A proposal announced by Interior Secretary Ken Salazar Monday could increase by 70-fold the existing installed capacity of solar electricity-generating plants in the United States. The plants would be located on federal land and eventually provide a capacity of 100,000 megawatts, enough to provide the electricity needs of 15 million to 25 million residences. Today, slightly more than a gigawatt (1000 megawatts) of photovoltaic- generated electricity and 600 megawatts of concentrated solar pow