Swedish wave energy company CorPower Ocean has successfully completed a €6.5m funding round for the further development and testing of its novel wave energy converters.

The funding will enable the company to embark on the third stage of its development programme, which will entail taking a scale 1:2 25kW wave energy converter (WEC) through the next step of structured verification by dry testing it in a rig in Stockholm in 2016, followed by wet testing in the first and second quarters of 2017 at EMECs Scapa Flow nursery site on Orkney.

The CorPower device features a novel integrated WaveSpring module, that makes the buoy oscillate in resonance with incoming waves, strongly amplifying the motion and power capture compared to a passive buoy.

The device also houses a further three proprietary modules - a pre-tensioning module that enables a lightweight system with high natural frequency of oscillation, a Cascade gearbox - which converts the amplified linear motion into rotation - and dual flywheels with permanent magnet generators, which are used for damping, power smoothing and conversion of mechanical-to-electrical energy.

"Thanks to this innovative phase control technology, combined with a high efficiency drive-train based on a Cascade gear box, we can deliver more than five times as much annual energy per ton of device compared to previous state-of-the-art, taking wave power to the same level of structural efficiency as wind," said Patrik Möller, CEO at CorPower Ocean.

Across two previous rounds of testing alongside European partners, Möller claims that CorPower has already demonstrated a path for the wave energy sector to improve structural efficiency 'to a point where it could compete with modern wind turbines.'

"Stage one and two testing has proven that a significant improvement in the amount of annual energy per ton and annual energy per force can be offered compared to the current state of the art Wave Energy Converters," he said.

According to Möller, this 'step-change improvement' in performance is provided by a low-cost spring arrangement using 'proven pneumatic components' - adding a 'minimum of cost and complexity compared to the same system without phase control.' He is also keen to stress that WaveSpring provides a critical function for detuning the device in storms – making it move out of phase with the waves, thereby becoming more transparent to the energy flux.

"The detuning feature was shown to significantly reduce the loads on the equipment during the test campaign in Nantes," he adds.

The current stage three programs, called HiWave and HiDrive, are being carried out by a number of companies and other organisations, including CorPower Ocean, Iberdrola Engineering, EMEC, WavEC Offshore Renewables, University of Edinburgh and the Royal Institute of Technology, with financial support from Wave Energy Scotland, KIC InnoEnergy and the Swedish Energy Agency.

A key stage three aim is the demonstration of a scale 1:2 WEC with a PTO system providing functions for pre-tensioning and phase control, combined with a high efficiency mechanical drive train. According to Möller, this PTO is designed to integrate with different types of prime movers, offering the opportunity to improve the performance of various Wave Energy Converters 'by making them inherently resonant over a wide spectrum.' As well as the scale demonstration, Möller reveals that stage three also includes a number of 'high level objectives' (see Table 1).

When compared to other phase control methods such as latching, Möller says the WaveSpring principle offers similar amplification of power capture (+300% for a given absorber), with the important difference that 'it does not increase the machinery force and therefore enables a smaller and less costly PTO.'

"The device motion is continuous, avoiding the fatigue and wear challenges associated with more abrupt motion resulting from latching control. Combined with tribological advantages [relating to how the surfaces interact in relative motion], this is expected to improve reliability and component lifetime," he said.

"Since no real-time information on the incident waves is required for making the buoy resonant, the number of sensors and active control loops can be reduced, making the system less complex which is expected to improve robustness," he added.

In terms of future commercial development, Möller says that the company is currently working on project development with an eye on several markets along the European Atlantic coast, including the UK, Portugal, France and Spain – with a current focus on Scotland and Portugal. Following this, the next phase will focus on the U.S. west coast, South America, Chile, Japan, Korea and Indonesia.

Looking ahead, although Möller admits that CorPower has been quite successful with funding to date, he stresses that continued support from the EU and regional funds is 'absolutely critical' for Europe to maintain the lead position within wave and tidal.

"A strong partnership is also critical to bring this type of challenging technology to market, this is an area where we are seeing a tremendous value from our partners from Scotland, Portugal, Norway and Sweden that we are working closely with to deliver on our Stage three targets," he added.

By Andrew Williams