Vaisala Oyj Class A · OMXHEX:VAIAS
Vaisala Oyj Class A — Technical Presentation (2022)
19 slides from Vaisala Oyj Class A's technical presentation, 2022
Slide 1: Dual lidar: A cost-efficient and operational solution for offshore Wind Resource Assessments
Dual lidar: A cost-efficient and operational solution for offshore Wind Resource Assessments Dominic Champneys
Slide 2: Introduction to dual lidar
Introduction to dual lidar § A quasi-point measurement by pointing two scanning lidars at the same place § Can reconstruct the horizontal wind where the two beams intersect § A series of these measurements (“virtual cups”) can be arranged in a horizontal profile to create a “virtual met mast” § One
Slide 3: Why dual lidar for an offshore Wind Resource Assessment (WRA)?
Why dual lidar for an offshore Wind Resource Assessment (WRA)? § High flexibility to change between several measurement points § Can construct several “virtual met masts” § Easy to reconfigure to new locations § Very cost-efficient for the offshore WRA application § Cheaper and easier to install tha
Slide 4: Dual lidar horizontal wind reconstruction
Dual lidar horizontal wind reconstruction § If the measured radial velocity, 𝑉! , of a single lidar can be 𝑉! expressed in terms of vector components as: § 𝑉! = 𝑢. 𝑐𝑜𝑠𝜃. 𝑐𝑜𝑠𝜙 + 𝑣. 𝑠𝑖𝑛𝜃. 𝑐𝑜𝑠𝜙 + 𝑤. 𝑠𝑖𝑛𝜙 § Where 𝜃 is the azimuth angle and 𝜙 is the elevation angle § Then we…
Slide 5: Dual lidar reconstruction accuracy
Dual lidar reconstruction accuracy § To solve the reconstruction equation for u and v, we 𝑉! must assume that the term containing w vanishes to zero either because of vanishing vertical wind speed or elevation angle. 𝑢! &' 𝑉(' § = 𝑴!"#$%"# . 𝑣! 𝑉(! § The hat above the wind components…
Slide 6: Dual lidar error model
Dual lidar error model § Vaisala has developed a theoretical modelling tool that estimates the error of dual lidar measurements as a function of lidar, campaign, and atmospheric parameters. § The two largest components of dual lidar measurement error are: § Reconstruction error § Bias introduced by
Slide 7: Lidar positioning and campaign designs — Relative azimuth angles
Lidar positioning and campaign designs — Relative azimuth angles § Bias scales with: w = 1 m/s § The inverse of the sine of the difference between the azimuths § The sine of the alignment of the azimuths with the wind direction § In plain English: § You must keep the angle between the two beams a go
Slide 8: Lidar positioning and campaign designs — Elevation angles and range
Lidar positioning and campaign designs — Elevation angles and range ▪ At high ranges, small deviations in elevation angle can cause you to measure at a different point in the shear profile. ▪ 0.1° deviation in azimuth at 10km range = ~17m!! ▪ As this is caused by random deviations in elevation angle
Slide 9: Number of measurement points versus accumulation time
Number of measurement points versus accumulation time Less averaging Less More points More time to scan time per point (for representative targeted all points a given averaging estimation of period) mean wind Restricted
Slide 10: Number of measurement points versus accumulation time
Number of measurement points versus accumulation time Scan Time taken for Number of TI uncertainty configuration one complete samples per scan 10 minutes N = 100 1 virtual mast/2 ~6s ~100 δTI virtual cups 2 virtual mast/2 ~15s ~40 δTI * 1.36 virtual cups 3 virtual mast/2 ~24s ~25 δTI * 1.73 virtual
Slide 11: Numerical error estimations for nominal conditions
Numerical error estimations for nominal conditions ▪ Nominal error is estimated, considering the site of a dual lidar validation campaign done by Carbon Trust in 2014 – Dublin Bay ▪ Parameters: ▪ Vertical wind speed = 1.0 m/s ▪ Wind direction = 0° (North) ▪ Wind shear exponent = 0.11 Image source: C
Slide 12: Numerical error estimations for nominal conditions
Numerical error estimations for nominal conditions ▪ Nominal error is estimated, considering the site of a previous dual lidar validation campaign by Carbon Trust — Dublin Bay ▪ Parameters: ▪ Vertical wind speed = 1.0 m/s ▪ Wind direction = 0° (North) ▪ Wind shear exponent = 0.11 10km ▪ One virtual
Slide 13: Scan patterns
Scan patterns ▪ When choosing a scan pattern for multiple virtual met masts, a trade off has to be made between: ▪ The fastest pattern (more samples within the averaging period) and ▪ The most evenly spaced out (most representative averages) ▪ From internal tests performed by Vaisala, very few sampl
Slide 14: Practical installation guidelines
Practical installation guidelines ▪ Site selection and installation must be done with ensuring pointing accuracy as the highest priority. ▪ Transportation recommendations should be followed. ▪ The lidar should be installed on firm, flat, and rigid ground that will not change during the campaign (e.g
Slide 15: Perfecting the pointing accuracy of WindCube Scan
Perfecting the pointing accuracy of WindCube Scan ▪ The levelling of the lidar can be fine-tuned by adjusting its feet, using the in-built inclinometer. ▪ This can achieve an accuracy in pitch and roll of < ±0.1°. ▪ The levelling should be perfected through calibrating against a hard target, using t
Slide 16: Network and data retrieval recommendations
Network and data retrieval recommendations ▪ Data volumes can be high (GBs per lidar per day) and so considerations should be made toward an efficient “data pipeline.” ▪ Data should be regularly retrieved, using the API of WindCube Scan — recommended daily. ▪ If transferring to Vaisala for reconstru
Slide 17: Monitoring and data processing
Monitoring and data processing ▪ If reprocessed by Vaisala, the data provided includes statistical quantities over a 10-minute averaging period of: ▪ Radial wind speed ▪ Horizontal wind speed ▪ Wind direction ▪ Turbulence intensity ▪ Data availability – Combined and individual to each lidar ▪ Data m
Slide 18: Conclusions
Conclusions ▪ Dual lidar is robust, flexible, and cost-effective for offshore WRAs. ▪ Commercial dual lidar projects with our customers are already underway. ▪ Verification process against met mast is available. ▪ Attention must be paid to the siting, setup, and operation of a dual lidar campaign. ▪
Slide 19: VAISALA
VAISALA