Shu-Tsung Hsu, Yean-San Long and Teng-Chun Wu UNE NOUVELLE MÉTHODE DE TEST POUR LE TRANSPORT DE PALETTES DE PRODUITS SOLAIRES

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1 A NEW TEST METHOD FOR SHIPPING PALLETS OF SOLAR PRODUCTS Shu-Tsung Hsu, Yean-San Long and Teng-Chun Wu Center for Measurement Standards, Industrial Technology Research Institute, Hsinchu, Taiwan, R.O.C. IMETI 2015 J5009_SCI No. 16-CSME-05, E.I.C. Accession 3891 ABSTRACT The photovoltaic (PV) industry is expanding rapidly to meet the growing renewable-energy demands globally. The failure-rate analysis indicated that a large portion of the accelerated PV module qualification failures were related to the failure of PV cell itself, which was leading to the yield loss of PV products during shipping or transportation. Therefore, the damaged cell (or module) caused by shipping is always one of the serious problems to impact the long-term reliability of PV product. This paper aims to propose a new test method of reliability evaluation for shipping pallet of solar product. The first scenario is the test pallet shipped in fab (e.g., fork-lift truck or hand-pallet truck). The second scenario is the test pallet transported from fab to fab by different vehicle (e.g., truck, train, aircraft, and shipboard). Consequently, detailed results were applied to SEMI Doc and released as SEMI PV by voting in December The solar cell/module/system makers and buyers, or any other party interested like package design, can thus have a common document to refer to when desired. Keywords: solar; shipping; pallet. UNE NOUVELLE MÉTHODE DE TEST POUR LE TRANSPORT DE PALETTES DE PRODUITS SOLAIRES RÉSUMÉ L industrie photovoltaïque (PV) se développe rapidement afin de répondre à la demande globale d énergies renouvelables. L analyse statistique du taux de défaillance a démontré qu une des raisons principales de l accélération des rejets après le contrôle de la qualité venait d une défaillance des cellules PV ellesmêmes, ce qui pointe vers une baisse de rendement des produits PV due aux conditions de l envoi maritime ou du transport. Ainsi, les cellules (ou modules) endommagées en cours de transport constituent l un des principaux problèmes affectant la fiabilité à long-terme des produits PV. Cet article vise à proposer une nouvelle méthode d évaluation de la fiabilité des expéditions de produits solaires palletisés. Le premier scénario considère la pallette-test transportée dans l usine par le chariot-élévateur ou le transpalette manuel. Le second scénario considère la palette-test transportée d usine à usine par le biais de différents moyens de transport (par exemple, camion, train, avion et navire). Après quoi, les résultats détaillés ont été collectés selon le document SEMI 5431 et publiés sous le titre SEMI PV après avoir voté en décembre Les fabricants et acquéreurs de produits solaires, ou toute autre partie intéréssée comme les concepteurs d emballage, auront ainsi un document commun auquel ils pourront se référer chaque fois que nécessaire. Mots-clés : solaire; transport; palette. Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 4,

