Hydraulic system generates renewable power from ocean waves

The west coast of Scotland is home to some of the most powerful and consistent wave generating potential in the world. Despite 11,800km of coastline and the possibility to produce between 40-70KWh per metre, we do not currently use even 1% of this free, powerful resource.

With the increased demand for energy over the next 50 years, Renewable Wave Power (RWP) is attempting to remedy this situation with a new and efficient power take-off structure. RWP is a semi-submersible multi-axis wave energy converter, specifically designed to run in the Orkneys, Scotland. The design has the unique ability to absorb the forces from the peaks and troughs of the North Atlantic waves in any given direction. The multi-axis structure's test results highlighted the increased potential and efficiency to convert external movements into hydraulic pressure, compared to conventional linear devices. Inspiration for the project came from a variety of sources. First, as inventor Samuel Etherington puts it: "[I had a] personal awareness that there simply must be alternative energy generation sources in the mainstream energy production industry if we are to avoid destroying the landscape that we live in." Secondly, from kitesurfing and sailing off the west coast of Cumbria, he became conscious of the sheer power within waves and the real potential for energy generation. Finally, diving trips in the Orkneys has put the world's wave and tidal development technology at the European Marine Energy Centre firmly in mind. In addition, he claims, living in the Lake District, it is easy to see why developing renewable energy is vital as he feels the global environmental, social, and political effects will continue to escalate if renewable energy does not play a bigger part in energy production. RWP has undergone multiple simulations, CAD iterations, and a 40th scale, fully-functional prototype. Testing at Lancaster University's wave tank proved the principles behind the multi-axis structures, while displaying promising results for energy generation using the new and unique structure. The hydraulic power take-off system is a proven design capable of reacting and changing valve states in respect of the sea state. This variable setup allows the maximum energy to be harvested from the ocean in any given sea condition. Wave data recorded from a data buoy in the Orkneys was scaled and propagated down the wave tank to provide scaled wave heights and wave lengths in which to test the structure. A further successful round of tests to verify the initial results will see the commission of a scaled hydraulic test rig to develop and refine the hydraulic geometry for the structure. Beyond the hydraulic development, RWP will enroll on the European Marine Energy Centre's Nursery Programme for sea trials. The Renewable Wave Power generator seeks to overcome the limitations of some current wave power technologies.These work best when struck by waves travelling in one direction and are less efficient in more turbulent seas. So how does it work? A long chain of loosely-linked pistons draw power from the tidal waters that flow unpredictably. Energy is generated as the chain flexes in high and low points of each wave. As part of the project, data was taken from buoys moored in the Orkney Islands and used to make waves in a water tank at Lancaster University. The 3D nature of a wave front cannot to be approached in a two-dimensional way, since any attempt to resist the movement of a wave will eventually result in a stress, which in turn will lead to a fracture and an eventual failure. RWP is designed to absorb any movement that the structure encounters and effectively pumps up and pressurises the closed-loop hydraulic system. High pressure accumulators contain the pressure and adapt to the sea conditions to modify the pressures in real-time, allowing for optimum performance from the structure. As the high-pressure accumulator reaches its variable pre-determined limit, hydraulic fluid is released under pressure through a hydraulic motor mated to a generator and, as a result, energy is created. Regardless whether the unit is cresting a wave or sitting in the trough of a wave, the cylinders remain capable of pumping hydraulic fluid around the system. The setup allows rotary motion to be converted via linear hydraulic cylinders into fluid pressure. The pressure within the stystem is stored in accumulators that, at a capped pressure, allow fluid to be released through a hydraulic motor. This generates rotary motion on the hydraulic motors' output shaft, which is mated to a generator. The fluid that has travelled through the hydraulic motor is fed into a low-pressure accumulator reservoir. Consequently, redraw of the hydraulic cylinder draws fluid from the low-pressure reservoir and the closed loop cycle continues. Further tests are planned to demonstrate his device's efficacy. Commenting on the device's future, Dr. David Forehand of the Institute for Energy Systems, a research institute in the engineering school at the University of Edinburgh, told BBC News that "The real test for a device is its cost of energy". Scotland is aiming to be the world's leader in wave and tidal power, but it is still largely in the development and commercialisation stage. The Scottish government has the Saltire Prize, which will award $15.8 million in 2017 to one of the wave and tidal energy companies competing for the prize. The winner will be the technology that has the greatest volume of electrical output over 100 gigawatt-hours over a two-year period using only the sea. Renewable Wave Power has many steps before it could compete for an award such as the Saltire Prize, however. Etherington's submission to Dyson noted that he would require further tests to verify the initial results. If those tests were successful, Etherington would commission a scaled-up rig to be tested at the European Marine Energy Centre on Orkney Island, which has a variety of test facilities for wave and tidal powers in various stages of development.