The interaction between the atmospheric boundary layer and wind turbines has become an important issue with wind energy the fastest growing renewable energy resource worldwide. As larger wind farms are developed, concerns are emerging over potential impacts on downwind agriculture and other economic activities.

The development of a new wind farm parameterization for the mesoscale numerical weather prediction model WRF (released in version 3.3) provides a tool to improve understanding of the interaction between wind farms and the boundary layer. Wind turbines are represented as a sink of momentum and source of turbulence (turbulent kinetic energy) at model levels containing turbine blades. The parameterization can represent a wide range of turbines based on hub height, blade diameter, nominal power and cut-in/cut-out speeds.

Results are presented for a series of idealized experiments which investigate the impact of large wind farms on the boundary layer. For an idealized offshore wind farm covering 10x10 km, significant impacts on wind speed, turbulent kinetic energy and momentum fluxes were found. The wind speed deficit was found to extend throughout the depth of the neutral boundary layer, with a long wake extending behind the farm of e-folding length-scale 60 km. Above the farm to the top of the boundary layer, the turbulent kinetic energy was increased due to vertical transport and shear production caused by the momentum deficit within the farm, significantly enhancing turbulent momentum fluxes. The turbulent kinetic energy was also increased by a factor of two near the surface below the turbines, causing the wind to increase as well as the turbulent fluxes.