阿特斯_NP_IEC_TC82_WG8_guidelines-testing-and-sorting-bifacial-cells_V5

CSIQ NASDAQ Guidelines for I-V measurement and sorting of bifacial photovoltaic cells in production line 2018.10.25 2Canadian Solar Inc. Contents Background Draft Proposal of Standard Appendix: Deviation Analysis of Bifacial Fitting Method 3Canadian Solar Inc. Background • The market share of bifacial cells has increased rapidly in 2008, particularly for PERC bifacial PV cells. • The ongoing standard IEC 60904-1-2 DTS is mainly for I-V measurement of bifacial PV modules, not suitable for bifacial PV cells. • It is of great urge to legislate standard for I-V measurement of industrial bifacial PV cells, especially for inline production. 4Canadian Solar Inc. Draft Proposal of Standard Guidelines for I-V measurement and sorting of bifacial photovoltaic cells in production line 5Canadian Solar Inc. 1. Scope • This part of IEC 60904 describes procedures for the measurement of the current-voltage (I-V) characteristics of bifacial photovoltaic solar cells in simulated sunlight and guidelines to the sorting of bifacial PV cells in production line. It is applicable to single bifacial PV cells. • The requirements for measurement of I-V characteristics of standard monofacial PV devices are covered by IEC 60904-1 and the additional requirements for measurement of I-V characteristics of bifacial PV devices are covered by IEC 60904-1-2 (DTS). • The purpose is to provide bifacial PV cells with precise I-V measurement and proper binning for bifacial module fabrication, in order to reduce mismatch loss and mitigate reliability risk. 6Canadian Solar Inc. 2. Normative references • IEC 60891, Photovoltaic devices – Procedures for temperature and irradiance corrections to measured I-V characteristics • IEC 60904-1, Photovoltaic devices – Part 1: Measurement of photovoltaic current-voltage characteristics • IEC 60904-1-2, Photovoltaic devices – Part 1-2: Measurement of current-voltage characteristics of bifacial photovoltaic (PV) devices (CDV?) • IEC 60904-2, Photovoltaic devices – Part 2: Requirements for reference solar devices • IEC 60904-3, Photovoltaic devices – Part 3: Measurement principles for terrestrial photovoltaic (PV) solar devices with reference spectral irradiance data • IEC 60904-4, Photovoltaic devices – Part 4: Reference solar devices - Procedures for establishing calibration traceability • IEC 60904-7, Photovoltaic devices – Part 7: Computation of the spectral mismatch correction for measurements of photovoltaic devices • IEC 60904-8, Photovoltaic devices – Part 8: Measurement of spectral responsivity of a photovoltaic (PV) device • IEC 60904-9, Photovoltaic devices – Part 9: Solar simulator performance requirements • IEC 61836, Solar photovoltaic energy systems – Terms, definitions and symbols 7Canadian Solar Inc. 3. Terms and definitions Bifacial fitting