A proposed 706 kilowatt solar panel project for the Sonoma County juvenile justice campus in the Valley of the Moon was given a go-ahead Tuesday by the Board of Supervisors.

The project is to be built, owned and operated by SPG Solar of Novato. It would add to a county-owned $4.6 million, 750 kilowatt system of 3,750 rooftop and ground-mounted panels installed last year at the Los Guilicos campus off Highway 12.

The existing project provides about half the power needs for the site, which includes the juvenile justice center, the Valley of the Moon Children's Home, the Sierra Youth Center for girls and other buildings.

The combined 1.5 megawatt solar array — equivalent to the electricity needs of about 250 homes — is expected to meet 100 percent of the campus' electricity demand.

The board approved a 20-year power purchase agreement with SPG Solar. Due to projected higher power costs from PG&E over that time, the county expects to save about $1.4 million in energy costs over the 25-year life of the project. Projected greenhouse gas reductions over the same period are estimated at 324 tons.

The county has the option to buy the system at years seven, 10 and 15 of the power purchase agreement. At the end of the 20-year agreement, the county has three options: buy the system at fair market value and operate it; enter into one-year contracts with SPG Solar for up to 10 years; or have SPG Solar remove the system at their cost.

The new project calls for ground-mounted panels in an open field between Los Guilicos Road and Pythian Road, about 500 feet from Highway 12 but screened from the roadways by a landscaped berm. SPG Solar is to lease the three-acre site for $1 a year.

Construction is set to begin in a month or so and be completed in four months.