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Wind speeds: maybe lower, but not at turbine height

Wind speeds: maybe lower, but not at turbine height

by Michael Goggin, AWEA Manager of Transmission Policy

The question of diminishing winds due to climate change has surfaced again (see “Diminishing winds? Not yet”), this time in the form of a study finding lower winds at a number of locations in the U.S. Pacific Northwest.

The reassuring consensus of wind resource assessment experts is that wind speeds at the height of modern wind turbines, several hundred feet above the earth's surface, have not declined (see, for example, “AWS Truepower Questions Reported Diminishing Wind Speeds”). As a result, there has been no significant change in wind energy output, and one is not expected going forward. There is often very little relationship between wind speed at the earth's surface and wind speed 300 feet up, particularly when surface wind speeds are being slowed by friction with objects on the surface.

Most surface wind observation sites are located near urban areas and far from areas where wind development tends to occur, and it appears that the observation sites used in the study follow that pattern. As a result, the study may not tell us much about what is happening to surface wind speeds in the areas where wind development is occurring, and may simply be capturing the impact of recent land use changes near urban areas, particularly the regrowth of forested areas.

In the unlikely event that there is an impact on hub height winds in some areas, the impact will be extremely localized to the small area just downwind of the area that has seen land use changes. A wind developer planning a project can simply choose to position the turbines differently within that wind plant, or move to a nearby site that hasn't been affected. In an absolute worst case, a developer could simply shift to building wind plants in other regions. Even if there were a decrease in wind speed at some wind sites, the U.S. would still have an almost absurd overabundance of wind resources, more than enough to meet our country's electricity needs a dozen times over. The U.S. is called the “Saudi Arabia of wind” for a reason. The diversity of our wind resources (in terms of the diversity of meteorological phenomena that create our winds) also guarantees that if turbine-height wind speeds do decline at some sites, other sites are likely to be unaffected or even experience an increase in wind speed.

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