2 NOMENCLATURE PV c-si EL G rms P max R s R sh photovoltaic crystalline silicon electro-luminescence root-mean-square acceleration (g) maximum power (W) series resistance (ohm) shunt resistance (ohm) 1. INTRODUCTION For c-si technology, one of the main difficulties is to identify and eliminate the sources of mechanical defects such as thermo-elastic stress and cracks leading to the loss of wafer integrity and ultimate breakage of as-grown and processed Si cells. A significant challenge about using thinner crystalline silicon wafers for solar cell manufacture is the reduced yield due to increased cell breakage. Cell breakage generally depends on the stresses induced during the process, handling and transportation, and also relies on the presence of defects such as micro-cracks. Therefore, shipping damage is one of the key problems of photovoltaic (PV ) failures in the field now. In addition, to avoid cell breakages or cracks during transportation, the detailed documents and industry standards are necessary. Since 2009, three task forces (TF) were held in Taiwan to develop SEMI PV shipping Standards, such as Photovoltaic Module Vibration TF (2010), Photovoltaic Cell Vibration TF (2011) and Package Performance TF (2012). ITRI coordinated the TFs to set up a series of experiments [1 7], and focused on the performance evaluation for PV-cell and PV-module caused by transportation and shipping. Consequently, the TFs released SEMIPV [8] for PV-module in 2011 and SEMI PV [9 11] for PV-cell in Nevertheless, these two standards only focus on the scenario during transportation from fab to fab. This paper aims to propose a new test method to characterize c-si PV cell and module, especially for the coherent application scenarios occurred in fab (for process and handling) and from fab to fab (for transportation). The quality of PV product (cell and module) during different transit environments (e.g., hand-pallet truck, fork-lift truck, truck, train, aircraft, and shipboard) can be monitored and controlled. It also documents the best practices for reducing costs to benefit the end customers, further speeding up the development of package design for PV product shipping. Consequently, detailed results were applied to SEMI Doc and released as SEMI PV [12] by voting in December DEFECT OF PV CELLS INDUCED BY SHIPPING Recent failure-rate analysis indicates that a large portion of the accelerated PV module qualification failures are related to the failure of the cell itself [13]. The damage of shipping is always one of the top problems of the PV failures in the field. The cell breakage mostly depends on the stresses induced in the processing, handling and transportation, and also depends on the presence of defects such as cracks. The other main defects are broken cell into pieces, crack or micro-cracks, cell with chips, holes in cells and cell bow, etc. Ideally, PV cells with micro-cracks are already identified and rejected before they are integrated into the cell string. This is achieved on the production by using e.g. ultrasonic methods [14] and electroluminescence (EL) imaging [15]. However, even if this is done perfectly, during transportation, new micro-cracks may occur. It is therefore imperative to develop reliable guidlines to facilitate the decision of cell or module rejection. Damage of cells will remain undetected if it is not apparent at first glance or it cannot be traced back to its origin later when it is discovered. In addition, the defect of micro-crack seems not to affect power loss initially, but the expanding of micro-crack seriously exposed the high reliability problem. Therefore, 482 Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 4, 2016

3 Table 1. Reliability test for each shipping scenario of packaged solar product. Reliability test Scenario Allocation Incline impact shock Test pallet sliding along the inclined plane due to in fab (ISTA 3E) [16] improper operation Rotational flat drop shock Test pallet is turned by a corner or loaded by a in fab (ISTA 3H) [17] lifting rope Rotational edge drop shock Test pallet falling off due to improper operation in fab (ISTA 3E) Apply and hold compression Static stacking loading of test pallet in fab (ISTA 3E) Random vibration Shipping test pallet in fab by a fork-lift truck or a in fab (ISTA 2A) [18] hand-pallet truck Random vibration Transporting test pallet from a fab to the other fab by f2f (ASTM 4169) [19] vehicles such as truck, train, aircraft and shipboard degradation rate, induced by either micro-crack or abnormal electrical data (P max,r s,r sh ) [5], is more robust than breakage rate to qualify the quality of cells. In addition, for cell boxes (or carton) inside each layer of a package during shipping, the boxes allocated at top layer generally experienced higher G rms (response acceleration) than the boxes at bottom layer, which certainly induce the relative motions seriously between different cell boxes during shipping [5 7]. Furthermore, shipping package design need to evaluate how to avoid unit s resonance frequency happened during transit mean frequency, particularly in low frequency region, which could make shipping cells have more excited vibration response and lead to damage cells during transportation [7]. 3. SCENARIOS FOR SIMULATION SHIPPING SOLAR PRODUCT The scenario for shipping PV product in fab is handled by hand-pallet truck or fork-lift truck, the other condition in the transportation environment from fab to fab (f2f) is using vehicles such as truck, train, aircraft and shipboard. For a packaged PV-cell (or PV-module) or one-unit pallet composed of many PV-cell (or PVmodule), these test methods are based on the following application scenarios (Table 1), as appropriate. 4. TEST SAMPLE OF SOLAR PRODUCT 4.1. PV-Cell of Test Pallet There are variable PV-cell packing format to be simulated in the transportation test. For example, a test block means the stacking PV-cell in one block (Fig. 1a), a test carton means the stacking blocks of PV-cell in one carton (Fig. 1b), and a test pallet means the complete packaging and filled unit- loads (or cartons) of PV-cell for testing (Figs. 1c d) PV-Module of Test Pallet There are two scenarios of test pellet to simulate PV-module during shipping or transportation. One is the stacking PV-module for shipping in fab (Fig. 1e), and the other is the complete packaged PV-module for transportation from fab to fab (Fig. 1g). Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 4,

4 484 Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 4, 2016 Fig. 1. (a) one carton of PV-cell (in fab); (b) stacking cartons of PV-cell (in fab); (c) packaged PV-cell for vibration test; (d) packaged PV-cell for transportation (f2f); (e) stacking PV-module (in fab); (f) packaged PV-module for vibration test; (g) packaged PV-module for transportation (f2f).

