turbulence intensity

Turbulence Intensity: unlocking the mystery

  • By saralarde
  • oct 20th, 2021
  • News

Turbulence is one of the most elusive factors of wind production, impacting both on-shore and off-shore wind turbines.

Turbulence, expressed as Turbulence Intensity or the standard variation from an average wind speed , most often 10 minutes, is not only difficult to understand, but its impact and importance also vary with wind speed. At medium speeds though, productivity will decrease due to turbulence ; but this impact will diminish as speed increases towards cut-out.

The impact of Turbulence Intensity is most certainly inversely proportional to our efforts, and up to now, our ability to measure it.

Curtailment strategies: an optimal plan for wind turbines      ? 

Turbulence Intensity can reduce productivity by up to 20%[1] while at the same time causing important wear through excessive loads thus reducing life-span. Additionally, curtailment strategies, if based on inaccurate or false information, can lead to important productivity losses.


On the other hand, wind turbines are poorly equipped to measure Turbulence Intensity. Anemometers, which are placed behind the blades, measure a Turbulence Intensity which is a mix of upstream turbulence and wake from the blades. Thus, the information is biased. MET masts measure turbulence intensity in front of the wind farm but these measures are inadequate as uneven terrain and wake from other wind turbines will create different turbulence environments. Finally, nacelle based long distance LiDAR focus on contractual measurements 400 meters in front of the wind turbine. Again, this is inadequate to understand the Turbulence Intensity specific to a single turbine.


With the pressing need to increase our renewable energy output globally, it is urgent to address this potential productivity improvement margin. The key to any undertaking of this kind is precise data. Only with relevant and accurate information can we make and measure improvements.


This is where the most advanced and cost-effective technology comes into play, notably with Epsiline’s WindEagle system. This combination of advanced sensors and algorithms provides accurate (error < 0,5°) wind information for advanced monitoring, diagnostics and improvement.


At the core of the WindEagle lies a patented LiDAR technology which measures wind characteristics 10 meters in front of the device, in other words, directly in front of the blades. This cancels out the deficiencies from Anemometers and long distance measurement devices. Turbulence measurement from Epsiline’s WindEagle will not be impacted by the wake from the blades nor the distortion caused by distance.


Beyond its turbulence intensity measurement accuracy, Epsiline’s WindEagle brings this advanced technology to all by reducing cost by an order of magnitude. Where traditional LiDAR are priced around 100 000€, Epsiline’s approach makes it affordable to all by reducing the cost by a factor of 10.




Epsiline’s Lidar: an autonomous control 


Epsiline’s LiDAR technology forms the cornerstone of an advanced yet easily useable solution. Accurate measurements of wind Speeds, Intensity and Direction are completed by further sensors including Pressure, Temperature & Humidity (PTU), vibration, true north compass and GPS. All these sensors are contained in the compact WindEagle which is installed in less than 2 hours on top of the nacelle.


Data is transmitted via cellular networks directly to Epsiline’s secure servers where the information can then be processed either through Epsiline’s advanced algorithms or through an API key for more customized analysis. Algorithm results and parameters are then accessed through Epsiline’s Webportal, giving full diagnostics to understand, monitor and improve performance.


Epsiline’s WindEagle contributes to productivity improvements in many ways. The first is by understanding the cause of unusually low productivity. By superposing on a wind rose the source of the Turbulence Intensity with the source wind production, Epsiline has helped operators and owners understand the cause of deficient wind productivity ; by comparing the Turbulence Intensity wind rose with the curtailment strategy, Epsiline provides relevant information to improve the productivity spectrum ; Turbulence Intensity surveillance by Epsiline’s WindEagle allows for mitigation of load stress ; and with the WindEagle’s accuracy, real wake steering strategies are now possible and accessible.



 Machine learning boosts the value of wind energy 


Indeed, machine learning needs precise information to improve the performance of a system. With Epsiline’s accurate data, algorithms can accurately draw conclusions on how to steer wind turbines so as to strongly increase the productivity of wind farms.


Beyond analysis and productivity improvement through wake steering, when the WindEagle is left permanently on the nacelle, automatic monitoring can be implemented to improve maintenance and ensure optimal productivity. Alerts are programmed to have email notifications sent whenever preset or customized thresholds have been crossed.


Epsiline’s WindEagle is positioned to support the Wind Industry in its transformation, by focusing on optimal performance through state-of-the-art sensors allowing for real-time and real-life data transmission, analysis and improvement.


[1] The impact of turbulence intensity and atmospheric stability on power deficits due to wind turbine wakes at Horns Rev wind farm – Authors: Hansen, Kurt Schaldemose; Barthelmie, Rebecca J.; Jensen, Leo E.; Sommer, Anders ;How turbulence can impact power performance – Authors: Lundquist, Julie; and Clifton, Andrew