WMOD00522

• Title: Projected Impacts of a Very Large Windpower Complex
• Date: 9/26/1978
• Weather Modification - Doc Type: Report

economic systems of which it is an important part, Analysis of environmental
impact on these higher levels must be considered also,

1. Environmental Impacts of Windfarms

The Energy Research and Development Administration (now emerged into
the Department of Energy) examined the impacts of wind machines as one element
of the Federal Wind Energy Program. A contract was let with the University of
Michigan to study interference in radio, TV, and other communications systems.
Battelle Memorial Institute was given a contract to study microclimatic
effects and impacts on migratory birds, Preliminary reports of the findings
have been published 13, 14 and further reports are due shortly. Howell 15
has examined the environmental impacts of large arrays of individual wind
machines aggregated into windfarms,

a. Microclimatic, - The large windfarms projected in this thought-
experiment would increase the roughness of the earth's surface in their
immediate area, thus affecting both the distribution of wind in the vertical
and the details of wind swirl patterns at the ground. These changes would in
turn affect the local details in the patterns of tempera ture, prE~cipitation,
snow drifting, and evaporation.

The effects of increased terrain roughness have been studied in
connection with the microclimatic effect of cities, which roughen the earth's
surface to an even greater extent and over eVlen larger areas than would be the
case with windfarms. In light to moderate wind, the effects of surfacle rough-
ness are relatively trivial. When the wind is strong, one of these windfarms
would tend to increase the rate at which air 1within a few tens of meters of
the ground mixes with air at higher levels up to a height of as Dluch as 1.5
km, depending upon the strength of the wind and the distribution of temperature
aloft. The roughness also decreases the average speed within the turbulent
layer. '.

The windfarms would cause some decrease in average windspe4ed and
some increase in turbulence above a few tens of meters with relatively little
effect closer to the ground where the air is turbulent anyway whenever the
wind is strong,

Increased turbulence through a considerable depth above the ground
tends also toward a somewhat more even distribution of potential temperature
during episodes of strong wind. The range of temperature variation would
therefore be somewhat -decreased at such times.. Since the moisture content of
the air near the ground normally decreases up..~ard, the mixing would tend to
decrease the relative humidity slightly next to the ground and perhaps
increase it slightly at the top of the mixing layer several hundred meters
higher.

Precipitation from large storm systems, either winter storms or
large organized systems of convective clouds in summertime, would be almost
entirely unaffected by local changes in surface roughness associated with
windfarms. During the weather conditions that: make for small, scatterE!d
summertime showers, it is conceivable that the braking effect of the windfarm
on the airstream crossing over it could lead to slight local convergenc:e along