AWAKEN Testable Hypotheses

By both observing and simulating the atmospheric boundary layer in the region within and around operational wind farms, the AWAKEN project aims to address several testable hypotheses, which were identified and prioritized at a technical experts meeting (Moriarty et al. 2020) and are listed here in order of decreasing priority:


  1. Wind farm wakes propagate on land for tens of kilometers and lower the energy production of neighboring wind farms. Characteristics (magnitude and extent of momentum deficits, magnitude and extent of region of increased TKE) of wind plant wakes depend primarily on the spacing of turbines in a wind farm along the primary wind direction, turbine size, individual turbine power level and hub-height turbulent kinetic energy (or turbulence intensity), wind speed at hub height, and atmospheric stability. Wind farm wakes can be steered using coordinated individual turbine yaw control, although topography and yaw-misalignment will also influence wake propagation.


  1. Wind turbines in the interior of land-based wind farms tend to have more turbulent inflows resulting in higher damage-equivalent loads than those on the exterior. The turbulence levels in land based wind farms asymptote to a fully developed condition after the first three rows of wind turbines.


  1. The decrease in hub-height velocity 1-30D upwind of a land based wind farm due to the wind-farm induction zone, which distorts power production and predictions, depends on atmospheric stability, inflow wind speed, boundary-layer height, wind shear and veer (interacting with wind turbine characteristics, wind farm layout, terrain & surface roughness, and operative conditions); the induction zone may create speed-up along the edges of the wind farm.


  1. Wake steering and turbine consensus control increase full wind farm power production and reduce structural loads of turbines under a specific range of atmospheric conditions. The overall benefit of wind farm control is primarily dependent upon inflow winds, atmospheric stability, boundary layer height, wind shear and veer, and wind direction variability (interacting with the turbine type, orography, inter-turbine spacing and alignment), with maximum benefit coming when columns of turbines are aligned with wind direction under stable conditions.


  1. The maximum energy produced by a large (>100MW) land-based wind farm is constrained by the momentum flux between the surrounding atmosphere and the flow within the wind farm.


  1. Turbine wake morphology, evolution, and wake interactions are affected by a complex interplay of events connected to turbine settings, control, and short-term variability of the incoming wind conditions. Including a stochastic component to wake, turbulence, and turbine models will enable higher accuracy for predictions of wind turbine wakes and their interactions.


  1. Intermittent turbulent bursting events related to Kelvin-Helmholtz instability, gravity waves, and bores lead to fluctuations in wind farm power production and structural loading of wind turbines.


More details can be found here:

P. Moriarty, N. Hamilton, M. Debnath, T. Herges, B. Isom, J. K. Lundquist, D. Maniaci, B. Naughton, R. Pauly, J. Roadman, W. Shaw, J. van Dam, and S. Wharton, “American WAKE experimeNt (AWAKEN),” Tech. Rep. NREL/TP-5000-75789 (National Renewable Energy Lab. (NREL), Golden, CO (United States), 2020).