System performance loss due to LeTID

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Energy (2017) 000–000 540–546 EnergyProcedia Procedia124 00 (2017) www.elsevier.com/locate/procedia

7th International Conference on Silicon Photovoltaics, SiliconPV 2017 7th International Conference on Silicon Photovoltaics, SiliconPV 2017

System performance loss due to LeTID System performance loss due to LeTID

The 15th International Symposium on District Heating and Cooling

Friederike Kerstenaa*, Fabian Fertigaa, Kai Petteraa, Bernhard Klöteraa, Evelyn Herzogaa, Friederike Kersten *, Fabian Fertig , Kai Petter , Bernhard Klöter , Evelyn Herzog , a b a Matthias Strobel , Johannes Heitmann b, Jörg W. Müllera Assessing theB. of using the heat Matthias B.feasibility Strobela, Johannes Heitmann , Jörgdemand-outdoor W. Müller a

HanwhaFreiberg, Q CELLSInstitute GmbH, 17-21,Leipziger 06766 Bitterfeld-Wolfen, temperature function for aofSonnenallee long-term district demand TU Bergakademie Applied Physics, Straße 23, heat 09599Germany Freiberg, Germany forecast b b

a

Hanwha Q CELLS GmbH, Sonnenallee 17-21, 06766 Bitterfeld-Wolfen, Germany

TU Bergakademie Freiberg, Institute of Applied Physics, Leipziger Straße 23, 09599 Freiberg, Germany

I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc Abstract a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Abstract b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c If not adequately suppressed, Light and elevated Temperature- Induced Degradation (LeTID) has44300 beenNantes, shownFrance to cause severe Département Systèmes Énergétiques et Environnement IMT Atlantique, 4 rue Alfred Kastler, If not adequately suppressed, Light andsilicon elevated Inducedwith Degradation has rear beencell shown to cause severe degradation of multicrystalline (mc-Si) solarTemperature cells and modules passivated(LeTID) emitter and (PERC). Within this degradation of multicrystalline (mc-Si) silicon solar cells and modules with passivated emitter and rear cell (PERC). Within this work, the system performance of LeTID-sensitive mc-Si modules is investigated when operated in temperate and mediterranean work, the system performance of LeTID-sensitive mc-Si modules is investigated when operated in temperate and mediterranean climates, and a correlation to predict the observed field performance based on accelerated laboratory testing is presented. Severe climates, a correlation to predict observed field performance based on accelerated presented. testing, Severe Abstractandinduced degradation by LeTID of up the to 7% in maximum output power is detected after onelaboratory thousand testing hours ofis laboratory degradation induced by LeTID to of~up to 7%of in field maximum outputtime power is detected after one LeTID-sensitive thousand hours of laboratory testing, 3 years installation in Cyprus. In contrast, modules installed in which is shown to correspond of field installation time inDue Cyprus. In the contrast, modules installed in in which is shown correspond tocommonly ~ 3 years District heating areof addressed intime the literature as to onelower of most LeTID-sensitive effective solutions fortemperature decreasing the Germany show atonetworks degradation 2.5% within the same period. irradiance values and module Germany show a degradation of 2.5% within the same time period. Due to lower irradiance values and module temperature in greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat Germany the LeTID rate is lower than in Cyprus. A significant dependence of system performance loss and energy yield due to Germany the LeTID rate than in Cyprus. Ainsignificant dependencedue of system performance loss energy yielddecrease, due of to sales. on Due to the changed climate conditions and building renovation policies, heat demand in theand future could LeTID installation siteisislower shown. Hence, the loss system performance to LeTID affects one-to-one the levelized cost LeTID on installation site isreturn shown. Hence,without the lossLeTID. in system performance to LeTID affectsinone-to-one thebe levelized cost by of prolonging the investment period. electricity (LCOE) compared to reference Furthermore, it isdue shown that LeTID the field can suppressed electricity (LCOE) tois reference without LeTID. itdemand is shown–site. that LeTID in the field can befor suppressed by The main scope of this paperQ.ANTUM to assesstechnology, the feasibility of Furthermore, using the of heat outdoor temperature function heat demand applying Hanwha Qcompared CELLS’ independently installation applying Q CELLS’ Q.ANTUM technology, independently forecast.Hanwha The district of Alvalade, located in Lisbon (Portugal), of wasinstallation used as asite. case study. The district is consisted of 665 buildings that vary in both construction © Authors. Published by Elsevier Elsevierperiod Ltd. and typology. Three weather scenarios (low, medium, high) and three district © 2017 2017 The The Authors. Published by Ltd. © 2017 The Authors. Published by Elsevier Ltd. of SiliconPVdeep). renovation scenarios were developed (shallow, To estimate the error, obtained Peer review by the scientific conference committee 2017 under under responsibility of PSE PSE AG. heat demand values were Peer review by the scientific conference committeeintermediate, of SiliconPV 2017 responsibility of AG. Peer reviewwith by the scientific committee SiliconPV 2017 under responsibility of PSE compared results from conference a dynamic heat demandofmodel, previously developed and validated byAG. the authors. The results showed when only weather change is considered, the margin of error could be acceptable for some applications Keywords: mc-Si PERC;that light-induced degradation Keywords: PERC;demand light-induced (the errormc-Si in annual was degradation lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. * Corresponding author. Tel.: +49 (0)of3494 Peer-review under responsibility the 6699-52134. Scientific Committee of The 15th International Symposium on District Heating and * Corresponding Tel.: +49 (0) 3494 6699-52134. E-mail address:author. mailto:[email protected] Cooling. E-mail address: mailto:[email protected]

