Inside San Francisco’s Biggest Solar Power Project (And the History Behind It)

Written by Sharon McDonnell

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Sharon McDonnell

Ecotourism Writer

Sharon McDonnell is a travel writer who is passionate about sustainable living and ecotourism.

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Sunset reservoir is San Francisco’s largest solar project, here is what you need to know about its history and capacity for producing green energy.

The 4.5 megawatt project, which more than tripled solar generation for the city of over 850,000 people, generates electricity for the city’s public transit system (called MUNI for short), schools, libraries, streetlights, City Hall and San Francisco International Airport, which is located in San Mateo county, south of the city. 

The solar power generated by Sunset Reservoir was expected to reduce the city’s carbon emissions by over 100,000 metric tons over 25 years, which roughly equals taking about 1,000 city homes off the grid.

The History of the Sunset Reservoir

Located in the Sunset, a residential district of low-rise pastel-colored homes, stretching four city blocks by two blocks, it became the city’s biggest solar power project when finished, eclipsing Moscone Convention Center, whose 2004 solar installation was the city’s biggest before that. 

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The San Francisco Public Utilities Commission (SFPUC) agreed to buy the electricity under a public/private 25-year power purchase agreement from Recurrent Energy, the local company who built it.

The solar plant is owned and operated by Duke Energy Sustainable Solutions, who acquired it in 2013 from Recurrent Energy. The Charlotte, North Carolina-based Duke Energy has nearly 150 solar projects for utilities, electric cooperatives, municipalities, corporations, and other large energy customers, plus 23 wind farms, across 22 states. BASS Electric (Bay Area Systems & Solutions) designed and installed the panels.

The Sunset Reservoir

While the city of San Francisco set a goal to be 100% powered by renewable energy by 2030, SFPUC announced last year it would meet that goal by 2025 for all its 385,000 CleanPowerSF customers, a community choice option for clean energy from solar, wind, geothermal and biomass sources throughout California.

The commission completed its first solar plus battery storage installation in the city 2021, atop a police academy carport, while its second is this year at a library branch. (Battery storage keeps excess generated energy from being wasted, e.g. during the night when demand may be high but solar energy produced is low.)

Solar Superstar Cities

But putting things in a national perspective, Los Angeles is the nation’s city with the most total solar power capacity, with 649.9 megawatts, according to a 2022 report on the top US cities for solar power by the Environment America Research & Policy Center and the Frontier Group.

Among the “solar superstars,” San Francisco is now #18. But LA is a much bigger city of about four million people: it also led all US cities in total solar power capacity installed in 2014-16 and 2018-2020. (San Diego, which has 3.3 million people, dethroned LA in 2017.)

After LA, San Diego is second, Las Vegas third, Honolulu fourth, and San Antonio, Texas fifth in the rankings of total solar power installed in cities in the annual report compiled by the Denver-based nonprofit and Santa Barbara-based Frontier Group. (Per capita, Honolulu boasts the most solar power, followed by Las Vegas, San Diego, Albuquerque and San Jose.)  

Sunset Reservoir’s Water Source

But Sunset Reservoir’s solar plant isn’t the only remarkable thing about the reservoir, which contains about 87 million gallons of water. The main water source for about 2.8 million residents and businesses in the Bay Area, its water comes largely from Yosemite National Park.

The water comes from Hetch Hetchy, a reservoir in a majestic glacier-carved valley, located on the main stem of the Tuolumne River, which starts in the Sierra Nevada mountains above. Swimming and boating are banned in Hetch Hetchy to keep the water pure. (Some water in Sunset Reservoir comes from two reservoirs in San Mateo County, Crystal Springs, and San Andreas.) 

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Water in the Hetch Hetchy Reservoir, which often holds about 93 billion gallons of water, then travels 160 miles from Yosemite to the Bay Area through pipelines and tunnels using gravity alone, without pumping stations, to supply drinking water for 43% of San Francisco, plus Alameda county (which includes Oakland and Berkeley), Santa Clara county (Silicon Valley) and San Mateo county.

Hetch Hetchy dam controversy

Intense controversy ensued over a century ago when a dam over the river was built in Yosemite to satisfy San Francisco’s growing water needs. John Muir, who pushed Congress to pass a law in 1890 to establish Yosemite National Park, voiced strong objections to dam the river, calling Hetch Hetchy “one of Nature’s rarest and most precious mountain temples.”

The Sierra Club, which he founded, But the city of San Francisco won approval in 1913 from Congress, after a five-year debate, to build the O’Shaughnessy Dam. Called the nation’s most controversial dam, the fight to prevent it was called the first major battle of the environmental movement.

An engineering marvel, the dam was the second-biggest civil engineering project at the time, second only to the Panama Canal, built in 1904.

But while the Scottish-born preservationist died the year after he lost the struggle to preserve the wilderness, the controversy lingers today. A nonprofit, Restore Hetch Hetchy, sued San Francisco in 2015, but lost.

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