Turbulence Intensity (TI) is a critical parameter in wind resource assessment and turbine design. But measuring it accurately from a Floating LiDAR System (FLS) presents a unique challenge: the measurement platform itself is moving.
The Offshore Wind Accelerator (OWA), run by the Carbon Trust, introduced Stage 2+ in Version 3 of its Floating LiDAR roadmap to provide greater confidence in the quality of TI measurements from floating LiDAR.
For developers using Floating LiDAR to inform increasingly complex offshore wind projects, this represents an important step forward.
Why is Turbulence Intensity important?
Before the widespread adoption of Floating LiDAR, turbulence measurements were typically collected using fixed meteorological masts.
These measurements feed into a number of important aspects of wind farm development and turbine design, including:
- Turbine site suitability and selection
- Assessment of turbine structural loading
- Wake modelling
- Large-rotor and high hub-height projects
- Floating offshore wind design
- Design optimisation and certification
Accurate TI data therefore has a direct influence on how confidently developers can make decisions about turbine suitability and project design.
The challenge with measuring Turbulence Intensity from Floating LiDAR
Floating LiDAR has brought significant advantages to offshore wind measurement. Systems can be deployed more flexibly and economically than fixed met masts, while providing high-quality wind measurements at multiple heights.
However, there is an important difference between measuring wind from a fixed platform and measuring it from a buoy – the buoy moves.
That movement can introduce additional variability into the measurements and, without appropriate correction, can result in TI being overestimated.
An overestimation of TI can become a problem when that data is used in turbine and project design. Accounting for greater levels of turbulence and loading than are actually present can contribute to more conservative design assumptions.
What does Stage 2+ demonstrate?
Stage 2+ was introduced by the OWA in its Version 3 roadmap for Floating LiDAR.
The assessment is designed to demonstrate that a floating LiDAR system has been subjected to a long-duration trial in continuous offshore conditions, with its TI measurements assessed against a trusted reference. That reference is traceable to a cup anemometer TI value.
This provides an important benchmark for assessing the quality and accuracy of TI measurements from a moving platform.
Not all Floating LiDAR systems have achieved Stage 2+ to date.
Partrac’s approach to corrected TI
The Stage 2+ certification, provides insight into the quality of the TI measurement and the sensitivities of the measurement across heights and various wind speeds. For developers, this enables better decision making in how the data is used, where the measurement is valuable and what uncertainties are propagated through the modelling chain.
For Partrac the results provided insight into measurement quality performance and limits and support data quality control procedures.
What could more accurate TI mean for developers?
The value of accurate TI isn’t simply about achieving a measurement KPI. It is about what that improved data enables further down the project development process.
Greater confidence in TI assumptions can help developers and designers make more informed decisions around turbine selection, loading and overall project design.
And where conservative assumptions can be reduced without compromising safety or performance, there may be opportunities to optimise designs, reduce material requirements and ultimately lower project costs.
For large-scale and floating offshore wind projects in particular, where turbine sizes and hub heights continue to increase, having confidence in the underlying atmospheric data becomes increasingly important.
Moving Floating LiDAR forward
Floating LiDAR has already transformed the way offshore wind developers collect metocean data. As the technology continues to mature, attention is increasingly turning towards the quality and suitability of the individual data products it provides.
The introduction of Stage 2+ is an important part of that progression, giving the industry a clearer framework for demonstrating the quality of FLS-derived TI.
At Partrac, we are continuing to develop and validate our approach to ensure that Floating LiDAR can provide the accurate, reliable data developers need, not just for wind speed, but for the wider range of parameters that influence offshore wind design.
Because when it comes to Turbulence Intensity, getting the number right matters.