SAN DIEGO -- San Diego Gas & Electric Thursday announced a 20-year agreement that will result in one-quarter of its renewable energy coming from windmills in Imperial County.

Enough juice from the Ocotillo Wind Energy Facility will be delivered over the Sunrise Powerlink transmission lines to provide electricity to 130,000 customers, according to SDG&E.

The facility will be built by San Francisco-based Pattern Energy on a 15,000-acre site 25 miles west of El Centro, said Jennifer Ramp of SDG&E.

With the contracts signed so far, 600 megawatts of energy transmitted to San Diego via Sunrise Powerlink will be generated by wind or solar power. The company is working on getting the remaining 400 megawatts to come from renewable sources, too, Ramp said.

"We've been working diligently to fill the Powerlink with renewable energy," she said.

Construction began on Sunrise Powerlink late last year following stiff opposition from environmentalists and residents of San Diego's back country, who said that rather than renewable energy, the lines would carry electricity generated by coal-fired plants in Mexico.

Ramp estimated completion of the transmission line in the middle of next year.

The Ocotillo Wind Energy Facility is scheduled for completion at the end of 2012, she said.

The deal between the two companies requires approval from the California Public Utilities Commission.