The company Alabatern Wave Energy from Scotland has created WaveNET, an offshore array-based wave energy converter that uses the motion of waves to generate electricity. The floating structure of the WaveNET is flexible in all directions, and capable of capturing power from the ocean regardless of wave direction and array orientation.
WaveNET arrays are formed by interconnecting the unique SQUID generating units. The first development scale of WaveNET is Series-6, designed to operate in in a minimum water depth of 20m and to generate electricity in waves with heights ranging from 0.3m to 6m. WaveNET's strongest features come from being designed and engineered from the start to function as an array of linked units. Each SQUID unit comprises a hollow central riser tube connected to 3 buoyancy floats by linking arms. The connections between each of these components is made by 6 identical fully articulated pumping modules. The buoyancy floats also have hollow structures, allowing them to house the PTO (Power take-off unit) along with other components for communications and hydraulic operation.
The PTO module comprises a hydraulic motor, electrical generator, control apparatus and communications. A WaveNET array will contain a number of PTO modules - the optimum quantity depends on the available energy at the site, the number of units in the array and the degree of redundancy required.
The most significant benefits of this array-based approach to wave energy come from improvements in power yield and potentially dramatic reductions in project costs. By increasing the length of the array WaveNET can capture more power from longer waves, increasing the width allows it to capture more energy from lower density sites. When interconnected as an array, WaveNET's movement is like a three-dimensional Mexican wave: the ocean's energy pushes and pulls the array's structure; each SQUID unit's articulated joints flex, absorb some of the wave's energy, with any unabsorbed energy passing to the next unit, all the way through the array. This unique design allows the array to respond to the full orbital motion of the waves, from any direction, and allows power capture from 5 of the 6 elements of wave energy: pitch, roll, heave, surge and sway.
The space-frame type construction of the array allows these large amounts of sea area to be covered using comparatively small amounts of material, resulting in a high power to weight ratio.
The SQUID generating units feature an innovative patented pumping module design, which avoids the use of mechanical end-stops. This is an extremely important feature for wave energy converters where storm conditions can create large waves with very high energy levels that can destroy normally robust systems added to this, WaveNET's low profile in the water, flexible structure and a mooring system featuring multiple points of connection allows large waves to pass over and submerge some or all of the array, minimising any potential damage.
WaveNET arrays appear from the surface as a series of isolated buoys, similar to those of mussel farms, reducing visual impact and potential conflict with other sea users. As much as 300 MW per km² is possible for large arrays. This compares to 15-20 MW/ km² for other wave devices, with offshore wind typically in the range of 10 MW/km².
Source and images: Albatern Wave Energy
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