Tidal power system will use an underwater kite to generate electricity

Tidal power system will use an...
A conceptual design of the Manta system, which is somewhat different than the version described
A conceptual design of the Manta system, which is somewhat different than the version described
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A conceptual design of the Manta system, which is somewhat different than the version described
A conceptual design of the Manta system, which is somewhat different than the version described

We've already heard about renewable energy systems that use aerial kites to generate electricity via the wind. Well, the Manta system is kind of similar, although it uses an underwater kite that "flies" in tidal or river currents.

Manta was conceived by scientists at the California-based SRI International research institute, who recently received a three-year, US$4.2 million award to develop the technology in partnership with colleagues at the University of California, Berkeley. That award was granted by the US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E), as part of its Submarine Hydrokinetic And Riverine Kilo-megawatt Systems (SHARKS) program.

At the heart of the system is a polymer-composite-coated foam kite, the shape of which was inspired by the manta ray. That kite is attached to a reeled tether, which is anchored to the floor of the ocean or a river in an area where there are strong currents. The tether reel is equipped with both an electric motor and a generator.

At the start of each of its runs, the kite is angled so that it catches the full force of the current, allowing it to be carried downstream by that current. The reel spins quickly as it releases the tether, spinning up the generator in the process – this generates electricity, which could be stored in a battery or fed directly into the municipal grid.

Once the kite reaches the end of its tether, it turns so that it presents a more streamlined profile to the current. The reel motor then winches it back in, so that it can subsequently perform another downstream run. Although the winching process does require some energy, the amount is reportedly much less than the system generates. According to a report on IEEE Spectrum, SRI is aiming for an average output of about 20 kilowatts per kite.

As compared to other tidal power systems that incorporate structures such as underwater turbines, Manta is claimed to be considerably cheaper and easier to install, plus its kite can simply be reeled in when there's a chance that it may interfere with human activities or nearby wildlife. That said, because the kite itself is quite lightweight, its designers believe that it shouldn't present much of a hazard even when it is moving.

SRI has stated that it now plans on building and operating a prototype to demonstrate the Manta technology, although we're still waiting to hear back regarding where it will be located and when it will be completed.

Source: SRI International via IEEE Spectrum

They winch it upstream through the current?! I would expect it's more efficient to *inflate it* so you winch it upstream on the surface.
It seems a lot more complex and susceptible to problems (snagging debris, etc) than other type of water turbines. The main benefit of aerial kites is that they allow easy access to winds higher up; underwater kites lack that benefit.
Malcolm Jacks
Why not have one in one out, so no loss of energy ????
Bob Stuart
Underwater, kites are far easier to build than in the air. With compact buoyancy available, and predictable currents, life is easy. The Makani system with the generator on the kite could drop down to allow shipping, or float for service. Moorings for a tether are far cheaper than foundations for a cantilevered post, and kite string is nearly free compared to those posts, as well as allowing the generator to range across the current for more effective area. Getting out of the bottom boundary layer does matter, and extra string is cheap. Deep water is less of a problem. This is definitely the way to go.
I prefer a concept investigated back in the 70s. An endless loop of underwater parachutes. They would open into the current then collapse on the return.
Their cycle description sounds very ineficient.. basicslly a high drag "downwinder" followed by a streamlined tow to restart... Losing all thr dynamic advantage of a kite - working in the "broad reach" configuration....

Don't worry, while we may love kites for their theoretical potential (sailing as well as wind power), they need too much babysitting and realtime control to be viable... there are other "windmills to tilt at" Don Quixotte will always have a battle to fight and a war to win just choose wisely. Lol...
Elegant design! This style could enable shallow low-head environments to capture a lot more energy.