Meteorological Phenomena Impacting Spatial Consistency of Ramp Events in Wind Farms

Previous research has shown the importance of improving overall wind resource predictions and predictions for what are known as wind ramp events. Wind ramp events are sudden increases or decreases in power output from a wind turbine. In this research they are more precisely defined as a minimum change of ±3 m/s between 6 m/s and 12 m/s in wind speed over a 4-h period. Earlier investigations could not identify some of the causes of wind ramp events and found that in the wind farm not all turbines have ramps of the same type as other turbines currently ramping. Nacelle data from 13 wind turbines in central Iowa, along with archived meteorological data (including surface pressure, 850-mb height wind speeds and directions, and thermal stability, etc.) were used in the present study to identify and classify ramp events and attribute meteorological causes to the ramps. Statistical analysis was used determine the conditions most likely for these ramp events to occur. It was found that ramps only occurred 0.17% of the time in unstable atmospheric conditions. We also that some conditions lead to uniformity of wind ramps (all turbines ramping in the wind farm) or the variability of the wind ramps (some turbines ramping while others are not or having opposite ramps within the same wind farm). Lower pressure, higher wind speeds at 850mb, and neutral atmospheric stability suggest more uniformity in ramps. Night time conditions for net heat radiation and more stable atmospheres seemed to correlate with more variability in wind ramping. Future research should refine some classifications made in this research and ultimately improve wind forecasting models.