There is currently significant standardisation work ongoing in the context of wind farm energy yield warranty assessment and wind turbine power performance testing. A standards maintenance team is revising the current IEC (EN) 61400-12 Ed 1 standard for wind turbine power performance testing. The standard is being divided into four documents. Two of them are drafted for evaluation and verification of complete wind farms and of individual wind turbines within wind farms. This document, and the project it describes, has been designed to help provide a solid technical foundation for this revised standard. The work was wide ranging and addressed ‘grey’ areas of knowledge, regarding existing methodologies or to carry out basic research in support of fundamentally new procedures. The work has given rise to recommendations in all areas of the work. These cover: • Improved definition of site calibration procedures using two met masts • Procedures for using nacelle mounted anemometry for site calibration • Methods for checking the consistency of site calibration results • Advice on defining nacelle-to-free-wind-speed relationships to be used for power curve verification • Advice on placement of nacelle anemometers to minimise errors • Recommendations on how to account for and minimise the shortcomings of the nacelle anemometer method related to inflow, induction and wake influences • Methods for checking the consistency of power curve verifications using nacelle anemometry • Advice on exercising caution when making estimates of the in-service uncertainties associated with wind speed and electrical power monitoring equipment • A step-wise procedure for applying multi-variate regression analysis methods using partial residuals for identifying the functional dependency of power performance on secondary parameters • Suggestions for more sophisticated density normalisation for actively controlled turbines The current work was supported partly by the European Union Fourth Framework research program through the SMT project: ”European Wind Turbine Testing Procedure Developments” , contract no. SMT4-CT96-2116. ISBN 87-550-2752-0 ISBN 87-550-2753-9 (Internet) ISSN 0106-2840 Print: Danka Services International A/S, 2001