The international standards and conformity assessment body for all fields of electrotechnology, the International Electrotechnical Commission (IEC), has published a standard to deliver the technical basis for the acceptance of lidar measurements for wind turbine power performance testing and wind resource assessments.
The release of the new standard, IEC 61400-12-1:2017, is considered a major milestone in lidar’s growing maturity, formally allowing lidar as a supplementary or alternative measurement technique to mast-mounted cup anemometers. ZephIR Lidar’s ground-based wind profiler, ZephIR 300, can therefore be used for formal measurement of a wind turbine’s power performance characteristics.
The IEC guidance now recognises the imperfect relationship between cup anemometers at hub height and full swept area of the turbine and the new guidance introduces the concept of “Rotor Equivalent Wind Speed” (REWS), which considers the impact of wind shear and wind veer on turbine power performance. This is especially relevant for ever-larger blade lengths and hub heights. Further, the use of ZephIR 300:
- Reduces planning permits required
- Removes the need for annual instrument maintenance and working at height
- Measures higher and more cost effectively than previously possible
The guide also covers resource assessment measurements for forecasting annual energy production, following the increased use of lidar by the wind industry offshore and onshore. There is an increasing number of offshore wind farms that have opted out of using tall masts and are instead deploying Continuous Wave (CW) lidar, as well as onshore sites all over the world moving to lidar for all stages of development and operation.
ZephIR Lidar has improved the performance of CW lidars over many years, showing consistency between units, sites and data. This experience has fed back into the development of the IEC guidance that has now been released.
Ian Locker, Managing Director, ZephIR Lidar stated: ‘What a fantastic result to see lidar implemented for formal wind turbine power curve measurements in the new IEC 61400-12-1 standard.
When we set out to create our first CW lidar over 15 years ago, we always hoped that our systems would play a role in changing the stance on wind measurements and masts in the wind energy industry. We very much look forward to the future and seeing how the wind industry will further expand on the use of wind lidar.’
Although the new IEC standard does not cover nacelle-mounted lidar, the ZephIR DM nacelle-mounted product has the capability of outputting a REWS-compliant set of measurements. A major benefit is that measurements can be acquired for any wind direction, covering the full 360 degrees of the wind turbine’s operation, allowing for an increased chance of detecting wind characteristics that are warranted without too much shear or turbulence present.
Even though the detected measurements are not considered formally IEC compliant, several independent studies have demonstrated their close equivalence. One of the biggest benefits of nacelle lidar can be realised offshore, where the cost implications are far greater - giving the opportunity of saving millions of pounds for the construction of tall masts.
ZephIR staff have been actively involved in the development of the new IEC standard, and also participate in the Power Curve Working Group, which strives to broaden warrantable wind characteristics and define a set of generic best practice guidelines.
Dr Scott Wylie, Wind Engineer at ZephIR and closely involved in the development of the standard, comments: “The new IEC standard represents a clear acceptance of the now mature lidar technology. It has come about through a major team effort by all sectors of the wind industry. We expect to see the use of lidar widen as a result of its publication.”