The OE35 billed as the world’s largest capacity floating wave energy device is certainly an imposing thing to look at. While no dimensions have yet been drawn up for the machine to be built for Scotland as yet, the machine the company built for testing at a US Navy test site in Hawaii measures 125 x 59 ft (38.1 x 18 m), with a draft of 31 ft (9.4 m) and a total weight of 826 tons.
In testing, it ran at a capacity of 500 kW, but the device was, and is, capable of 1.25 MW. Building these things requires shipyard-level facilities – in the Hawaii machine’s case, those of Oregon company Vigor. After construction there, the machine was towed to its test site for commissioning.
It works on a relatively simple principle. Moored to the ocean floor, the OE35 sits in the sea as waves lap in and out of three large airtight chambers. As the water level in these chambers rises, the air is pushed out the top. As it falls, the air is sucked back in.
OceanEnergy makes use of a piece of Northern Irish technology to harvest energy from this bidirectional air pressure: the Wells turbine was invented in Belfast in the late 70s. These use a series of symmetrically-designed fan blades, designed to convert air pressure coming through in either direction into the same direction of rotation. Thus, the turbine turns continuously in one direction as the air pumps in and out of the wave chambers, rather than requiring the turbine to keep switching directions every time the airflow reverses.
This is in contrast with Wave Swell Energy’s (WSE’s) blowhole generator, which works on similar principles, but only harvests energy from the air on the in-stroke, allowing the out-stroke air to push out through a valve. Wells turbines are less efficient than unidirectional turbines, and independent analysis appears to suggest WSE’s approach of using a single, relatively cheap unidirectional turbine is likely to lead to some of the world’s cheapest renewable energy, so perhaps there’s something to it. But it’s hard to imagine the Wells turbine being so inefficient that it can’t harvest more energy from wind in two directions than WSE’s device can in one.
According to newatlas