Wind energy is another form of renewable energy. Modern wind turbines have become very efficient at transferring the energy of the wind to electricity. To demonstrate the potential of wind energy, electrical generation from wind turbines grew by 28.8 percent world-wide last year. Two innovative new uses of wind energy are: (1) specially designed new wind turbines that can be mounted on the roofs of urban buildings; and (2) the idea of creating a smart grid where wind energy can be exported from areas of high winds to urban areas needing the energy. Another innovative proposal is to build a grid of wind turbines in the upper midwest of the U.S. to provide cheap energy to extract natural gas from lands containing oil shale.