1876-6102 2017demand; The Authors. Published Elsevier Ltd. Keywords:©Heat Forecast; Climatebychange 1876-6102 The Authors. Published by Elsevier Ltd. Peer review©by2017 the scientific conference committee of SiliconPV 2017 under responsibility of PSE AG. Peer review by the scientific conference committee of SiliconPV 2017 under responsibility of PSE AG.

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer review by the scientific conference committee of SiliconPV 2017 under responsibility of PSE AG. 10.1016/j.egypro.2017.09.260



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1. Introduction In 2012, mc-Si solar cells with plasma-enhanced chemical vapor deposited (PECVD) aluminum oxide (AlOx) passivated rear side have been reported to potentially degrade more than their Czochralski silicon (Cz-Si) counterparts at elevated temperatures [1]. Furthermore, mc-Si aluminum back-surface field (Al-BSF) solar cells have been shown to degrade more at elevated temperatures [2]. Both studies excluded the observed behavior to be due to boron-oxygen (BO) defect formation or iron-boron (FeB) pair dissociation, which has been speculated to be the root cause of the light-induced degradation (LID) observed at lower temperatures in mc-Si in previous studies, e.g. [3-8]. Since then, many groups have investigated the degradation of mc-Si, confirming cells with dielectrically passivated rear side to be significantly more affected than Al-BSF solar cells [9], showing local inhomogeneities of the defect characteristics [10-12], and more recently, ways to mitigate excessive LeTID [13-20]. As the observed LID is significantly more pronounced at elevated temperatures, Hanwha Q CELLS has introduced the term LeTID for "Light and elevated Temperature Induced Degradation" [14] as denomination for this new degradation mechanism at the time. If not suppressed, LeTID can lead to a loss in relative conversion efficiency of more than 10% [14]. LeTID is relevant under field conditions [14] and, therefore, needs to be suppressed to enable mass production of mc-Si solar cells with PERC technology. A methode to suppress LeTID in mass production of dielectrically passivated solar cells and modules has been developed by Hanwha Q CELLS [14] as part of its Q.ANTUM technology [21]. In this work, performance loss measurements for LeTID-sensitive modules in system installations at temperate and mediterranean climates and a correlation between field operation time and accelerated laboratory testing are shown. 2. Observations of LeTID on module level in the laboratory and field 2.1. Experimental LeTID-sensitive PERC modules were manufactured on standard industrial mc-Si substrates. Furthermore, neighbored mc-Si substrates were used to process modules with Q.ANTUM technology [21]. The module degradation experiments in the laboratory were performed at a temperature of 75°C in climate chamber, with excess carriers injected by current (CID, current-induced degradation). The current was set to a value to simulate the excess charge carrier density during operation at maximum power point (MPP) and 1 sun illumination, which was previously proposed as standard accelerated test conditions for LeTID [14]. With this method, a high number of modules could be tested in parallel at moderate cost in the laboratory. LeTID-sensitive PERC and LeTIDsuppressing Q.ANTUM modules were installed on outdoor test fields in Thalheim, Germany (DE) and Nicosia, Cyprus (CYP). The irradiance (Gmod) in module plane and module temperature (Tmod) were logged and averaged every 5 min. The energy yield of each system was averaged in 15 min intervals. All night values were eliminated by using a data filter which excluded all values with Gmod < 10 W/m2 due to increased measurement uncertainties. Once every three months, the modules installed in Germany and Cyprus were removed from the system racks and then tested by means of current-voltage measurements under standard test conditions (STC) in the laboratory. After each testing cycle, the modules were re-installed outdoors. 2.2. Outdoor behavior of LeTID-sensitive modules at temperate and mediterranean climate Fig. 1 shows the annual irradiance distribution measured at the module installation sites in Germany and Cyprus. Each Gmod bar shows the sum of irradiated energy for one year in 100 W/m2 steps. For Thalheim, located in temperate climate compared to mediterranean climate in Cyprus, lower irradiance values with a maximum of 150 kWh/m2 for the intervals 700 W/m2 < Gmod < 1000 W/m2 are measured. For Gmod values under 400 W/m2 and, therefore, comparably low-light conditions, the modules operate for ~ 30% of all operation time in Germany. In Nicosia, the highest irradiated energy value of 434 kWh/m2 was measured in the range of 900 W/m2 to 1000 W/m2. As shown in Fig. 2, these relatively high irradiance values around 1000 W/m2 in Cyprus resulted in comparably high module temperatures. In contrast to the depicted irradiation profile in Fig. 1, the module temperature measured in Nicosia showed a Gaussian distribution curve. The weighted average Tmod of 35°C to 40°C is shifted to higher

