In order to stand a greater chance of being commercially viable, wave energy developers must quickly recognise and define their strengths and weaknesses.
Interview with Thomas Royle, Gurit - by Wave Energy Today staff writer
The marine energy industry may still have a long way to go but emerging technologies like wave power seem to be making steady progress.
If on one hand, wave energy converters have showed signs of delivering commercially viable electricity, then on the other, support for the industry, too, is on the rise. For instance, Scotland’s first Marine Bill has been introduced to the Scottish Parliament. Key measures include a new marine planning framework (to ensure that the increasing use of the seas for energy, fishing, aquaculture, recreation and other purposes is well managed). It also features a simpler licensing system that will reduce the administrative burden and cut bureaucracy reducing business costs.
The industry can definitely benefit from such moves as licensing regimes promise to relieve developers of the administrative burden of securing sites to install and test their devices.
Learning curve
It is being suggested that wave energy could catch up with offshore wind power in as early as five years.
A company like Gurit, which is a specialist in structural composite materials, processing and design, acknowledges that the timescale is likely to be reduced given experience gained in other sectors.
“On the design side, the wind energy industry has learned a great deal in the last 10-15 years, much of which can be directly applied to wave energy structures: Characterisation of fatigue properties; understanding of manufacturing quality issues and their influence on machine reliability; environmental resistance of surface coatings. These are just a few examples,” said Thomas Royle, Head of Strategic Business Development, Gurit.
Clearly, there are other challenges that are more specific to marine structures where wind energy can’t help, but a company like Gurit says its engineers and materials specialists draw on their extensive experience of subsea and marine composite structures to help solve these issues.
Connection to the grid of onshore wind turbines has been problematic, but nowhere as difficult as for the offshore wind farms. The experience already gained in this relatively new renewable technology is directly applicable to wave energy, and yet remains one of the biggest hurdles to jump, said Royle.
“Perhaps the key issue however is cost of energy production. For wave energy devices to be commercially viable they will have to produce power at a cost close to or lower than that for an offshore wind generator. This, for many companies, will prove to be the hardest lesson,” added Royle, who is scheduled to speak at the 2nd Annual International Wave Energy Summit 2009 in London (June 30 – July 1) this year.
Supply chain
Many attempts to design wave energy converter (WEC) devices have been made in the past, and many have failed due to the hostile environment the devices have to endure.
The challenges involved in WEC cover a range of engineering disciplines, including civil, electrical, and control engineering. Projects that fail to consider all of these disciplines will not succeed.
Royle said it is vital that everyone involved knows exactly what they know and what they don’t know.
This basis assists in the creation of an experienced and capable supply chain.
In order to stand a greater chance of being commercially viable, developers must quickly recognise and define their strengths and weaknesses and use this knowledge to develop contracts or partnerships with companies that can bridge the gaps.
“Many companies are yet to determine what expertise they lack, and this places them in a weak position when they move to seek funding from third parties,” said Royle.
Structural design of WECs
It is critical to ensure that material and manufacturing costs are kept at cost effective levels and at the same time the product is robust.
Explaining the process, Royle said definition of the load cases and functional requirements is obviously the fundamental step but by the time designs have reached the prototype stage, this has normally been covered. A common problem thereafter is that designers try to convert designs that have been prototyped in conventional materials directly to composite without optimising the design.
They then incur costs due to complex manufacture and high parts count without realising the benefits that the materials can bring.
“If instead the designer is prepared to go right back to the original functional requirements, albeit within the same geometric envelope as the prototype, the composite design can be developed in a way that will often result in a lower cost product than would be possible with conventional materials and with greatly improved reliability and maintenance requirements,” said Royle, who added that this of course requires experience of designing in composite materials.
Material options
Every project is different, the choice of material and processing technology depends on many factors: load cases, size and geometry, build cost target, life cost target, manufacturing cycle time and corrosion resistance.
The main material properties required for survivability of marine energy structures are strength, fatigue resistance, damage tolerance (toughness) and corrosion resistance, which makes composites a clear favourite for many applications, according to Gurit.
Corrosion resistance is obvious, but often people don’t realise that composite structures can resist fatigue and damage better than steel or concrete, said Royle.
“In choosing fibre types, most devices will be made with glass or carbon fibre reinforcement. The latter however is rarely cost-effective except in very slender structures such as turbine blades,” he said.
“For the resin, whilst polyester and vinylester are less expensive than epoxy, more fibre is generally required, which in turn means more resin and more labour. More importantly, the water resistance of epoxy laminates is significantly better, as is the fatigue performance, both prime drivers for the reliability of any marine structure,” added Royle.
On a reciprocating structure, less energy is wasted with each cycle if the structure is lighter and it is also better able to respond to changing conditions. Rotating structures can accelerate faster, allowing them to operate closer to their optimum design point in varying conditions.
For structures that are tuned to resonate with the waves, a lighter structure provides improved options for varying ballast to suit changing wave frequency.
And finally, composite structures may be designed with in-built flexibility where appropriate, allowing peak loads to be mitigated by providing structural compliance. This technique is already well exploited in the design of wind turbine blades for instance, said Royle.
2nd Annual International Wave Energy Summit 2009
Wave Energy Today is organising its 2nd Annual International Wave Energy Summit 2009 in London (June 30 – July 1) this year.
For more information, click here: http://www.waveenergytoday.com/IWES Or
Contact: Gargi Iyer by email gargi@waveenergytoday.com
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