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Photovoltaic Module Energy Yield Measurements: Existing Approaches and Best Practice

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Recording at https://youtu.be/kiLmtTvM_N0

In this Webinar we present a summary of the technical report ‘Photovoltaic Module Energy Yield Measurements: Existing Approaches and Best Practice’ [IEA-PVPS Report T13-11:2018], prepared within the Photovoltaic Power Systems Programme (PVPS) of the International Energy Agency (IEA).

The presentations will focus on the measurement of modules in the field for the purpose of energy yield or performance assessments. The aim is to help anyone intending to start energy yield measurements of individual PV modules to obtain a technical insight into the topic, to be able to set-up his own test facility or to better understand how to interpret results measured by third parties.

Therefore, fifteen Task members with experience in PV module monitoring from over 30 test facilities installed all over the world have been interviewed . The questionnaire covered all aspects, starting from general questions on the scope of testing to the test equipment, procedures, maintenance practice, data analysis and reporting.

The current practices for energy yield measurements of individual PV modules applied by the major international research institutes and test laboratories will be presented together with some best practice recommendations. Beside the recent research activities will be presented by the two presenters, including test results from different climatic regions and different technologies such as bifacial and colored modules.

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Photovoltaic Module Energy Yield Measurements: Existing Approaches and Best Practice

  1. 1. Photovoltaic Module Energy Yield Measurements: Existing Approaches and Best Practice Gabi Friesen, SUPSI-PVLab, Switzerland Johanna Bonilla, TÜV Rheinland, Germany Webinar - 12 march 2020
  2. 2. PVPS 2 What is IEA PVPS? • The International Energy Agency (IEA), founded in 1974, is an autonomous body within the framework of the Organization for Economic Cooperation and Development (OECD). • The Technology Collaboration Programme was created with a belief that the future of energy security and sustainability starts with global collaboration. The programme is made up of thousands of experts across government, academia, and industry dedicated to advancing common research and the application of specific energy technologies. • The IEA Photovoltaic Power Systems Programme (PVPS) is one of the Technology Collaboration Programme established within the International Energy Agency in 1993 • 32 members - 27 countries, European Commission, 4 associations • “To enhance the international collaborative efforts which facilitate the role of photovoltaic solar energy as a cornerstone in the transition to sustainable energy systems”
  3. 3. PVPS 3 Content • Introduction (G. Friesen) • IEA PVPS Task 13 Survey on best practice (G. Friesen) • Test environment and hardware: Requirements & recommendations (J. Bonilla) • Field experiences TÜV Rheinland (J. Bonilla) • Field experiences SUPSI PVLab (G. Friesen)
  4. 4. PVPS 4 Content • Introduction (G. Friesen) • IEA PVPS Task 13 Survey on best practice (G. Friesen) • Test environment and hardware: Requirements & recommendations (J. Bonilla) • Field experiences TÜV Rheinland (J. Bonilla) • Field experiences SUPSI PVLab (G. Friesen)
  5. 5. PVPS 5 What is it about? We talk here about:  medium to long term energy yield measurements  single module  real operating conditions … and not about:  system monitoring  measurements for STC extrapolation  energy rating
  6. 6. PVPS 6 Energy Rating vs. Energy Yield Standard Reference Conditions Short term measurements Field Conditions Long term measurements
  7. 7. PVPS 7 Energy Rating for different climates accord. IEC61853 part1: Irradiance and temperature performance measurements and power rating Pmax,Isc,Voc (G,T, AM1.5, AOI=0) IEC61853-1:2011 part3: Energy rating of PV modules IEC61853-3:2018 part4: Standard reference climatic profiles (5 data sets) IEC61853-4:2018 part2: Spectral response, incidence angle and module operating temperature measurements Isc(λ), Isc( AOI),Tmod(G,Tamb,wspeed) IEC61853-2:2016 kWh/Wp
  8. 8. PVPS 8 Why test in different climates? Different local conditions • irradiance • temperature • spectrum • soiling • … • different module rankings Validation of IEC 61853 approach! • and degradation rates How to perform comparable measurements!