coefficient • Bifacial fitting coefficient is used to fit I-V characteristic of bifacial cells under double-side illumination by the measured I-V characteristics of bifacial cells under single-side illumination, typically at Standard Test Conditions (STC) unless otherwise specified. • It contains a series of fitting coefficients: ✓ the short-circuit current fitting coefficient 𝑘𝐼𝑠𝑐 ✓ the open-circuit voltage fitting coefficient 𝑘𝑉𝑜𝑐 ✓ the maximum power fitting coefficient 𝑘𝑃𝑚𝑎𝑥 Overall efficiency • Overall efficiency is the compositive efficiency in consideration of front side efficiency and rear side efficiency for bifacial cells. It is a parameter which would assess the power generation capacity of a bifacial cell in bifacial illumination. 𝜂𝐵𝑖𝐹𝑖𝑁 = 𝑃𝑚𝑎𝑥𝐵𝑖Fi𝑁𝑆 ×1000𝑊 ·𝑚−2 ✓ 𝑆 is the area of the cell. ✓ 𝑃𝑚𝑎𝑥𝐵𝑖Fi𝑁 is the overall maxim power at bifacial illumination condition 𝐵𝑖𝐹𝑖𝑁, which is STC on front side and 𝑁 on rear side. ✓ 𝑁 can be 0, 100, 200, 300, etc, corresponding to rear illumination conditions of 0𝑊 ∙𝑚−2、 100𝑊 ∙𝑚−2, 200𝑊 ∙𝑚−2, 300𝑊 ∙ 𝑚−2 etc. In these cases, illumination condition could be marked as 𝐵𝑖𝐹𝑖0, 𝐵𝑖𝐹𝑖100, 𝐵𝑖𝐹𝑖200, 𝐵𝑖𝐹𝑖300, etc. 8Canadian Solar Inc. 4. Apparatus 4.1 For measurement by double-side simultaneous illumination • A solar simulators system, as defined in IEC 60904-9, with the capability to provide illumination on both sides of the bifacial PV cells simultaneously and illumination on each side of the bifacial PV cells separately; • Front illumination must be able to provide irradiance levels above 1000 Wm-2. Rear illumination must be able to provide adjustable irradiance level from 0 to 1000 Wm-2. • The spectra of rear illumination should be the same as front illumination. • Optional simultaneous simulator systems are showed as below: Front simulator Sample Rear simulator Front simulator Sample Rear reflective light source Double simulator system Single simulator and reflector system 9Canadian Solar Inc. 4. Apparatus 4.2 For measurement by double-side sequential illumination • A solar simulators system, as defined in IEC 60904-9, with the capability to provide illumination on single side of the bifacial PV cells separately; • Front illumination must be able to provide irradiance levels above 1000 Wm-2. Rear illumination must be able to provide adjustable irradiance level from 0 to 1000 Wm-2. • The spectra of rear illumination should be the same as front illumination. • Optional sequential simulator system is showed as below: Front simulator Sample Rear simulator Sample Sequential simulator system Flipper 10Canadian Solar Inc. 5. Measurement method • Due to the mismatched spectral responses between front-side and rear-side of the bifacial PV cells, separate calibrations to both sides of the bifacial PV cells are necessary. • The measurement by double-side simultaneous illumination is