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Tidal power is an old idea in new clothes. Harnessing water is as venerable as water wheels, a technology that can be traced back to ancient Rome and China in the first century A.D. Using tides for power is much more recent, however. If tardy, it seems an obvious concept, for the hydraulic power of tides is unchanging, unlike such other alternate power sources as wind driven electric turbines that can be useless on calm days.
Nova Scotia Power has been extracting energy from tides since the mid-1980s, says James Taylor, the Halifax-based company's manager of environmental planning.
A subsidiary of Emera Inc., the only publicly-traded company in the tidal power industry, it has used the Bay of Fundy, which has the highest tides in the world, for a barrage type of generator.
"A barrage is a dam," Mr. Taylor explains. "Water comes in and fills the dam, then it runs out through turbines, creating electricity. We built a facility in the Annapolis River Basin, which flows into the Bay, to make 20 megawatts of power, which it gets from the tidal movements. The basin fills twice a day and then runs out twice."
Nova Scotia Power gets relatively little power out of the small dam, just 60 megawatt hours of its total generation of 33,000 megawatt hours each day. However, it is financially efficient, for the Government of Canada provided $70-million of the $100-million cost with the provincial government providing the rest, Mr. Taylor notes.
Barrage based tidal power needs huge water movements. The Bay of Fundy and a few other places on the planet can provide the tidal surges that the dams require. But tidal streams that ebb and flow with currents are much more easily found. There are perhaps 1,300 to 1,500 sites in the world that can use tidal currents in streams, says Glen Darou, president and CEO of Clean Current Power Systems Inc. of Vancouver, a company that specializes in generators for in-stream power. The principle is to put a turbine on the bed of a river or other body of water. The Clean Current design can produce power for 12 to 23 cents per kilowatt hour, he explains. That's more than the 7 to 10 cents that power costs when generated from coal or other thermal sources, but less than the 42 cents per kilowatt hour solar power costs in Ontario, he notes. His company will put a commercial scale generator in the Bay of Fundy in late 2009, he says.
The appeal of underwater stream power is its environmental neutrality, Mr. Darou notes. "Our power has no emissions of any kind," he explains. "It is out of sight and totally submerged and has few environmental impacts." In tidal streams that are at least 40 metres deep, underwater generators leave 15 metres of clearance to the surface for passing vessels. "Only aircraft carriers and submarines would be bothered by the units," he says. Clean Current hopes to sell equipment for farms of these submerged generators, each able to produce up to 5 million kilowatt hours a year, depending on the size of the unit and the strength of tidal currents. Service needs are modest, he explains, for the machines have only one moving part the rotor that contains the blades. He figures the units will have a service life of up to 30 years.
Comparable units already operate in Scotland. OpenHydro Group Ltd., a Dublin, Ireland-based company, began to generate power for the United Kingdom's power grid in May, 2008, according to a press release. The company has won tenders to supply water turbine generators for use in the Bay of Fundy and in the Channel Islands, according to Brendan Gilmore, chairman of the OpenHydro Group. "Tidal farms can silently and invisibly generate renewable energy under the world's oceans," he notes.
OpenHydro's units stand less than 15 metres above the floor of bodies of water. That makes them much smaller than the 100 metre spans of wind turbines with large blades that can harm birds and whose whirring noise can irritate nearby homeowners. The company's tidal power generators, which look like large life preserver rings with blades within their holes, have no exposed tips, have no oils to leak, and provide a 5 metre hole in the centre for passage of fish or marine mammals, some of which can hear the vibrations of the machines and steer clear of them.
Tidal current power offers many of the advantages of power from conventional dams with few of their environmental problems. There are no residents of land to be flooded to be compensated and moved, no trees to fall into the water and release pollutants and greenhouse gases as they rot, no problem of silt jamming intakes and turbines, and, given that there is no need to build a massive concrete or earthen dam, the capital cost of tidal power is relatively modest, Mr. Taylor says. Moreover, tidal power generation can be installed incrementally, with additional units hooked into
the systems as need arises. They can grow with demand and even produce a sufficient profit to finance installation of additional units, he adds.
"We think that tidal power will compete head to head with wind power," Mr. Taylor says. "Tidal power has comparable costs, but unlike wind generation, it is out of sight. It takes up no land, makes no noise, harms neither birds nor bats, and, so far as we know, hurts no marine life. Where the water can support it, tidal power can be an important source of electricity."
Andrew Allentuck writes about investments for The Globe and Mail, and reviews books on finance for globefund.com and globeinvestor.com. He is also the author of several books.