Changing Currents

In May, the San Francisco Board of Supervisors voted to allow a pilot project to generate power from the San Francisco Bay’s strong tides, the first such project in the nation. HydroVenturi, a London- and San Francisco-based company, is funding the estimated $3-million to $4-million cost and plans to recoup its investment through sale of power to the city. Unlike other technology designed to turn the flow of water into electricity, HydroVenturi’s has no moving parts. It uses a series of open pipes, placed at least 30 feet below the water’s surface, to capture tidal energy and drive on-shore air turbines. Possible sites for the project include Alcatraz Island and west or east of the Golden Gate Bridge. Environmental groups say they need much more information before they can evaluate the project’s impacts, especially on fish, plankton, and sediment. There may also be onshore effects at the turbines, substation and connection to the power grid. A tidal generation project in England has shown minimal effects on marine life, some of which can pass through the pipes unharmed. According to company projections, the cost, spread over 20 years, would be about seven cents per kilowatt hour, comparable to current PG&E rates. HydroVenturi aims to complete the EIR and permitting phase by 2005, and to be generating power by January 2007. If it works as predicted, says city energy specialist Peter O’Donnell, the tidal energy system could be generating 200–250 MW—close to one-half of current in-city power generation—by 2015.

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