Harnessing the tides In the eternal search for renewable energy, Maine looks to undersea turbines BY ALEX IRVINE

The next time you’re driving out to Ferry Beach, you might notice a sign for Tidal Mill Road. "Tidal mill?" you might think. "Huh. How come nobody does that any more?"

As far back as the eighth century, it was fairly common for people in coastal areas of Europe to partially dam narrow tidal channels and use what is essentially moon power to turn mill wheels or perform other pre-industrial tasks, and tidal mills didn’t go belly-up until the final victory of steam in the 19th century. The energy is free, after all; the tides have been coming in and going out as long as there’s been water on the planet, and unless the moon blows up tomorrow, that won’t stop. (Actually, even if the moon blew up tomorrow, there would still be tides, albeit much smaller.)

Now, forward-thinking researchers and government officials are taking a lesson from the past and looking anew at the possibility of harnessing the power of the ocean to generate electricity. The state of Maine, through its Office of Energy Independence and the Maine Technology Institute, is participating in a multi-state study conducted by the Electric Power Research Institute (EPRI) to determine whether tidal power is more economical than other forms of renewable energy — such as wind and solar — currently under development.

Last year, the state spent $60,000 to find out that Maine coastal waters don’t generate enough surface wave power to merit further exploration of that resource, but all parties are more optimistic about Maine’s tides, particularly Downeast. There, the Gulf of Maine begins to narrow into the Bay of Fundy with its famous 50-foot tides, and water roars in and out of the narrower river channels just begging to have its energy harvested.

So how do you do it? The trick is to gather power without impounding the water because, as we all know, building dams wrecks ecologies both upstream and down-. And the technology that has proven most effective at generating electricity underwater without either stopping the water or mincing the fish is — surprise, surprise — the windmill.

Water has a thousand times the density of air, which makes it a much more efficient generator of energy. A turbine with blades spanning 30 feet will generate approximately as much power underwater as a 300-foot windmill will generate on top of a mountain, and the biggest drawback of wind power — the fact that the wind isn’t always blowing — contrasts sharply with the certainty and predictability of the tides. In addition, underwater turbines are invisible, removing the NIMBY aesthetic objections stalling large wind-power projects even in wind-fertile regions such as the waters off Cape Cod.

You’ve never heard about this before because this is an old idea that’s brand new. The technology for harvesting energy from the tides is in its infancy, with only a handful of commercial-scale tidal generating facilities in the world, as well as imminent pilot projects in, among other places, Manhattan’s East River.

Maine, says Michael Mayhew, energy efficiency engineer at the Public Utilities Commission, has "the biggest hydropower resource in the continental US," with tides ranging from nine to 18 feet, but big tides alone won’t make or break the case for tidal energy. Other issues come into play: transmission capacity, workforce, shipping lanes, fisheries, and environmental impacts, among others. Properly sited tidal turbines would be about the least environmentally intrusive means of producing energy this side of rooftop solar panels, but the details have yet to be worked out.

"We want to find where the best place is, how much power we’re looking at, and what might be the best technology," Mayhew says.

He’s excited about the study’s potential. "When you start looking at tidal power versus wind," he says, you can get the same energy return with much smaller machines, and fewer of them. "And you can count on it. You know the tides a hundred years from now." This makes tidal power more useful because energy-intensive work in the area of a tidal generating plant could be scheduled around the tides, increasing efficiency. Location is a tricky issue in Maine, though, since the resource tends to be Downeast and the transmission and construction facilities are closer to Portland; how to solve that is one of the questions the feasibility study is supposed to answer.

"It’s an international effort," Mayhew says of the EPRI study, ticking off the participants: six states as well as two Canadian provinces — Nova Scotia and British Columbia — and the city of San Francisco, which is looking into the feasibility of bolting turbines onto the Golden Gate Bridge.

Roger Bedard, ocean energy program manager at EPRI, credits state director of energy independence Beth Nagusky with orchestrating Maine’s involvement. "Without Beth," he says, "I don’t think we would have gotten Maine involved."

Especially since the state had just blown 60 grand to find out, in Mayhew’s words, that "Maine has a bigger wave resource than Idaho," but not one that’s going to make anybody money. However, what Maine did have, last year’s wave report showed, was "current out the wazoo," Mayhew goes on, and Bedard recalls that Mayhew approached him after the results of the wave study came in.

"Michael said that we had this great methodology," Bedard says, "and why didn’t we apply it to a tidal-energy project?"

Bedard got Alaska, Washington, Oregon, Massachusetts, Nova Scotia, and British Columbia to chip in, and the $400,000 study effort kicked off a couple of weeks ago. Site surveys will continue throughout the summer, with a report issued in the fall.

Once the site studies are completed, a state energy team including Mayhew and Jim Atwell at the Maine Technology Institute will select a site and device for a design and economic study, slated to begin at the end of the summer. "In the beginning of next spring, we should have a feasibility report," Mayhew says, "and go on and try to find somebody who wants to build it for us." What "it" will be is anyone’s guess; the state is evaluating what Mayhew says is "the full gamut" of existing technologies, prototypes, and patents looking for someone to make them a reality.

Bedard has a good feeling about what will happen once the state team settles on a place and technology. Although Maine is a lousy state for wave energy — "A good wind site," Bedard says, "will always be more economical than wave energy in the state of Maine" — the state’s big tides and innumerable narrow channels make it prime territory for harvesting the energy of the tides.

Three primary factors determine a site’s suitability: tidal range, the narrowness and shallowness of the channel, and the amount of water that has to pass through the channel. Speed is also important, since the kinetic energy of water increases with the cube of its speed (for the numbers-challenged, that means that if the water moves twice as fast, it carries eight times as much energy).

Downeast, as anyone who’s ever been there knows, is rife with perfect spots, and EPRI’s designated site surveyor, Virginia Tech University oceanographer George Hagerman, will be looking at several of them this spring and summer in an effort to answer Bedard’s primary question: Is there "a rational and compelling case to invest funding to develop and implement in-stream tidal energy technology?"

Bedard’s guessing there is. "My instinct," he says, is that Maine’s tidal-energy potential "is very, very positive." And, if the wave results in other states were any indication, this might mean a shift away from wind research in a state with only moderate wind resources.

"At the same cumulative production volume," Bedard says — i.e., if there was as much wave power online as there is wind power — "wave will do better than wind" everywhere studied except for Maine, and Bedard is looking for Maine to be much more rewarding on the tidal front than the wave front for one simple reason: The Bay of Fundy has the highest tidal range in the world.

If this sounds too good to be true, it probably is. Commercial tidal power is probably years away, and there are obstacles, notably the hostile environment an undersea turbine would have to deal with. In addition, although the EPRI study is focused on "tidal in-stream energy conversion," meaning no dams or other forms of impoundment, there is still no clear understanding of how much energy can be harvested from a tidal flow before the local ecosystem starts to suffer noticeable effects. The working best guess, Bedard says, is 10 to 20 percent of the water’s available energy, but there just isn’t enough information.

He means to get that information, though, and this year’s multi-state/province/city study will be an ambitious step in that direction. Twenty years from now, there might not be a wind farm along the Appalachian Trail, but there might well be water turbines spinning away on the seabed at the Lubec Narrows — and the ghosts of eighth-century European farmers will say, "Duh."

Alex Irvine can be reached at airvine@phx.com