Redefining wave power – tapping into the global potential

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(www.renewableenergyfocus.com)

From a eureka moment in the bath to the observation of an apple falling from the tree, inspiration often strikes at the least expected moments. For Dr. Stig Lundbäck, a cardiologist from Stockholm, it was the pumping mechanisms of the human heart that led to his idea for a viable wave energy converter. 

A serial inventor and holder of more than 100 patents, Lundbäck understood the gap between a good idea and a feasible technology. He eventually secured the support of InnoEnergy – the innovation engine for sustainable energy.

“We were immediately interested because wave energy remains the last great untapped source of cost-effective renewable energy,” says Kenneth Johansson, InnoEnergy’s CEO in Stockholm. “Although we have seen commercially viable technologies for harvesting tidal energy emerge, realistic solutions for taking advantage of wave energy are much rarer. Dr Lundbäck’s concept was a significant advance on other technologies, so we arranged for our business coaches and technology experts to evaluate it both technically and economically.”

The wave energy potential

The opportunity presented by wave power is significant. More predictable, consistent and controllable than either wind or solar power, with the right infrastructure in place, it could be a sustainable alternative for supplying base-load power. It also has a very low impact, that neither disturbs aquatic life nor spoils the coastal view that prompts so much ire from the public.

Wave power also fits within the new energy framework being created by distributed energy resources and off-grid applications. Although major utilities, particularly those with extensive offshore wind portfolios, are likely to be the major developers of wave energy farms, single installations can also serve more remote, smaller island-based or coastal communities – and even tourist resorts – particularly in developing economies.

Studies show that wave energy is five times more concentrated than wind and 10 times more concentrated than solar. In fact, wave energy could supply 10 per cent of global energy demand – or four times the installed capacity of nuclear energy today. That wave energy has not achieved its potential is our big opportunity,” says Johansson.

“Anyone concerned with developing wave energy in Europe will look to the Atlantic coast of France, Spain and Portugal, or the waters around Scotland and Ireland and see enormous possibilities – but until now, have not seen the technology to harvest it.”

Realising the concept

The possibilities inherent in wave energy is what has driven the product development of CorPower – from an initial concept to the creation of a company that is preparing to launch a complete prototype system later in 2017. Following positive assessments of the initial technology by InnoEnergy and various external experts, CorPower Ocean has been able to develop the wave energy converter concept into a practical, feasible and competitive product.

Patrik Möller, CEO of CorPower Ocean explains the challenges of bringing a viable wave energy technology to market. Despite many trials, to date no one has succeeded in making a commercial product. The challenge is to have a device that is robust enough to survive a tough ocean environment while generating enough revenue over time to make it a viable business case. Many concepts found storm conditions challenging – or their size and weight made them too expensive compared to their energy output.

“The more we explored, we realised there was a significant and principle difference in the way the CorPower device can harvest wave energy and overcomes these reliability problems. In 2012 when we took the idea to wave energy research centres like WavEC Offshore Renewables in Lisbon and NTNU in Trondheim, they agreed that we were on to something. We have been working with their research groups ever since.”

Innovative, efficient – and storm-proof

CorPower Ocean’s wave energy converters comprise a heaving buoy on the surface of the sea that is connected to the seabed by a taut mooring line, and which absorbs energy from the combined surge and heave motion of the waves. A pneumatic pre-tension module runs between the mooring line and the buoy, creating a system with high natural oscillation frequency that is smaller and lighter than conventional gravity-balanced converters.

While CorPower was developing the product, researchers at Trondheim University invented an innovative phase control technology, which CorPower and NTNU agreed to co-develop. Known as WaveSpring, the patented control system makes the buoy inherently resonant over a broad range of wave periods. It amplifies the motion of and power capture from regular waves, while allowing the system to be naturally ‘de-tuned’ during storm conditions. Tank testing has shown that the buoy can survive waves of up to 32 metres without excessive load on the structure. This significantly improves the system’s ability to survive in harsh conditions and so lengthens its productive lifecycle. After proving the WaveSpring technology with CorPower, the NTNU inventor Jörgen Hals Todalshaug joined the company as Lead Scientist.  

In addition, a proprietary, highly durable drive train is responsible for transforming amplified linear motion into rotation motion. Because the cascade gear divides a large load onto a number of smaller gears – much like a planetary gearbox – it is capable of providing high-power density and high efficiency.

To eliminate the peaks and troughs of power supply, the buoys incorporate a dual set of flywheels/generators that provide power absorption and temporary energy storage. These generators and the power electronics behind them are based on standard components used in the offshore wind industry. Finally, a programmable logic controller is located inside the device to allow the buoy to operate autonomously, while an interface enables remote control and data acquisition by onshore engineers over fibre and a radio-link.

 

Tests show that the technology delivers optimal performance at sea-depths between 50 and 100 metres.

From prototype to commercial product

According to Möller, CorPower’s success can also be attributed to its development approach as well as its innovative technology: “We are one of the first wave energy companies to strictly follow a structured verification approach set by the IEA-OES and Wave Energy Scotland. We started on a small scale to prove the reliability and performance of the different pieces of the technology and gradually scaled up, securing funding for further tests as we went along.

There are no short cuts – you can’t build and scale before basic principles of hydrodynamics, system stability and robustness have been proven.”

In accordance with this philosophy, the CorPower device has been through a number of iterations since the first bench top prototypes were developed. The concept was first validated in 2012 on a 1:30 scale model with €500,000 funding. Wave tank and HIL tests were performed with WavEC, NTNU and KTH on 1:16 to 1:3 scale prototypes, with a further €1.7 million.

CorPower has just started dry testing a half-scale device in a custom-built test environment that emulates wave impacts on the device to prove reliable operation up to full storm and mechanical loading. In the second half of the year, ocean testing will begin at EMEC’s Scapa Flow site in Orkney, with project partners Iberdrola, EDP, University of Edinburgh, WavEC and EMEC. After completing this Stage 3 program the company aims to start work on the next stage 4 pilot together with leading partners of the sector.

Throughout the Stage 3 program, CorPower has attracted funding from the Swedish Energy Agency and Wave Energy Scotland, in addition to InnoEnergy. A new program named WaveBoost, supported by EC’s Horizon 2020 funding, was recently started to further develop innovative concepts that can be introduced at the point of market introduction, without disrupting the architectural design that has been tested. 

A viable future

Möller is confident about CorPower’s prospects: “All the testing and prototyping shows that the technology can generate five times as much energy per tonne and three times as much energy per force compared to previously known solutions to harvest wave energy. We’ve also been able to design it to be robust, compact and significantly lighter than traditional models, so installation, service, maintenance and decommissioning are much easier – giving a low OPEX per kilowatt.”

Möller acknowledges that developments in subsea power cabling and related technologies in both the offshore wind and oil and gas sectors, are also contributing to an increasingly favourable technological and commercial environment for wave power.

“There is an extent to which we are piggy backing on the developments made in offshore wind,” he explains. “But the trajectory is very different. Wind turbines have been optimised over 30 years to achieve 10 megawatt hours per tonne of device. Our device aims to show a similar level of structural efficiency within five years. We anticipate that this will allow the technology to be competitive with most advanced wind and solar implementations after reaching a moderate install base, and better than nuclear, oil and coal.”

If all goes according to plan, 2017 could be the year that wave energy finally comes in from the deep.