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Underwater Windmill Helps Power Arctic Village

John Roach
for National Geographic News
October 9, 2003
 
Energy derived from the moon now trickles into a village near the Arctic tip of Norway via a novel underwater windmill-like device powered by the rhythmic slosh of the tides.

The so-called tidal turbine is bolted to the floor of the Kvalsund Channel and was connected to the nearby town of Hammerfest's power grid on September 20. It is the first time in the world that electricity directly from a tidal current has been fed into a power grid.


The gravitational tug of the moon produces a swift tidal current there that courses through the channel at about 8 feet (2.5 meters) per second and spins the 33-foot-(10-meter) long blades of the turbine.

The blades automatically turn to face the ebb and flow of the tide and rotate at a pace of seven revolutions per minute, which is sufficient to produce 700,000 kilowatt hours of non-polluting energy per year—enough to power about 35 Norwegian homes (70 U.S. homes).

"Basically it's like putting a windmill in the water," said Bjørn Bekken, a project manager for Hammerfest Strøm, the company that built the device.

Richard Charter, a marine conservation advocate with Environmental Defense in Oakland, California, said the system has the potential to be a significant contributor to the natural energy mix, but warrants careful development.

"The good news is there are no carbon emissions, no radioactive plume or nuclear waste, no oil spill trajectory, and no chemical pollution," he said. "The thing is estuarine ecosystems are very sensitive."

The technology is so new, said Charter, that its impacts on things such as fish migration and water circulation patterns are not well understood. Environmental Defense is concerned the technology will be widely implemented too quickly.

"As an organization, we are generally supportive of a careful, methodical look at this technology," said Charter, "but it is too soon to make a call as to if it is the Promised Land of renewable energy."

Alternative Energy

Proponents of the tidal turbine technology say it is a welcome, environmentally friendly alternative-energy option. One key advantage over wind and solar power is that the energy output is 100 percent predictable, said Bekken.

"The tidal stream is going to be there and it is going to be exactly the same, you can predict it at all times," he said.

Breezes can be too weak or too strong for windmills to work properly and in places like the north of Norway the sun completely disappears for several months each year, rendering solar power inefficient in winter. The tides, however, are as sure as the moon.

Tidal turbines are also hidden beneath the surface of the water and thus do not blight the visual horizon. Windmills have been criticized as an eyesore by several community and environmental groups.

The tips of the blades are 66 feet (20 meters) below the water's surface, allowing clear passage for ships and slowly rotate led by their rounded edge, thus posing little threat to fish and other sea critters, according to Bekken.

The one adverse impact recognized by proponents of the technology is to the fishing industry, as fishing equipment could get tangled up in the turbines. As a result, fishing must be restricted in turbine locations.

Technological Advance

Since the 1960s, energy producers have reaped electricity from the tides by trapping the high tide in artificial lagoons with dams. When the tide goes out, gravity sucks the water through turbines to generate electricity, much like a hydroelectric system on a river.

Environmentalists and fisheries groups, however, said the projects—the largest of which is in la Rance, France—damage habitat and alter water circulation patterns as far out as 300 miles (500 kilometers) from the power plant.

The tidal turbines, by contrast, do not require a dam. The structures are simply plunked into the water and bolted to the seafloor.

"This one may have the ability to harvest enough energy to make it worthwhile and not interfere with circulatory patterns, but it will probably be a site-specific equation," said Charter.

The tidal turbine technology is only just now being attempted because it has taken several decades for the wind industry to perfect the windmill, a design the tidal turbine engineers borrow heavily from, said Bekken.

"Also, advances in sub-sea technology have been brought up to the level where we can use it for this kind of project as well," he said.

For example, Charter said that advances in materials science in the last decade have allowed engineers to design equipment that can withstand the corrosive effects of salt water.

Once the technology is scaled up, Bekken hopes the costs of tidal turbines to be comparable with windmills. The development cost of the prototype is about U.S. $11 million to date.

In order to keep maintenance costs down, duplicates of all important systems are built into the turbine so that if one breaks the other can be switched on instead of having to dispatch a scuba diver to fix it.

The project's backers, which in addition to Hammerfest Strøm include the Norwegian oil group Statoil, the international engineering group ABB, Norwegian arm of Rolls Royce, and local Norwegian utilities, hope to sell thousands of the units to help Europe meet its green energy requirements.
 

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