training youths with ocean wave energy converter

*** g91 10/8 pp. 26-27 Power From the Tides ***

Power From the Tides

By Awake! correspondent in Canada

ENERGY! Modern society has an insatiable thirst for it. And since the oil embargo of 1973, which resulted in a huge increase in oil prices, scientists have searched for alternatives to fossil fuels. The recent Persian Gulf war showed how seriously the nations viewed a possible interruption of oil supplies from the Middle East.

Experimental projects once proposed but cast aside in less critical times are now being reexamined. For example, what about the ocean’s mighty tides? Could they be economically harnessed to generate electricity?

Some years ago Canadian engineers began eyeing the phenomenal tides of the Bay of Fundy. The bay is located between two of Canada’s Atlantic coastal provinces, Nova Scotia and New Brunswick, and is famous for its tides—some of the highest in the world, with a rise of up to 53 feet [16 m]. Tidal power plants were already operating in France and the Soviet Union, so why not in Canada?

A full-fledged project was thus proposed that would generate 4,800 megawatts—6.5 million horsepower—of electrical energy. (By comparison, an entire nuclear plant in neighboring New Brunswick generated only 600 megawatts.) The cost of such a tidal power project, though, would be astronomical—estimated in 1981 at about $5,000,000,000 (Canadian)!

The Pilot Plant

First, the government prudently funded a pilot plant to test for design and efficiency. Called the Annapolis Tidal Power Project, it is located in a dam across the Annapolis River, which flows into Annapolis Basin, a tidal river basin that flows into the Bay of Fundy, near the town of Annapolis Royal, Nova Scotia. Completed at a cost of $55 million, the plant began generating electricity in 1984.

More than 40,000 people visited the Annapolis Tidal Power Project site in a recent year, some from as far away as Siberia and China. At first glance, though, the plant might appear disappointing because all you see is a simple, two-story concrete bunker on a short causeway—little evidence that this is North America’s first tidal power station.

Further, you do not see a large staff of busy engineers there. The plant is operated by computers situated about 60 miles [100 km] away and requires only a few maintenance people on duty. Yet the station generates some 30 million kilowatt-hours of power a year—enough to supply 8,000 homes. How does it do it?

How It Works

Hidden within an excavation over a hundred feet [30 m] below the surface lies the secret to the plant’s success—the water-driven turbine. The way it works is surprisingly simple. The turbine is housed on a small island joined to the shore at each end by a damlike causeway. As the Fundy tides rise, water flows from Annapolis Basin through gates in the dam to a large holding pond on the up-river side of the dam. When the tide reaches its greatest height, all gates are shut.

As the tide drops on the downstream side of the dam (as much as 15 feet [4.6 m]), the gates open, and the holding pond empties water back into Annapolis Basin through the turbine. The force of the rushing water spins the turbine and thus generates electricity. Since the plant operates as water flows out, it generates power only about 11 or 12 hours per day.

To meet these conditions, an experimental turbine was developed, 25 feet [7.6 m] in diameter. The magnetic poles of the generator, which produces electricity as the turbine revolves, are fixed to the rim of the turbine and turn with it. (Conventional turbines usually turn a shaft that drives the generator.) The result is a more compact turbine that operates efficiently when water velocity is relatively low.

Would not the salt content of the water pose problems for this equipment? The corrosive effect of salt water has been a major problem, but engineers have dealt with it by putting a very small electric current in the water passage to offset corrosion.

Tidal Power’s Future

Should the larger tidal plant planned for the Bay of Fundy materialize, it will incorporate more than a hundred turbines of the general size of the one at Annapolis. These will be positioned on a causeway five miles [8 km] in length across the east arm of the bay.

However, partially damming the Bay of Fundy for electrical power could cause serious problems. For one thing, the huge cost of construction is a worry. In addition, there is concern about environmental damage. The possible alteration of the tides of Fundy by several inches could result in flooding great areas of coastline with salt water. Patterns of fish migration could also be changed, blocking the return of shad to fresh water.

Nevertheless, North America’s first tidal power plant, the pilot project at Annapolis, continues to generate power for the electrical grid in eastern Canada. Yet, that is only a tiny drop toward quenching the nation’s large thirst for energy.