The NREL study considered four scenarios, three at the 20 percent level of wind generation, and one at the 30 percent level, the scenarios being differentiated by the number of onshore versus offshore wind turbines that would be built. The 20 percent scenario requires about 225,000 megawatts of additional wind capacity and the 30 percent scenario about 335,000 megawatts. That’s 9 to 13 times greater than the wind capacity that existed at the end of 2008. And it would require that 16,000 to 24,000 megawatts to be constructed each and every year. By comparison, the largest amount of wind capacity actually constructed in a year was slightly less than 10,000 megawatts, in 2009. [ii] Because wind generation is intermittent, the capacity of the new wind units needs to be above the target generation level. The offshore component would represent 0 to 28 percent of the required generating capacity, depending on the scenario. Offshore units are more expensive to build than the onshore units, but fewer transmission upgrades may be needed.