preferred, especially for inline measurement in production line. • Alternatively, the measurement by double-side sequential illumination and determining overall I-V characteristics by fitting can be used. • Alternatively, if the variation in bifaciality of to-be-test bifacial PV cells is within ±5% range, the measurement by single-side STC illumination and determining overall I-V characteristics by fitting can also be used. 11Canadian Solar Inc. 5. Measurement method 5.1 Measurement by double-side simultaneous illumination Procedure • Step 1: Measure the front STC I-V characteristics (𝑃𝑚𝑎𝑥𝑓, 𝐼𝑠𝑐𝑓, 𝑉𝑜𝑐𝑓). • Step 2: Measure the rear I-V characteristics (𝑃𝑚𝑎𝑥𝑟, 𝐼𝑠𝑐𝑟, 𝑉𝑜𝑐𝑟). • Step 3: Measure the overall I-V characteristics, under STC illumination on the front side and 𝑁 𝑊 ∙ 𝑚−2 on the rear side (𝑃𝑚𝑎𝑥𝐵𝑖𝐹𝑖𝑁, 𝐼𝑠𝑐𝐵𝑖𝐹𝑖𝑁, 𝑉𝑜𝑐𝐵𝑖𝐹𝑖𝑁). • Typically, 𝑁 is 200. 𝐵𝑖𝐹𝑖200 means STC illumination on the front side and 200𝑊 ∙𝑚−2 on the rear side. • Step 1, step 2 and step 3 can be conducted in any sequence. Example of an irradiance and measurement procedure Step A: Rear-side STC irradiance, measure the rear STC I-V Step B: Bifacial irradiance, measure the overall I-V Step C: Front-side STC irradiance, measure the front STC I-V 12Canadian Solar Inc. 5. Measurement method 5.2 Alternative measurement by double-side sequential illumination Procedure • Step 1: Measure the front STC I-V characteristics (𝑃𝑚𝑎𝑥𝑓, 𝐼𝑠𝑐𝑓, 𝑉𝑜𝑐𝑓). • Step 2: Measure the rear I-V characteristics (𝑃𝑚𝑎𝑥𝑟, 𝐼𝑠𝑐𝑟, 𝑉𝑜𝑐𝑟). • Step 3: Calculate the overall I-V characteristics equivalent to double-side simultaneous illumination (𝑃𝑚𝑎𝑥𝐵𝑖𝐹𝑖𝑁, 𝐼𝑠𝑐𝐵𝑖𝐹𝑖𝑁, 𝑉𝑜𝑐𝐵𝑖𝐹𝑖𝑁, 𝐹𝐹𝐵𝑖𝐹𝑖𝑁) as below : • Step 1 and step 2 can be conducted in any sequence 𝑃𝑚𝑎𝑥𝐵𝑖𝐹𝑖𝑁 = 𝑃𝑚𝑎𝑥𝑓 +𝑃𝑚𝑎𝑥𝑟 × 𝑁1000×𝑘𝑃𝑚𝑎𝑥 𝐼𝑠𝑐𝐵𝑖𝐹𝑖𝑁 = 𝐼𝑠𝑐𝑓 +𝐼𝑠𝑐𝑟 × 𝑁1000 ×𝑘𝐼𝑠𝑐 𝑉𝑜𝑐𝐵𝑖𝐹𝑖𝑁 = 𝑉𝑜𝑐𝑓 +𝐿𝑛(1+𝐼𝑠𝑐𝑟𝐼𝑠𝑐 𝑓 × 𝑁1000)×𝑘𝑉𝑜𝑐 𝐹𝐹𝐵𝑖𝐹𝑖𝑁 = 𝑃𝑚𝑎𝑥𝐵𝑖𝐹𝑖𝑁𝑉𝑜𝑐 𝐵𝑖𝐹𝑖𝑁 ×𝐼𝑠𝑐𝐵𝑖𝐹𝑖𝑁 ✓ 𝑘𝑃𝑚𝑎𝑥, 𝑘𝐼𝑠𝑐 and 𝑘𝑉𝑜𝑐 are bifacial fitting coefficient of maximum power, short-circuit current and open-circuit voltage. 13Canadian Solar Inc. 5. Measurement method 5.3 Alternative measurement by single-side STC illumination Alternatively, if the variation in bifaciality of to-be-test bifacial PV cells is within ±5% range, the measurement by single-side STC illumination can be used. Procedure • Step 1: Sample the front STC and rear STC I-V characteristics of bifacial PV cells in the production line. Sampling rate greater than 1% is recommended. Then calculate the average maximum power bifaciality 𝜑𝑃𝑚𝑎𝑥 and short circuit current bifaciality 𝜑𝐼𝑠𝑐. • Step 2: For the to-be-test bifacial PV cells, measure the front STC I-V characteristics of to-be-test bifacial PV cells (𝑃𝑚𝑎𝑥𝑓, 𝐼𝑠𝑐𝑓, 𝑉𝑜𝑐𝑓). • Step 3: For the to-be-test bifacial PV cells, calculate the rear STC I-V characteristics of to-be-test bifacial PV cells (𝑃𝑚𝑎𝑥𝑟, 𝐼𝑠𝑐𝑟, 𝑉𝑜𝑐𝑟), using the sampled 𝜑𝑃𝑚𝑎𝑥 and 𝜑𝐼𝑠𝑐 as below: 𝑃𝑚𝑎𝑥𝑟 = 𝑃𝑚𝑎𝑥𝑓 ×𝜑𝑃𝑚𝑎𝑥 𝐼𝑠𝑐𝑟 = 𝐼𝑠𝑐 × 