3. The U.S. auto industry produces approximately 6 million vehicles a year, each containing roughly 1.5 metric tons of fabricated metal. Consider a future wind-turbine industry having half of the auto industry's mass throughout of wind turbine units. Each unit has a specific weight of 75 kg/kW rated (nacelle components plus tubular tower only).

a. At a wind-turbine capacity factor of 0.3, how long would it take to replicate the 2008 U.S.-installed average electric power rating of 1035 GW?

b. Discuss (5-10 sentences) the relevant factors that would determine whether a wind machine industry of this size could be successfully operated sustainably over periods on the order of several centuries.