SAN FRANCISCO, Calif. — San Francisco took a major step today toward building California's largest solar photovoltaic system -- a plan that would more than triple the city's solar energy output by carpeting the rooftop of its biggest reservoir with almost 25,000 panels.

Recurrent Energy
, a San Francisco firm, will install and operate the 5 megawatt array atop the reservoir, an area roughly the size of 12 football fields.

Standing atop the Sunset Reservoir -- so named because it lies in the city's Sunset District -- Newsom signed an ordinance into law this morning that enables the installation project and a 25-year contract with the distributed power firm Recurrent Energy to go forward.

The city's Board of Supervisors approved the arrangement, which involves a power purchase and site lease agreement between the San Francisco Public Utilities Commission and Recurrent Energy, on a 7-4 vote on Tuesday.

In power purchase agreements, the firm that finances, developments, operates and maintains the solar system has the rights to the energy it produces. Typically, the host site -- in this case the SFPUC -- commits to buying the energy generated at competitive rates for the duration of the contract.

Under the arrangement, Recurrent Energy will be able to take advantage of a 30 percent federal tax credit that is available to the private sector in power purchase agreements, which effectively lowers the cost of the project.

City analysts estimate that over the life of the contract, the power purchased will cost $50.3 million -- $36 million less than a lifetime cost of $86.3 million, which is what San Francisco would have to pay to build and finance the project itself.

Recurrent Energy says that with Newsom's signature in hand, construction is to begin immediately and will result in 71 green collar jobs. The installation project is expected to be complete by early next year.

Critics of the project had expressed concerns that the Sunset District is notoriously foggy and that the contract period is too long.

Recurrent Energy has said that the site gets only 15 percent less sunlight than the sunniest places in town. Under the contract, San Francisco will have the option to purchase the operation at the seven-year and 15-year anniversary.

Organizations that advocated the project included the Sierra Club, the Union of Concerned Scientists, the IBEW, Vote Solar, Luminalt, the Ella Baker Center for Human Rights, the Apollo Alliance, Green for All and San Francisco Community Power.

The solar power system is expected to reduce carbon emissions by more than 100,000 metric tons over a 25 year period, according to John Rizzo of the Sierra Club San Francisco Bay Chapter.

In October, Newsom challenged the San Francisco's 1,500 largest firms to enlist in his movement to ramp up the city's capacity to generate renewable energy. At the time, he had asked businesses to collectively install systems that would increase the city's capacity to generate solar power from its current 2MW to 5MW.

Image courtesy of Recurrent Energy.