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Wave Power Boost with Offshore Wind Turbines

From the work on the Ocean Treader, a derivative machine of simplified design, Wave Treader, has arisen using aspects of Ocean Treader and mounting them on the foundation of an Offshore Wind Turbine. This shows promise to be highly commercially attractive, to have low technical risk, and to be quick to market. Npower has supported a Feasibility Study into the commercial application of Wave Treader via their Juice Fund and we expect to start building a full size prototype of Wave Treader in 2009 with commercialisation in 2011.

Wave Treader - How it Works

The Wave Treader concept utilises the arms and sponsons from Ocean Treader and instead of reacting against a floating Spar Buoy, will react through an Interface Structure onto the Foundation of an Offshore Wind Turbine. Between the Arms and the Interface Structure hydraulic cylinders are mounted and as the wave passes the machine first the forward Sponson will lift and fall and then the aft Sponson will lift and fall each stroking their hydraulic cylinder in turn. This pressurises hydraulic fluid which is then smoothed by hydraulic accumulators before driving a hydraulic motor which in turn drives an electricity generator. The electricity is then exported through the cable shared with the Wind Turbine.

Periodically the Interface Structure moves vertically to allow for the effects of tidal range, and it also can rotate to ensure that the Sponsons are optimally aligned with the wave direction.

An initial study commissioned by us, indicates that the additional loads placed on the foundation of an Offshore Wind Turbine from Wave Treader are relatively small, and therefore Wave Treader will not adversely affect the stability of the Wind Turbine.

Wave Treader - Design

The structure comprises of steel load bearing members with the floating bodies molded from GRP (Glass Reinforced Plastic). This allows standard offshore manufacturing techniques to be used, and importantly a wide range of fabrication yards across the world.

Wave Treader - Reliability

Due to the machine’s remote locations where access will not always be possible, reliability has to be one of the key features. To maximise reliability, all the hydraulic and electrical equipment will be to standard, industry proven marine specifications, with the systems designed and assembled by experienced and skilled personnel. Additionally in the design of the machine care will be taken to minimize the possibility of single point failure modes. Typically this will be done by having duplication of the equipment, so that in the event of a failure in one item, the remaining items will continue producing electricity. The failed set can then be left shutdown until a weather window allows for it to be changed out for a replacement unit. The experience of the design team in handling heavy objects offshore and sub-sea will ensure that the mechanisms are in place to allow this to happen smoothly and safely. The machine is designed for an overall design life of 25 years, with refits every 5 years. It is anticipated that the refits will comprise of replacing arm and sponson bearings, generator skids, and cylinders as well as painting where required.

[greenoceanenergy]