Current atmospheric models are not perfect predictors of wind conditions or “inflow” at heights spanned by industrial-scale wind turbines (~40 to 200 m above ground level). Wind forecasting improvement of as little as 10% to 20% could result in hundreds of millions of dollars in annual operating cost savings for the U.S. wind industry. One candidate for improving wind forecasts is the choice of a land surface model (LSM) employed in numerical weather prediction models. The LSM controls the exchange of energy between the surface and the atmosphere and may have a large effect on inflow in the lower boundary layer.
Scientists used the Weather Research and Forecasting (WRF) model and data from the Department of Energy’s Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site to investigate the LSM’s impact on the near-surface wind profile, including heights reached by multimegawatt wind turbines.
Simulations of wind profiles and surface energy fluxes were made using five LSMs of varying degrees of sophistication in dealing with soil-plant-atmosphere feedbacks. Surface flux and wind profile measurements from the ARM SGP site in Oklahoma were used to validate the model simulations. WRF was run for three different two-week periods covering varying canopy and meteorological conditions. The LSMs predicted a wide range of energy flux and wind shear magnitudes even during the cool autumn period when less variability was expected.
Simulations of energy fluxes varied in accuracy by model sophistication; LSMs with very simple or no soil-plant-atmosphere feedbacks were the least accurate. However, the most complex models did not consistently produce more accurate results. Errors in wind shear were also sensitive to LSM choice and were partially related to energy flux accuracy. The variability of LSM performance was relatively high, suggesting that LSM representation of energy fluxes in WRF remains a large source of model uncertainty for simulating wind turbine inflow conditions. Future simulations could be done during periods of concurrent wind power data to assess the relationship between surface energy exchange, wind shear, and power production at the wind farm located a few miles west of the SGP site.
Reference: Wharton, S., M. Simpson, J. L. Osuna, J. F. Newman, and S. C. Biraud. 2015. “Role of Surface Energy Exchange for Simulating Wind Turbine Inflow: A Case Study in the Southern Great Plains, USA,” Atmosphere 6, 21-49. DOI: 10.3390/atmos6010021. (Reference link)
Contact: Sally McFarlane, SC-23.1, (301) 903-0943
SC-23.1 Climate and Environmental Sciences Division, BER
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