Photo: PantherMedia

Danish technology revolutionizing wind measurement

Wednesday 21 Dec 16
by Marianne Vang Ryde


Torben Krogh Mikkelsen
DTU Wind Energy
+45 46 77 50 09

Wind scanner

Foto: PantherMedia, Torben Krogh Mikkelsen

The wind scanner is also used for meteorological measurements and for measuring wind conditions in connection with the construction of bridges etc..

MSc Eng programmes

If your are interested in wind techonolgy, the following MSc Eng programmes will blow you away:

The more you know about the wind a wind turbine is exposed to, the better you can optimize the turbine's lifetime and power output. DTU researchers have invented a wind scanner which measures the actual wind conditions around wind turbines in three dimensions. The invention is now making inroads into the European research landscape.

If you want to get better at controlling windmills—ultimately making them last longer and perform better—you need to know exactly what happens when the blades slow down and deflect the wind. Wind measurement and wind energy are therefore inextricably linked.

Wind speed is traditionally measured using a cup anemometer, either placed behind the blades on the turbine's nacelle, or in front of the wind turbine on a pole of the same height. A more advanced wind measurement technique is based on remote measurement using a laser beam—but both the cup anemometer and the laser beam can only measure one point at a time, making it difficult to get the full picture of the wind and turbulence around a wind turbine.

Researchers at DTU Wind Energy decided to address this problem back in 2007. Their work resulted in a 3D wind scanner with three laser beams and a controllable system of prisms, which together detect a three-dimensional image of the wind field. The system has been patented and registered with the WindScanner trademark. In 2009 it was established as Danish infrastructure, and the following year it was put on the ESFRI Roadmap, which recognizes it as key European infrastructure that can improve the utilization of wind energy.

One principle—several measuring instruments
The wind scanners are based on the remote measurement technology known as lidar (light detection and ranging), where an intense laser beam focuses on dust particles floating around in the wind. The particles reflect the laser light like tiny mirrors, but with different colours, depending on their movement speed and direction. By analysing the colour (frequency) of the backscattered light, the wind scanners can therefore determine the wind speed in the measuring point.

However, one measuring point is not enough to provide a picture of the entire wind field, so Professor Torben Mikkelsen and his colleagues worked to develop a method to scan the wind in three dimensions using three simultaneously controllable lasers. Their efforts resulted in an innovative idea for how the focused laser beams could be deflected using two prisms on rotatable axes. This idea was patented and has now been put to work in several different types of wind scanner.

Illustration: Torben Krogh Mikkelsen
DTU's WindScanner reads wind speed and direction using laser beams. Illustration: Torben Krogh Mikkelsen.

Short range wind scanners, which currently have a range of up to 300 metres, are placed on the ground and scan around the wind turbine. The scans provide detailed knowledge of what happens when the wind interacts with the turbine rotor, and this knowledge can be used to evaluate and improve the computer models used to simulate load and control, and to generally optimize the turbines.

In some situations, for example in relation to offshore wind turbines, 300 metres is not enough. So researchers at DTU have also developed a long-range wind scanner with a range of 5-10 km.

"The wind scanner can become for the wind industry what x-ray images became for the medical world. It is possible for the first time to get a detailed picture of the complex and until now virtually invisible turbulent wind flows in and around wind farms. By combining our knowledge and the new infrastructure facility, we can literally shine a light inside the 'black box' wind resources still are in many ways."
Dr Stephan Barth, Managing Director of Forwind, Centre for Wind Energy Research for the universities in Oldenburg, Hannover, and Bremen. Forwind is one of the EU partners in the consortium.

Finally, the WindScanner technology has also been used in a SpinnerLidar, installed either in front of the blades on the rotor, or behind the blades on the nacelle. By measuring the slipstream behind the turbine, we can gain knowledge of how much the rotor has blocked the wind field, and how much turbulence is created in the turbine's wake. This is useful when planning how to position the wind turbines in a wind farm and control them in relation to each other, so as to minimise stresses and achieve the longest possible lifetime.

Build one yourself, or request the mobile wind scanner
The 3D measuring technology is now in high demand far beyond Denmark's borders, thanks in part to its inclusion in the European roadmap. Several European countries have become WindScanner partners. These are now working to build their own national versions of the wind scanners based on DTU's original design, with the associated software and data platform, and training users.

The future is user-friendly
The scanners are constantly being developed. For example, taller wind turbines require longer range. Work is also being done to make the infrastructure more user-friendly, so that the complicated calculations that follow the measurements are automated and presented more intuitively.

Torben Mikkelsen and his colleagues at DTU Wind Energy also hope to establish a wind scanner hub at DTU Wind Energy, where wind scanners can be coordinated as pan-European infrastructure and the results can be distributed. There are also several projects in the pipeline in cooperation with Danish partners and Danish industry, including the Danish Meteorological Institute (DMI), Vestas and Aalborg and Aarhus universities. These aim to use the wind scanning technology in connection with the spread of urban air pollution in cities and mapping wind fields around bridges and buildings.

“Although we have already developed a future business plan for WindScanner with the aim of one day becoming a partially user-funded research infrastructure, it is still necessary to maintain close ties with the research environments at the universities. To date, WindScanner has been structured as a multidisciplinary activity with contributions from Danish industry, IPU, DTU Mechanical Engineering, and DTU Fotonik. We also have a steady stream of MSc thesis and PhD students conducting various projects here, which help ensure the continued development of the technology,” says Torben Mikkelsen.

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