The Crescent Dunes Solar Energy Project near Tonopah, Nevada, uses 17,500 heliostat mirrors that collect and focus the sun’s thermal energy to heat molten salt flowing through a 540-foot (160 m) tall solar power tower. Seen here during its construction in 2015, the molten salt at its center then circulates from the tower to a storage tank, where it is used to produce steam and generate electricity.In a recent report, the International Energy Agency (IEA) just declared solar to be the cheapest form of electricity worldwide, saying the cost per megawatt to build a solar plant is now cheaper than any fossil fuel facility.