In the United States, solar-powered energy plants are starting to come into their own. San-Diego based Sempra Generation finished construction on the largest photovoltaic solar power plant in the country, located in Boulder City, Nev., about 40 miles southeast of Las Vegas. The 48-megawatt Copper Mountain Solar facility has 775,000 thin-film solar panels, which should be able to power about 14,000 homes, on average.