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Tuesday, 11 March 2014
11:15 - 12:45 Optimising measurement strategies to maximise project value: Is the industry making false economies at the expense of project value?
Resource Assessment  

Room: Llevant
Session description

Striking the right balance between costs and benefits when designing a measurement campaign has always been a challenge. Nowadays the situation is more complex due to:

  • sophisticated instrumentation options (and their limitations);
  • wind farms of larger spatial extent located in more diverse climates;
  • advanced flow modelling.

It is no longer a straightforward process deciding on the optimal measurement strategy to minimise uncertainties in the energy assessment for a specific project. Assessing the resulting financial benefit is just as challenging. The interpretation of the data for site classification and thus choice of turbine has also become more complex.

Learning objectives

  • Evaluate the most efficient use of instrumentation for a specific site
  • Understand and quantify the connection between measurement uncertainty and project economics and loads
  • Make a more accurate choice of turbine type
  • Express uncertainty variations across the site as the basis for cost-efficient measurement campaigns
Lead Session Chair:
Wiebke Langreder, Wind Solutions, Denmark

Jan Coelingh, Vattenfall
Henrik Stensgaard Toft Aalborg University & EMD International A/S, Denmark
Henrik Stensgaard Toft (1) F P Lasse Svenningsen (2) John Dalsgaard Sørensen (3)
(1) Aalborg University & EMD International A/S, Aalborg, Denmark (2) EMD International A/S, Aalborg, Denmark (3) Aalborg University, Aalborg, Denmark

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Henrik Stensgaard Toft is industrial Post. Doc at Aalborg University and EMD International A/S in Denmark working on the project Optimized Integration of Load Calculations in Development and Design of Wind Farms supported by the Danish National Advance Technology Foundation (Højteknologifonden). Henrik Stensgaard Toft has a M.Sc. degree in Civil Engineering and a Ph.D. degree in Probabilistic Design of Wind Turbines.


From measurements to site approval: A new and more accurate approach for site suitability analysis


Wind turbines are normally designed and certified according to standard wind turbine classes specified in IEC 61400-1. These classes define the mean wind speed distribution, turbulence intensity, wind shear, air density and inflow angle as a set of deterministic parameters. Turbulence is dependent on the mean wind speed but the remaining climate parameters are assumed independent of the mean wind speed, wind direction and time. Since the response of a turbine is nonlinear with the climate parameters this can lead to significant errors in a site suitability assessment. In this paper the accuracy of using deterministic climate parameters is investigated.


Wind measurements from two very different site locations are considered. The first site is located in the in-land southern Brazil where large variations in the wind shear are observed due to the changing stability conditions of the atmosphere. The other site is representative for North European coastal conditions. For both sites fatigue loads are determined using both time dependent climate parameters and deterministic climate parameter in order to investigate the accuracy of the deterministic IEC 61400-1 approach. The accuracy of using effective climate parameters to account for increased fatigue due to variability is investigated for the turbulence and wind shear.

Main body of abstract

When using deterministic climate parameters instead of time-series, the variation and correlation between the climate parameters are neglected along with their possible dependence on the mean wind speed and wind direction. The effects of most of these simplifications and assumptions on the fatigue damage equivalent loads are quantified in the present paper for the main structural components of a generic wind turbine. The paper focusses mainly on the turbulence and wind shear which influences fatigue loads most.
Measured time-series will not be efficient to use for estimating fatigue damage equivalent loads in a site suitability analysis due to the computational costs. In addition a time series approach would not account for inter-annual variations in the wind climate using typical on-site measurements of 1-2 years. The use of deterministic “effective” climate parameters is therefore investigated. An effective climate parameter is here defined as a deterministic value derived based on the distribution function for the parameter, the physical response and the Wöhler exponent.
The IEC 61400-1 standard already defines effective turbulence as an integration of turbulence over all directions approximating the fatigue accumulation. Hence, the resulting effective turbulence is a function of wind speed only, but accounts for the fatigue effect from directional variation of turbulence. A similar approach may be adopted for wind shear, but also for the remaining wind speed dependence of turbulence.
The accuracy and efficiency of the proposed effective climate parameter models are evaluated and demonstrated for the two considered sites.


The accuracy of the existing method in IEC 61400-1 for determining climate parameters in site suitability analysis is investigated for fatigue loads. We investigate the accuracy and efficiency of using effective climate parameters to account for fatigue caused by the variability of the climate parameters via their distribution function and a given Wöhler exponent. The comparisons are performed based on real measurements from two typical sites and a generic wind turbine.

Learning objectives
The paper gives the reader more insight in the accuracy obtained by using deterministic climate parameters in site suitability analysis. Additionally, the reader obtains knowledge about the effect of using climate parameters derived based on other principles than those specified in IEC 61400-1.