Analysis of Some Major Limitations of Analytical Top-Down Wind-Farm Models

Analytical top-down and bottom-up wind-farm models have become major tools for quick assessment of yields from larger wind farms and the extension and properties of their wakes and have proven their principal applicability from recently obtained in situ observations. We review some of the limitations of top-down wind-farm models, partly in light of basic atmospheric boundary-layer findings which have been coined by the late Sergej Zilitinkevich. Essentially, for the applicability of such analytical models, the wind-farm turbine hub height should be small compared to the atmospheric boundary-layer height, and very small compared to the horizontal extension of the farm and the distance to the nearest surface inhomogeneities. Possibilities and options to include recently discovered blockage effects are also discussed.