  9. 9. PVPS 9 Energy Yield Monitoring - Reference documents DERLAB Technical Guideline (2012) Long-term PV Module Outdoor Tests IEC 61724-1 (2017) PV system performance Part 1: Monitoring IEA Technical report (2018) on Photovoltaic Module Energy Yield Measurements: Existing Approaches and Best Practice. MODULE MONITORING SYSTEM MONITORING ©TÜV Rheinland ISO 9060 (2018 update) Pyranometers and Pyrheliometers ©SUPSI
  10. 10. PVPS 10 IEA Survey on Best Practice Participants CSIRO – Australia AIT - Austria GANTNER – Austria KU LEUVEN - Belgium LABORELEC - Belgium IEE.AC - Cina University of Cyprus - Cyprus INES – France Fraunhofer ISE – Germany TUV Rheinland - Germany University of Utrecht - Netherlands SUPSI - Switzerland NIST - USA NREL - USA SANDIA - USA 5 5 5 new comers 2-4 years experienced 5-10 years veterans >10 years, >100 module types tested 8 2 4 1 none only electrical performance + module qualification + energy yield  15 test laboratories  33 test facilities distributed worldwide Climates Experience ISO17025 accreditation
  11. 11. PVPS 11 Fact Sheets
  12. 12. PVPS 12 General test requirements The measurement accuracy depends as much on the conditions around the measurement system as on the test equipment itself! test device • reference power (kWh/Wp) • selection of modules test site • irradiance uniformity • temperature uniformity • soiling • hardware exposure test equipment • hardware definition • Pm measurement accuracy • E measurement accuracy • G, Tmod measurement accuracy test processing • data quality • failure identification • reporting Survey questions: • Background • Sampling procedures • Test equipment • Stand configuration • Maintenance • Data processing • Uncertainties • Reporting
  13. 13. PVPS 13 Survey results: testing scopes and test requirements Module benchmarkingDegradation studies Model validations Example: Thin Film technologiesExample: PV Klima project Example: public NREL data • relative meas. accuracy • comparability of modules • long term data reliability • comparability of different sites • absolute measurement accuracy • synchronization of data 80%87% 73% Prototype testing Example: Coloured modules 67% ©TÜV Rheinland ©SUPSI PVLab ©SUPSI PVLab ©NREL
  14. 14. PVPS 14 Survey results: special test requirements Special modules Specific losses Example: BIPV modules Example: PID testing Special modules Example: Bifacial modules • different orientations and albedo • additional sensors • thermal insulation • additional sensors • 0-2000 bias voltage • monitoring of leakage currents ©SERIS©SUPSI PVLab©SANDIA
  15. 15. PVPS 15 Survey results: electrical performance measurement MPP tracker (MPPT)IV-tracer (IV) e.g. micro-inverters or high precision laboratory equipment IV-tracer with MPPT e.g. programmable bidirectional power supplies or capacitive loads e.g. all-in one solutions or assembled instruments. Example: Power one Example: Kepco Example: MPPT3000 0%19%81% The primary choice for test laboratories is to have the lowest measurement uncertainty and highest number of information (Isc, Voc, Pmax, Rs, Rsh, …). The low cost solution which would be sufficient for benchmarking lacks in information on tracking accuracy (static and dynamic).
  16. 16. PVPS 16 Survey results: irradiance measurement e.g. filtered and unfiltered cells for different spectral response e.g. fast responding broadband thermopile pyranometers e.g. spectrum radiometer Reference cellsPyranometers Spectrumradiometer Example: Kipp & Zonen CMP21 Example: ISE reference cell Example: EKO MS-711/712 100% 80% 73% The pyranometer is the primary choice for the calculation of the incoming broadband irradiance (comparability requirement), whereas the reference cells and the spectral irradiance data are used for the correction to standard test conditions (STC) or for other data analysis purposes.
