Thunderstorm downburst risks to wind farms

As has been noted in recent experiences, thunderstorms can cause damage to turbine units that are part of a wind farm because of the correlated wind inflow fields that these units can be subjected to simultaneously. We extend a model for simulating thunderstorm downburst events and their effects on a single turbine unit to situations where multiple units in a wind farm are subjected to correlated input from moving downbursts. The end-to-end simulation we describe involves first the generation of a downburst touchdown with associated downburst wind field and subsequent movement in the vicinity of a wind farm, comprised of a 6 × 4 rectilinear arrangement of 5 MW 90-m hub-height turbines. The downburst model includes a slowly varying (non-turbulent) component and a turbulent component. The wind field model is developed and calibrated based on Doppler radar data on recorded downbursts. Results show that downbursts with different physical characteristics can lead to highly variable loads on units in the wind farm.