Exploring a Finite Wind Farm for Partial Repowering by Vertical Staggering of Low Performing Horizontal Axis Wind Turbines /

Abstract

Vertical staggering (VS) of horizontal axis wind turbines is explored to eliminate the effects of inter-farm wakes and partially repower the existing arrays for enhanced power production. Nine turbines of the FFCEL wind farm of Jhimpir, Pakistan were considered for a micro-scale numerical study; these turbines were identified as the most affected ones by a mesoscale numerical simulation for the same site. A RANs model was employed to simulate the flow through a domain that acquired boundary condition data from the results of the WRF study for the wind farm under consideration. Furthermore, the convective atmospheric boundary layer was also considered for the investigation. The hub heights were changed from 80 m to both 60 m and 100 m in separate cases. By elevating the turbines to 100 m the cumulative power extraction of the 9 turbines increased by 13.5 % and reducing the hub height to 60 m decreased the power output by 11.5 % of that of the current configuration. The effect of the compound wakes appeared mild at 100 m, modest at 80 m, and high at 60 m; as the maximum velocity deficit observed under the influence of compound wakes is 13.26 %, 14.06 %, and 15.17 %, respectively. The comparison of wake recovery for neutral atmospheric boundary conditions with that of the convective atmospheric boundary layer revealed the latter to speed up the wake recovery. The lateral repositioning of some of these turbines was also performed for the 100 m case. The power generation of the laterally optimized layout at 100 m hub height was 23 % more than that of the existing layout. Therefore, the increase of the hub heights of onshore horizontal axis wind turbines proves to be an affordable strategy to partially repower finite wind farms affected by compound wakes.