The U.S. electric network is operated by 3,000 utility companies (Bangor Hydro-Electric Co., Central Maine Power Co., etc.) using 146,000 miles of high-voltage transmission lines. These transmission lines are, in turn, owned by another 500 transmission line companies. Good sources of wind and solar energy are not close to these grids. The U.S. Department of Energy projects that $60 billion will be required to connect renewable sources to the networks that deliver the electricity to customers.