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Four-in-one wind turbine

Posted December 21, 2016

Vestas’ new demonstration wind turbine at the DTU Risø Campus is a radical new approach to making the price of wind power even more competitive.

Vestas’ four-rotor wind turbine challenges the accepted norms. The idea is to increase the area the rotors’ cover without increasing the turbine’s total weight correspondingly. The experimental turbine is 74 metres high and has a total capacity of 900 kW. Vestas expects that the turbine will run for two years initially. Photo: Tom Nervil.

We are used to wind turbines having one rotor with three blades. Vestas is now challenging this paradigm with a new wind turbine with four rotors. At this stage it is simply an experimental turbine to demonstrate the concept, and not a pilot turbine—the forerunner of a commercial wind turbine. The wind turbine has been erected on the DTU Risø Campus, and researchers from DTU Wind Energy are contributing advice and measuring services to the project.

Background: Vestas’ four-rotor turbine at the test centre on the Risø Campus. Foreground: DTU’s WindScanner, which you can read more about in the article: Danish technology revolutionizing wind measurement.

“Sometimes innovation calls for a radically new approach. We are demonstrating this by installing this concept turbine,” says Jorge Magalhaes, Senior Vice President in Vestas Innovation & Concepts.

“It’s extremely important to constantly innovate and explore new principles. This gives us key knowledge which can help us in our efforts to make wind power even more competitive with other energy sources. We strive to reduce the customers’ costs of purchasing our products, while also integrating key technologies which address customers’ challenges. The ultimate goal of the project is to evaluate whether we can build an even more cost-effective wind turbine by challenging the accepted laws of scale.”

Reducing weight is key
Wind turbines have grown incredibly in size over the last few decades, but the basic model—known internationally as ‘the Danish design’—has been virtually unchanged. Economies of scale have done a lot to reduce the kilowatt-hour price for wind power. When you double the size of a wind turbine, the area covered by the rotating blades increases fourfold, as does the amount of electricity generated. But unfortunately there is downside: the total weight of the blades becomes eight times as large. The weight of the other mechanical components is also significantly increased.

The higher weight naturally reflects the use of more materials, which means that the cost of the wind turbine will be higher.

The idea behind Vestas’ new turbine concept is to increase the swept area without increasing the weight correspondingly. The four rotors jointly cover an area roughly equal to the area covered by a single rotor on a wind turbine with the same height and power output. But their total weight is only half as much.

Vestas’ four-rotor wind turbine challenges the accepted norms. The idea is to increase the area the rotors’ cover without increasing the turbine’s total weight correspondingly.

Under commercial market conditions
Although the turbine has been erected on a DTU campus, it is not a traditional research collaboration project. DTU researchers cannot take credit for the four-in-one concept, notes Senior Development Engineer Søren Lind, DTU Wind Energy.

“The idea for the innovative concept originated with Vestas,” says Søren Lind. “However, we have been involved at an early stage without realising it. Vestas has used the HAWC2 program, developed by DTU Wind Energy, to perform the basic aero-elastic calculations. We are very pleased that the software has proved so flexible that it could be used even with such a new concept.”

Source: DTU

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