  17. 17. PVPS 17 Survey results: temperature measurement Equivalent cell temperature calculation accord. IEC 60904-5 e.g. Pt100 RTD or thermocouples e.g. contact less thermometer Voc methodContact methods Infrared methods The most used is the contact method (73% RTD versus 27% thermocouples). The majority applies a single sensor to the module. Only 4 laboratories increase the number of sensors to 2-4 (non- uniformity or redundancy checks). The infrared method is only used for uniformity checks and the equivalent cell temperature for the analysis of backsheet-to-cell temperature differences and the monitoring of BIPV modules. 100%
  18. 18. PVPS 18 Survey results: maintenance measures daily - weekly daily - montly daily 1-5 times /week 1-10 min monthly ND >1 month daily-weekly ND 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 LOG BOOK VISUAL INSPECTION SENSOR CLEANING ALERT SYSTEM MODULE CLEANING PICTURES 12 11 11 9 9 8 8 7 6 3 3 Data filterMaintenance The level of quality control measures is generally very high and a large number of data quality markers are implemented. A case sensitive filtering of erroneous or low-quality data is so easily possible. E-mail alerts are the most commonly used tool for the notification of problems. • Optical inspection • Cleaning procedures • Maintenance report • Definition of error markers • Alert/intervention procedures • Filter procedures
  19. 19. PVPS 19 Survey results: module selection and screening 27% 6% 27% 20% 20% none STC only + VI/EL/IR + GD, MATR, SR, TK, … + INS/WL The sampling procedure and STC power used for the normalization of the module energy yield (Ya) and the module performance ratio (MPR) is different depending on the scope for which the measurements are performed or the testing capabilities of the laboratories. Legend: performance at (STC) visual inspection (VI) electroluminescence (EL) infrared imagining (IR) irradiance dependency (GD) temperature coefficients (TK) full matrix (MATR) spectral response (SR), insulation test (INS) wet-leakage (WL) 2-3 modules /type 1 reference module 1 or more spare modules 1 module/type 3-5 modules/type 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 MODULES TESTED IN THE FIELD MODULES STORED IN THE DARK SPARE MODULES • Test/spare modules • Reference modules (dark storage) • Electrical characterisation • Optical inspection • Safety testing
  20. 20. PVPS 20 Survey results: reference power Nominal STC power Pnom as stated by the manufacturer  commercial approach (sensible to labeling strategies) Stabilized real STC power Pstab as measured accord. IEC 61215  most suitable approach for benchmarking, lowest measurement uncertainty, degradation has to be controlled Actual STC power Pout as measured during outdoor exposure  most suitable for the study of meta-stabilities or degradation effects, higher measurement uncertainty, requires additional measurement of correction parameters, requires IV-tracer system
  21. 21. PVPS 21 Survey results: typical uncertainty contributions 𝑀𝑀𝑃𝑃𝑃𝑃 = ⁄𝐸𝐸 𝑃𝑃𝑠𝑠𝑠𝑠𝑠𝑠 ⁄𝐻𝐻𝐻𝐻 1000 𝑈𝑈𝑀𝑀𝑀𝑀𝑀𝑀 = 2 𝑈𝑈𝑃𝑃𝑠𝑠𝑠𝑠𝑠𝑠 2 2 + 𝑈𝑈𝐸𝐸 2 2 + 𝑈𝑈𝐻𝐻 2 2 + 𝑈𝑈𝑇𝑇 2 2 + 𝑈𝑈𝐴𝐴 2 2 + 𝑈𝑈𝑈𝑈 2 2 Error Source Value k Comment STC Power: UPstc module calibration 1.3-3% 2 accredited laboratory accuracy > 3% 2 STC correction of outdoor data data sheet value (in alternative to module calibration) > 3% 2 manufacturer tolerance (incl. meas. uncertainty) Irradiance/irradiation: UG, UH sensor calibration 1.0 – 5% 2 matched reference cell with T corrections 2-8% 2 typical pyranometer calibration calibration drift (%/year) 0.5 – 1% 2 soiling effects, sensor change Module performance: UPmax, UE, UYa, UMPR Power, Umpp current/voltage measurement 0.05 - 0.1% 2 data acquisition error 1% 2 error due to non-optimal measurement range selection maximum power 0.1 – 1.5% 2 error in maximum power point tracking, Equipment temperature error over expected T range (-10 to 30 °C) 0.0 – 1.0% 2 calibrate at 22 °C but use over much wider range. resistance losses 0-50% 2 2-vs.4-wire measurement capacitive effects 0-50% 2 module technology and sweep speed dependent Time, UT synchronization 0-1% 2 simultaneous or separate measurement of power and solar irradiance. Stable or variable sky conditions Alignment, UA module/sensors and module/module 0 - 5% 2 depends on average angle of incidence. 0.5 degree alignment error on a 60° incidence angle is 1.5% Uniformity, UU irradiance 1% 2 single module, large area, albedo, … temperature 1-4°C 2 single module, large area, wind , mounting, … Key performance indicator Module Performance Ratio (MPR) Uncertainty contributions Module Performance Ratio (MPR)
