Since the 1960s, a new type of farm,a wind farm, has appeared. A wind farm is not covered with waving wheat but rather with giant wind mills. Like water wheels, wind mills have long been used to turn wheels to grind grain. But these new wind mills use wind energy, or air movements, to generate electrical energy.The wind mills often have blades that are up to 30m[100 feet] long. They take up much space but they don't cause air or water pollution and require very little maintenance.