan to accelerate power line construction to accommodate about 18,000 megawatts of wind generation by 2012, less than the 24,000 MW wind supporters are seeking, following a two-day hearing in Austin....
...Major power lines are needed to transfer wind generation from sparsely populated West Texas to Dallas, Houston and San Antonio, where electric demand is highest.
The commission questioned witnesses about benefits and costs of four transmission-route scenarios proposed by the Texas electric grid operator to accommodate from about 12,000 MW to as much as 25,000 MW over the next four years.
Estimates from the Electric Reliability Council of Texas (ERCOT) to transfer wind power on new 345-kilovolt lines range from $3.4 billion to more than $7.4 billion, depending on the number of lines built.