Measurement ยท 6 min read
Two ways to measure the same wind
A meteorological (met) mast carries instruments at fixed heights: cup anemometers for speed, vanes for direction, and sensors for temperature, humidity and pressure. It measures the wind directly, at the point where each sensor sits.
A ground-based wind LiDAR sits on the ground and uses laser light scattered by particles in the air to work out wind speed and direction at a series of heights above it. It measures remotely, across a volume of air rather than at a single point.
What each approach does well
- Met mast: long-term, direct measurement at fixed heights; a well-understood reference for advisers; low power demand once installed.
- Wind LiDAR: measurement up to and across the rotor without building a structure of that height; relatively quick to deploy and relocate; useful for profiling wind shear and veer.
Questions that usually decide it
- What will the data be used for? Early screening, a full energy yield assessment and power performance testing have different requirements.
- What will the technical adviser and lenders accept? Ask early. Many campaigns use a mast as the long-term reference and a LiDAR to extend measurements to hub height and above.
- What is the terrain like? In complex terrain, the way a ground-based LiDAR interprets the wind needs particular care, and advisers may ask for additional verification or correction.
- How tall would the mast need to be? Modern hub heights often sit well above the tallest practical mast for a site, so extrapolation or remote sensing becomes part of the plan.
- Power, access and security. A LiDAR needs a steady power supply on an unattended site; a mast needs space for foundations, guy anchors and permissions.
Combining both
A common arrangement is a met mast for the long-term reference record, with a LiDAR placed nearby for part of the campaign to measure the wind profile across the rotor. The two datasets are then compared and combined by the resource analyst.
Standards and guidance
Advisers commonly refer to the IEC 61400-50 series when assessing wind measurements: part 50-1 covers met mast and other mounted instruments, and part 50-2 covers ground-based remote sensing such as LiDAR. Industry guidance from bodies such as MEASNET is also widely used. Your adviser will specify what applies to your project.
In short
There is no single right answer. Decide what the campaign must prove, agree the approach with your technical adviser, and then design the measurement set-up, power and maintenance plan around it.