Offshore wind turbine power curve tests using lidar

Offshore wind turbine power curve tests using lidar 14 June 2021 Peter Clive

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Measuring Wind Offshore Met mast: £ 15 M 4

Measuring Wind Offshore Lidar and fixed platform: £ 7 M 5

Measuring Wind Offshore Floating lidar: £ 1 M 6

Measuring Wind Offshore Nacelle mounted lidar: £ 0. 2 M

Measuring Wind Offshore TP lidar: £ 0. 1 M 8

Capabilities Scanning lidar installed on the transition piece offers a variety of capabilities • Highest degree of IEC compliance • Measurements in global reference frame (making adjacent assets addressable) • Programmable configuration (making multiple use cases addressable) • Operates independently of turbine status (allowing replication of operational conditions during calibration, and avoiding complex direction calibration in situ) 9

Limitations Conventional scanning lidar is a 2 nd generation measurement system with important limitations • Trade off between time and space resolution (acquisition must alternate between measurement volumes) • Wind field reconstruction assumptions (w = 0, horizontal homogeneity, stationarity over acquisition timescales of final values i. e. time taken to acquire intermediate values in all the probe volumes defined by the scan geometry) 10

Installation 11

Installation 12

Installation 13

Installation 14

Installation 15

Installation 16

Setup Recommended wind speed measurement 4 D 3 D 2. 5 D Wind speed measured in this range 2 D D H/H 1 D Flow influenced by wind turbine

Setup D H/H 4 D 3 D 2. 5 D 2 D 1 D

Setup

Setup D H/H 4 D 3. 5 D 3 D 2. 5 D 2 D 1 D

Setup Lo. S 1 Lo. S 2 2. 5 D Lo. S 3 Lo. S 4 Lo. S 5 Freestream sector

Setup Alpha Ventus scan geometry • Simple arc scan • Reference mast ~ 1 km away • 30 degree azimuth range

Setup “Typical” setup • Compound scan geometry • RHI and PPI elements

Power Typical outputs / sample data Wind speed

Typical outputs / sample data

Typical outputs / sample data • • Agreement to within 0. 5% Lowest uncertainty compared to nacelle or mast anemometry

Typical outputs / sample data

Typical outputs / sample data sources of “black box” uncertainty • dominant contribution is uncertainty of reference anemometry during performance verification • further reduction of uncertainty will likely require multiple references during performance verification

References - procedures • Procedure: remote mast lidar measurements for offshore power curve tests Sgurr. Energy, 2013 • Specimen Lidar Calibration Test Report Sgurr. Energy, 2015 • Specimen Galion T-Piece Installation Method Statement Sgurr. Energy, 2015 • Specimen Galion T-Piece Installation and Commissioning Risk Assessment Sgurr. Energy, 2015

References - general • Offshore power curve tests for onshore costs: a real world case study Clive, P. J. M. , Schulte, B. , Pintilie, F. , Needham, S. , and More, G. , Wind. Europe, 2014 • Robust low cost offshore power curve tests with lidar: the t-piece method update Clive, P. J. M. , DEWEK, 2015, available here: • Power curve measurement with a sector scanning lidar from the TP and a nacelle lidar at Greater Gabbard Wagner, R. , and Vignaroli, A. , DTU Wind Energy GG I-0016 (EN), 2015 • Results from the Offshore Wind Accelerator (OWA) Power Curve Validation using Li. DAR Project Cameron, L. , Clerc, A. , Stuart, P. , Feeney, S. , and Couchman, I. , presented at the 17 th Meeting of the Power Curve Working Group (PCWG) at UL, Frankfurt, Germany, 20 th May 2016 • Arc scan wind measurements for power curve tests Clive, P. J. M. , Meas. Net meeting, 26 th September 2016 • Application of nacelle-based lidar and scanning lidar for power performance tests: experiences and results Lohbeck, U. , AWEA Windpower, 2017 • Verification of Lidars for Wind Energy Applications: Lidar Verification Protocol (LVP 0. 9) Clive, P. J. M. , Consortium for the Advancement of Remote Sensing, 2018

References – third party review • Galion lidar performance verification Gottschall, J. , Fraunhofer IWES, May 2013 • Review of Offshore Wind Turbine Power Curve Testing Procedure Using a Scanning Lidar on the Transition Piece - TPiece Method Albers, A. , Deutsche Windguard, June 2014 • Third party review of Wood's Transition-Piece (TP) Power Curve Testing (PCT) procedure Gottschall, J. and Lange, B. , Fraunhofer IWES, April 2018

References – third party review • Gottschall, J. , Fraunhofer IWES, May 2013 – scanning lidar’s arc scan capability allows measurements “where a horizontal distance between the location of the measurement device and its measurements is necessary. ” – “[Scanning lidar] may be recommended. . . for a power performance assessment offshore with the [scanning lidar] installed on the transition piece of the test turbine. ”

References – third party review • Albers, A. , Deutsche Windguard, June 2014 – DWG “considers the application of arc scanning lidars mounted on the transition piece of offshore wind turbines for the purpose of wind turbine power curve testing as an attractive alternative to other possibilities of testing power curves of offshore wind turbines” – “The T-piece method is almost fully consistent to the draft revision of the power curve testing standard [. . . ] The only non-compliance [. . . ] is that no monitoring met mast is applied” – “DWG does not see that as a relevant burden for an application of the T-piece method, as there are different other appropriate procedures available” – “Overall, DWG has high hopes for the T-piece method and is looking forward to perform power curve tests with this procedure”

References – third party review • Gottschall, J. and Lange, B. , Fraunhofer IWES, April 2018 – "The TP PCT procedure is almost fully in line with the requirements specified in the IEC 61400 -12 -1: 2017 standard. A single non-compliance arises from the missing monitoring met mast" – "Obviating the expense of a met mast is a key motivation for the adoption of lidar methods offshore" – "Non-compliance of any PCT procedure should be dealt with in accordance with section 10 (Reporting format) point l) 'Deviations from the procedure' – "The absence of a monitoring met mast may be considered an easily mitigated deviation by implementing the following actions • "Pre- and post-calibration [. . . ] fulfilling the requirements of L. 5. 4 [. . . ] on insitu comparison" • "Establishing a relationship with nacelle anemometry [. . . ] to identify obvious outliers [. . . ] addressing the requirements of sections L. 5. 2 and L. 5. 3"

Conclusions Scanning lidar installed on the transition piece walkway of the test turbine has a number of distinct advantages: • Highest degree of IEC compliance (equivalence to ground-based operation means the normative reference is IEC 61400 -12 -1: 2017) • Measurement range sufficient to acquire genuinely free stream measurements (3. 5 D and beyond, even for the largest turbines) • No need to calibrate turbine yaw position or measurement height (measures in global reference frame, rather than local frame of the nacelle) • Replication of operational conditions during calibration (exact same device configuration during operation and calibration) • Measurements in global reference frame mean the incident wind resource at adjacent assets can be addressed • Versatility: scan geometries can be modified and multiple measurement objectives can be considered, such as complex shear and wakes • Lowest cost of all available tried-and-tested options

Peter Clive Principal Wind Energy Consultant +44 173 785 6383 / +44 7739 909 040 Clive. P@bv. com 14 June 2021