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temperatures compared to Thalheim (5°C to 10°C). In Nicosia, elevated temperatures with Tmod > 50°C occured for ~ 25% of field operation time per year.

Irradiance Gmod [W/m²] Fig. 1. Annual irradiance distribution of irradiated energy measured in module plane in Thalheim (DE) and Nicosia (CYP).

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Module Temperature Tmod [°C] Fig. 2. Annual module temperature distribution measured in Thalheim (DE) and Nicosia (CYP).



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Hence, these climatic conditions in Cyprus are well-suited for the characterization of LeTID in comparison to the temperate climate in Germany with annually ~ 70% of field operation time with Tmod < 25°C. 2.3. Comparison of field data and accelerated degradation tests in the laboratory As illustrated in the previous subsection, the real irradiation in module plane and module temperatures over several months and years at two different test fields in Cyprus and Germany were measured. Together with a correlation for the irradiance and temperature dependence of LeTID kinetic, a test-site-specific time constant corresponding to the proposed accelerated laboratory test performed at 75°C is deduced; e.g. 290 h laboratory test correspond to 1 year of field installation time in Cyprus. Fig. 3 shows as filled symbols the relative module power loss due to LeTID for LeTID-sensitive PERC and LeTID-suppressing Q.ANTUM outdoor-tested modules in Cyprus and Germany, referring to the lower x-axis (field operation time tField). Furthermore, the corresponding values for degradation tests in the laboratory are shown as open squares. The time-dependent relative module power loss under laboratory testing at 75°C with CID in MPP mode refers to the upper x-axis (tLab). A similar degradation behavior was determined for outdoor and laboratory tests, see Fig. 3. LeTID-sensitive PERC modules showed a significant loss in module power of ~ 7% due to LeTID, both in the field and under accelerated aging in the laboratory. Equivalently installed modules in Germany showed a degradation of ~ 2.5% for the same time period. Due to lower irradiance values and module temperature in Germany the LeTID rate is lower than in Cyprus. Fig. 4 shows the relative loss of specific yield on the left and LCOE on the right y-axis to reference system during 3 years of field installation in Cyprus. The loss in system output power due to LeTID shown in Fig. 3 affects one-to-one the energy yield and the LCOE compared to a reference system without LeTID. It can be seen that the LeTID-suppressing Q.ANTUM modules show a better specific yield and revenue than the reference system. The lower specific yield after approximately 2 years field installation time results from a soiling of the Q.ANTUM system in Cyprus, which was cleaned at the end of October. As shown in Fig. 3-4, applying the optimised defect engineered Q.ANTUM process, LeTID could be fully suppressed in the field. Additional Fig. 5 shows no degradation of Q.ANTUM modules also in the extended laboratory test up to a laboratory time of several thousand hours. With the developed model and test site specific time constant the laboratory degradation time of 4300 h can be calculated to correspond to 15 years of field installation in mediterranean climate.

Rel. Module Power Loss due to LeTID [%]

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Fig. 3. Relative module power loss due to LeTID during laboratory degradation time (upper x-axis) and field operation in Thalheim (DE) and Nicosia (CYP) (lower x-axis).

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Field Operation Time tField [a] Fig. 4. Loss in specific yield and LOCE relative to reference due to LeTID during field operation in Nicosia (CYP).

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Fig. 5. Time-dependent relative module power degradation due to LeTID. The lower x-axis corresponds to real field operation time in Nicosia (CYP) and the upper x-axis to CID laboratory time in MPP mode at 75°C in climate chamber.



