Abstract
Downwind turbines have favorable characteristics such as effective energy capture in up-flow wind conditions over complex terrains. They also have reduced risk of severe accidents in the event of disruptions to electrical networks during strong storms due to the free-yaw effect of downwind turbines. These favorable characteristics have been confirmed by wind-towing tank experiments and computational fluid dynamics (CFD) simulations. However, these advantages have not been fully demonstrated in field experiments on actual wind farms. In this study—although the final objective was to demonstrate the potential advantages of downwind turbines through field experiments—field measurements were performed using a vertical-profiling light detection and ranging (LiDAR) system on a wind farm with downwind turbines installed in complex terrains. To deduce the horizontal wind speed, vertical-profiling LiDARs assume that the flow of air is uniform in space and time. However, in complex terrains and/or in wind farms where terrain and/or wind turbines cause flow distortion or disturbances in time and space, this assumption is not valid, resulting in erroneous wind speed estimates. The magnitude of this error was evaluated by comparing LiDAR measurements with those obtained using a cup anemometer mounted on a meteorological mast and detailed analysis of line-of-sight wind speeds. A factor that expresses the nonuniformity of wind speed in the horizontal measurement plane of vertical-profiling LiDAR is proposed to estimate the errors in wind speed. The possibility of measuring and evaluating various wind characteristics such as flow inclination angles, turbulence intensities, wind shear and wind veer, which are important for wind turbine design and for wind farm operation is demonstrated. However, additional evidence of actual field measurements on wind farms in areas with complex terrains is required in order to obtain more universal and objective evaluations.
Highlights
Downwind turbines have the advantages of being able to generate power efficiently—even under up-flow wind conditions in complex terrains
This correction method was shown to provide the same of data consistency as when measurements are performed on flat terrains. Since this method degree of data consistency as when measurements on flat terrains. Since this could not be used at the present site, the reliabilityare of performed the vertical-profiling measurements in method could not be used at the present site, the reliability of the vertical-profiling complex terrains was evaluated by simultaneous measurements using a meteorological mast installed measurements in tocomplex was evaluated at a location close the windterrains farm, as described above. by simultaneous measurements using a meteorological mast installed at a location close to thethe wind farm, as described
The correlation between the horizontal wind speed measured with a verticalprofiling light detection and ranging (LiDAR) and with a cup anemometer was as good as the correlation between the horizontal
Summary
Downwind turbines have the advantages of being able to generate power efficiently—even under up-flow wind conditions in complex terrains. They are at reduced risk of collapse due to the free-yaw effect—even when electrical network failures occur during storms. The ultimate goal of the present study was to demonstrate the characteristics of downwind turbines in complex terrains. We conducted field measurements on a wind farm with downwind turbines installed over complex terrains. We used a vertical-profiling light detection and ranging (LiDAR) system to evaluate the wind conditions around the downwind turbines
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