By Michael McCarthy

Hi, how are you doing today? Glad to see you out here.” “Fine, sir,” says the National Guardsman, surprised to hear words of praise. “Thanks for your support.” Peter O’Donnell, wearing a shiny black vest over a formal white dress shirt with a colorful tie, stands out from the casually-attired tourists wandering about old Fort Point under the south end of the Golden Gate Bridge this rare fog-free summer day. O’Donnell, Senior Energy Specialist with the Department of the Environment for the City of San Francisco, stands out in another way. He isn’t here to gaze up in the air like a tourist at the magnificent Golden Gate Bridge towering high above, or to stroll around the Civil War-era fort looking at relics of yesteryear. Instead, O’Donnell wants people to look down at the immense flows of water surging under the Golden Gate Bridge and give some serious thought to the future.

“There are nearly 400 billion gallons of water rushing through the Gate every day,” says O’Donnell, pointing at the murky, fast-flowing ebb tide racing under the bridge. “That’s four billion gallons of energy each and every tide, flowing at up to six knots, four times a day. Forty per cent of the fresh water in California drains through that opening every year. The potential for tidal energy generation here is incredible.”

While the National Guard stands ready to protect our world famous treasures like the Golden Gate, O’Donnell is one of the few people fully aware that another national treasure flows underneath. With the world rapidly running out of oil, politicians—and the huge corporations that bankroll their campaigns—are proposing to frantically punch holes in the permafrost, drill into the ocean deeps, and hastily erect more polluting fossil fuel plants. O’Donnell is one of the very few who knows there is a much better way to provide for our future energy needs. Now that his Department of the Environment has chosen to go public with its research, pretty soon everyone else will know too. What happens then is anybody’s guess.

The City of San Francisco is surging ahead with planning and research into alternative and renewable energy sources in an effort to keep the lights on a few short years from now. Last year, San Franciscans voted overwhelmingly for two renewable energy bond measures totaling over $100 million. This year, voters will be asked to express their views on public power on the November ballot. While alternative energy generation has been discussed for years, the focus to date has been on wind and solar power. O’Donnell, however, knows that tidal power stands the best chance of providing the city with a massive supply of clean, dependable energy—all from one location right in the heart of the city—forever.

“You see the west tower of the bridge out there in the shipping channel?” says O’Donnell, pointing under the bridge. “We could run a ‘tidal fence’ between the tower and the shore and turn Fort Point into a substation and a tidal energy demonstration facility. Over there, between the bridge and Alcatraz, is an underwater navigational hazard known as Shag Rock. Instead of blowing the top ten feet off to prevent any ships from running aground, as has been proposed, we could install a tidal turbine and beacon instead.”

Then O’Donnell turns and points in the other direction. “Outside the Gate, the piece of water known as the ‘Potato Patch’ is perfect for a ‘water farm’ with tidal turbines just like the wind farm at Altamont Pass.”

The Golden Gate has a span of one mile. With two meters of tide height at a velocity of two meters per second, up to 2.5 billion cubic meters of water races through the Golden Gate every six hours. Since seawater is 832 times as heavy as air, installation of tidal turbines at this strategic location could provide up to 1500 megawatts of clean, dependable power to the City (a megawatt is the amount of energy sufficient to power 1,000 homes). For many environmentalists, scientists and far-thinking researchers like O’Donnell opposed to the ongoing degradation of the planet, it makes no sense to destroy valuable resources like oil or natural gas just to produce another resource like electricity. Why not harness the natural energy of the sun, wind, tides, and waves instead?

Yet tidal energy projects have never been tried in the Bay Area, and proposals to provide new energy generation almost invariably turn to exploitation of fossil fuels. In Vallejo, although the plan has run into stiff opposition from local residents, Bechtel Corporation and Shell are proposing a $1.5 billion liquefied natural gas (LNG) plant on Mare Island that will produce 1500 megawatts, enough to service a city of 1.5 million people. Calpine plans to open a 600-megawatt, $400 million natural gas-fired plant in Hayward by 2004 to go along with the 500-megawatt $300 million Los Medanos natural gas-fired plant it is finishing in Pittsburg. Nine huge gas-fired plants are being built throughout the state, all powered by fossil fuels, at an estimated cost of $3.7 billion. The California Energy Commission is also considering 14 more power plants, including three in the Bay Area. All this, even though experts warn that the world is rapidly running out of natural gas and, as supplies dwindle, its price can be expected to rise sharply.

