Improving the Wind Farm efficiency by simple means

Abstract

Wake effects in wind farms are a major source of power production losses and fatigue loads on the rotors. It has been demonstrated that in large wind farms the only source of kinetic energy to balance that extracted by the turbines is the vertical transport of the free-stream flow kinetic energy from above the wind-turbine canopy. This chapter explores the possibility to enhance such process by introducing tethered kites in steady flight within a small wind-turbine array. In a first step, an array of four wind turbines, aligned with the streamwise velocity component, is simulated within the Large Eddy Simulation framework. The turbines are placed in a pre-generated turbulent atmospheric boundary layer and modelled as actuator discs with both axial and tangential inductions, to account for the wake rotation. The main part of the study considers an identical wind turbine configuration with kites suspended half the inter-turbine spacing distance. The kites are modeled as body forces on the flow, equal in magnitude and opposite in direction to the vector sum of the lift and drag forces acting on the kite surfaces. A qualitative comparison of the mean flow statistics, before and after the introduction of the kites is presented.