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Ebb and Flow Energy by Jared Blumenfeld San Francisco Chronicle - August 2, 2002

"We must take the current when it serves, or lose our ventures."

-- William Shakespeare

I was fishing under the Golden Gate Bridge recently with my 3-year-old son. We turned off the engine and began to drift -- but before we knew it, the tide was pulling us out to sea at a good six knots. My boy was dubious when I told him that tides are caused by the gravitational pull of the moon on the ocean, but he could witness the power of the tides.

More than 40 million cars travel over the Golden Gate Bridge every year, but what really gives us something to talk about is what's happening beneath the bridge. Each day, nearly 400 billion gallons of water rush through the mouth of San Francisco Bay. If harnessed, the energy from this water could be an answer to the city's power needs.

We've been hearing a lot about wind and solar power lately, but tidal power has been used since the early 1900s as a reliable source of electricity. Tidal technology has advanced since its early years with improvements in turbine technology. Canada, France, Britain, Japan, Russia and China are all working on large-scale tidal projects.

San Francisco ought to meet all of its electricity needs through renewable sources. We got a good start in November when we passed two ballot measures to fund solar and other renewable power projects. The city's goal is to put solar panels on 20,000 rooftops, which would produce roughly 50 megawatts of electricity. But the city's peak demand is 875 megawatts, so we're clearly going to have a significant shortfall.

According to Martin Berger of the Canadian company Blue Energy, the tides flowing at the Golden Gate can generate at least 1,000 megawatts. That would make the city power-positive, clean, and green -- and would give us the necessary in-city electricity generation to shut down the Hunters Point power plant.

Underwater fans could be sited in rows at the mouth of the Golden Gate, leaving the navigation channel open and unobstructed. Unlike the sun and wind, tidal current is as consistent and predictable as the tidal charts. Fair weather or foul, the tides will ebb and flow. Tidal generators could produce renewable, emissions-free electricity up to 16 hours a day. About 80 percent of the time this energy would coincide with our peak demand. During the early morning hours when we use very little energy, the tidal power could be used to process hydrogen for fuel cells that we could tap for use when needed.

When I was telling my son this story, he asked whether underwater turbines would hurt the fish. I told him that the new high-tech propellers are geared to spin slowly, at only 25 to 50 rpm, so the fish can dart in and out of the turbines, where they can continue to elude weekend fishermen like us. Additionally, new tidal energy systems are calibrated not to impede the natural water flow, or trap silt.

San Francisco and surrounding Bay Area communities would be wise to explore tidal power as part of a comprehensive clean-energy portfolio, along with solar and wind. San Francisco, with its voter-approved $100 million bond for clean energy development, would profit in particular from an immediate assessment of the possibilities. The first step is to evaluate the environmental impact of such a project, and to conduct sonar modeling and other necessary scientific studies to determine whether we can attain the desired results.

The benefit to our neighborhoods is clear. Tidal power could help us ease the environmental burden on the communities in the city's southeast, where we operate some of the oldest and dirtiest power plants in California.

Within 10 years, San Francisco could build enough clean tidal power to meet its daily energy needs, as well as generate surplus energy to sell -- all with a price tag of about one-third the cost per megawatt of solar power. When that happens, I hope to be fishing with my son, telling him about how the pull of the moon on the bay keeps our lights burning bright.