The Ivanpah Solar Electric Generating System is a concentrated solar thermal plant in the California Mojave Desert, 64 km (40 miles) southwest of Las Vegas, with a gross capacity of 392 megawatts. It deploys 173,500 heliostats covering 4,000 acres, each with two mirrors, focusing solar energy on boilers located on three centralized solar power towers. Unit 1 of the project was connected to the grid in September 2013 in an initial sync testing. The facility formally opened on February 13, 2014, and it is currently the world's largest solar thermal power station. The total cost of the project is about $2.18 billion. The facility has contracts to sell about two-thirds of the power generated at Ivanpah to Pacific Gas and Electric, and the rest to Southern California Edison.