5 Table 2. Pre-test and post-test examination. Test item Test condition PV-cell PV-module Visual inspection Carefully inspect each cell under an IEC [25] illumination of not less than 1,000 lux Maximum power determination IEC [26] IEC determination 5. APPARATUS FOR RELIABILITY TEST In order to simulate each scenario for shipping solar product, the necessary equipment for reliability test in this paper is as follows: temperature and humidity recording apparatus (ASTM D4332 [20]), chamber and control apparatus (ASTM D4332), incline impact tester (ASTM D880 [21]), rotational edge drop test system (ASTM D6179 [22]), rotational flat drop test system (ASTM D6179), compression test system (or weight and load spreader) (ASTM D642 [23]), and random vibration test system (ASTM D4728 [24]). 6. TEST METHOD AND TEST SEQUENCE This paper presents a new test method for determining performance of c-si PV-cell and PV-module in fab during shipping (handled by fork-lift truck or hand- pallet truck) or in transportation environment (shipped by truck, train, aircraft or shipboard) from fab to fab. This work aims to simulate and consider all the handling, process and transportation scenarios for test pallet of solar product. Test pallet means a complete, filled unit- load during the test of PV-cell or PV-module (Figs. 1c d and e g), based on different application scenario (Table 1) and specific testing procedure (Fig. 2). The testing flow includes pre-test, reliability test and post-test Pre-Test Examinations and Requirements 1. PV product: The pre-test examination consists of a selection of IEC tests and measurements on the samples according to the items listed in Table 2. If a test of sample fails, it shall be replaced by a good sample. All of recommendable samples are in the same efficiency classification. All the samples visual inspection, maximum power, and sample condition shall be recorded. 2. Packaged materials: Record the outside dimensions of length, width and height (L W H) for each test package appearance Reliability Test In accordance with standards include ISTA and ASTM, five reliability tests shall be performed for test pallet of PV product, and the test sequence is indicated in Table Post-Test Examinations and Requirements 1. PV product: The post-test examinations consist of a selection of IEC tests and measurements on samples according to the items listed in Table 2. All the test samples visual inspection, maximum power, cell condition shall be recorded. 2. Package materials: Record the outside dimensions of length, width and height (L W H) for each package of PV product by visual inspection, and take photos of package appearance for reference. No serious distortion of appearance, no damage which would influence the protective performance of package materials is required [27]. Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 4,

6 Fig. 2. Test plan and testing procedure for pallet test of PV-cell or PV-module ( means test item for cell or module; only for package). 3. Power degradation (%): The average power (P max ) degradation of packaged PV-cell (or PV-module) does not exceed 3% after the test. 4. Breakage rate (%): Breakage rate is defined as the broken cells over to the total cells in each carton, and average breakage rate does not exceed 1% at least [9]. 486 Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 4, 2016

7 Table 3. Reliability test and test level. Reliability test (1 5) Test level Temperature and humidity (ASTM D4332) ambient Controlled temperature and humidity (ISTA 3E) temperature and humidity chosen from chart 1. incline impact shock (ISTA 3E) V = 1.1 m/s 2. rotational flat drop shock (ISTA 3H) H = 100 mm 3. rotational edge drop shock (ISTA 3E) H = 200 mmm 4. apply and hold compression (ISTA 3E) calculated test load (kg) 5. random vibration (ASTM 4169) overall G rms level, 0.52g, Hz, 180 min. Table 4. SEMI PV shipping standards [28, 29]. Note: 1. Pre-test; 2. Reliability test; 3. Post-test; refer to Table 2. Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 4,

