How wind speed shear and directional veer affect the power production of a megawatt-scale operational wind turbine
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Published:2020-09-11
Issue:3
Volume:5
Page:1169-1190
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ISSN:2366-7451
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Container-title:Wind Energy Science
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language:en
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Short-container-title:Wind Energ. Sci.
Author:
Murphy PatrickORCID, Lundquist Julie K.ORCID, Fleming PaulORCID
Abstract
Abstract. Most megawatt-scale wind turbines align themselves into the wind as defined by the wind speed at or near the center of the rotor (hub
height). However, both wind speed and wind direction can change with height across the area swept by the turbine blades. A turbine aligned to
hub-height winds might experience suboptimal or superoptimal power production, depending on the changes in the vertical profile of wind, also known as
shear. Using observed winds and power production over 6 months at a site in the high plains of North America, we quantify the sensitivity of a wind
turbine's power production to wind speed shear and directional veer as well as atmospheric stability. We measure shear using metrics such as α (the log-law wind shear exponent), βbulk (a measure of bulk rotor-disk-layer veer), βtotal (a measure of total
rotor-disk-layer veer), and rotor-equivalent wind speed (REWS; a measure of actual momentum encountered by the turbine by accounting for shear). We
also consider the REWS with the inclusion of directional veer, REWSθ, although statistically significant differences in power
production do not occur between REWS and REWSθ at our site. When REWS differs from the hub-height wind speed (as measured by either the lidar or a transfer function-corrected nacelle anemometer), the turbine power generation also differs from the mean power curve in a
statistically significant way. This change in power can be more than 70 kW or up to 5 % of the rated power for a single 1.5 MW
utility-scale turbine. Over a theoretical 100-turbine wind farm, these changes could lead to instantaneous power prediction gains or losses
equivalent to the addition or loss of multiple utility-scale turbines. At this site, REWS is the most useful metric for segregating the turbine's
power curve into high and low cases of power production when compared to the other shear or stability metrics. Therefore, REWS enables improved
forecasts of power production.
Publisher
Copernicus GmbH
Subject
Energy Engineering and Power Technology,Renewable Energy, Sustainability and the Environment
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