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4. Conclusion The presented results show for the first time performance loss measurement due to LeTID in system installations in different climates. Long-term degradation tests in a climate chamber with LeTID-sensitive PERC modules resulted in performance loss of up to 7% and the same was observed in mediterranean climate in Cyprus in the first 3 years after installation. Equivalent modules installed in Germany showed a degradation of 2.5% within the same time period. This demonstrates the high LeTID susceptibility of mc-Si PERC modules without LeTID suppression in the field when being installed in areas with high module temperature such as in mediterranean climates. It is to be expected that the sensitive modules show a regeneration after more exposure time in field installation, as shown in [14]. Furthermore, it is shown that the observed degradation behavior in the field can be adequately predicted by using a test site specific time constant, which is easily adaptable to any climate zone. Hanwha Q CELLS’ Q.ANTUM modules are shown to suppress LeTID, both during outdoor installation in the field and in long-term degradation in a climate chamber. With the determined time constant the laboratory degradation time can be calculated to correspond to 15 years of field installation in mediterranean climate. Beyond that, the benefit of Q.ANTUM technology in energy yield and LCOE were shown in field installation. Acknowledgements The authors would like to thank George Makrides and George Georghiou from PV Technology Laboratory at University of Cyprus and the entire team of the Reiner Lemoine Research Center, Pilot Line, Energy Yield and Module Test Center at Hanwha Q CELLS for their contribution to this work. References [1] K. Ramspeck, S. Zimmermann, H. Nagel, A. Metz, Y. Gassenbauer, B. Birkmann, A. Seidl. Light induced degradation of rear passivated mcSi solar cells. Proc. 27th EU PVSEC 2012, Frankfurt, Germany, pp. 861–865. [2] F. Fertig, K. Krauß, I. Geisemeyer, J. Broisch, H. Höffler, J. O. Odden, A.-K. Soiland, S. Rein. Fully Solderable Large-Area Screen-Printed Al-BSF p-Type mc-Si Solar Cells from 100% Solar Grade Feedstock Yielding  > 17%: Challenges and Potential on Cell and Module Level. Proc. 27th EU PVSEC 2012, Frankfurt, Germany, pp. 1031–1038. [3] S. De Wolf, P. Choulat, J. Szlufcik, I. Périchaud, S. Martinuzzi, C. Häßler, W. Krumbe. Light-induced degradation of very low resistivity multi-crystalline silicon solar cells. Proc. 38th IEEE PVSC 2000, Austin, Texas, pp. 53–56. [4] B. Damiani, K. Nakayashiki, D. S. Kim, V. Yelundur, S. Ostapenko, I. Tarasov, A. Rohatgi. Light induced degradation in promising multicrystalline silicon materials for solar cell fabrication. Proc. 3rd World Conference on Photovoltaic Energy Conversion 2003, Osaka, Japan, pp. 927–30. [5] S. Dubois, N. Enjalbert, J. Garandet. Slow down of the light-induced-degradation in compensated solar-grade multicrystalline silicon. Applied Physical Letters 2008;93:103510. [6] J. Junge, A. Herguth, G. Hahn, D. Kreßner-Kiel, R. Zierer. Investigation of degradation in solar cells from different mc-Si materials. Energy Procedia 2011;8:52–57. [7] K. Peter, P. Preis, P. E. Díaz-Pérez, J. Theobald, E. Enebakk, A.-K. Soiland, A. Savtchouk, M. Wilson, J. Lagowski. Light induced degradation in multicrystalline solar grade silicon solar cells evaluated using accelerated LID. Proc. 26th EU PVSEC 2011, Hamburg, Germany, pp. 1856–1858. [8] K. Ounadjela, O. Sidelkheir, C.S. Jiang, M. M. Al-Jassim. Light-Induced Degradation in Upgraded Metallurgical-Grade Silicon Solar Cells. Proc. 38th IEEE PVSC 2012, Austin, Texas, pp. 2739–2743. [9] F. Fertig, K. Krauß, S. Rein. Light-induced degradation of PECVD aluminium oxide passivated silicon solar cells. Physical Status Solidi RRL 2014;9:41–46. [10] K. Krauß, F. Fertig, D. Menzel, S. Rein. Light-Induced Degradation of Silicon Solar Cells with Aluminium Oxide Passivated Rear Side. Energy Procedia 2015;77:599–609. [11] M. Selinger, W. Kwapil, F. Schindler, K. Krauß, F. Fertig, B. Michl, W. Warta, M. C. Schubert. Spatially Resolved Analysis of Light Induced Degradation of Multicrystalline PERC Solar Cells. Energy Procedia 2016;92:867–872. [12] T. Luka, S. Großer, C. Hagendorf, K. Ramspeck, M. Turek. Intra-grain versus grain boundary degradation due to illumination and annealing behavior of multi-crystalline solar cells. Solar Energy Materials and Solar Cells 2016;158:43–49. [13] S. Frigge, H. Mehlich, T. Grosse. LID free module made from high performance PERC solar cells. Proc. 31st EU PVSEC 2015, Hamburg, Germany. [14] F. Kersten, P. Engelhart, H.-C. Ploigt, A. Stekolnikov, T. Lindner, F. Stenzel, M. Bartzsch, A. Szpeth et al. Degradation of multicrystalline silicon solar cells and modules after illumination at elevated temperature. Solar Energy Materials and Solar Cells 2015;142:83–86.

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