A federal voluntary renewable energy purchasing partnership has reached a milestone, hitting the 600-member mark, said U.S. Environmental Protection Agency Administrator Stephen L. Johnson.

Fortune 500 companies, universities and local, state and government agencies participate in the program, called the Green Power Partnership. They purchase more than 3 billion kilowatt-hours of renewable energy annually, enough to power 300,000 average American homes.

Renewable energy from sources that include solar, wind, water, geothermal, biomass and biogas account for about 2 percent of the nation’s electricity supply. The federal government’s voluntary program supports more than 2,200 megawatts of green power generating capacity.

Under the Green Power Partnership, which the EPA launched in 2001, partners pledge to switch to green power for a specified amount of their electricity needs in return for EPA technical assistance and recognition.