𝜑𝐼𝑠𝑐 14Canadian Solar Inc. 5. Measurement method • Step 4: For the to-be-test bifacial PV cells, calculate the overall I-V characteristics equivalent to double-side simultaneous illumination (𝑃𝑚𝑎𝑥𝐵𝑖𝐹𝑖𝑁, 𝐼𝑠𝑐𝐵𝑖𝐹𝑖𝑁, 𝑉𝑜𝑐𝐵𝑖𝐹𝑖𝑁, 𝐹𝐹𝐵𝑖𝐹𝑖𝑁) as below: 𝑃𝑚𝑎𝑥𝐵𝑖𝐹𝑖𝑁 = 𝑃𝑚𝑎𝑥𝑓 +𝑃𝑚𝑎𝑥𝑓 ×𝜑𝑃𝑚𝑎𝑥 × 𝑁1000×𝑘𝑃𝑚𝑎𝑥 𝐼𝑠𝑐𝐵𝑖𝐹𝑖𝑁 = 𝐼𝑠𝑐𝑓 +𝐼𝑠𝑐𝑓 ×𝜑𝐼𝑠𝑐 × 𝑁1000 ×𝑘𝐼𝑠𝑐 𝑉𝑜𝑐𝐵𝑖𝐹𝑖𝑁 = 𝑉𝑜𝑐𝑓 +𝐿𝑛(1+𝜑𝐼𝑠𝑐 × 𝑁1000)×𝑘𝑉𝑜𝑐 𝐹𝐹𝐵𝑖𝐹𝑖𝑁 = 𝑃𝑚𝑎𝑥𝐵𝑖𝐹𝑖𝑁𝑉𝑜𝑐 𝐵𝑖𝐹𝑖𝑁 ×𝐼𝑠𝑐𝐵𝑖𝐹𝑖𝑁 ✓ 𝑘𝑃𝑚𝑎𝑥, 𝑘𝐼𝑠𝑐 and 𝑘𝑉𝑜𝑐 are bifacial fitting coefficient of maximum power, short-circuit current and open-circuit voltage. ✓ These bifacial fitting coefficients are calculated by minimizing the deviation from the fitted overall I-V characteristics and the directly measured overall I-V characteristics by double-side simultaneous illumination. 15Canadian Solar Inc. 6. Sorting suggestion • The overall I-V characteristics is more relevant to the actual outdoor operation of bifacial PV cells and modules with both side illumination. • Sorting the bifacial PV cells by overall I-V characteristics is recommended in production line. • Alternatively, sorting the bifacial PV cells by front-side I-V characteristics only can be used. • Alternatively, sorting the bifacial PV cells by both front-side and rear-side I-V characteristics can also be used. 16Canadian Solar Inc. 6. Sorting suggestion 6.1 Sorting by the overall I-V characteristics • Sorting the bifacial PV cells by overall efficiency 𝜂𝐵𝑖𝐹𝑖𝑁 is recommended in production line. • The binning by overall efficiency with 0.1% gap (or 0.15%, 0.2% etc.) is recommended. • Sub-binning by short-circuit current 𝐼𝑠𝑐 or current at maximum power point 𝐼𝑚𝑝𝑝 in the same efficiency bin is highly desirable in order to reduce the mismatch loss in bifacial module fabrication. • In the case of rear illumination condition 𝑁 is 0 𝑊 ∙𝑚−2 , the bifacial PV cells are sorted only by front STC I-V characteristics. • The choose of rear illumination condition 𝑁 is determined by the manufacturer and customer needs. 17Canadian Solar Inc. 6. Sorting suggestion 6.2 Sorting by front-side I-V characteristics only • Sorting the bifacial PV cells by front-side I-V characteristics only. • The binning by front-side STC efficiency with 0.1% gap is recommended. • The sub-binning by 𝐼𝑠𝑐 or 𝐼𝑚𝑝𝑝 in the same efficiency bin is highly desirable. • The choose of efficiency gap for binning and sub-binning is determined by the manufacturer and customer needs. 6.3 Sorting by both front-side and rear-side I-V characteristics • Sorting the bifacial PV cells by both front-side and rear-side I-V characteristics. • The binning by front-side STC efficiency with 0.1% gap and also rear-side STC efficiency with 0.5% efficiency gap is recommended. • The sub-binning by 𝐼𝑠𝑐 or 𝐼𝑚𝑝𝑝 in the same efficiency bin is highly desirable. • The choose of efficiency gap for binning and sub-binning is determined by the manufacturer and customer needs. 