Tidal energy to 'fly' undersea kites

Start-up Minesto receives more funding to test its Deep Green system. Will this new tidal stream technology bring tidal energy industry into deeper and calmer seas?
Written by Melissa Mahony, Contributor

Kites on the beach soar on wind power. Kites beneath the ocean surface? They glide with the tide.

At least that’s whatMinesto hopes their underwater “kites” will do—and produce 500 kilowatts of electricity while they do it. I discussed last May how the Swedish start-up procured $2.5 million for its Deep Green tech. Recently their upcoming pilot project off the Northern Irish coast gained another $565,000 (£350,000) from The Carbon Trust.

According to Minesto, the system is lightweight, more portable and easier to install compared to other tidal energy apparatuses, such as barrages.

At 7 tons, the tidal tech entails a kite-like device tethered to the ocean floor by more than 300 feet of “string.” As demonstrated below, the kite glides through the water in a figure-8 pattern. A 3-foot turbine rides beneath the kite’s 40-foot wing, capturing tidal stream energy and sending it to a generator on the seabed. Underwater cables then transport the electricity to shore.

As the kite travels through the water, the velocity of the water running through the turbine is about 10 times the amount of the speed of the ocean current.

While the tide forces the kite to move, an automatic rudder system controls the device’s trajectory. The control system also monitors for depth, turbulence and large objects coming/swimming nearby. For environmental, aesthetic and safety concerns, the company says the kites would also “fly” at least 65 feet below the surface.

The kites could potentially collect the energy of deeper waters with lower current velocities, expanding the geographic potential for tidal power.

In November, Time Magazine named Minesto's Deep Green technology as one of its "50 best inventions of 2010." Now it's time to see if these aquatic kites work in the Irish Sea's Strangford Lough.

The Guardian's Damian Carrington writes:

Ander Jansson, Minesto's managing director, tells me the kite should work in flows of 1-2.5 metres per second, while first-generation devices need over 2.5m/s. Depending on the location and size of the kites, each will have a capacity of between 150 and 800kW, and be deployed in waters 50-300m deep. The test will be at one tenth scale.

If Deep Green does work in the deep blue, Minesto aims to fly enough kites around the UK's coastline to generate 530 gigawatt-hours by 2020.

Benj Sykes of The Carbon Trust says in a statement:

The UK boasts some of the best tidal resources in the world and we are focused on bringing down the cost of extracting that energy. Minesto’s Deep Green is a very exciting technology as it could provide a step change reduction in the cost of tidal energy and open up swathes of the UK’s coast to generating electricity. Tidal energy has the potential to produce up to 18 terawatt hours of electricity, equivalent to over 5% of the UK’s electricity consumption.

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