Harnessing the vast energy of the UK"s coastal tides could become much simpler and cheaper with a new design for the next generation of underwater turbines. The device, unveiled by a team of engineers from Oxford University, re-thinks the way power is generated underwater and the inventors believe it will be more robust, more efficient and cheaper to build and maintain than anything in operation today.

There is an immense potential resource of clean energy from the tidal flows around the UK: conservative estimates suggest there is at least five gigawatts of power, but there could be as much as 15GW, equivalent to 15 million average family homes. Tidal generators can harvest the energy of these moving streams, with the added advantage that the resource is, unlike wind, predictable.

There are only a few underwater turbines in operation today and they all operate like underwater windmills, with their blades turning at right angles to the flow of the water. In contrast, the Oxford team"s device is built around a cylindrical rotor, which rolls around its long axis as the tide ebbs and flows. As a result, it can use more of the incoming water than a standard underwater windmill.

At full size, a Transverse Horizontal Axis Water Turbine (Thawt) rotor would be 10m in diameter and 60m long. Connecting two of these together with a generator in the middle could produce around 12MW of power, enough for 12,000 average family homes.

"To do that, you only need three foundations and one generator," said Martin Oldfield, senior research fellow of engineering science at Oxford University. "To do that with a [windmill] would require five foundations and 10 generators."

The Thawt device is mechanically far less complicated than anything available today, meaning it would cost less to build and maintain. "The manufacturing costs are about 60% lower, the maintenance costs are about 40% lower," said Malcolm McCulloch, head of the electrical power group at Oxford"s engineering department.

Underwater turbines that harvest tidal currents have already become an established technology in the world of clean energy. So in order to push the frontier further, a group of engineers at Oxford have been tinkering away on a design that promises to be even more powerful and efficient. The group recently introduced an innovative Transverse Horizontal Axis Water Turbine that will not only collect more energy but require 60% lower manufacturing costs and 40% lower maintenance costs.

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