One of Sonoma County's main government facilities in the Valley of the Moon soon will harness the sun for all of its electricity, making it possibly one of the first municipal centers of its kind in the state.

County contractors two weeks ago activated 2,400new solar panels at the Los Guilicos center along Highway 12, which includes juvenile hall, courtrooms, Valley of the Moon Children's Home and other county services and buildings.

The 708-kilowatt system covers three acres off Pythian Road and joins a 750-kilowatt array of 3,500solar panels installed in 2011 on the center's roofs and behind buildings against the foothills.

Together, the two systems are expected to cover the center's electricity needs, or about 1.5 megawatts, enough to power about 350 homes.

County officials say the center could be one of the first "zero net energy" municipal campuses in California, meaning it generates all of its electricity with clean renewable power.

"It could be the first," said Sam Ruark, the county's energy and sustainability coordinator. "In our asking around and asking PG&E, we haven't heard of any other ones."

The two solar systems will work together but are separate, with the newer system owned, built, paid for and operated by Petaluma-based SPG Solar, a commercial installer with a power purchase and lease agreement with the county. The company expects to recoup its investment via the power purchase agreement. The new system will be unveiled at 11a.m. Friday in a public ceremony at the site at 6600 Los Guilicos Road.

The larger county-owned system was built for $4.6 million, including $3.4 million in low-interest, clean energy bonds overseen by the federal government and issued by the county, plus federal stimulus money and county greenhouse gas mitigation funds.

The two systems will feed power into the wider grid — generating more electricity in the summer and less in the winter — to meet the center's annual projected energy demand.

They fit within a larger county effort to cut greenhouse gas emissions and upgrade county facilities for energy self-sufficiency and savings. That $22 million Comprehensive Energy Project includes a 1.4-megawatt natural gas fuel cell that now powers the county's main administrative center in Santa Rosa, plus water and energy retrofits to dozens of buildings.

County officials have hailed the project as a long-term investment that will cut costs for taxpayers and achieve environmental goals. But the investment comes with risks.

Over 25 years, the county expects to recoup a combined $4.6 million in savings from the off-grid power supply for the Los Guilicos center, officials estimate. Before the two projects, electricity from the grid to the campus cost $350,00 annually.

The overall savings, which include an estimated $1.4 million savings from the newer set of panels, are based on projections showing higher yearly cost increases for PG&E power over the next two decades. Still, actual rates can vary widely in a volatile power market, and sometimes such projects do not work out in taxpayers' favor.

David Rabbitt, chairman of the county Board of Supervisors, acknowledged the projections are not foolproof and the longterm payoff is uncertain.

"We know what our costs are going to be. We're trying to figure out what PG&E's costs are going to be," he said. They could be more, they could be less, he said.

He nevertheless voiced support for the project.

"I love new infrastructure going in, I love new technology," he said. "We just have to make sure it fits within a business plan that makes sense."

The two solar systems are set to go live together in about three months after safety upgrades are complete to ensure the grid can handle the influx of new power. Until then, the county has temporarily taken its solar panels at Los Guilicos offline.

Combined, the county and the county Water Agency have about 3.6 megawatts of installed solar power, or enough to supply about 850 homes.

The Water Agency is pursuing what would be the largest solar project in the county, with plans to cover 50 vacant acres near the county airport with 54,700panels, costing about $100 million

You can reach Staff Writer Brett Wilkison at 521-5295 or brett.wilkison@pressdemocrat.com.