With hundreds of miles of coastline and strong prevailing winds across the Atlantic reach, Britain is well placed to exploit wave power as a key source of renewable energy - provided it can be made commercially viable. Investors need costs to be reduced to around 10p/kWh by 2020 (ETI/UKERC Marine Energy Roadmap 2014).
Traditional wave-powered generation extracts energy from a single float - which moves with the waves. However such floats are limited to movement in a single mode of motion – usually heave (vertical movement) or pitch (side-to-side movement).
Engineers at The University of Manchester have developed a moored, three-body system that simultaneously generates power from each of the three body’s various modes of motion and the relative motion between the bodies. A linear mathematical model can predict the power output and will allow the engineers to optimise the system. The model also confirms previous hypotheses that heave, pitch and surge generate power, and highlights that surge produces 50% of the total power.
“Previous wave devices did not exploit the potent power of surge - but my ‘M4M’ system can,” notes Professor Stansby. “This may provide a step change in power generation.”
The amount of power that a wave energy generator can produce is known as its ‘capture width’: the ‘M4M’ system already boasts capture width values as high as 30%.
“Unlike other devices, the ‘M4M’ system has high values for both regular wave swells and irregular waves. It even boasts high values for the full range of wave frequencies found in typical coastal conditions,” enthuses Professor Stansby. “These are key breakthroughs in wave technology.”
The ‘M4M’ system has been tested at a 1:10 scale in an ocean wave basin at Plymouth University and at a 1:50 scale in the Manchester’s wide wave flume. Scaling laws indicate that a single ‘M4M’ device will generate an average of 200-300 kW in offshore conditions. “But we can increase yields even further by optimising the design to suit specific wave sites,” adds Professor Stansby.
According to a report published by the Energy Technologies Institute and UK Energy Research Centre, marine energy needs a dramatic reduction in cost. The Engineering and Physical Sciences Research Council recognise the potential of the ‘M4M’ system to rise to this challenge and have awarded Professor Stansby a major research grant through its Supergen Marine Challenge. He hopes that his new technology will address this and make a significant contribution to UK and global power supplies.
For now the engineers will focus on optimising the devices responsiveness to wave motion, before optimising its design and control strategies in preparation for tests at sea.
Name: Step-WEC: Step change for wave energy conversion through floating multi-body multi-mode systems in swell
Lead researcher: Professor Peter Stansby
Research group: Wave Energy Systems
Research centre: Tyndall Manchester
Industry partners: Cammell Laird and Rexroth Bosch
Dates: June 2013 – June 2016
These are key breakthroughs in wave technology.