Tuesday, June 8, 2010

Sailing ships could capture energy

Presentation of sailing yacht powered with fuel cell

From NewScientist

Sailing ships could effectively harvest energy from the wind blowing over the vast tracts of ocean too far from the shore for wind turbines, claimed a scheme unveiled last month, according to a story being reported from London.
The ships would turn wind power into hydrogen, which would be stored on board, to be unloaded later and will eventually be used to generate electricity, according to the Asian News Service.

The idea is the brainchild of Max Platzer and Nesrin Sarigul-Klijn at UC Davis.

"Our proposal makes ocean wind energy available for exploitation -- a huge energy reservoir because the oceans cover 70 per cent of the globe," New Scientist quoted Platzer as saying.
It "offers the opportunity to make a decisive contribution to the solution of the energy and climate crisis," he added.

The ships would tow hydropower generators consisting of two wing-like underwater blades that would be made to oscillate by the force of the water as they plough through it.
This motion would turn a crankshaft connected to a generator.
The electricity this produces could then be used to split seawater into hydrogen and oxygen.

Sailing ships can reach speeds of up to 25 knots (46 kilometres per hour).
A ship with 400 square metres of sail, operating in a moderate force 4 breeze of 15 metres per second, could generate up to 100 kilowatts of electrical power, Platzer and Sarigul-Klijn calculate.
They also say it should be possible to build larger ships capable of generating up to 1 megawatt.
With enough ships, the energy needs for the entire planet could be met this way, said Platzer.

"Obviously, this is a roundabout way of generating electricity instead of converting wind or water flow energy directly into electricity using stationary windmills or hydroturbines," said Platzer.
This will clearly lead to some losses, but he calculates that the electricity can be converted into hydrogen and back again with about 30 per cent efficiency. Concentrated energy.

Extracting energy from flow of water rather than directly from air has advantages, as the power density is much higher.
Platzer said that the water flow through the underwater generator has a power density of 36 kilowatts per square metre - far more than the 1.2 kilowatts per square metre typical of air blowing through a rotating wind turbine.
The more concentrated energy means that the equipment needed to harvest it can be smaller.

The researchers presented their paper at an American Society of Mechanical Engineers energy sustainability conference in Phoenix, Ariz.

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