Oilweek - March 2008

“We have two proprietary technologies. One is the design of the ducting and blades. The second is a permanent magnet generator designed specifically for the very hostile environment of deep salt water to reduce the need for maintenance. Every five years we’ll pull up the rotor-blade-generator module, lift it onto a barge and replace it with a new or reconditioned one.”

The unit has a 5.5-metre hole in the centre to allow for laminar flow-through, which helps to pull away the turbulence caused by the spinning of the blades. That allows more water to move by the blades, making more energy available. The hole is also a sea life escape hatch big enough for everything but a blue whale to slide through.

The generator is at the centre; blade tips are surrounded by a duct so there’s no exposed blade. Although the ducting shields some of the sound, fish and sea mammals will feel the back pressure and hear the low frequency humming and steer around.

The leading edge of the blades (moving perpendicular to the flow of the water around the hole) is rounded to protect sea life; the trailing edge is sleeker. Just as air flows over the wing of an airplane, water flows over the blade and a pressure differential is created.

In a farm containing several hundred turbines, spacing the units about 50 metres apart and staggering them downstream by about 500 metres would minimize the drag of turbulence. An installation of 200 units would power a city of 200,000.

“The depth of water is our limiting factor,” Darou says. “Our product line requires about 40 metres of water. We’ve designed the height of the stem to avoid gravel piles that move. We measure the speed of the entire water column to find the sweet spot where it flows at a consistent speed with not much turbulence. We have to be 15 metres below the low tide mark so a big ship could go overhead.”

RESEARCH AND DEVELOPMENT

Clean Current is the only completely Canadian participant selected to install its turbine in the bay, once the conditions outstanding for the project as a whole are met. Each of the three will spend between $10 million and $15 million on what could be a turning point for the industry worldwide as well as a boost for Nova Scotia tidal projects.

The other two are industry partnerships between Canadian companies and tidal power companies, one based in Ireland and one in the United States.

Which turbine is most successful is
“a question of cost, efficiency, and
[the degree of] disturbing nature.”

— Philippe Vauthier, UEK Hydrokinetic

Nova Scotia Power Inc. supplies electricity to something approaching half a million Nova Scotia homes and businesses. Privatized in 1992, it operates North America’s only tidal power station, on the Bay of Fundy at Annapolis. The facility has been online since 1984.

Nova Scotia Power is teaming up with Ireland’s OpenHydro Group, which has a tidal generator installed at Scotland’s full-scale wave and tidal power testing site in Orkney.

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