Natural gas, even when fitted with the latest advances in technology to contain emissions of nitrous oxide, emits large amounts of carbon dioxide, the greenhouse gas blamed for global warming. At the same time the state government is passing laws to reduce the emission of C02 in automobiles, it is allowing vast amounts of carbon dioxide to be emitted from another source.

In his recent report titled Tidal Current Technology Generation, O’Donnell remarks on the close comparisons between wind and water for renewable energy generation. “Wet wind” is clean and pollution free with negligible land use or environmental impact. Tidal projects are advancing rapidly in Canada, several European countries, and in Alaska. Several North American companies are “closing the gap between concept and commissioning of projects” and some tidal installations are expected to be “on the wire” in the next few years. As a new technology, however, initial capital costs are high and not currently competitive with fossil fuels. Technical improvements, however, along with economies of scale, mass production, and improved methods of installation are expected to result in significant cost reductions.

Although untried in America, tidal power is hardly new. Rough, river-fed, turbine-type devices have been used to grind grain since the 11th century in Britain and France. In the 1960s, France commissioned a huge dam-like tidal “barrage” system in St. Malo to block an entire estuary. Using ten 240-watt turbines, the system still works perfectly. At the Bay of Fundy in Nova Scotia, a 20-megawatt barrage fence was built 30 years ago and is still in use today. (Barrage generation systems, which block water flows entirely like hydropower dams, have fallen out of favor due to the buildup of silt.). Today, Scotland, England, Norway, Canada, and other countries with fjords and major ocean inlets are experimenting with several different types of wave and tidal power including “tidal fences.”

Tidal fences are composed of individual, vertical axis turbines mounted in caissons to comprise a pier (or fence) with an approximate 12-foot “above-water profile.” These fences are attached to the marine bottom on a rock-filled bed and secured by piles at the joints. Their ducted caissons channel current flow past vertical turbine rotors connected to above-water generators and make electricity. Large marine animals such as seals, whales, and dolphins instinctively shy away from the pull of underwater turbines and can swim under a tidal fence. Propeller towers, river turbines, wave generation devices, monopile installations, and other ingenious tidal generation devices are being tested in many locations worldwide.

O’Donnell describes two “jetty-constructed tidal fences” that could function here in the Bay. Under the Golden Gate Bridge, between Fort Point and the west tower of the bridge, cement pilings would be driven to a depth of 150 feet to penetrate the gaseous mud layer down to bedrock. Individual caissons, approximately 20 feet tall by 40 feet wide, would be aligned and sited on a gravel bed of crushed rock. Injections of cement may be required to firm up the mud bottom.

At East Brothers Island, just north of the San Rafael Bridge at Point Richmond in the East Bay, a Canadian company called Blue Energy recently proposed a 1000-foot tidal fence between the shoreline and the island. The fence would double as a bridge for guests at the historic lighthouse inn. Such a fence, with a tidal flow of three knots, could produce 30 megawatts per tide (a minimum of one knot is required to turn the turbines). O’Donnell, who spoke on behalf of Blue Energy to Richmond’s City Manager, admits that proposal exemplified the problems inherent in tidal generation projects.

“Among other things, that project included construction of a renewable energy demonstration facility on the shoreline,” says O’Donnell. “The project stalled because I think the council looked at Blue Energy as some sort of real estate development firm. They were more interested in the rehabilitation of the shoreline than a public-private sector partnership that would provide new sources of electricity for their municipality.”

O’Donnell has identified several other sites where tidal flow is sufficient to install tidal fences, tidal turbines, water farms, and other tidal generation devices in the Bay Area, including the Delta, Carquinez Strait between Vallejo and Martinez, and Raccoon Strait between Tiburon and Angel Island. He has shared his extensive research with members of Congress and the State Assembly, mayors and councils of various municipalities, and members of the San Francisco Board of Supervisors, among others.

