Windmills have been used for energy long before there was electricity. We are now returning to this source by building wind farms. Wind is actually a kind of solar energy, since it is produced by sunlight heating different parts of the earth differ­ently. Figure 3.1 shows a typical modern wind farm. The original concept was that these farms can be built on open land where it is usually windy and, consequently, where not many people live. Farmers can lease the land to power companies for $3,000-6,000 per turbine per year and still let their cattle graze among the towers. This seems ideal, but people began to object. The wind farm at Altamont Pass near San Francisco is notorious for the number of birds that its 5,000 turbines were killing every year. The Elk River Wind Farm in Kansas was built on a pristine prairie, the home of the sage grouse and the lesser prairie chicken.2 This habitat is now cut up by roads, transmission lines, and power stations. To get enough wind power to make a difference, the environment does have to suffer, but the benefits of this free energy far outweigh the disadvantages. China hopes to get half its electricity from wind by 2020, thus cutting its carbon emissions by 30%.3 The scenery will surely suffer, but there the objectors have less of a voice. Wind power is not free of technical problems, but these seem to be less severe than with other

green technologies. In some places, like Texas, the cost of wind energy is already competitive with that from oil.