  22. 22. PVPS 22 Content • Introduction (G. Friesen) • IEA PVPS Task 13 Survey on best practice (G. Friesen) • Test environment and hardware: Requirements & recommendations (J. Bonilla) • Field experiences TÜV Rheinland (J. Bonilla) • Field experiences SUPSI PVLab (G. Friesen)
  23. 23. PVPS 23 Test environment and hardware: Requirements & recommendations 1. Mounting structure & surroundings • Rack layout • PV module installation • Shading • Albedo • Sensor positioning 2. Current- voltage measurements • Hardware solutions & configuration 3. Measurement of enviromental parameters • In-plane irradiance • Module temperature • Meteorological data • Spectral irradiance ©TÜV Rheinland©TÜV Rheinland ©TÜV Rheinland
  24. 24. PVPS 24 Test environment and hardware: Requirements & recommendations • Most used: fixed open rack tilted and oriented optimized depending on the latitude: latitude < 25° •latitude *0.87 •Minimum 10°, self-cleaning by rainfall 25°<latitude < 50° •latitude *0.87 + 3.1° latitude > 50° •Fixed tilt angle 45° From: www.solarpaneltilt.com • Coplanar installation of test modules and irradiance sensors 1. Mounting structure & surroundings: Mounting Layout IEC 60904-1
  25. 25. PVPS 25 Test environment and hardware: Requirements & recommendations 1. Mounting structure & surroundings: PV module installation • Temperature gradient from bottom to top is typically observed. • Infrared image of the entire test sample at irradiance >800 W/m² . ©TÜV Rheinland Source: Soltec,, Bifacial gain and production analysis at Bifacial Tracker Evaluation Center (BiTEC • Installation at ≥1 m from ground and at least 10 cm away from any other object. • In a row, outer test samples (left & right) tend to operate at a lower temperature. • Additional dummy modules shall be installed in these locations to reduce the environmental variability. Lower Temp Devices under test Dummy module Dummy module ©TÜVRheinland
  26. 26. PVPS 26 Test environment and hardware: Requirements & recommendations 1. Mounting structure & surroundings: PV module shading • Sources: buildings, trees, fence, elevation profiles of landscape, mounting clamps (at high AoI). • Available commercial analysis tools superimpose the sun path over the course of a year on a panoramic 360° AoI: Angle of incidence • For bifacial: cables, structure, frame of module (if appl.), junction box(es), torque tube (tracking), etc. • Shading can also be modeled with a computer aided design (CAD) software ©TÜV Rheinland ©TÜV Rheinland ©TÜV Rheinland
  27. 27. PVPS 27 Test environment and hardware: Requirements & recommendations 1. Mounting structure & surroundings: PV module shading Calculation of the shading limit angle for parallel arrangement of mounting racks. The shading limit coordinates are (SAC, SHC). L: 2 m Θ:35° Row length (DM): 15 m Row spacing (DR): 4 m SAC=75.1° SHC=4.2° 𝑯𝑯𝟐𝟐 = 𝑯𝑯𝟏𝟏 + 𝑳𝑳 ∗ 𝐬𝐬𝐬𝐬 𝐬𝐬 𝜽𝜽 𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫 = 𝑫𝑫𝑹𝑹 𝟐𝟐 + 𝑫𝑫 𝑴𝑴 𝟐𝟐 𝑺𝑺𝑺𝑺𝒄𝒄 = 𝟗𝟗𝟗𝟗𝟗 − 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂 𝑫𝑫𝑹𝑹 𝑫𝑫 𝑴𝑴 𝑺𝑺𝑺𝑺𝒄𝒄 = 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂 𝑳𝑳 ∗ 𝒔𝒔𝒔𝒔 𝒔𝒔 𝜽𝜽 𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫
  28. 28. PVPS 28 Test environment and hardware: Requirements & recommendations 1. Mounting structure & surroundings: Albedo (ground reflectance) • Monofacial PV modules: The steeper the modules are, the more reflected radiation they receive. • Bifacial PV modules: One of the main influencing factor for performance Uniform as possible (relevant surroundings taken into account) Boost ground shall consider seasonalities and mantainance practices. Height (>1m) ©TÜV Rheinland
  29. 29. PVPS 29 Test environment and hardware: Requirements & recommendations 2. Current- voltage measurements: Hardware solutions (1) MPPT (2) IV-tracer (3) IV-tracer with MPPT Description Maintains the PV Module at its maximum power point (Pmax). Measures the current from open circuit to short-circuit (or vice versa) Combination of (1) for MPPT and (2) for IV-tracing. Pros • In accordance to operation in PV array. • Power production integration for accurate energy yield measurement. • Lower cost From the IV scan : • Non-uniformity effects (ISC spread) • I-V correction parameters • Low irradiance behavior thermal coefficients • Power measurement during most of the operation + full benefit of IV curve measurements. • User can see impact of different MPP tracking methods and validate impact between MPP tracking, VOC or ISC conditions. Cons • No other parts of the IV curve are measured (e.g. Isc , Voc). • Isc operation shall be avoided: reverse biasing of cells (heating) • Higher cost.