8 7. CONCLUSIONS This paper proposed a new test method to characterize for shipping pallet of solar product, especially for the coherent scenarios occurred in fab (for process and handling) and from fab to fab (for transportation). Results were applied to SEMI Doc and released as SEMI PV by voting in Table 4 also analyzed all the SEMI shipping standards includes SEMI PV , SEMI PV and SEMI PV [27]. Therefore, PV products makers and buyers, or any other party interested like package designers, can thus have a common testing standard to refer to when desired. Furthermore, this work is helpful to monitor the reliability and performance of PV product, and documents the best practices for reducing costs to benefit the end customers. ACKNOWLEDGEMENTS The authors appreciate the contributions from the Taiwan SEMI Package Performance TF, especially the co-leaders David Lee ( Jay Lin ( and Ivan Chou ( REFERENCES 1. Chen, C.W., Lin, I., Liao, J.Y., Wu, H.S., Wu, T.C. and Lee, K.T., Power degradation of crystalline-silicon PV module in transporting environment, in Proceedings 26th European PV Solar Energy Conference, Hsu. S.T., Long, Y.S., Wu, T.C., Lee K.D. and Chou, Y.H., Characterization of crystalline silicon PV cells in truck transportation environment, in Proceedings China PV Technology International Conference, Ke, K.H., Hsu, S.T., Hsu, T.C., Lee, K.D. and Long Y.S., Definition, classification and inspection methods of cracks in photovoltaic cell Cracks induced by vibration caused by transportation", in Proceedings China PV Technology International Conference, Ke, K.H., Hsu, S.T., Chen, Y.T., Hsu, T.C. and Long Y.S., Classification and inspection methods of cracks in photovoltaic cell Induced by transportation vibration, International Photovoltaic Science and Engineering Conference, Hsu, S.T. and Long, Y.S., Characterization and defect mechanism of c-si photovoltaic cells in truck and air transportation environment, International Photovoltaic Science and Engineering Conference, Hsu, S.T., Long, Y.S. and Li, Y.T., Characterization of solar cells in transportation, in Proceedings 40th IEEE Photovoltaic Specialists Conference, Hsu, S.T., Long, Y.S. and Ma, H.C., Vibration influence for transporting photovoltaic cell, Applied Mechanics and Materials, Vol , pp , SEMI PV , Test method for mechanical vibration of crystalline silicon photovoltaic (PV) modules in shipping environment. 9. SEMI PV , Test method for mechanical vibration of c-si PV cells in shipping environment. 10. Hsu, S.T., Long, Y.S. and Wu, T.C., Development a new standard for transport simulation on complete PV-cell shipping units, in Proceedings International Photovoltaic Science and Engineering Conference, Hsu, S.T. and Ma, H.C., Standardize test methods for determining performance of solar cells and package during transportation, in Proceedings 29th European PV Solar Energy Conference, SEMI PV , Test methods for performance criteria of photovoltaic cell and module package. 13. TamizhMani, G., Li, B., Arends, T., Kuitche, J., Raghuraman, B., Shisler, W., Farnsworth, K., Voropayev A. and Parker, D., Failure analysis of module design qualification testing-iii: vs vs , in Proceedings 35th IEEE Photovoltaic Specialists Conference, June, Dallas, W., Polupan, O. and Ostapenko, S., Resonance ultrasonic vibrations for crack detection in photovoltaic silicon wafers, Meas. Sci. Technol. Vol. 18, pp , Fuyuky, T., Kondo, H., Yamazaki, T., Takahaschi, Y. and Uraoka, Y., Photographic surveying of minority carrier diffusion length in polycrystalline silicon solar cells by electroluminescence, Applied Physics Letters, Vol. 86, p , ISTA 3E, Unitized loads of same product. 488 Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 4, 2016

9 17. ISTA 3H, Performance test for products or packaged-products in mechanically handled bulk transport containers. 18. ISTA 2A, Packaged-products weighing 150 lb (68 kg) or less. 19. ASTM D4169, Standard practice for performance testing of shipping containers and systems. 20. ASTM D4332, Standard practice for conditioning containers, packages, or packaging components for testing. 21. ASTM D880, Standard test method for impact testing for shipping containers and systems. 22. ASTM D6179, Standard test methods for rough handling of unitized loads and large shipping cases and crates. 23. ASTM 642, Standard test method for determining compressive resistance of shipping containers, components, and unit loads. 24. ASTM D4728, Standard test method for random vibration testing of shipping containers. 25. IEC 61215, Crystalline silicon terrestrial photovoltaic (PV) modules Design qualification and type approval. 26. IEC , Photovoltaic devices Part 1: Measurements of photovoltaic current-voltage characteristics. 27. SEMI PV , Specification for package protection technology for PV modules. 28. Hsu, S.T., An overview of photovoltaic products transportation standards: A case study developing SEMI PV standards in Taiwan, in Proceedings International Photovoltaic Science and Engineering Conference, Hsu, S.T., Research of photovoltaic products shipping test methods standards, Journal of Applied Sound and Vibration, Vol. 5, No. 1, pp. 1 10, Transactions of the Canadian Society for Mechanical Engineering, Vol. 40, No. 4,