The biggest photovoltaic solar panel array in the United States opened this week at a U.S. Air force base in Nevada and the biggest array that sells power to an electric utility began operation in Colorado, companies involved said.

A 14-megawatt solar farm covering 140 acres opened at Nellis Air Force Base near Las Vegas, Nevada on Monday. It will generate 30,000 megawatt hours a year and will supply about a quarter of the electricity used at the air base. About 12,000 people live and work on the base.

Nellis Base Commander Col. Michael Bartley said the solar array may be just one of many such projects by the U.S. military.

"The project also provides a future test bed for the Department of Defense to assess the benefits of similar arrangements on installations across the United States," said Bartley.