Successful launch for new wave energy converter

The experimental wave energy converter is suspended above Lyttelton harbour prior to launching.

A newly-developed experimental wave energy converter which was successfully launched recently in New Zealand’s Lyttelton harbour could well provide the answer.

Involving a partnership between Industrial Research Limited, the National Institute of Water and Atmospheric Research (NIWA^[?]) and energy industry consultants Power Projects Limited, the four-year project aims to make a compact, lightweight device which is small in mass but ‘thinks it’s large’, Industrial Research energy manager, Alister Gardiner says.

“Kiwis are not used to making a big noise about their efforts but, from what we can see of overseas wave generator progress, we are quietly confident that we may have a real winner here,” he says.
 
New renewable energy resources are needed in response to increasing energy demand, depletion of conventional resources, and global warming to which exploitation of fossil fuels is a major world wide contributor. In recent years wave energy conversion has attracted significant interest  from governments and developers looking for alternative carbon-free energy resources.

The project team aims to have a pre-commercial wave energy device completed and demonstrated in open sea conditions within the next 18 months.

The device will have controls that forecast incoming waves and adjust the response to changing wave patterns and will have a modular generation capability of up to 500kW.

While the New Zealand project is in the initial stages, several overseas wave energy devices have been under development for more than ten years, Power Projects director, John Huckerby says.

“The device which has the most advanced technology to date is a steel device about the size of a commuter railway train, 140 metres long, which floats on the surface. There are also a couple of devices being developed which generate electricity by resisting the waves. Our device is very compact and is what’s called ‘compliant’ — it doesn’t try to resist the waves, it extracts energy from the waves and therefore should have better survivability.

“It’s a simple idea and will be very sophisticated by the time it’s fully  eveloped. Industrial Research has done a lot of very valuable background research and computer physical modelling. The challenge now is to validate the models and use them to design and build a larger proof-of-concept system.”

The new device seeks to directly harness both kinetic and potential energy from passing waves.It will be largely sub-surface so that as much of  the device as possible interacts directly with the wave energy.

The waves arriving at a particular point in the ocean are often made up of wave trains coming from different directions.

Alister Gardiner says this has tripped up many earlier developers, who found that their devices did not perform anywhere near as well as expected from initial model tests in wave tanks.

“Interestingly, deep sea waves have much more energy than the waves crashing on our beaches, which have typically lost much of their energy through friction with the shallowing ocean bottom.”

An object immersed in a wave field is subjected to a complex mix of motions – heave (up and down), surge (back and forth) and pitch (a rolling back and forth motion). Most devices extract only a small proportion of the total energy of a passing wave.

The key to success is to extract as much energy as possible from more than one type of motion. This is the aim of the device development team, whilst still keeping the size and cost of the device within reason.