Section 1 Site conditions evaluation
Clasification Society 2024 - Version 9.40
Clasifications Register Guidance Information - Guidance Notes for Offshore Wind Farm Project Certification, October 2022 - Chapter 2 Project Certification Modules - Section 1 Site conditions evaluation

Section 1 Site conditions evaluation

Parent topic: Chapter 2 Project Certification Modules

1.1 Module requirements

1.1.1 The purpose of the evaluation required by this module is to examine the environmental (wind and marine), electrical power network and ground conditions (soil parameters) at the selected wind farm site.

1.2 Guidance on input requirements

1.2.1 The applicant should provide one or more reports summarising the assessment of the environmental, electrical power network and ground conditions at the project site(s), addressing the following:
  • wind conditions;
  • other environmental conditions (including air density, icing, humidity and temperature);
  • earthquake conditions;
  • electrical power network conditions;
  • geotechnical and geophysical conditions;
  • marine conditions (wave, current and water-surface elevation); and
  • weather windows and weather downtime (IEC 61400-22 only).

1.2.2 The applicant should submit the detailed methodology used to determine long-term environmental conditions for review as part of the site condition report. The methodology report should include full details in relation to all site measurements undertaken for the wind farm and for all long-term referenced data used for correlation and extrapolation purposes. As a general reference, see Annex E, IEC 61400-1 Wind turbines – Part 1: Design requirements. The applicant should provide justification for the methodologies and data sources used and any validation studies which confirm the suitability of that data as part of their analysis.

1.2.3 For wind conditions, the following parameters should be included as part of the site condition report, and should be determined for the measurement location at or near the site which is considered representative of the project area:
  • air density expected at site (mean and extreme), including consideration of diurnal and seasonal air density variation (if appropriate);
  • sector wise wind speed probability distribution or frequency table (long term corrected) at hub height;
  • wind speed probability density function (as per Section 12.3, IEC 61400-3 Wind turbines – Part 3: Design requirements for offshore wind turbines);
  • spatial variation of mean wind speed within the project area or at each WT location;
  • wind rose (measured and long term corrected);
  • hub height extreme wind speed (10 minutes, 50-year extreme) and selected gust factors for the site, whether measured or taken from Section 6.4.3, IEC 61400-3-1 Wind energy generation systems – Part 3-1: Design requirements for fixed offshore wind turbines;
  • wind shears measured at the site, including mean and extreme values, and assumptions made in relation to determining the values presented; and
  • ambient turbulence intensity (and standard deviation or 90 percentile) for each wind speed bin.

1.2.4 For WTs on floating structures, the influence of extreme operating gusts should be considered. In particular, the change in wind speed which is possible over the time period corresponding to the platform degrees of freedom should be considered, as per Annex O of IEC TS 61400-3-2 Wind energy generation systems – Part 3-2: Design requirements for floating offshore wind turbines.

1.2.5 The seismic hazard assessment for the site should be prepared in accordance with the requirements of ISO 19901-2 Petroleum and natural gas industries – Specific requirements for offshore structures – Part 2: Seismic design procedures and criteria, or equivalent. Where seismic hazard is significant, a detailed seismic hazard assessment should be performed to provide input to foundation and structure design.

1.2.6 For the electrical power network conditions, the following electrical power network conditions should be included as part of the site condition report: ype of electrical grid outages and average number per year;
  • type of electrical grid outages and average number per year;
  • fault current and typical duration at the connection point;
  • the grid’s normal connection point voltage range; and
  • permissible power quality requirements as per local grid code.

1.2.7 In general, it is expected that the design of offshore foundations for WTs will be performed considering the requirements of the ISO 19900 series of standards with reference to other good industry practice where appropriate. This includes site investigation, seismic requirements, foundation design and installation and inspection. Ch 3 Additional Guidance on Geotechnical Aspects provides additional interpretation and guidance in support of the ISO 19900 series of standards. The site condition assessment should not only consider the current condition of the seabed and soil conditions but also the potential for changes to the site prior to and throughout the life of the assets.

1.2.8 The site wave, current and water surface elevation conditions documents should comply with the requirements of ISO 19901-1 Petroleum and natural gas industries – Specific requirements for offshore structures – Part 1: Metocean design and operating conditions (except Section 7), or other industry standards as agreed with LR. The wave, current and water levels provided in the report should be sufficient to develop design load cases as per the IEC 61400-3 series of standards.

1.2.9 Along with the submission of the site conditions report, the applicant shall also submit the accredited test laboratory’s ISO/IEC 17025 accreditation or the RETL’s approval, as applicable per the selected certification scheme. In case the measurements have been carried out by non-ISO/IEC 17025 accredited test laboratories or an IECRE-approved RETL, then the applicant shall submit the following test laboratory information for evaluation:
  • equipment calibration certificates, supported by calibration methods;
  • data acquisition methodology and traceability, along with evidence of measurements;
  • personnel qualification records and confirmation they meet the laboratory’s requirements; and
  • quality assurance processes (including any accreditations, e.g. ISO 9001).

1.3 Evaluation methodology

1.3.1 For projects in accordance with the IEC 61400-22 Wind turbines – Part 22: Conformity testing and certification scheme, LR will undertake the evaluation activities as detailed in Ch 2, 1.3 Evaluation methodology 1.3.2, and for projects in accordance with the IECRE OD-502 Project Certification Scheme, will undertake the evaluation activities as detailed in Ch 2, 1.3 Evaluation methodology 1.3.3.