  30. 30. PVPS 30 Test environment and hardware: Requirements & recommendations 2. Current- voltage measurements: Hardware characteristics and configuration DC Load: Dedicate current and voltage sensing lead (4-wire connections) Loads at controlled- temperature environment Requirements & accuracy of the equipment have to comply with IEC 60904-1 and IEC 61829-Voltages and currents instrumentation accuracy of at least ±0,2 %. I-V Scan Sweep time<1-2 sec. (scatter variable clouds) ≥50 measurement points, optimized at relevant parameters (ISC, VOC, PMAX) ≥10 Sample points per meas. point ©TÜV Rheinland
  31. 31. PVPS 31 Test environment and hardware: Requirements & recommendations 3. Measurement of enviromental parameters: Irradiance measurement ©TÜV Rheinland In-plane irradiance Tilted Pyranometer (ISO-9060) Direct normal irradiance Tracking First class pyrheliometer Diffuse horizontal irradiance Horizontal Pyranometerwith a with shading ball Global horizontal irradiance Horizontal Pyranometer©TÜV Rheinland ©TÜV Rheinland In-plane diffuse irradiance Tilted Pyranometer with a with shading ball Spectrally sensitive ‘effective’ irradiance Tilted Reference cell(s) spectrally /angular selective  Tilted sensors and modules coplanar installation at module close proximity and height.  Regulary cleaning and inspection.  Regulary calibration at least every two years and track the drift and bias on a quarterly basis
  32. 32. PVPS 32 Test environment and hardware: Requirements & recommendations 3. Measurement of enviromental parameters: Meteorological data & spectrum Ambient temperature (Tamb)± Win speed & direction Air pressure Precipitation Real humidity Soiling ratio/snow coverage Environmental sensors: IEC 61724-1 requirements Spectral irradiance • Measured spectrum- Spectroradiometer : • Simulated spectrum: Radiative Transfer Models (RTM), given a set of atmospheric parameters and geographic coordinates RTM has three categories: Sophisticated rigorous, parametric and statistical models Wavelength range depending on type: From 220-350 nm to 1100,1700 or 2500 nm ©TÜV Rheinland ©TÜV Rheinland
  33. 33. PVPS 33 Summary of best practices recommendations General requirements Measurement requirements & accuracy of the equipment IEC 60904-1 IEC 61829 Data acquisition requirements IEC 61724-1 (systems) • V-I instrumentation accuracy of at least ±0,2 %. • Irradiance: Calibrated reference device or a pyranometer, spectrally matched or correction. • Temperature accuracy ± 1°C with repeatability 0.5°C. • Coplanar installation of module and irradiance sensors ±2°. Less than 0.5° is recommended • Tamb accuracy better than 1K • Sampling interval: irradiance-depended parameters ≤1min, others 1-10 min • Measurement uncertainty of ±2.0% at the inverter level for a class A measurement (highest accuracy). For single modules, a better accuracy is aspired • Synchronization needed when comparing different devices • Number and positioning of sensors should be adapted to the scope and type of device under test. • All system maintenance, including cleaning of sensors and modules, or soiling state of modules, shall be documented • Data availability = recommended > 90%
  34. 34. PVPS 34 Content • Introduction (G. Friesen) • IEA PVPS Task 13 Survey on best practice (G. Friesen) • Test environment and hardware: Requirements & recommendations (J. Bonilla) • Field experiences TÜV Rheinland (J. Bonilla) • Field experiences SUPSI PVLab (G. Friesen)
  35. 35. PVPS 35 Field experiences TÜV Rheinland • MPP tracking (30 sec) • I-V curve (10 min) • Temperature of the back of the module, TBoM (30 sec) • In plane spectral irradiance (1min) • Meteorological data (30 sec) • Grear pyranometers (30 sec) Four unique outdoor testing locations with identical setups
  36. 36. PVPS 36 Field experiences TÜV Rheinland Cologne, Germany: August 2017 to July 2018 16 PV modules: monofacial vs. bifacial Mounting conditions 2 racks, fixed, pitch 11m Height above ground 1.5 m Tilt angle 35° South Ground gravel (albedo 30%) Annual in-plane solar irradiation HPOA, Annual 1231.1 kWh/m² Annual in-plane rear irradiation Hrear, Annual 169.4 kWh/m² HPoA_rear/HPoA_front [%] 13.8% 1st Rack 2nd Rack Monofacial c-Si Bifacial c-Si thin-film
