The IEC 61400 series of standards addresses wind energy generation technical requirements up to the point of interconnection with the utility grid system. Part 12 of the IEC 61400 series of standards comprises a sub-set of standards which are to be used in the evaluation and measurement of the power performance characteristics of wind turbines. The power performance characterisation of wind turbines of all types and sizes is covered.
Wind turbine power performance characteristics are determined from a measured power curve and an associated estimated annual energy production (AEP) and its uncertainty. The measured power curve, defined as the relationship between the wind speed and the wind turbine power output, is determined by collecting simultaneous measurements of meteorological variables (including wind speed), as well as wind turbine signals (including power output) at the test site for a period that is long enough to establish a statistically significant database over a range of wind speeds and under varying wind and atmospheric conditions. The AEP is calculated by applying the measured power curve to reference wind speed frequency distributions, assuming 100 % availability.
Part 12-0 provides a general introduction to the available options for power performance measurement and the contributing evaluations which are further detailed in the other parts of the IEC 61400-12 series. Although the -12 series also defines the specifications of the meteorological variables (and in particular wind speed) required for the power performance evaluation, the methods and procedures for measuring or otherwise acquiring the wind speed data are defined in the IEC 61400-50 wind measurement series of standards.
The evaluation of the wind turbine power performance characteristic according to this series of standards requires the measured power curve and derived energy production figures to be supplemented by an assessment of uncertainty sources and their combined effects. The basis of the uncertainty assessment is ISO/IEC Guide 98-3. The wind measurement uncertainty sources shall be identified and quantified from procedures described in the relevant wind measurement standards contained in the IEC 61400-50 series. The wind measurement uncertainties shall be propagated through to and combined with the other sources of uncertainty in the power curve and annual energy production using methods and assumptions described in the IEC 61400-12 series of standards.