Okay, so T. Boone Pickens is building a big wind farm near Pampa, Texas with 2,700 wind turbines generating a combined total of 4,000 megawatts. The cost is estimated be $1.2 billion. In the construction business we call an estimate "an opinion of probable final cost". (grin)
So, to get wind power up to 20% of our total, that would be 9,600,000 MW (megawatts). So, we would have to build 2,400 wind farms just like this one at a cost of $2,880,000,000,000 (two trillion, eight hundred eighty billion dollars).
Damn! We're already over budget! Pickens said it could be done for $1.2 trillion.