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Catching waves

23 September 2014

There’s enough wave energy in one metre of the ocean to light ten thousand 100-watt light bulbs. But how to harvest all this energy? Wout Prins, project manager of the Ocean Grazer project and lecturer at the Institute for Technology, Engineering and Management, thinks he has found the perfect solution. In a shed next to the Chemistry and Physics building, he is working on a scale model of the Ocean Grazer.

Wout Prins | Photo Science LinX
Wout Prins | Photo Science LinX

‘I’m not an engineer’, says Prins in his office. ‘But while surfing the internet to find wave-energy extractors, it struck me that their designs were not very smart.’ So he tried to think of a better way to harvest the energy of ocean waves.

First, he shows the ‘not very smart’ Pelamis Wave Power . ‘Look, there are three segments connected by a hinging mechanism with hydraulic pistons. When a wave passes under the system, the parts go up and down, moving the pistons. The problem is, however, that the parts are optimized to one type of wave, but ocean waves are incredibly variable!’

Prins, a social scientist by training and lecturer in the Industrial Engineering and Management programme, downloaded information from several research buoys that measure wave characteristics in the oceans west of the European continental shelf. ‘The most common wave is three meters high, but that accounts for just over 12 percent of all waves.’ Most of the wave-harvesting mechanisms are optimized for one particular wave. ‘Which means they are not optimized for most waves.’

That was the problem. Prins dedicated two years’ worth of evenings to finding a solution. ‘I finally thought I was on to something, a design I called the Ocean Grazer. It was a bit scary to show it to others. Would I manage to convince them?’ Prins went first to Research and Valorisation , the University department that helps scientists with patents and valorization plans. They liked what they saw. ‘We filed a patent application, and a year ago, the Board of the University and the Faculty Board gave me some time and funding to help develop my ideas.’

Map showing available wave energy (yellow highest, blue lowest) | Illustration Wout Prins
Map showing available wave energy (yellow highest, blue lowest) | Illustration Wout Prins

What is this Ocean Grazer? ‘My system adapts to different waves’, Prins explains. The basic mechanism is a ‘floater blanket’, small units that rise with the wave. ‘Small waves lift one or a few of these absorber units; big waves lift more.’ As each absorber rises, it pulls a plunger up through a pipe to pump water into a basin. But that’s only half of the story.

Each absorber is connected to a set of plungers. One, all or any combination of plungers can be activated, thus varying the weight on the absorber. A wave with little energy would not be able to lift a heavy weight. ‘But the weight can’t be too low either. We therefore devised a system of three different plungers, which allows us to set seven different weights under each absorber unit.’

Impression of the Ocean Grazer platform, with the two submerged water tanks. | Illustration Wout Prins
Impression of the Ocean Grazer platform, with the two submerged water tanks. | Illustration Wout Prins

A regulating system couples or uncouples the available weights to optimize the energy harvest. ‘This does mean that we have to know the height and energy of each wave that hits our system.’ A German firm specialized in wave radars is working on this problem.

The absorbers pump water from a low to a high basin. ‘This is how we store potential energy. The water flows back to the lower basin through a turbine, and that produces the energy.’ According to Prins’s calculations, Ocean Grazer could harvest around 90 percent of the available wave energy.

The system will be huge: ‘We envisage a 230-meter-high circular platform with a diameter of four-hundred meters.’ Most of this will be under water, with the upper basin 80 meters below surface. ‘That is about the maximum depth of ocean waves, so with the lower basins below that level, the entire platform will be very stable, as the waves won’t affect the deeper parts.’ A platform of this size could produce enough power for 80,000 homes.

Scale model of the pumping mechanism (left), and detail of plunger setup (right) | Photo Science LinX
Scale model of the pumping mechanism (left), and detail of plunger setup (right) | Photo Science LinX

In the shed next to the Physics and Chemistry building, Prins shows us a model of the pumping system. It’s a wooden frame more than five meters in size, with water tanks at two levels that are connected by three big pipes. When the absorber unit rises, it lifts a plunger in one, two or three pipes, depending on the power of the wave.

When the plungers rise, they suck water from the lower basin. When they stop, a valve closes to prevent backflow to the lower basin. The plunger then drops again. ‘There are two valves on the plunger. The open valves allow the plunger to drop through the water column. We may patent this system, as it is quite new.’ With each passing wave water is thus pumped from the lower to the upper level.

The entire model was built by Bachelor’s and Master’s students. ‘They love working on this project, as it has a very concrete application.’ Over the last year, three Bachelor’s and eight Master’s students from a number of different countries have participated in the project.

‘Our aim is to prove the concept can work not only in modelling studies but also in these kinds of scale experiments.’ The entire project runs on a shoestring budget. ‘We are applying for funding, but a growing network of partners are already interested in the project.’ Prins’s main focus is to conduct his research and train his students. ‘The project should keep me busy for the next ten years or so.’

For more information, visit the Ocean Grazer website.

Last modified:16 December 2015 3.40 p.m.
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