Conference programme

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Wednesday, 18 November 2015
17:00 - 18:30 Annual energy production - let's get it right!
Resource assessment  
Onshore      Offshore    

Room: Montparnasse

To improve investor confidence in our energy yield assessments it’s vital that we can demonstrate improvements in the accuracy of our predictions. Only through doing this will be able to access cheaper sources of capital which will in turn reduce the cost of energy.

Learning objectives

  • Identification of the errors in the model chain.
  • How using multiple models can improve prediction accuracy.
  • How to use vertical extrapolation models in combination with long term correlation techniques.
  • Using the due diligence process to add project value.
Lead Session Chair:
Mike Anderson, RES Ltd.
Niels Gylling Mortensen Technical University of Denmark, Denmark
Niels Gylling Mortensen (1) F Morten Nielsen (1) Hans Joergensen (1)
(1) Technical University of Denmark, Roskilde, Denmark

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Presenter's biography

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

Niels G. Mortensen works as a senior researcher at the Department of Wind Energy, Technical University of Denmark. Niels has been a member of the WAsP development team since 1987 and thus jointly responsible for developing, maintaining and supporting the various WAsP software packages for more than 25 years.
Niels acted as editor of the European Wind Atlas (1989) and has further participated in the development of wind atlases for Denmark, Finland, Egypt, Cape Verde, India, and North East China. He currently works on the Wind Atlas for South Africa project.


Comparison of Resource and Energy Yield Assessment Procedures 2011-15: what have we learned and what needs to be done?


In the 4-year period from 2011 to 2015, EWEA arranged four “Comparison of Resource and Energy Yield Assessment Procedures” exercises, in order to benchmark the wind power industry, to provide high-quality data for the industry’s in-house training and R&D, and to identify current R&D issues.

Two exercises focussed on wind farms in hilly and complex terrain in Scotland, and two on medium- to large-scale offshore with farms in the Irish Sea. A total of 156 submissions were received, each of which containing detailed wind resource and energy yield assessment results for one of the four wind farms. This work has led to a unique dataset which provides insight into the status of the industry and which further points to areas where knowledge is lacking and research is needed.


All four “Comparison of Resource and Energy Yield Assessment Procedures” (CREYAP) exercises were analysed and presented by DTU Wind Energy. The four data sets are therefore readily available for review and more detailed analyses. The present study aims to review, summarise and present the results of all four exercises together, and will further seek to illustrate the aggregate results in new ways.

Main body of abstract

Wind resource and energy yield assessments are undergoing rapid changes in recent years. Not only has the industry been benchmarked by the EWEA CREYAP exercises, but new and very powerful technologies are developing fast: non-linearized microscale models, mesoscale modelling, new reanalysis data sets, numerical wind atlases, and global high-resolution wind resource mapping. By reviewing and analysing further the results of the four CREYAP exercises, the present status of the wind power industry can be assessed and we can provide typical values for the current bias and uncertainty of the most important steps in wind resource and energy yield assessments.

The models and procedures evaluated are: long-term adjustment methods, vertical extrapolation methods, flow modelling, wake modelling, systematic technical losses estimation, and uncertainty estimation. Where possible, we will also compare the industry’s annual energy production (AEP) estimates to actual, observed AEP from operating wind farms – and provide the bias and spread of these estimations. This will facilitate a comparison to the European Wind Energy Technology Platform (TPWind) ‘3% vision’.

Finally, based on the conclusions of the analysis, we will try to sketch specific areas where knowledge is lacking and more research and development is needed.


The last of the four CREYAP exercises, Offshore CREYAP Part 2, will be presented in Helsinki, Finland, in June 2015. The compilation and analyses of all four datasets have therefore not been completed at the time of writing, and the conclusions have yet to be drawn.

Learning objectives
A conference delegate who has seen the presentation and read the paper will be able to list:
• The most important limitations in present wind resource and energy yield assessment procedures.
• Typical values for the bias and uncertainty of the main steps in present-day energy yield assessment.
• Areas where knowledge is lacking and where novel technologies can and must play a role.