Site suitability assessment and site classification of wind turbines
Wind turbine site suitability assessment to IEC 61400-1 or DIBt: site classification and suitability check by the accredited EWS Testing Center.
Not every wind turbine suits every site. Whether for planning, permitting or financing, correct site classification and a sound, standard-compliant site suitability assessment are the key to safe, long-term and economic wind farm operation. Our accredited testing body, the EWS Testing Center, checks whether the chosen turbines and the planned wind farm layout match the conditions at the site: wind speed, turbulence and extreme wind events. This is a technical assessment for your specific project, not a search for land or potential.
Technically, the site suitability assessment compares the wind conditions at the site with the assumptions for which the turbine type was designed and tested. Compared are, for example, the 50-year extreme wind speed, the distribution of mean wind speed, turbulence intensity, the vertical wind profile, the inflow angle and air density, each at hub height. Reference values from IEC 61400-1 include, depending on turbine type and the edition of the standard applied, for example a wind profile exponent of 0.2, an inflow angle of no more than 8 degrees and an air density of 1.225 kg/m³. A valid type or individual assessment of the turbine is a prerequisite for the verification. If a design value is exceeded, suitability can be demonstrated by comparing loads: operating loads if wind speed or turbulence exceed the design, extreme loads if the extreme wind exceeds the reference value.
In non-complex terrain, a simplified procedure with mean annual wind speed, turbulence intensity and, where applicable, extreme wind is sufficient. If the wind distribution deviates strongly from the usual shape, the frequency distribution must be compared. Complex terrain is classified in three levels because it can increase turbulence and oblique inflow. In a wind farm there is a further influence: neighbouring turbines generate wake turbulence, which is accounted for through the effective turbulence intensity. Suitability therefore also depends on the layout. The basis is the edition of IEC 61400-1 applicable to the project and, in Germany, the technical building regulations and DIBt rules on actions and structural stability verifications for tower and foundation that apply in the verification procedure. Where several editions of the standard are permissible, the chosen edition must be applied in full. The influence of neighbouring turbines acts mainly through turbulence, but can also affect wind speed and loads. It must be examined specifically for the layout and the site; the relevant distances and procedures depend on the standard applied and the specific verification.
With us, this comes from a single source: from wind measurement at the site, through the site assessment, to standard-compliant evaluation and documentation with an assessment of results and recommendations for further action. The results are reliable and traceable for authorities, banks and manufacturers. The yield side is covered by our wind assessment with yield forecast. In permitting, the technical plant reports complement the documents; for financing, the technical due diligence does.
