The under water kite
Swedish company Minesto has found way of producing tidal power at a reasonable price and without the need for large infrastructure.
The tides are changing. Minesto has come up with a novel idea to harness the power of the tide (Photo: Minesto.com)
Harnessing tidal power is not an entirely new idea. As long ago as the middle ages, possibly even in Roman times, farmers built tide mills. A tide mill is a type of water mill that is driven by the rise and fall of the tide. When the tide comes in it enters through a one way gate and fills up a reservoir. When the tide goes out, the gate closes and when the tide is at the lowest the water is released to turn a water wheel.
In modern times engineers have worked hard to find a practcial way of generating electricity out of tidal power. Most of the solutions are in principle not that different from the ancient tidal mills. Usually they involve utilizing the shifting tide to drive a stationary rotating turbine, which in turn produces electricity. A Swedish company called Minesto have however come up with an totally different approach. They have developed something that is best described as an underwater kite, anchored to the ocean floor. Instead of flying through the air, this kite swoops and dives in ocean currents generating electricity from a turbine attached to the wing. According to Minesto, a single kite, wtih a wingspan of twelve meters, will generate enough electricity for 250-300 households. The technology is called Deep Green and Time Magazine thought the idea was so good that they rated it one of the top 50 inventions in 2010.
So what makes this way of harnessing power so clever? Compare it to an on- or offshore windmill. Deep Green requires less space, ocean currents are more stable and predictable than wind, and last but not least the power plants are totally invisible to the naked eye. As mentioned, the wingspan of Deep Green is only twelve meters, they weigh only seven tons and they do not need large structures, you just anchor it to the sea bed. This means a lower visual and environmental impact as the Deep Green is alway 20 meters or more under the surface. Maintenance is also said to be easier and cheaper than with larger structures, since it is mainly done onshore, only attachment and detachment is done offshore.
Another advantage compared to wind power is that water has a much higher density than air. This means that even at low velocities the Deep Green will generate power. The kinetic energy in water flowing at 5 knots (2.5 m/s) is more than in a 260 km/hr wind, as seawater is 832 times denser than air. According to Minesto, the design could increase the market for tidal power by 80%. The first scale model will be unveiled next year off the coast of Northern Ireland.
- We have made contacts all over the world, and there is huge interest in what we do. If we were able to do magic, we could be selling finished power plants today. But developing new technology takes its time, wind power took ten years before it was economically viable, Anders Jansson from Minesto said to Swedish newspaper Expressen.
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