18Canadian Solar Inc. 7. Report • Report should include at least: ✓ Specifications of the tested bifacial PV cells; ✓ Measurement method, i.e. double-side simultaneous illumination or single-side STC illumination; ✓ Rear illumination condition 𝑁, i.e. 0, 100, 200 or 300 𝑊 ∙𝑚−2. ✓ Measurement results, i.e. the front STC I-V characteristics (𝑃𝑚𝑎𝑥𝑓, 𝐼𝑠𝑐𝑓, 𝑉𝑜𝑐𝑓), the overall I-V characteristics (𝑃𝑚𝑎𝑥𝐵𝑖𝐹𝑖𝑁, 𝜂𝐵𝑖𝐹𝑖𝑁, 𝐼𝑠𝑐𝐵𝑖𝐹𝑖𝑁, 𝑉𝑜𝑐𝐵𝑖𝐹𝑖𝑁, 𝐹𝐹𝐵𝑖𝐹𝑖𝑁), bifaciality coefficient (𝜑𝑃𝑚𝑎𝑥 , 𝜑𝐼𝑠𝑐). ✓ Sorting information, i.e. average efficiency, average power and bifaciality coefficient of each binning. ✓ In case of measurement by single-side STC illumination, the RMSE deviation (Root Mean Square Error) between the fitted overall I-V characteristics and the measured overall I-V characteristics by double-side simultaneous illumination should be provided. ✓ Other measurement details, i.e. personnel, equipment, data. 19Canadian Solar Inc. THANKS Q&A 20Canadian Solar Inc. Appendix 1 Validation of fitting by single-side illumination: A Deviation Analysis 21Canadian Solar Inc. 1st round • Canadian Solar mono-PERC and multi-PERC bifacial cells, 1200 cells each. • The front STC, rear STC and bifacial illumination (STC on front side and 200 𝑊 ∙𝑚−2 on rear side) I-V characteristics are measured by the HALM bifacial I-V tester at AIKO Solar. 0 .7 7 00 .7 5 60 .7 4 20 .7 2 80 .7 1 40 .7 0 00 .6 8 60 .6 7 2 L S L U S L L S L 0 .6 6 3 目标 * U S L 0 .7 6 3 样本均值 0 .7 1 3 1 8 样本 N 9978 标准差（组内） 0 .0 0 7 4 4 0 3 1 标准差（整体） 0 .0 1 1 5 9 7 4 过程数据 Cp 2 .2 4 C P L 2 .2 5 C P U 2 .2 3 C p k 2 .2 3 Pp 1 .4 4 PPL 1 .4 4 PPU 1 .4 3 P p k 1 .4 3 C p m * 整体能力 潜在（组内）能力 P P M U S L 4 0 0 .8 8 P P M 合计 5 0 1 .1 0 实测性能 P P M U S L 0 .0 0 P P M 合计 0 .0 0 预期组内性能 P P M U S L 8 .7 0 P P M 合计 1 6 .2 7 预期整体性能 组内 整体 单晶双面电池实测效率双面率分布（7 1 .3 ± 5 %）的过程能力 Mono-PERC bifacial cells Average bifaciality 71.3% STDEV (1σ) 1.16% Multi-PERC bifacial cells Average bifaciality 73.6% STDEV (1σ) 1.34% 22Canadian Solar Inc. Step 1 Measure the I-V characteristics of 1200pcs sampled bifacial cells. Step 2 Calculate the overall I-V characteristics BiFi’ of the cells 1-600 by front STC, rear STC and initial fitting coefficient k. Step 3 Determine optimum fitting coefficient k by minimizing RMSE_1 for cells of 1-600 Step 4 Calculate the overall I-V characteristics BiFi’ and RMSE_2 of the cells 601-1200 by front STC, rear STC and optimum fitting coefficient k. Step 5 Sample the bifaciality by average of cells 1-50 (~4% sampling rate), to present the bifaciality of 1200pcs of cells. Step 6 Calculate the overall I-V characteristics BiFi’’ and RMSE_3 of the cells 1-1200 by front-side STC, sampled bifaciality 𝜑, and optimum fitting coefficient k. Front STC: 𝑃𝑚𝑝𝑝 𝑓 , 𝑉𝑜𝑐 𝑓 , 𝐼𝑠𝑐 𝑓 , 𝐹𝐹 𝑓 Rear STC: 𝑃𝑚𝑝𝑝 𝑟 , 𝑉𝑜𝑐 𝑟 , 𝐼𝑠𝑐 𝑟 , 𝐹𝐹 𝑟 BiFi: 𝑃𝑚𝑝𝑝 𝐵𝑖𝐹𝑖 , 𝑉𝑜𝑐 𝐵𝑖𝐹𝑖 , 𝐼𝑠𝑐 𝐵𝑖𝐹𝑖 , 𝐹𝐹 𝐵𝑖𝐹𝑖 𝑃𝑚𝑝𝑝 𝐵𝑖𝐹𝑖′ = 𝑃𝑚𝑝𝑝 𝑓 +𝑃𝑚𝑝𝑝 𝑟 ∗0.2∗