Sound emission measurement on wind turbines (follow-up measurement)
Sound emission measurement on wind turbines: we fulfil the permit's follow-up measurement with accredited measurement and a standards-compliant report.
In the course of permitting a wind farm, the authorities usually prescribe a follow-up measurement of the permitted sound emission, or sound power level, as a permit condition. The predicted noise situation has to be compared with the actual one. With accredited sound emission measurements from EWS you fulfil this condition professionally. Whether and to what extent measurements are repeated after construction is governed by the respective permit decision and can differ depending on the turbine and the federal province. Sound emission describes how much sound the wind turbine itself radiates, whereas sound immission describes what reaches neighbours. The turbine itself can already be made quieter at the design stage, for example through noise-optimised rotor blades.
Measurement follows the IEC 61400-11 standard, adopted in Austria as ÖVE/ÖNORM EN in the edition currently in force. It determines the sound power level of the turbine and the tonality of the noise. The microphone is placed on a ground board downwind of the turbine. To eliminate background noise, measurements are also taken with the turbine switched off. The results are evaluated in wind speed classes 0.5 m/s wide and referred to a standardised wind speed at a height of ten metres. With the turbine running, wind speed is derived from the turbine's power output or the turbine anemometer; at standstill it is taken from the measurement mast. A minimum number of measurement points is required per wind speed class.
Tonality shows whether individual tones stand out from the noise, which residents may find particularly noticeable. It is determined from a frequency analysis. In addition, the one-third-octave spectrum from 20 Hz to 10 kHz shows in which frequency ranges the turbine emits sound. This frequency analysis makes visible anomalies that a single sound level hides. The measurement campaign is carried out site-specifically by our accredited testing body, the EWS Testing Center. We measure in the required wind speed classes during the daytime and, if required, at night, with current calibrated or verified measurement equipment and to internationally recognised standards. Thanks to substantial staffing and technical resources, the measurement campaign is carried out promptly. With the turbine manufacturer and neighbouring operators we coordinate technically and solution-oriented on an equal footing.
Your benefit: possible sound reductions can be limited to the necessary minimum, and the yield of your wind farm can increase. We give practical recommendations for wind farm optimisation and prepare standards-compliant reports for final inspection ("Kollaudierung"). The forecast for this is produced in the operational and construction noise assessment, and the effect on residents is checked by the sound immission measurement. The power curve measurement complements this on the yield side. The results of the sound emission measurement on your wind turbine also serve as a comparison basis for later control measurements, for example after changes to operating mode or rotor blades. In supply contracts, sound tests after takeover are often agreed and linked to contractual penalties; the measurement provides the evidence. For photovoltaics there is sound emission measurement for PV plants.
