Technical notes about accuracy of wind monitoring systems for wind energy applications


  1. Accurancy data of the windlogger EKO21B
  2. Accuracy data of some other suppliers
  3. Accuracy of the energy prediction
  4. Conclusions

Total system - accuracy of wind monitoring systems

Accuracy data of the windlogger EKO21B

Thanks to many years research of the MAX40+ anemometer in wind tunnels the exact calibration curve of the anemometer is programmed in the instrument.The resolution of the stored average values is only 0.01 m/s.
The total system-accuracy is typ. 0.2 m/s by using the MAX40+ anemometer.
This has been achieved by an excellent anemometer calibration, the right way of signal conditioning & sampling.

An optional individual calibration certificate with 0.1 m/s calibration accuracy (including calibration report) can be supplied, according to the latest European MEASNET procedure. This certificate is a guarantee for the high accuracy, but is not required in all cases, as the standard accuracy is typ 0.2 m/s.
The EKO 21B meets all the accuracy recommendations of IEA, IEC, WMO and AWEA.

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Accuracy data of some other suppliers

By simplifying the calibration curve to a "straight line" (without offset), deviations up to appr. 0.5 m/s are possible. Moreover the resolution of the samples of the MAX40 anemometer for puls counting inputs is 1 pulse, or 0.7 m/s with sample period of 1 second! This will affect the accuracy of the recorded values! Most other suppliers, who use the MAX40 anemometer, probably meet (or not) the accuracy standard of the WMO/AWEA: 0.5 m/s.
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Accuracy of the energy prediction

As the energy production of a wind turbine is proportional to the cube of the long-term average wind speed (v3), a small deviation in wind speed will highly affect the calculation of the energy production.
The relative deviation of the expected energy production is equal to:

3 * total system accuracy / average wind speed

Accuracy of the energy prediction

For example: when the average wind speed is 6 m/s, measured with a system accuracy of 0.5 m/s, the error in the prediction of the energy production is approx. 25%.
As a valuable feasibility studie should give the energy prediction within appr. 5-10 %, the required system- accuracy should be in the range of 0.1 to 0.2 m/s when the long term average wind speed is < 10 m/s.
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For wind energy feasibility studies accurate measurements with total system accuracy of 0.1 to 0.2 m/s is required. Especially in areas with low or moderate average wind speed it is important to measure the wind accurately as the economic feasibility of windpower may be critical in that case. The EKO 21B may be some more expensive than less accurate instruments, but it can save a lot of money as it can prevent wrong decisions for investments in wind energy projects! The EKO 21B is an appropriate sytem for feasibility studies, the evaluation of wind energy projects and even as a low-cost system for scientific wind-research projects and meteorological studies.
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If you are interested in Ekopower's products please contact us.

P.O. Box 4904, 5604 CC Eindhoven, the Netherlands.
Tel: +31.40.2814458 Fax: +31.40.2814119