Camilty Wind Farm - Partnerships for Renewables

Camilty Wind Farm
8.3.30 A wind shear analysis has been undertaken by RPS to derive standardised 10 m wind speed
data (refer to Appendix 8.4 for technical details of the wind shear assessment). This analysis
has been undertaken with reference to the guidance set out in the IoA Bulletin article. The 10
minute average wind speed at the proposed maximum turbine hub height (80m) has been
calculated using the ratio of wind speeds measured simultaneously at anemometer heights of
30 m and 70 m on the anemometry mast. A standardised extrapolation to 10 m has been
undertaken using a standard roughness length of 0.05 m.
8.3.31 It should be noted that the relative heights of the anemometers in relation to maximum hub
height do not match exactly the requirements of the methodology set out in the IoA Bulletin
article, which requires one anemometer to be at 40-50% of hub height and a second at
greater than 60% of hub height. These specific requirements were not taken into account in
the anemometry mast design. It is considered, however, that the calculation undertaken
provides adequate assessment of any local wind shear effects, given that the lower height
(30 m) is representative of 38% hub height, which is close to the requirement for 40%. The
higher height (70 m) meets the IoA Bulletin recommendation of greater than 60% of hub
height. The full procedure for wind shear analysis is included within Standard IEC-61400-11
Wind turbine generator systems – Part 11: Acoustic noise measurement techniques.
Measured Baseline Noise Levels at Parkview Cottages
8.3.32 Charts 8.1 and 8.2 below present the results of the baseline noise survey at Parkview
Cottages for quiet day and night time periods. The charts show the measured L A90,10min
background levels correlated with the synchronous wind speed, derived to 10m above local
ground height as previously described.
8.3.33 For each data set, the prevailing background noise level at each wind speed has been
ascertained by applying a best fit curve. Both charts have had a second order polynomial line
applied as it is considered that this is the most appropriate curve for the shape of the data
sets. The formula for each curve is shown on the chart.
8.3.34 ETSU-R-97 suggests that atypical data points should be removed from the scatter plot prior
to ascertaining the best fit line which is representative of prevailing background during quiet
day and night time periods.
8.3.35 Atypical data may include ‘periods of significant rainfall’ or points which sit outwith the main
body of data for no apparently obvious reason – this may have been due to other noise
events in the acoustic environment of the monitoring location which are sporadic and do not
form part of the typical environment (e.g. car engine idling / grass cutting / persistent alarm
etc.). This is common in such long unattended surveys.
8.3.36 For the data set presented below, no obvious atypical data outwith those removed for periods
of significant rainfall were present and so all other points remain in the data set.
March 2013 8-8 ES Chapter 8
Noise
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