Effects of changing atmospheric conditions on wind turbine performance

The atmospheric boundary layer is well known as a dynamic, hard-‐to-‐predict environment. Some large scale trends are clear, for example a switch from stable nighttime stratification to convective conditions during the day. In comparison, other effects, such as changes in shear, turbulence and wind veer are less obvious and can be influenced by terrain and synoptic conditions as well as the diurnal cycle. Wind turbines are designed to operate almost continuously for 20 years or more, and so must work reliably and produce predictable amounts of power in very variable wind conditions.

Using data from the observations on turbines at the National Wind Technology Center and other sites, together with simulations of turbine performance at different fidelities, we show some of the ways in which turbine performance and loads are affected by changes in the atmosphere. We compare and contrast our results with some of the methods frequently used in the wind industry to predict turbine power output, and discuss how the wind resource assessment process could be improved to account for variations in the atmosphere. Finally we highlight combinations of conditions that may be particularly advantageous or challenging for the wind turbines we have studied.