Power Performance Measurements of Electricity Producing Wind Turbines

At the end of 2016, in the United States alone, the installed wind capacity totaled 82,183 Megawatts. The energy produced by the 52,000 operating wind turbines in the nation is the equivalent of powering 24 million homes.  However, the tallest wind turbine in the world, the Nordex N131/3300, is located in Hausbay, Germany, and it stands 164 meters tall (230 counting the rotors) with a capacity of 3.3 MW.

The performance of wind turbines, regardless of their size, is influenced by several factors. According to IEC 61400-12-1 Ed. 2.0 b:2017 – Wind energy generation systems – Part 12-1: Power performance measurements of electricity producing wind turbines, wind turbine power performance characteristics are determined by the measured power curve (the relationship between the wind speed and the wind turbine power output) and the estimated annual energy production (AEP).

The IEC 61400-12-1 Ed. 2.0 b:2017 standard specifies a procedure for measuring the power performance characteristics of a single wind turbine through the determination of the measured power curve and annual energy production. It applies to the testing of wind turbines of all types and sizes connected to the electrical power network, but it can also be used to determine the power performance characteristics of small wind turbines when connected to either the electric power network or a battery bank.

Anticipated users of IEC 61400-12-1 Ed. 2.0 b:2017 include wind turbine manufacturers, purchasers, operators, and planners or regulators.

Measured Power Curve

The measured power curve, as addressed in the standard, is determined by collecting measurements of meteorological variables and wind turbine signals simultaneously. These two characteristics together are the primary determinants of a wind turbine’s performance, and, by collecting data for a long enough period, users of the standard can establish a statistically significant database over a range of wind speeds and under varying wind and atmospheric conditions.

Meteorological variables touched upon in IEC 61400-12-1 Ed. 2.0 b:2017 include wind shear, wind veer, wind speed, air density, and turbulence. The power curve, as per the standard, is climate-specific, and it abides by certain rules. For example, “the wind speed at a point in space is defined as the horizontal wind speed”.

Wind turbine signals include the power output of the rotor, and other turbine-specific considerations that are to be determined for the measured power curve.

Annual Energy Production (AEP)

The AEP is calculated by applying the measured power curve to reference wind speed frequency distributions. In adherence to IEC 61400-12-1 Ed. 2.0 b:2017, AEP should be calculated in two ways, one designated “AEP-measured”, and the other “AEP-extrapolated”. This value serves as an estimate of the total energy of a wind turbine throughout a one-year period.

IEC 61400-12-1 Ed. 2.0 b:2017 Standard

The methods for determining the measured power curve and annual energy production, along with supplementary information and formulas for calculating the necessary values, are detailed in IEC 61400-12-1 Ed. 2.0 b:2017. The procedure covered in the document can be used for performance evaluation of specific wind turbines at specific locations, but it also can be used to make generic comparisons between different wind turbine models or different wind turbine settings when site-specific conditions and similar influences are considered. This methodology should be assisted by uncertainty sources and their effects.

IEC 61400-12-1 Ed. 2.0 b:2017 updates and supersedes the first edition of the standard, which was published back in 2005. This revision includes the following significant technical changes:

  • new definition of wind speed
  • inclusion of wind shear and wind veer
  • revision of air density correction
  • revision of site calibration
  • revision to definition of power curve
  • interpolation to bin centre method
  • revision of obstacle model
  • clarification of topography requirements
  • new annex on mast induced flow distortion
  • revision to anemometer classifications
  • inclusion of ultrasonic anemometers
  • cold climate annex added
  • database A changed to special database
  • revision of uncertainty annex
  • inclusion of remote sensing

IEC 61400-12-1 Ed. 2.0 b:2017 – Wind energy generation systems – Part 12-1: Power performance measurements of electricity producing wind turbines is now available on the ANSI Webstore.

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