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Conference programme 

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Poster session

Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
John Korsgaard LM Wind Power, Denmark

(1) LM Wind Power, Lunderskov, Denmark

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Presenter's biography

Biographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited

John Korsgaard has a background as Mechanical Engineer(Msc. Mech. Engineering)from Aalborg University, Denmark. He has been employed at LM Wind Power since March 1990, working in various positions from Research to Product Management. John is currently working as Director of LM Wind Power´s Test and Validation Center.


Flexible blade length concept reduces cost of offshore wind energy by up to 10 percent


Offshore wind energy is relatively expensive compared to alternative renewable energy sources and the challenge is to reduce the Cost of Energy (CoE). The most critical factor to reach the targeted 9 ct/kWh by 2020 is to increase the Annual Energy production (AEP) by optimization of the wind turbine performance. Blades are the engine of the turbine and therefore constitute the key enabler for increasing the AEP.


The most efficient way to boost the AEP of a wind turbine is to increase the swept area of the rotor by extending blade length. By varying the rotor diameters along the wind farm and by using more optimal blade geometries, a significant increase in AEP and overall wind power plant performance can be achieved. The challenge, however, is to develop a flexible blade length concept which will enable realization of the potential AEP increase of a wind power plant while maintaining the cost at the equivalent level of a standard single-sized blade.

Main body of abstract

In the offshore wind power plant, wind turbines are inevitably in each other’s wake. This leads to loss of energy.
Most turbines are actually not loaded to the full designed capacity due to wind conditions on specific sites or the location of the wind turbine in a wind farm. Hence, there is an untapped potential to increase AEP, if flexible blade lengths could be offered to the same wind turbine.

The flexible blade length can be achieved by splitting the blade into a main blade part, and a tip part that can vary in length. Split blade concepts have been investigated in the past mainly to overcome logistics challenges during transport of large blades. LM Wind Power has previously worked with partners in an EU-Project on split blades (JOR3-CT97-0167), where two designs were developed and tested. The conclusion of the EU-project was that split blades are significantly more expensive compared to standard blades. On a 60 meter blade, the manufacturing cost increased by 19%, whereas the logistic/transport cost savings due to segmentation were only 5%. Hence, the split blade concept is far too expensive.

The solution is a flexible blade length concept which enables separate manufacturing of the blade and tip part, followed by the application of a traditional joining technique leading to a permanently assembled blade. The concept potentially enables central production of the blade tips and decentralized assembly, e.g. on-site or near site to take advantage of manufacturing scale effects and increase flexibility.


Based on the analysis of the Horns Rev offshore project (wake characterisation), assuming a flexibility to change the rotor diameter of up to 10% on a layout matrix, it is possible to achieve a potential increase of the AEP by 8% – 10% and an equivalent decrease in CoE.

By manufacturing the blade and tip part using separate manufacturing technology and assembly and using a traditional joining technique leading to a permanently assembled blade, the blade cost and blade characteristics, e.g. blade weight and root mass moment of the flexible (variable) blade concept, will be comparable to a standard single-sized blade.

Learning objectives
The presentation provides insight to the increase of AEP and overall wind power plant performance by varying the rotor diameters along the wind farm and by using more optimal blade geometries. Furthermore, it provides insight into how the design and manufacture of the blade and tip component separately followed by traditional assembly result in blade cost and characteristics comparable to a standard single-size blade.