So far, two factors inhibiting the installation of any form of tidal device have become apparent. First, no corporation or commercial interest is interested in the major expenditure of capital required for research because the initial costs are prohibitive and profits—huge as they may be—lie too far in the future. Secondly, whenever and wherever any tidal generation systems are built, they will likely be using public funds. That will require the cooperation of many different levels of government.
“The average cost of electricity derived from wind energy has dropped 50 per cent since the 1980s. The reliability and construction techniques of wind turbines has increased significantly as well,” says O’Donnell. “Tidal projects will go through the same kind of improvement once we start getting projects in the water. Costs will come down and reliability will be increased. However, dedicated pre-commercialization research is required.”

“To generate one megawatt of electricity from tidal turbines in the Golden Gate right now,” says O’Donnell, “would require an initial investment of $1.3 million. A single tidal fence or water farm could produce 20 megawatts. Those costs are relatively high, but the way to do it is the way Thomas Edison did it a century ago. Edison got funding to wire one city block, sold the power, then went back and borrowed more money to wire three more city blocks. The way to build tidal energy here in the Bay Area is the same, one project at a time.”

While initial pre-commercialization costs can be met, the political problem is more complex. In his Tidal Generation report, regarding just one specific assessment site in San Francisco Bay, O’Donnell had discussions with the Coast Guard, the Bureau of Land Management, the U.S. Army Corp of Engineers, the California Energy Commission, the U.S. Federal Energy Regulatory Commission, the State Lands Bureau, state and federal fisheries bureaus, the Department of Water Resources, the Water Quality Board, the County of San Francisco for land use permits, and an endless number of environmental and community land use groups.

But while initial costs are daunting and the politics more than complex, there is also the enticing prospect of an endless stream of clean energy at great profit. Once built, tidal farms and fences are fairly easy to maintain and, unlike power plants fired by natural gas, obviously have no ongoing fuel costs. While the City of San Francisco currently needs 800 megawatts to fulfill its daily needs, a tidal generation plant underneath the Golden Gate could provide much more than that when fully built out. The City could turn around and sell excess energy to municipalities throughout the Bay Area. O’Donnell points out that the Hetch Hetchy water system wasn’t cheap or easy to build either, yet it was done with technology that today would be considered ancient.

“The City has a mandate to explore all forms of energy to provide for its future needs,” he says. “That’s exactly what we have been doing.”

At the Department of the Environment, a nondescript office building on Grove Street across from City Hall, Director Jared Blumenfeld is busy today in board meetings dealing with renewable energy generation. While it may be news to many, his office has been researching and planning for implementation of tidal energy for 18 months.

“Our office and the Public Utilities Commission are currently developing an electricity generation plan for the entire City. Our goal is to shut down polluting Hunters Point Power Plant by 2005,” says Blumenfeld, “so we need to develop adequate clean sources of electricity by that date. We’re looking at the entire renewable energy portfolio, including solar, wind, and tidal generation. Once we accomplish that first, important goal of shutting down Hunters Point Power Plant, we’re setting our sights at 100 percent clean energy generation in San Francisco by 2012.”

While the technology behind tidal power is neither new nor overwhelmingly complex, Blumenfeld points out that every tidal generation plant in the world faces the same problem of “re-inventing the wheel.” There are no ready-made “one size fits all’ designs.

“There are no examples of tidal generation anywhere in the world that reflect the specific conditions of San Francisco Bay,” says Blumenfeld. “Before we proceed with any tidal projects, we must be certain that we can answer all of the environmental concerns. We will need to determine the effect of the turbines on fish and marine mammals, we will need to know what kind of sedimentary deposits might be disturbed in construction, and we will need to know that the project would not create visual blight or interfere with seagoing commerce. Also, if the tidal power installation constitutes Bay fill, we will need to identify remediation projects to offset the impact.”

“Regardless of whether San Francisco votes to create a municipal power agency this November,” he says, “the city will have to facilitate or develop renewable energy projects if it’s going to meet its goal of shutting down the Hunters Point Power Plant by 2005.”