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In Depth

Energy
| 08/31/16

First commercial tidal array goes live off Scottish coast

TCE

The first array of tidal turbines to deliver electricity to a grid went live this week off the coast of Scotland’s Shetland Islands, home to some of the most powerful tides in Europe.

The world first, operated by Nova Innovation, is not the first tidal energy endeavour, but the first commercial, operational tidal array, with the company turning on the second of five 100 kW turbines. Other tidal power schemes involve single installations rather than an array of turbines. A French firm is also nearing completion on a two-turbine pairing off the coast of Brittany, this time potentially offering 1 MW of power at full capacity.

Electricity can be generated from the tides in two main ways. Most environmentally controversial has been via a barrage, in essence a type of dam that exploits potential energy much like a hydroelectric dam and reservoir. As the tide begins to come in, water rushes in behind the barrage. When the tide goes out, the water drives turbines that produce electricity via generators. A barrage straddles an entire estuary, inhibiting the flow of water—a process that increases turbidity and can disrupt marine animal migration patterns, devastating fish populations.

The second option, ‘current generation’, exploits the kinetic energy of tidal currents directly, with moving water driving turbines similar to the way we produce electricity from the wind. Here, the turbines are situated on the estuary floor to take advantage of greater tidal velocities. This has less—but still some—negative environmental impact. But the trade-off is a much lower capacity than barrages.

Tidal power receives less public attention than wind and solar even though it is much more predictable, keeping to its daily schedule. Its lower profile is due to high up-front construction costs and a limited number of sites globally with sufficient tidal ranges and velocities. The Bay of Fundy, between New Brunswick, Nova Scotia and Maine, however offers probably the world’s best potential for tidal power, as it has the highest vertical tidal range on the planet. The Annapolis Royal Generating Station, a tidal barrage testing site, was built there in 1984. It was the first in North America and is the third largest tidal power plant in the world, with a capacity of 20 megawatts—which would be about enough to service the demand of about 20,000 homes, and a daily output of roughly 80-100 megawatt hours, depending on the tides. The plant produces electricity twice a day with each tide, and each time for about six hours.

Canada’s second tidal test facility, the Race Rocks micro plant near Victoria, BC, launched in 2006, is a current generator that can deliver up to 65 kW, which would be enough to service 10 homes.

BC has been identified in studies as offering the largest number of viable tidal sites in the country (a possible 89 locations). Some 4,000 MW could be tapped off the coast of the province. Nunavut meanwhile offers the greatest total potential.

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In Canada, BC, Nova Scotia and Nunavut offer the greatest potential for tidal power

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