A sun-powered generating station in southern Colorado's San Luis Valley will finish this year as the nation's most productive utility-scale solar electricity plant. The 8.22-megawatt SunEdison plant produced enough power for 1,652 homes. That makes it the largest plant of its kind in the country. But the Alamosa plant might not be the biggest for long. Construction was recently completed on a 10-megawatt photovoltaic plant in southern Nevada that will serve customers of Pacific Gas and Electric Co. Xcel Energy is using the plant's power to help it meet the renewable-energy standards approved by Colorado voters and the Legislature.