Developing a dynamic wind turbine blade

A research project with REHAU expertise

Inspired by nature

Every creature in the animal kingdom that uses flows and currents to move relies on dynamics. Birds spread their wings wide and rotate them, while fish tilt their fins and shift them to move forward or upwards. Using bionics, humans have learned how to implant nature’s mechanisms into technological developments – planes extending their landing flaps, or car spoilers moving according to the speed of the vehicle.

This inspired Professor Helge Aagaard Madsen of the Technical University of Denmark (DTU) to apply dynamics to wind power, too. Siemens Gamesa have already made initial steps toward bionics, equipping their rotor blades with ‘dino tails’ to reduce noise produced by air turbulence. REHAU is currently working on the next stage of development: dynamisation.

Yet the blade ultimately remains static. In an interview, Professor Madsen explains the possibilities that dynamisation opens up for wind power.

Interview with Prof. Helge Aagaard Madsen, DTU, Denmark

Interview by Peter Michels, Project Manager and Cornelia Martin, Corporate Communications at REHAU

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Professor Madsen, wind power is an integral component of the renewable energy mix. What possibilities do you see in wind power in particular for electricity supply in the future?

We still have a huge amount to do to cover the demand for renewable energies. The proportion of solar energy and wind power alone needs to rise from 4.5% in 2015 to around 60% in 2050 (Source: IRENA, 2018b).

What percentage of the electricity mix are we talking about in Europe, now and in the future?

According to WindEurope’s central scenario, we would need to install 323 gigawatts of wind energy capacity in the EU by 2030. Around three quarters of this onshore, and a quarter off-shore. This would be more than double the output installed as of late 2016 (160 GW). This capacity would produce 888 TWh of electricity from wind energy, which amounts to 30% of the EU’s electricity demand.

In 2018, the average renewable energy share in Europe was 14%. At 41%, Denmark is leading the way, followed by Ireland with 28% and Portugal with 24%. Germany is currently at around 14%. 

A crucial factor will be simultaneous development of technologies that store or save the energy produced. Using hydrogen, for instance. 

How long have you been conducting your research, and how did this collaboration between DTU, Siemens Gamesa and REHAU come about?

From 2006 to 2009, we conducted the basic research at the Technical University of Denmark in Roskilde. By the end, we could prove in the wind tunnel that dynamisation contributed to increased efficiency. In the lab, we were able to prove that a variable blade shape can increase the entire energy yield from a wind turbine.

Martin Heisterberg, Head of REHAU Nordic, read about the project in a newspaper article and got in touch with me. It was just the right time, because our project had just got new tailwind. Equipped with EUR 1.2 million from the Danish funding programme EUDP, we were in search of industrial partners to prove the technical feasibility of the project.

Have other companies worked on this issue?

Yes. There have been theoretical approaches since 2000. Yet our research colleagues were unable to progress far when it came to technical implementation.

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What was special about this project?

Everything. We needed to rethink materials, mechanics and production. There was nothing you could latch onto. But the REHAU team had the pioneering spirit to grapple with an ‘unsolvable’ task. 

The new blade surface had to be dynamic, last 25 years, and not contain any metals, metal components, electric wires or electronics. The entire system also has to withstand massive fluctuations in heat and cold. The requirements for modern wind turbines are huge. 

We achieved the first technical breakthrough for a flap model with REHAU in autumn 2014 – a flexible hose profile combination that met all these exacting requirements. This solution was composed of a profile that could be inflated (making it dynamic) and integrated hoses that enabled the flap to be moved with nothing but mechanical technology, using compressed air. The steering unit and compressed air generator could be positioned in the hub of the rotor blade. 

The flap prototype was installed at an outdoor test site in Delft in the Netherlands that was developed as part of the project. Here, the new flap technology could be tested in a practice-oriented context. Tests confirmed that the flap prototype withstood real operating conditions. So things like the high centrifugal load and reduction in fluctuating air loads also formed part of the research.

Did you also encounter setbacks?

We were delighted that REHAU had actually found a material that could resist the extreme conditions at play. However, initially we didn’t have the right adhesive to connect it to the powerful Siemens blades. We eventually solved the issue of adhesion through profile co-extrusion.

Finally, in 2018, we were at the large-scale turbine for the field tests. Then a lightning strike destroyed the entire system, setting the project back by six months. 

What are the benefits of the technology being developed in this project?

I can tie this to four key criteria:

  1. Durable and robust – in all weather No mechanical wear and tear 
  2. Easy to integrate – even into existing blades 
  3. Scalable – for different blade lengths (from 60 to 100 metres) 
  4. Commercially attractive – with reliable amortisation times

Why was REHAU’s expertise so crucial?

The REHAU team was able to immerse itself in our research. Our project became their project, too. Their expertise in materials, formulations and processes is like nothing else I’ve experienced. Research and development seem to be deeply rooted in REHAU’s DNA.

What are the next steps?

For REHAU, the wind power project entered its third phase in autumn 2019. This phase is led by Siemens Gamesa, and commercialisation is now the name of the game. The aim is to make wind turbines around 8% more energy-efficient. This equates to an additional 6 to 15 gigawatts, depending on the size of the turbine.

2) Wind energy in Europe: Scenarios for 2030, September 2017, Wind Europe

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