1.3.2 LR will confirm that all measurements of site conditions have been carried out by a body accredited to ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories, where applicable; otherwise, LR will confirm that the measurements are reliable and of satisfactory quality. This will include evaluation of:
  • test and calibration methods;
  • equipment used;
  • traceability of measurements;
  • assurance of quality and calibration results; and
  • reporting.
1.3.3 LR will confirm that all data acquisition, analysis and reporting of site conditions has been undertaken by suitably qualified personnel. For projects in accordance with the IECRE OD-502 Project Certification Scheme, LR will confirm that all measurements of site conditions have been carried out by either:
  1. an RETL;
  2. the RECB or a body accredited to ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories (and accepted by the RECB) which has accompanied the measurement campaign (where feasible) to verify the quality and reliability of the measurements. This evaluation will include:
    • test and calibration methods;
    • equipment used;
    • ensuring suitably qualified personnel have carried out the measurements;
    • traceability of measurements;
    • assurance of quality and calibration results;
    • reporting of results; and
    • confirming that all data acquisition, analysis and reporting of site conditions has been undertaken by suitably qualified personnel.
  3. If (a) and (b) are not available, because the measurement campaigns have been executed prior to the engagement of the RECB or a body accredited to ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories (and accepted by the RECB), then the certification body will evaluate and verify the following:
    • equipment calibration certificates, supported by calibration methods;
    • data acquisition methodology and traceability, along with evidence of measurements;
    • suitably qualified personnel have carried out the measurements;
    • quality assurance processes (including any accreditations, e.g. ISO 9001).
1.3.4 LR will review the appropriateness of the derivation of the wind conditions parameters as outlined in Ch 2, 1.2 Guidance on input requirements to ensure they are suitably robust. This will include evaluation of:
  • appropriateness of installed measurement equipment for the purpose of evaluating site conditions including, where appropriate, checks against IEC 61400-12-1 Wind energy generating systems – Part 12-1: Power performance measurements of electricity producing wind turbines and IEC 61400-12-2 Wind turbines – Part 12-2: Power performance of electricity-producing wind turbines based on nacelle anemometry and other industry best practice guidelines including MEASNET Evaluation of Site-Specific Wind Conditions and applicable IEA Recommended Practice documents;
  • completeness and integrity of wind data used as basis for site conditions assessment;
  • suitability of reference wind data sources for both long-term correction and extreme conditions analysis. This will include consideration of source, type, time period, consistency of measurements, similarity and correlation. Review of confidence levels associated with consideration of multiple sources will also be undertaken;
  • quality of long-term adjustment process followed to extrapolate site measured data to represent long-term conditions;
  • wind shear distribution including consideration of diurnal and seasonal variation and results of comparison between modelled and measured values;
  • wind flow modelling approach followed including consideration of model inputs, such as terrain, roughness and atmospheric stability, model configuration and assumptions;
  • correct calibration of hindcast modelling (if used) against measured data;
  • confidence in extreme wind analysis approach followed through consideration of results of multiple statistical techniques applied to measured data; and
  • appropriateness of derivation of air density figures, including inputs and extrapolation methods.

1.3.5 Following initial document review, LR will determine appropriate areas and levels of simplified parallel calculations of selected parameters to perform on a spot check basis. These spot checks are not pre-defined (before the initial review) to allow for flexibility in the approach on a project-specific basis and to focus on the critical areas for the site. Parallel calculations will not be performed for parameters which are fully defined and additional independent checks would not bring additional confidence in the results presented. Independent calculations may consist of analysis of raw data, or alternatively build on steps performed by the client as part of the calculation of other site conditions parameters. Parallel calculations are intended as a check on reported values and are not suitable for mitigation of incomplete reporting of parameters or the methodology in derivation of these parameters. In circumstances where parallel calculations support the figures presented by the client, the client values will be taken forward within the design basis. When parallel calculations raise concerns with the parameter values presented by the client additional discussion and analysis may be required to resolve the discrepancy and confirm the adequacy of the selected parameter.

1.3.6 LR will review the seismic hazard assessment for the project site to confirm its consistency with the requirements of ISO 19901-2 Petroleum and natural gas industries – Specific requirements for offshore structures – Part 2: Seismic design procedures and criteria; or equivalent.

1.3.7 For the evaluation of the site conditions relating to the electrical power network conditions, LR will confirm that the grid requirements and grid connection parameters as listed in Ch 2, 1.2 Guidance on input requirements 1.2.8 have been adequately defined in the site condition report.

1.3.8 The review of the site condition assessment for geotechnical and geophysical aspects will confirm that the seabed and soil conditions across the site are sufficiently well understood to enable design, installation, operation and maintenance of the WT structures and associated foundations.

1.3.9 LR will review the site metocean report to confirm that there is sufficient confidence in the data (wave, current and water surface elevation) to enable design to proceed, using as reference ISO 19901-1 Petroleum and natural gas industries – Specific requirements for offshore structures – Part 1: Metocean design and operating conditions, or other industry standards as agreed by LR. The wave, current and water levels provided in the report should be sufficient to develop design load cases as per the IEC 61400-3 series of standards.

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