Siting - Wind Energy: Renewable Energy and the Environment - page 179

FIGURE 9.6 Wind turbines, 1 kW each, mounted on parapet of building. (Photo courtesy of AeroVironment.
With permission.)

the neighbors. The noise from a small wind turbine is around the level of noise in an office or in a
home. Noise from a small wind turbine is rarely a problem since the level drops by a factor of 4 at a
distance of 15 m, and it is generally masked by background noise. A sound study with a 10 kW wind
(wind speeds were 9-11 m/s) showed levels of 49-46 dBA for the turbine running and off at a dis-
tance of 15 m, and essentially no difference at a distance of 30 m and greater. However, if the wind
turbine rotor is downwind, then there is a periodic sound every time the blade passes the tower, and
even though the sound is the same level as the background sound, it can be annoying. In California,
noise from a wind turbine must not exceed 60 dBA at the closest inhabited building.

9.1.2 V ISUAL I MPACT
The State of Vermont has a scoring system for possible adverse visual impact of small wind turbines
from two different vantage points [17]: private property (the neighbors' view) and public views
(roads, recreation, and natural areas). For the neighbors' view the considerations are: (1) What is the
position of the turbine in the view? (2) How far away is the turbine seen? (3) How prominent is the
turbine? (4) Can the turbine be screened from view? For public views there are two additional con-
siderations: (5) Is the turbine seen from an important scenic or natural area? (6) What is the duration
of the view? Each is rated by a point system (Table 9.1), with a total of 12 points for the residential

TABLE 9.1
Criteria for Points for Visual Impact of Small Wind Turbines

Neighbor View Public View

1 2 3 4 5 6

View Angle Distance Prominent Screened Vista Duration

Points Degree m sec

0 Below treetops Complete Degraded 0

90 900

1 0-45 450-900 At horizon line Multiple trees Common

15

Single tree,

2 50-60 150-450 Above horizon line 1/2-2/3 Scenic

30

3 60-90 150 Above tallest mountain No screening Highly scenic 60