Developing renewable energy sources such as wind, solar, and geothermal power is one of the main goals of Google's nonprofit arm, Google.org. The project concentrates on solar-powered turbine engines to create electricity, as well as on low-cost heliostats, which are mirrors that track the sun and concentrate solar energy. Google also supports efforts to map the world's potential geothermal energy sources. The goal is to create renewable sources that are cheaper than burning coal, which currently generates most of the power in the United States