Photo: Crestwing's Tordenskiold wave energy prototype (Courtesy of Crestwing)

Crestwing’s wave concept robust, with room for efficiency gains, NIRAS report finds

Danish-based multidisciplinary engineering consultancy NIRAS has produced a detailed technical report on the Crestwing’s wave energy concept, finding its mechanics robust and flexible with room for efficiency improvements in converting wave energy to electricity.

Photo of Crestwing's Tordenskiold wave energy prototype (Courtesy of Crestwing)
Crestwing’s Tordenskiold wave energy prototype (Courtesy of Crestwing)

The technical report from NIRAS is based on the most relevant data from tests in wave tanks with scale models at Danish Hydraulic Institute (DHI) in 2010, and Aalborg University (AAU) in 2008, as well as on the information obtained from the 14-month offshore trial on the Tordenskiold prototype in the Kattegat Sea in Denmark.

In total, Crestwing provided data collected over the course of 15 years for NIRAS to analyse.

Based on the analysis, the Tordenskiold prototype has shown its ability to withstand the marine environment without significant wear or damage, which demonstrates a strengthening of the design concept’s robustness.

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Towing the system in place in the Kattegat has proven to be straightforward and can be done in a few hours with a single tugboat.

The coupling to and from its elastic mooring has been achieved several times without problems. In addition, the mooring system has worked as expected, the report states.

Analysis of movements of the Tordenskiold plant at sea has demonstrated that it follows the movement of the waves as historically predicted. This shows that a Crestwing hinge-pontoon concept for electricity production is possible on a plant size at the scale of the Tordenskiold, when combined with the Seaflex mooring system, according to NIRAS.

One of the challenges that Crestwing failed to tackle successfully during the offshore tests with Tordenskiold was to validate the power efficiency curve that previous tank tests have predicted.

This was partly because the wave environment at Kattegat did not provide enough energy, and that the generator in the device was too small, according to Crestwing, which also stated that it was not possible to calculate the correct size based on the data obtained.

Peter Høstgaard-Jensen, Chairman of the Board at Crestwing, said: “We are in a good development process, which I am sure will bring us forward. It is an important milestone that we have passed the mechanical part of our machine. Now there are other tasks and challenges that we must solve. It just means that we continue our development work a little longer”.

One of the things NIRAS found interesting about the Crestwing wave power plant is its simple construction with two hinged barges, designed and built on the existing knowledge from the shipbuilding sector.

The machine and power transmission system, as well as the generator and monitoring systems, are also based on well-proven and available techniques, Crestwing said.

Moving forward, Crestwing will go back to tank testing at the DHI in collaboration with ABB who will oversee data collection during tests planned for May 2021.

The collaboration is expected to ensure the development of the best-possible power take-off (PTO) system both for the future tests on the Tordenskiold prototype, as well as for a planned full-scale plant that could be deployed off Norway.

“If we succeed in our plans, it means that we can have a commercial product ready in 2024, and we are considering a location in Norway for its deployment”, Høstgaard-Jensen concluded.