Fish point way to turn water to power

West Australian
Monday 1/12/2008 Page: 31

A revolutionary device that can harness energy from slow-moving rivers and ocean currents could provide enough power for the entire world, scientists claim. The technology can generate electricity in water flowing at a rate of less than one knot - about 1.6kmh - meaning it could operate on most waterways and sea beds. Existing technologies that use water power and rely on waves, fast tides or rushing currents from dams are far more limited in where they can be used and cause bigger obstructions when built in rivers or the sea.

Turbines and water mills need an average current of five or six knots to operate efficiently, while most of the Earth's currents are slower than three knots. The new device, which was inspired by the way fish swim, has a system of cylinders horizontal to the water flow and attached to springs. As water flows past, the cylinder creates vortices, which push and pull the cylinder up and down. The mechanical energy in the vibrations is then converted into electricity.

Cylinders arranged over a cubic metre of the sea or river bed in a flow of three knots can produce 51 watts but the power produced increases sharply if the flow is faster or more cylinders are used. Systems could be sited on river beds or suspended in the ocean. The scientists say that generating power in this way would potentially cost only about 80 a kilowatt hour, compared with about 10.5¢ for wind energy and between 23.5¢ and 73¢ for solar energy.

Michael Bernitsas, a professor of naval architecture at the University of Michigan, said the system was based on the changes in water speed caused when a current flows past an obstruction. "This is a totally new method of extracting energy from water flow," Professor Bernitsas said. "If we could harness 0.1 per cent of the energy in the ocean, we could support the energy needs of 15 billion people." The engineers are putting a prototype device in the Detroit River, which has a flow of less than two knots. Their work is published in the current issue of the quarterly Journal of Offshore Mechanics and Arctic Engineering.