  37. 37. PVPS 37 Field experiences TÜV Rheinland Cologne, Germany: 1st Rack [%] 1000/ / 2 , −             = ∑ ∑ WmG PP MPR months PoA STCMPP months MPP  MPR=1 The mean PV module efficiency corresponds to its STC efficiency  MPR≠1 Performance gain/losses due to module temperature, low irradiance behavior, spectral or angular effects, degradation or meta-stability More @ Bonilla J. et al (2018): Energy Yield Comparison between Bifacial and Monofacial PV Modules: Real World Measurements and Validation with Bifacial Simulations, EUPVSEC 2018. +11.6% +6.6%
  38. 38. PVPS 38 Field experiences TÜV Rheinland Tempe, USA: Sep 2018 to August 2019 11 PV modules: monofacial vs. bifacial Height above ground 1.3 m Tilt angle 33.5° South Ground Dark gravel + sand (albedo 13.4%) In-plane (front) solar irradiation HPoA_ front 2237.3 kWh/m² In-plane rear irradiation HPoA_rear, 229.2 kWh/m² HPoA_rear/HPoA_front [%] 10.2% 1st Rack ©TÜV Rheinland More @ Saal J. et al (2019): Energy Yield Comparison between Bifacial and Monofacial PV Modules: Real World Measurements in Desert climate (BWh), EUPVSEC 2019. +8.2%
  39. 39. PVPS 39 Field experiences TÜV Rheinland Thuwal, Saudi Arabia: Oct 18 to Sep 2019 8 PV modules: monofacial vs. bifacial Height above ground 1.3 m Tilt angle 25° South Ground Sand with gravel (albedo: 30.1%) In-plane (front) solar irradiation HPoA_ front 2029.2 kWh/m² In-plane rear irradiation HPoA_rear, 306.3 kWh/m² HPoA_rear/HPoA_front [%] 15.1% 1st Rack ©TÜV Rheinland +12.7%
  40. 40. PVPS 40 Field experiences TÜV Rheinland Chennai, India: Sep 18 to Aug 2019 8 PV modules: monofacial vs. bifacial Height above ground 1.3 m Tilt angle 15° South Ground White stones (Albedo 49.9%) In-plane (front) solar irradiation HPoA_ front 1857.1 kWh/m² In-plane rear irradiation HPoA_rear, 472.8 kWh/m² HPoA_rear/HPoA_front [%] 25.5% 1st Rack @TÜV Rheinland +22.4%
  41. 41. PVPS 41 Summary field experiences TÜV Rheinland Cologne (Germany) Tempe (Arizona) Chennai (India) Thuwal (Saudi-Arabia) Installation height above ground 1.5 m 1.3 m 1.3 m 1.3 m PV module Inclination and orientation 35° South 32.5 South 15° South 25° South Ground surface Colored gravel Dark gravel with sand White gravel Sand with gravel Ground albedo factor 0.3 0.14 0.5 0.3 Monofacial PV modules 12 modules 8 modules 4 modules 4 modules Bifacial PV modules 4 modules BF = 0.85 - 0.89 3 modules BF = 0.75 - 0.85 4 modules BF = 0.74 - 0.91 4 modules BF = 0.74 - 0.90 Monitoring period AUG 17 – JUL 18 SEP 18 – AUG 19 SEP 18 – AUG 19 OCT 18 – SEP 19 Ratio Rear/Front irradiance 13.8% 10.2% 25.5% 15.1% Average bifacial gain +11.6% +8.2% +22.4% +12.7%
  42. 42. PVPS 42 Content • Introduction (G. Friesen) • IEA PVPS Task 13 Survey on best practice (G. Friesen) • Test environment and hardware: Requirements & recommendations (J. Bonilla) • Field experiences TÜV Rheinland (J. Bonilla) • Field experiences SUPSI PVLab (G. Friesen)
  43. 43. PVPS 43 History of Outdoor testing at SUPSI 1991 set-up of R&D outdoor test facility 1993 1º test cycle 1994 2º test cycle 2006 new MPPT3000 2007 1º BIPV test stand 2008 11º test cycle 2009 industry oriented services 2010 remote testing for industry 2011 12º test cycle (4 years) on thin film modules 2-6º BIPV test stand 2018 13º test cycle colored and bifacial modules 2020 14º test cycle innovative modules (summer 2020) 1989-1996 MPPT 1º generation 2006-today MPPT3000 aprox. 70 units 2020 Gantner OTF 36 units ····· 3-10º test cycle meas. accuracy module technologies quality control meas. parameters building simulations extra stress factors 1991 outdoor testing 2001 indoor testing 2010 reliability testing Swiss Solar Price 2001 More then 190 different PV module types tested! 1996-2006 MPPT 2º generation ···
