Wind Plant Impacts on Planetary Boundary Layer Height

As wind energy deployment has increased in recent years, the need to understand the impact of wind plants on the atmosphere has grown. Wind plants harness energy from the wind, leaving slower, more turbulent flow in their wakes. This effect has the potential to significantly modify the atmospheric characteristics of their surroundings¹ such as the planetary boundary layer height (PBLH), which is used as a key length scale in atmospheric modeling. Lab-scale studies have suggested that wind plants affect PBLH², but this impact is not well understood, especially under real-world conditions, as acquiring large-scale measurements remains a challenge.

In the current study, data from the American Wake Experiment (AWAKEN) are used to assess the impact of wind farms on PBLH. The AWAKEN campaign is an extensive field study taking place in Northern Oklahoma, at the location of five neighboring wind plants. The project site is heavily instrumented with in-situ and remote-sensing devices in the upstream, interior, and downstream regions of the wind plants based on the prevalent wind direction. These instruments include ceilometers, profiling lidars, thermodynamic profilers, and radiosondes, each of which collects data that can be used to estimate PBLH through various methods.

We first compare a suite of PBLH estimation methods from the various instruments, exploring the advantages and limitations of each. This evaluation is carried out during observational periods when wind direction ensures that the relevant instruments remain unaffected by wind plant wakes. We find that, while each method produces slightly different estimates for PBLH, all approaches capture characteristic diurnal variations, exhibiting shallow stable boundary layers at night and deep daytime convective conditions, and transitional periods during mornings and evenings.

We then focus on assessing the change in PBLH caused by the wind plant. The extensive deployment of diverse instruments in various locations permits the measurement of PBLH both upwind and within the wake of the wind plant over a range of wind directions. Furthermore, the long deployment time of these instruments makes it possible to conduct such analysis for a range of atmospheric conditions such as wind speed and stability. The impact of these atmospheric conditions on the PBLH perturbation induced by the wind plant wake is explored.

By characterizing the impacts of wind plants on PBLH, the results of this study will facilitate predictions of atmospheric phenomena such as aerosol distribution, pollution dispersion, and cloud formation in the vicinity of wind plants. With improved comprehension of the intricate interactions between wind plants and their surroundings, this research equips developers and stakeholders with valuable insights into the impact of future and existing wind plants on the local meteorology, facilitating social acceptance of wind energy and improving the accuracy of wind resource assessments in areas with a high density of wind generators. Furthermore, this work advances our understanding of atmospheric flow at the wind plant scale, a topic that has been listed as one of the “grand challenges” that must be addressed if wind energy is to reach its full potential³.

References:

¹Bodini, N., Lundquist, J. K., & Moriarty, P. (2021). Wind plants can impact long-term local atmospheric conditions. Scientific reports, 11(1), 22939.

²Wu, K. L., & Porté-Agel, F. (2017). Flow adjustment inside and around large finite-size wind farms. Energies, 10(12), 2164.

³Veers, P., et al. (2019). Grand challenges in the science of wind energy. Science, 366(6464), eaau2027.