The resurgence of tidal power

OpenHydro's test rig at Orkney, Scotland. The Canadian version will sit permanently below the waves. (OpenHydro, Dublin)

Twice a day, in accordance with nature's clock, the Atlantic Ocean pours through the Bay of Fundy with a controlled fury that is unmatched anywhere in the world.

By the time these waters reach their ultimate destination in Minas Basin, nearly 14 billion tonnes of seawater will have sloshed into that channel — equivalent to the combined flow, some have calculated, of every river on earth. Little wonder the Nova Scotia countryside sags slightly under the weight.

Little wonder, as well, that visionaries have long thought to harness the power of that current, with decidedly mixed results. Nearly a quarter century ago, Nova Scotia Power, the provincial utility, began a modest tidal power pilot project in the bay.

It is still operating, producing 20 megawatts of electricity every day, and is considered one of only three professionally-run tidal power operations in the world.

But time and tides wait for no man. New technologies such as turbines mounted to the floor of the seabed — like "little wind machines on steroids," in the words of one proponent — have come along and so has the need for more non-polluting energy.

As a result, Nova Scotia Power wants back into the bay with another pilot project and the latest in tidal power technology, the precursor to what it hopes will be a veritable tidal farm of underwater sea turbines.

Two weeks ago, it selected an Irish company called OpenHydro to be its partner in this endeavour over 20 other potential suppliers, including a couple of local consortiums.

The plan is to have what would be one of the world's largest single underwater turbines in the six-kilometre-wide Minas passage by late 2009, depending of course (this being Canada) on some federal funding and jurisdictional approvals, and raises the question: Are we finally getting serious about tapping the power of the tides?

The vision's there

Yes, we are, says Margaret Murphy, the corporate spokeswoman for Nova Scotia Power. "There is real excitement now," she says. NSP president Ralph Tedesco is behind it and has been talking about doubling the 10 per cent of the power NSP currently gets from renewable sources over the next five or six years.

At the same time, Murphy cautions, NSP is only going to go ahead with the $12 million pilot project if Ottawa kicks in $4 million or so from its sustainable development fund and the utility is also planning to step up the tidal farms only in manageable chunks.

"The vision is there," says Murphy. "But we haven't committed yet to the larger stage. We want to do this one step at a time."

The vision for now is to build one large OpenHydro turbine to test in the wicked waters of the Bay of Fundy. Designed to generate a megawatt (one million watts) of power, the donut-shaped unit would be the world's first utility-scale in-stream turbine and would have to be at least twice the size of the six-metre test rig that OpenHydro has installed in the North Atlantic near Orkney, Scotland.

If it works as planned — and if the unit can withstand the bustling waters of the Minas passage and whatever debris can be hurled at it — then NSP is considering as many as 300 more, in strategic locations around the bay.

That 300 or so megawatts of power would be enough to supply the electrical needs of well over 200,000 homes.

Canada's the place

If Canadian utilities are getting serious about tidal power, then the Bay of Fundy is clearly the place to start. According to a study by the California-based Electric Power Research Institute, one of the world's biggest renewable energy research organizations, the Bay of Fundy is by far the best of eight sites that have been studied in North America and may even be the best in the world.

Roger Bedard, the chief tidal power scientist at EPRI (and one of the "gurus" of the field, according to Murphy at NSP), says there is as much as a gigawatt (a billion watts) of potential at a dozen or so different sites in the Bay of Fundy. (However, sites on the New Brunswick's side might conflict with the large number of salmon farms in the area, some have noted.)

"Canada is the place," Bedard enthuses. The tidal power potential in the Bay of Fundy is much greater than can be captured from solar or wind, he says.

Critics note that tidal power is intermittent — it only generates electricity for 10 to 12 hours a day while the tides are moving in and out. But Bedard says that with today's computerized system, that shouldn't be a concern.

Utilities want "firm power," he says. They want to know a day ahead what they will have on tap for their system, and the beauty of the tides is that they are "perfectly deterministic," meaning they flow like clockwork every 12 hours and 25 minutes.

EPRI's research also says that, amortized over 20 years, today's in-stream turbines look to be just as cheap as a current coal-fired power plant (about 4 to 4.5 cents US a kW-h) — but that would be a coal-fired plant without any new carbon capture equipment to try to cut down on greenhouse gases.

Of course, no one really knows yet whether these little underwater "windmills" will be rugged enough to stand up to the whims of the Atlantic's currents, or the deadheads and beach ice that may be thrown at them during spring thaw. But early test cases, like the one in New York's East River, suggest that the fish at least don't mind sharing the passageway with the turbines.

Says Bedard: "We think they are going to be pretty environmentally benign."

New generation technology

With our many rushing rivers and coastal fiords, Canada may well be the place for tidal power, or at least what is called in-stream generators. (Some countries, like Britain, are experimenting with offshore wave farms that tether generators in the midst of a powerful current.)

To date, however, we only have two experiments on the go: The old Nova Scotia Power pilot project in the Bay of Fundy that dates from 1984, and a new, $4-million experiment with Clean Current Power Systems at Pearson College on Vancouver Island, which is being used to power the school's marina.

The biggest tidal power system in the world is near St. Malo, France, dates from 1966 and generates nearly 240 megawatts of power. But, like the old NSP project near Annapolis, N.S., it is a dam-based system that halts the tides in a holding area before releasing them through a generator. As a result, the headpond is subject to silting and other concerns about fish habitats. (French engineers also hypothesized once that if the whole world followed its example, the Earth would slow in its rotation and lose a day every 2000 years.)

The latest technology, which has really only been experimented with over the past four to eight years, is quite different in that it relies on small propellers or turbines that can be anchored to the sea floor, in this case at least 15 metres below low tide, so as not to interfere with shipping.

Some of these turbines are like steel kites, they are tethered to the floor and turn to face whichever way the current is flowing.

The OpenHydro design that NSP is going ahead with is different still, in that it has no gear box, just a simple blade technology that moves within an enclosed tube and requires no lubricating oils that might escape into the water.

OpenHydro has only one of these rigs in the water now. Its test turbine near Orkney is mounted on two steel poles so it can be brought to the surface for examination.

The one for NSP will be twice that size and fixed to the floor of the bay. To be financially feasible, each of these little tidal funnels will have to live in the water for four years before being replaced, which, given the unremitting churn of the Fundy tides, would be quite a lifetime.