Wind Turbine Visibility and Visual Impact Threshold Distances in ...

2) Solar Azimuth: The solar azimuth was determined by inputting the date, time, and
location for the observation into a web-based application provided by the National Oceanic
and Atmospheric Administration. 2
3) Bearing: This value was calculated using a GIS-based computer program. The bearing
represents the direction in which the observation was made. It was calculated using a
central turbine within each wind energy facility. This provides for consistency among the
bearing calculations, but does introduce some error as the actual turbines in view may in
fact have a slightly different bearing.
4) Wind turbine lighting angle: The lighting angle for each observation was calculated to
indicate what the lighting conditions would have been for the wind turbines, on the basis of
the geometry of the sun and the location of a central wind turbine. This calculation was
derived from a calculated value of the solar azimuth and the bearing.
5) Average Visibility Rating: The average visibility was calculated by averaging the ratings
from all viewers for each observation. The database querying capability was used to extract
subsets of the observations for analysis.
IV. Results
Phase 1: Maximum Visibility Distance Analysis
The maximum visibility distance portion of this study utilized a combination of field-based
observations of wind turbines and geospatial analyses to determine the maximum limit of
visibility of the wind turbines in a variety of lighting and atmospheric conditions, and the
maximum limit of visibility of blade movement on the wind turbines. The observation points
were determined by conducting viewshed analyses for the wind facilities to determine areas
with potential visibility of the wind turbines, and then driving the roads within the viewsheds to
determine the outer limits of visibility for the particular weather and lighting conditions at the
time. Both daytime and nighttime observations were made. Observations were made for both
the Cedar Creek and Happy Jack/Silver Sage wind facilities. Most observations for this phase
of the study were conducted in January 2011, but additional observations were made on the
subsequent trips in March, July and October 2011.
Note: distances reported below were measured to the nearest visible turbine; however, for all
observations, other turbines were visible at slightly longer distances.
2 http://www.esrl.noaa.gov/gmd/grad/solcalc/.
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