The other principal goal of Glen Canyon Dam is hydroelectricity generation. It is the second-biggest producer of hydroelectric power in the Southwestern United States, after Hoover Dam. Revenues derived from power sales was integral in paying off the bonds used to build the dam and has also been used to fund other Bureau of Reclamation projects, including environmental restoration programs in the Grand Canyon and elsewhere along the Colorado River. For this reason, it has long been known as a "cash register" dam. The dam also serves as a primary peaking power plant and black start power source for the Southwest electrical grid. The power plant has a total capacity of 1,320 megawatts from eight 165,000 kilowatt generators. Each generator is driven by a 254,000 horsepower vertical-axis Francis turbine. The gross hydraulic head is . The units were installed between September 1964 and February 1966 at an original rating of 950 megawatts; an upgrade project between 1985 and 1997 brought it to its present capacity.