  44. 44. PVPS 44 Examples of outdoor testing facilities at SUPSI • Standard open-rack’s • Façade elements • Solar windows • Roof tiles • Bifacial modules • Antisoiling coatings • Colored modules • … Façade mock-up1° test cicle (1990-1993) 13° test cicle – bifacial modules Semi-transparent modules Roof mock-up 12° test cicle
  45. 45. PVPS 45 Example 1: colored modules Questions: • How much energy is lost by increasing the aesthetics of PV? • Can this loss be predicted by applying the measurement techniques proposed by the IEC 61853 Energy Rating standard part 1 and part 2? Project funded by the Swiss Federal Office of Energy (SFOE) under the project ENHANCE. 13° test cicle – colored modules (prototypes delivered by manufacturers or from pilot projects)
  46. 46. PVPS 46 Example 1: colored modules Answers: • Depending on the color technology, yield differences respect to the reference modules of 16-45% have been observed. • Light absorption, thermal, Isc (AOI + Spec), bifacial and low irradiance losses/gains were calculated. Thermal and bifacial gains partially compensates absorption losses. Project funded by the Swiss Federal Office of Energy (SFOE) under the project ENHANCE. 9.5% 4.8% -0.1% -3.9% -4.4% -5.3% -5.5% -23.8% -44.5% -28.3% -34.4% -16.0% -45.1% -38.8% ΔWh/W (Pmeas) ΔWh/m² (active area) For details see http://www.supsi.ch/isaac_en/eventi-comunicazioni/eventi/2019/2019-11-08.html
  47. 47. PVPS 47 Example 1: colored modules (white module) The white module reaches up to 10ºC lower temperatures respect to its reference module and a thermal gain of 3.3%. 0 10 20 30 40 50 60 70 08:38 10:19 12:00 13:40 15:21 17:02 18:43 Backofmoduletemperature(°C) transparent REF white light grey white flag terracotta red facade ©SUPSI
  48. 48. PVPS 48 Example 2: Degradation study on insulated modules Questions: • Does insulated BIPV modules are more affected by degradation than ventilated modules due to the higher temperatures? • Are the c-Si Glass/PVB/Glass modules less affected by degradation than the Glass/EVA/Tedlar modules? Tmax,vent = 67°C Tmax,ins= 92°C ©SUPSI
  49. 49. PVPS 49 Example 2: Degradation study on insulated modules Answers (ongoing activity done within PEARL PV COST action): • Different degradation rates was observed for the insulated respect to the ventilated modules. An increase in visual defects is observed for the insulted modules, but degradation rates are below 0.5%/year. Gok, A., et al. The influence of operating temperature and thermal insulation on the performances of different BIPV modules. Submitted to IEEE Journal of Photovoltaics After 5 years the insulated modules shows significantly more • micro cracks • grid finger interruptions G/EVA/BS G/PVB/G
  50. 50. iea-pvs.org Thank you Gabi Friesen, Johanna Bonilla – IEA PVPS Task13 Gabi.Friesen@supsi.ch Johanna.Bonilla@de.tuv.com http://www.iea-pvps.org/index.php?id=493 The technical Report is available for download under:
  51. 51. PVPS 51 Test environment and hardware: Requirements & recommendations 3. Measurement of enviromental parameters: Module temperature Contact method •Pt100 RTD (Resistance Temperature Detectors) and thermocouples •uncertainty: 0.1-0.25 °C (k=1) PT100s: lowest , but higher cost •Backsheet-to-cell temperature correction: Open-circuit voltage (Voc) method •IEC 60904-5: One-diode model to convert the voltage into a temperature •Calibration of the model : contact temperature measurements at different irradiances •0.1-0.6 °C, if well calibrated on module IR method •Most important role: operator training. •Best results are obtained at higher irradiances •Rapidly deployable in the field, and allow temperature differences to be easily observed (hot spot). •0.1-1.0 °C, depending on quality (and cost) ©TÜV Rheinland ©indiamart.com
