Back to the programme printer.gif Print




Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Remote sensing: From toys to tools?' taking place on Wednesday, 12 March 2014 at 14:15-15:45. The meet-the-authors will take place in the poster area.

John Medley ZephIR Lidar, United Kingdom
Co-authors:

(1) ZephIR Lidar, Hollybush, Ledbury, United Kingdom

Printer friendly version: printer.gif Print

Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Muhammad Mughees Ahmad Mangat has an Honours Degree in Aerospace Engineering and a Masters in Renewable Energy from Kingston University London. After a period as a consultant at Isotrol, Spain, providing solutions for remote monitoring and control of renewable energy plants, he joined ZephIR Lidar as a Wind Data Analyst. His responsibilities include the validation and performance verification of the ZephIR Lidar anemometer, providing data analysis support for projects such as the remote sensing of turbulence, wind measurements in complex terrain, and power curve validation.

Abstract

The impact of tilt and inflow angle on ground-based lidar wind measurements

Introduction

Ground-based lidar is a valuable tool for providing finance-grade wind resource data. Hence, it is crucial that any sources of uncertainty are quantified. One such is the effect of an inadvertent tilt of the lidar unit, as can be caused by settling of the ground on which it sits, or from static tilts when mounted on a floating offshore platform. An investigation of the impact of tilt has been performed with a ZephIR 300 lidar at the Pershore remote sensor test site. The results are also used to verify measurements of inflow angle, which is relevant for turbine siting studies.

Approach

To assess the impact of static tilt on measured horizontal wind speeds, investigations have been performed in the laboratory against a calibrated moving belt, and against a 91m mast at the Pershore test site. ZephIR 300s were deployed with static tilt angles ranging from 5 to 15 degrees from the horizontal and data collected over a wide range of wind directions. Horizontal wind speeds measured by the tilted lidar are compared to mast measurements. In addition, a tilted lidar will measure a direction-dependent vertical wind speed. Results are compared to the laboratory trials and discussed in the context of theoretical modeling.

Main body of abstract

The Peshore remote sensing test site operated by Zephir Ltd provides an ideal location for testing lidars in general, and the impact of static tilts on horizontal wind speed measurements in particular. The simple site meets the IEC requirements for maximum terrain variation in all sectors and includes a well-instrumented IEC-compliant 91m mast. Co-located ZephIR 300s were deployed with static tilt angles ranging from 5 to 15 degrees from the horizontal. Data included in the investigation has been filtered for vertical wind components, using a sonic device on the reference mast, to ensure that the true wind flow was purely horizontal. ZephIR performance was assessed in terms of the least-squares regression parameters, gradient and R2 for a fit forced through the origin, from correlation of 10-minute averaged horizontal wind speed measurements against the mast.
Results show that, for static tilt angles of 10 degrees, ZephIRs demonstrate gradients within 2% of unity and R2 > 0.97, the criteria used for ZephIR’s standard performance verification, at all heights compared. A static tilt will also result in an induced vertical component, the magnitude of which can be derived from the tilt angle and the wind direction. The measured vertical wind speeds are found to be in strong agreement with the expected result.


Conclusion

This study has shown that ZephIR 300 is very insensitive to tilts up to 10 degrees for horizontal wind speed and direction. In addition, by tilting the lidar to mimic an inflow angle, excellent agreement has been obtained between measurements and actual inflow angle. These are important results in light of increased use of lidar for both onshore and off-shore wind resource assessment and should serve to increase user confidence that ZephIR 300 is capable of delivering bankable data in a wide range of deployments.


Learning objectives
Delegates will gain reassurance that one possible source of lidar measurement error can be neglected in its impact on horizontal wind speed. They will also learn of the validity of lidar inflow angle measurements, which is relevant to turbine siting studies.