On the impact of Wind Turbines on the Atmosphere Boundary Layer Thermodynamics and Turbulence Features: Application of Doppler lidars and a 200-meter meteorological tower

Due to a warming climate, there has been a push to transition to cleaner sources of energy production to combat greenhouse gas emissions caused by fossil fuels. One of the leading renewable energy sources in the world is wind energy. Wind turbines extract kinetic energy from the mean wind flow and convert it into electricity. After the energy is extracted from the mean flow, typically a wake occurs downstream of the wind turbines. Due to wind turbine wakes, there can be up to a 10% loss in power production from a wind farm which can cause a loss of $730,000 annually. Due to the loss in power production and financial impacts from wind turbine wakes, there is a need to further our understanding of the impacts that the enhanced turbulence caused by wind turbines on the exchange of energy, moisture, momentum, and heat from the surface within the lowermost part of the atmospheric boundary layer (ABL). Since wind turbines function within the lowermost portion of the ABL, they are directly influenced by ABL turbulence and thermodynamic processes. There is limited understanding, however, of how a wind turbine impacts the ABL thermodynamics and turbulence processes, and vice versa.

Within the turbine wake, there is a deduction of the mean wind speed and an increase in turbulence. How the wake progresses downstream is dependent on the dissipation rate. Specifically, this can be investigated through two questions: How does the wind turbine wake impact the ABL thermodynamics? Is there a potential relationship between the turbulence induced by wind turbine wakes, wind power production, and commonly used parameters in similarity theories (e.g., vertical velocity variance and Obukhov length) in our numerical weather prediction (NWP) models? We analyzed turbulence and thermodynamic processes within the lowermost ABL through high-resolution (50 Hz) observations of key thermodynamic variables (u,v,w, T, q) at 10 levels on a 200-m tower at the measurement site. Wind power estimates were derived from wind speed measurements. Concurrent measurements of vertical and radial velocities were obtained using two Doppler lidars. Additionally, the Doppler lidars were used to calculate the depth of the ABL and observe the wake induced by the 200-m tower. The combination of Doppler lidars and the 200-m tower provides the necessary measurements of wind, moisture, temperature, and pressure eeded to investigate how the wind turbine wake impacts the local ABL thermodynamic and turbulence processes under different stability regimes and how the current ABL state impacts wind energy production. Results from this work could help improve the efficiency of wind energy production and how a wind turbine is affecting the local environment. Furthermore, improvements in the relationships between wind turbine wake and surface-atmosphere exchange processes will provide the ability to better forecast wind energy and how to make wind power more efficient.