  52. 52. PVPS 52 Test environment and hardware: Requirements & recommendations 2. Current- voltage measurements: Hardware characteristics and configuration MPP tracking •Avoid operation at local maximum instead of at the MPP. Fast and accurate algorithms are needed. •Know the tracking efficiency (static and dynamic) •Optimize algorithms of MPPT for all technologies independently of the fill factor (FF) to allow a fair comparison of the results. •Systematic cross-checking of the MPPT data with IV-data (different conditions and technologies) Data sampling and synchronization •Eliminate or use only high quality multiplexers •Synchronize the IV scans of all PV modules. •Recommended interval for IV scans is 1 min. •The data acquisition rate for environmental parameters should be in the range of 1-10 Hz, with averaging to a target sampling frequency of 1-5min. Shunts •Typical range is 1 mΩ to 10 mΩ. •calibration certificates • low thermal drift characteristics •Calibrated shunt resistance uncertainty ≤0.01% • The temperature coefficient should be below ±5 ppm/K (20 to 60°C).
  53. 53. PVPS 53 Test environment and hardware: Requirements & recommendations 2. Current- voltage measurements: Hardware characteristics and configuration Cables •Four-wire connections : Two for the module power and a current •two wires for a zero- current voltage measurement •Wires cross sectional area: >20 m distance: ≥6 mm2 . <20 m: 4 mm2 •If a four-wire connection is not made, cabling lengths should be minimized and the voltage drop should be characterized. Connectors •Standard PV module connectors (e.g., MC4) •Y-connectors for splitting the PV module connectors into a 4-wire configuration •Periodically check the connection resistance Fuses and overvoltage protection •Do not use protection devices or design them so that there is minimal impact on the signals (uncertainty) Checks and validation •Quantify the voltage drop at the short-circuit condition and calculate the difference between the measured and true module Isc •Quantify any current flow at the open-circuit condition and calculate the difference between the measured and true module Voc Calibration •Calibrate the measurement equipment according to manufacturer specifications •Calibrate at least every two years and track the drift and bias on a quarterly basis
  54. 54. PVPS 54 Recommendations on sampling procedures Benchmarking  clear and same procedure for all modules for a fair rating  consideration of manufacturer distribution and binning  selection from flasher list values  characterization and stabilization in accordance with IEC 61215 Long-term measurements  min 2 modules/type for cross verification  dark reference module for control measurements with solar simulator  Sorting of damaged/not representative modules (VI, EL)
  55. 55. PVPS 55 Recommendations for uncertainty declarations  measurement accord. best practice guidelines (minimize uncertainties).  calculation accord. standards e.g. ISO/IEC Guide 98-1 and ISO/IEC Guide 98-3.  there exist no unique reference conditions for the module energy measurements → calculation of uncertainties specific to time, location and test facility.  reporting of integration time (year, month, day, hour or minute). Ref: A. Driesse; PVSENSOR project, Daily and annual profile of the measurement error (minute and weekly resolution) caused by angle-of-incidence, spectrum and temperature for a reference cell located in Golden Colorado, tilted 40° South.
  56. 56. PVPS 56 Further analysis : Linear performance loss analysis (LPLA) Quantification of Energy Losses/Gain: ∆𝑀𝑀𝑀𝑀𝑀𝑀𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 = 𝜑𝜑𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 ∗ 𝐻𝐻𝑟𝑟𝑒𝑒𝑒𝑒𝑒𝑒 [𝑘𝑘𝑘𝑘𝑘/𝑚𝑚𝑚] 𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻 + 𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻 [𝑘𝑘𝑘𝑘𝑘/𝑚𝑚𝑚] More @ Schweiger, M. et al. (2017), “Performance stability of photovoltaic modules in different climates, Progress in Photovoltaics: Res. Appl. [DOI: 10.1002/pip.2904]. bifiAOISMMSOIL LIRRTEMPCAL MPRMPRMPRMPR MPRMPRMPR ∆+∆−∆±∆− ∆±∆−= %100 For all PV modules ΔMPRSOIL= -0.5% was considered, based on the measurements of two reference cells, one soiled and one regularly cleaned.

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