A Sonoma County government site east of Santa Rosa will soon be home to one one of the largest municipal solar energy projects in California.

The project consists of 3,750 rooftop and ground-mounted panels that will help power the collection of buildings comprising the Los Guilicos Juvenile Justice Center off Highway 12.

Santa Rosa-based Aircon Energy will begin work on the $4.6 million project this summer with completion planned for later this year.

The bulk of the project's funding, about $3.4 million, comes through two low-interest, clean energy bonds overseen by the federal government and issued by the county through Bank of America.

The remainder comes from $700,000 in federal stimulus money and $480,000 in county greenhouse gas mitigation funds. No general fund cash will be used in the project, officials said.

"This is exactly the type of enterprise our county needs and it eloquently reflects our board's economic and environmental goals," Board Chairwoman Valerie Brown said Tuesday after supervisors gave the project the go-ahead.

Renewable energy for the Los Guilicos campus has been envisioned since construction of the juvenile justice center about eight years ago, when plumbing and wiring were installed to accommodate a future solar panel system, said John Haig, Jr., the county's energy and sustainablity manager.

Until now, the campus, including the juvenile hall, courtrooms, Valley of the Moon Children's Home and other facilities, have been linked to standard power provided by PG&E.

Once the panels are installed, they will provide up to 750 kilowatts — enough to power about 500 homes — or a supply equal to 80 percent of the juvenile hall's energy needs and 40 percent of the entire center's needs, Haig said.

Any extra power will go back into the grid and provide additional savings for the county, he said.

By the end of system's estimated lifetime in 2035 — and eight years after the project is to have paid for itself — the county expects to recoup about $3.2 million in savings from that off-grid power supply, Haig said.

The system also is expected to inch the county closer to the regional goal of cutting greenhouse gas emissions back to 1990 levels by 2015.

"This is exactly the sort of project about which we are enthusiastic," said Jake Mackenzie, board chair of the Sonoma County Regional Climate Protection Authority, the body of local governments that set the emissions goal.

The solar power system is among a group of clean energy retrofits approved last year by the Board of Supervisors as part of the county's $22 million Comprehensive Energy Project.

Other projects in that effort have included the replacement of four chilling units and an aging boiler in a mechanical plant that serves as the county's heating and cooling nerve center, lighting retrofits in 15 county buildings, water system retrofits in 20 buildings, and the planned installation of a 1.4-megawatt fuel cell that will make the county nearly independent of the outside power grid.