Submerged Sails Catch The Power Of Tides

Spanish researchers say that they have come up with the optimal way to arrange tidal sails – which raises a key question: What the heck are tidal sails?

Tidal sails, the brainchild of a Norwegian commercial airline pilot named Are Børgesen, are a means to capture the energy from tidal streams. Here’s how they work: Submerged sails are attached by rope at their tops and bottoms, angled against the tide flow. As the water pushes against the sails, generating lift forces, the sails churn in a triangular loop pattern, driving an electric generator. It’s that simple, and here’s the system in action:

One of the biggest advantages that Tidal Sails (the company) claims for its technology over tidal turbines, the most common new technique being developed to harness tidal energy, is efficiency. The company claims that a single €20 million, 400-ton, 10-megawatt device could produce 27 gigawatt-hours of energy per year in waters moving at 2 meters per second (4 knots). By comparison, it would take dozens of tidal turbines, adding up to 9,000 tons and costing €100 million, to produce the same amount of energy.

That’s the claim, at least.

The company says a small-scale, 28-kilowatt demonstrator placed in a stream outside Haugesund, Norway, has operated successfully and that it’s looking to scale up to at least 2 MW “in cooperation with an energy company to demonstrate and verify the commercial potential.”

If that happens we’ll know if this thing might be for real or not – although the fact that a group of researchers in Spain backed research into it suggests that some people are taking it seriously.

According to a press release from the American Institute of Physics, “In their analysis, the researchers found that the maximum amount of power could be generated using blades with a chord length (the width of the blade at a given distance along its length) equal to the separation between each individual blade, that are positioned at about a 79 degree angle relative to the oncoming current, and that move at a speed about one and half times faster than the current.”

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.