Study determines best arrangement of tidal sails device

Sep 17, 2013
This image shows velocity and pressure around a string of submerged blades. Credit: R.Fernandez-Feria/U.Malaga

In the long sprint to find new sources of clean, low-cost power, slow and steady might win the race—the slow-moving water of currents and tides, that is. Just as wind turbines tap into the energy of flowing air to generate electricity, hydrokinetic devices produce power from moving masses of water.

In a paper appearing in AIP Publishing's Journal of Renewable and Sustainable Energy, Ramon Fernandez-Feria, a professor of at Universidad de Málaga in Spain, and his colleagues Joaquin Ortega-Casanova and Daniel Cebrián performed a computer simulation to determine the optimum configuration of one such system to enable it to extract the maximum amount of energy from any given current.

The system, developed by a Norwegian company called Tidal Sails AS, consists of a string of submerged blades or sails, connected via wire ropes, angled into the oncoming current. The rushing current generates large lift forces in the sails, and as they are pushed along through a continuous loop, they drive a generator to produce electricity.

A small-scale version of the Tidal Sails device is already in operation at a test facility constructed in a stream outside Haugesund, Norway. The pilot project has a power-producing capacity of 28 kilowatts; a full-scale version could generate several megawatts of power. Installing several such units in a , the company says, could generate as much as 100 of electricity per year.

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.

"The next step would be to refine the design of the device with further hydrodynamic , complemented with small-scale experiments," Fernandez-Feria said. "For instance, trying more efficient aerodynamic blade profiles, and different angles between the string of blades and the current."

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More information: The article, "Lift and drag characteristics of a cascade of flat plates in a configuration of interest for a tidal current energy converter: Numerical simulations analysis" by Daniel Cebrián, Joaquin Ortega-Casanova and Ramon Fernandez-Feria appears in the Journal of Renewable and Sustainable Energy: dx.doi.org/10.1063/1.4816495

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julianpenrod
1 / 5 (7) Sep 17, 2013
Just as with windmills, flowing water carries out important services and slowing or eliminating it by stealing energy from it can produce significant results.
Among other things, just how much energy could be gotten from slow moving water? A huge amount of energy may be present in a tide, say, but a conventional system would have to be as big as the entire area experiencing a tide to get anything from it.
But, consider, taking energy from moving water causes it to stop moving so quickly. That causes a pile up or, in the case of a substance like water, where masses don't necessarily flow through each other, backed up bodies of fluid flowing around the other, forming, essentially, new tidal zones or new currents. And that can have very serious repercussions in the spawning of fish, the distribution of heat in the ocean, the deposition of silt. Changing tides can even change the motions of the moon and earth.
Urgelt
not rated yet Sep 17, 2013
Julian wrote, "...taking energy from moving water causes it to stop moving so quickly."

Okay, so tidal movements will slow to a crawl because some underwater kinetic harvesting devices have been emplaced, hence electricity production efficiency renders that economically useless, too.

"That causes a pile up..."

Oh, man, now we have to worry about kinetic energy harvesting resulting in floods and beach erosion.

Thank goodness Julian is here to warn us! So, everyone, let's support the fossil fuel industry, it's our only hope!

Only one problem. Julian is right to predict changes in flow due to kinetic harvesting, but the scale of the effects he describes are so small that they are utterly irrelevant.
Urgelt
5 / 5 (1) Sep 17, 2013
I'm not keen on this underwater sails scheme, because there are too many moving parts. Mechanical complexity in a salt water environment is a nonstarter.

But I am glad that companies are experimenting with different approaches. The amount of kinetic energy in tidal systems is beyond vast. Tapping even a tiny, tiny percentage of it could yield truly prodigious amounts of useful energy. I see no harm in throwing ideas at the problem and seeing what works.
julianpenrod
1 / 5 (7) Sep 18, 2013
Urgelt is demonstrating precisely the kind of "reasoning" the crooks pushing "alternative energy" want the public to resonate to. Namely, "fossil fuels are bad, therefore, anything other than fossil fuels must be good! We have to stop using fossil fuels, so, even if this technology does more damage, we have to use it!" And this all is predicated on the dangerous delusion that "Liberals aren't conservatives, therefore, Liberals necessarily are all good, all decent, all ethical, none of them are conniving malingerers seeking to soak the 'rank and file' for their own gain!" Yes, man is causing climate change, but it's chemtrails doing it, not fossil fuels.
julianpenrod
1 / 5 (7) Sep 18, 2013
As I pointed out, since the water being harvested is admittedly slow moving, there is no significant amount of energy in any reasonable sized pocket of fluid. The only way a major amount of energy is derived conventionally is by working with a gigantic body of moving fluid. And that means a huge amount of water affected, slowed down, backed up, diverted.