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Underwater kites could generate 500kW of electricity

An underwater kite aimed at generating electricity from tidal currents has received €2m of private funding to further its development.

Designed by Saab spin-out, Minesto, the system claims to be able to increase the potential energy generated from the global tidal market by up to 80 per cent.

‘The initial concept came from an idea to use kites to harness wind energy,’ explained Ted Rosendahl, chief technology officer at Minesto. ‘But as water is denser than air, we soon realised that using this system in the ocean could be far more effective.’

The kite, known as Deep Green, consists of a 12m wing, turbine, generator and rudder. Tethered 100m above the sea bed, it flies in a figure eight using the kinetic energy from the waves combined with an automatic steering system.

Minesto develops a new concept for tidal power plants based on underwater kites

While a full-scale model is yet to be developed, each unit is expected to be able to generate up to 500kW of electricity which will be transmitted onshore from the generators through a power cable inside the tether.

Rosendahl said: ‘We still have some big challenges to overcome. You have dolphins and sharks in the same environment and we don’t know very much about how they will react when the see the things floating around. So testing in an ocean environment is the next step.’

The €2m of funding will be used to test a quarter scale Deep Green prototype off the coast of Northern Ireland next year. If trials are successful, Rosendahl hopes that the technology will be available on a full-scale within the next five years.

Readers' comments (11)

  • Sounds very feasible - as long as the big fish don't attack it. Perhaps some noise or vibration could be generated to scare them off.

    I suppose there could also be weeds, barnacles etc. which could attach themselves to the foil.
    Probably one could coat the foil with something to prevent that happening.

    At least it would stop all these people protesting about the wind-farms.

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  • Sounds good, but if it's tidal wil it not just sink to the sea bed at the 1st turn of the tide??

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  • I makes me wonder whether with a 12m wingspan, wouldn't a static tide turbine with a 12m blade be just as efficient, safer for marine animals and shipping, more reliable an easier to maintain? You could build an even larger turbine than 12m when you take into consideration the overal footprint of the kite's path, presumably; because it needs to operate when the tide is flowing from any direction the footprint will be enormous? Has anyone asked these questions before funding was given to them? I hope we will get benefit from our money?

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  • To respond to DaveE: When the tide turnes, the kite will simply face the other way (like a wind turbine does when the wind changes.

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  • It would be logical for the kites to have slight positive bouyancy so they don't sink. I think the idea is that it tacks across the current thereby increasing the effective flow rate and increasing the efficiency/output as compared to a fixed turbine.


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  • So is it a 'Floating Kite' then? i.e. buoyant?

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  • How to control the direction of the kite? I think you may need more than one tether.
    I think the idea is good, but I am not sure about the price of this project.
    And the kite can be destroyed by big wave or earthquake, then the power will release under the ocean, that will be a danger for sea animals.

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  • I would imagine that once the kite has broken its tether, it would drift with the current and thus generate no power.

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  • To me, this makes most sense in deep ocean currents, which are steady. I'm not clear about why it is designed to fly in a figure 8? No need, as long as the torque of two turbines is equalmand opposite in each unit. I could be plaved below the depth at which barnacles are idea I toyed with in grad school 30 years ago.

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  • OK, imagine a kite flying in a very tight circle instead of a figure eight. Now imagine two or more and you've got a propeller. Apply a load and it slows down. If you want more torque, put the "kites" on shafts to extend them further from the hub. I don't see how the kites are an improvement over a propellor. A stack of galton wheels would be a much better tethered tidal generator. Add some discs as ducting for even more efficiency.

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