The Fraunhofer IWES has presented a series of proofs of the quality and reliability of its FLS wind measurements. By achieving maturity level 3, the Fraunhofer IWES ZX wind lidar buoy joins the short list of stringently validated FLS types capable of delivering high-quality offshore wind measurements with minimised risk.
Detlef Stein, FLS expert at Multiversum GmbH
Our Floating Lidar System (FLS) has now been validated as Stage-3 (full commercial use) on the basis of several successfully completed met mast verification trials and commercial measurement campaigns. This is the highest level of validation on the Carbon Trust OWA Roadmap for commercial acceptance of floating Lidar technology [1]. Fraunhofer IWES is now part of a select group of FLS providers who have succeeded in demonstrating the best possible measurement accuracy and operational reliability. Lowering the operational risk and maximizing the quality of the field measurements is very important to provide the best possible estimate of the wind resource and the expected energy yield of a wind farm derived therefrom.
Our expertise with Floating Lidar Systems
Today, Floating Lidar Systems (FLS) are the established and de facto standard technology for offshore wind resource assessment measurements in the wind industry. Fraunhofer IWES has been at the forefront of this development, not only as an expert in the development of guidelines and recommendations, but also by producing its own system. After a first prototype was tested at the FINO1 meteorological mast in the German North Sea in 2013, Stage-2 level was achieved in 2016, and the institute currently operates eight buoys for commercial measurement campaigns to assess the met-ocean conditions for future offshore wind farms. The buoys can be equipped with either a ZX300M lidar (Stage-3) or WindCube 2.1 lidar (Stage-2) to meet customer-specific requirements without compromising on accuracy or reliability.
Fraunhofer IWES offers not only customizable measurement campaign delivery, but also cutting-edge data analysis, measurement concepts, and the possibility to include data modeling.
What is the Carbon Trust OWA Roadmap?
The Carbon Trust launched the OWA Floating LiDAR Systems Roadmap in 2013 – updated in 2018 [1] – which was quickly adopted by the industry as a recognized benchmark for product design, capabilities, accuracy, and performance. The roadmap brought rigor to the industry’s OEMs and to the pursuit of quantitative key performance indicators.
The roadmap consists of three levels, with Stage-3 representing the highest level of maturity for measurement accuracy and data availability. Whereas Stage-2 requires a single six-month verification trial campaign against an acceptable reference (met mast or fixed lidar), Stage-3 demands an additional series of verification and classification trials to meet stricter criteria as well as five commercial measurement campaigns of 12 months with continuous high data availability. Achieving Stage-3 requires a great deal of effort for a Floating Lidar System manufacturer and operator, particularly for those with a smaller fleet.
The next step for the standardization of FLS measurements will be introduced by the upcoming IEC 61400-50-4 standard, to which our experts at IWES are contributing.
How is Stage-3 maturity assessed?
For each Stage of the OWA Roadmap, independent experts are involved in validating the body of evidence, which is in the form of data sets and campaign reports. The Stage-3 maturity of the Fraunhofer IWES Wind Lidar Buoy, equipped with a ZX300M lidar, was assessed and approved by highly recognized wind remote sensing expert Detlef Stein (Multiversum GmbH) with feed-in elements reviewed by Oldbaum Services and another prominent expert consultancy.
Detlef Stein, FLS expert at Multiversum GmbH stated: »The Fraunhofer IWES has presented a series of proofs of the quality and reliability of its FLS wind measurements. By achieving maturity level 3, the Fraunhofer IWES ZX wind lidar buoy joins the short list of stringently validated FLS types capable of delivering high-quality offshore wind measurements with minimised risk.«
All the required verification and classification trials as well as two of the assessed commercial wind measurements took place in the German North Sea. Some of the accuracy results from the verification trials are presented below:
| Stage–3 Long trials results overview at North Sea reference met masts | |||||
| Stage-3 criteria | WLBZ#4 vs NSO met mast | WLBZ#4 vs FINO3 met mast | WLBZ#6 vs FINO3 met mast | WLBZ#7 vs FINO3 met mast | |
| Duration | > 90 days | 272 days | 192 days | 160 days | 187 days |
| Overall System Availability | > 97% | 100.0% | 99.8% | 100.0% | 100.0% |
| Overall Processed Data Availability | > 90% | 99.4% | 96.0% | 99.5% | 99.5% |
| @100±6 m MSL with WS > 2m/s | |||||
| Wind speed slope | 0.98-1.02 | 0.985 | 1.002 | 0.998 | 0.993 |
| Wind speed R² | > 0.98 | 0.996 | 0.994 | 0.994 | 0.994 |
| Wind direction slope | 0.97-1.03 | 0.988 | 0.997 | 0.998 | 0.997 |
| Wind direction offset | < 5° | 0.37° | 2.16° | -0.81° | 1.35° |
| Wind direction R² | > 0.97 | 0.997 | 0.985 | 0.995 | 0.996 |
The other three qualifying commercial campaigns for the FLS maturity assessment were provided by Titan Technologies, which produces the Fraunhofer IWES Wind Lidar Buoys under license and has been operating them independently since 2017, primarily in Asia. In the OWA Roadmap, the commercial campaigns are mainly evaluated for the reliability of the FLS and therefore the availability of the measurement datasets obtained.
What’s next for the Fraunhofer IWES Wind Lidar Buoys?
Fraunhofer IWES will continue to offer commercial measurement services, on its own or through partnerships. We will also continue to improve the FLS technology, conduct research on relevant wind industry topics, and take a leading role in further standardizing FLS measurements for the industry.
In particular, we have developed an advanced motion compensation method to produce more accurate Turbulence Intensity (TI) measurements from an FLS. This parameter is of great interest to the wind industry as it impacts the design of turbines and foundations.
References:
[1] Carbon Trust Offshore Wind Accelerator Roadmap for the Commercial Acceptance of Floating LiDAR Technology. The Carbon Trust, 2018.