Application and validation of a new multi scale wind flow modeling system

Energy production studies are intended to provide the best estimate of lifetime annual energy output for a wind project. Such efforts focus on accurate wind resource characterization and turbine placement as these factors ultimately affect the power production and financial yield of the wind farm. Nowadays, wind flow modeling coupled with onsite meteorological measurements is the preferred method to characterize the wind resource and energy production potential for proposed wind projects.

Ten years ago, AWS Truewind (AWST) pioneered a method to couple a prognostic numerical weather prediction (NWP) model with a diagnostic microscale model for wind resource characterization at horizontal resolutions on the order of 50 to 100 m. In principle, fully compressible, non-hydrostatic NWP models can simulate a broad range of meteorological phenomena from synoptic to micro scales but the required computing power is substantial as the grid spacing decreases. To circumvent this issue, the NWP model is run using nested grids with the smallest grid spacing on the order of 1 km for a limited number of days over a multi-year period. These days are selected to provide a representative sample of conditions that might be encountered over the lifetime of a modern wind plant. Then, a diagnostic, microscale model uses the averaged conditions obtained from NWP model to downscale the wind flow from 1-km to 50-m grid spacing with high resolution terrain and land use data sets.

The most common diagnostic, microscale models are either mass-conserving such as WindMap developed by AWST or Jackson–Hunt type flow models such as WAsP and MsMicro. They are simplified versions of more complete dynamical models, and therefore run much faster while still performing reasonably well where the wind is not significantly affected by flow separations, thermal gradients, etc. However, microscale models are diagnostic tools using many simplifying assumptions and are not designed to model the wind flow in complex terrain or in coastal environments. To address these issues, AWST is developing a new wind mapping system based on the Advanced Regional Prediction System (ARPS) from the Center for Analysis and Prediction of Storms at the University of Oklahoma. The ARPS is configured to span a broad range of atmospheric motions using multiple nested domains with grid spacing from 50 km to 100 m.

Given sufficient computing resources, this approach is ideal because it relies on a single, state-of-the-science NWP model with appropriate physics and dynamics to handle all scales of motion relevant for wind mapping while overcoming the limitations of diagnostic microscale models. ARPS simulations are being conducted at grid spacings down to 100 m in moderate and complex terrain for comparison with standard wind mapping results using all available meteorological observations. The conference presentation will focus on several case studies as part of the application and validation of this new multi-scale wind mapping system using ARPS.