Systematic PV module optimization with the cell-to-module (CTM) analysis software

By Max Mittag, Max Mittag studied industrial engineering and management at the Freiberg University of Mining and Technology. In 2010 he completed his diploma thesis at Fraunhofer ISE and joined the department for photovoltaic modules. His current work includes the cell-to-module efficiency analysis and the development new photovoltaic module concepts.; Matthieu Ebert, Matthieu Ebert holds a ma s t er de g r e e i n r e n ewa b l e en e r g y s y s t ems f rom t h e University of Applied Science, Berlin. Before joining Fraunhofer ISE in 2011 he completed research stays at the Fraunhofer CSE in Boston and at the Australian National University in Canberra. Since 2011 he has been undertaking research on PV module technology. Since 2015 he has led the module efficiency and new concepts team. His main areas of research are module efficiency and CTM analysis, building-integrated PV and PV for automotive applications.

Understanding power losses in technical systems is vital to improve products in every industry and photovoltaic modules present no exception. Losses in solar modules are caused by optical and electrical effects or are determined by simple module geometry through inactive areas.

Cell modifications for preventing potential-induced degradation in c-Si PV systems

By Gaby Janssen, Gaby Janssen obtained her Ph.D. in quantum chemi s t r y f rom the University of Groningen in the Netherlands. At ECN she has been working as a research scientist on the simulation, characterization and optimization of materials for energy conversion technologies. Since 2011 she has been focusing on simulation and modelling of PV cells and modules; Maciej Stodolny, Maciej Stodolny received his M.Sc. in applied physics from Gdansk University of Technology in Poland. His Ph.D. research at ECN and the University of Twente dealt with Cr tolerance of solid oxide fuel cells. He now works as a solid state physicist and materials scientist at ECN Solar Energy.; Bas Van Aken, Bas Van Aken received his Ph.D. in solid state chemistry from the University of Groningen, after which he worked as a postdoc at Cambridge University and at the Max Born Institute for Nonlinear and Ultrafast Optics in Berlin. He is currently a researcher in the PV module technology group at ECN, where he focuses on fabrication, reliability and (outdoor) performance of bifacial and back-contact modules.; Jochen Löffler, Jochen Löffler holds a Ph.D. in physics from Utrecht University in the Netherlands, and has been working on PV and related topics since 1998. He joined ECN in 2005 and is currently a senior scientist and project leader in the field of crystalline silicon solar cells, with a focus on industrial high-efficiency cells and modules.; Hongna Ma, Hongna Ma holds an M.Sc. and has many years’ experience in silicon solar cell research. She joined Yingli in 2008 and is currently the leader of the group working on n-type Si solar cells. Her focus is on R&D of solar cells with ion implantation technology.; Dongsheng Zhang, Dongsheng Zhang has an M.Sc. and joined Yingli in 2004, where he currently leads the battery technology department. His work experience in silicon solar cell research spans many years, and he has acquired an in-depth understanding of all aspects of the crystalline silicon solar cell process; Jinchao Shi, Jinchao Shi holds an M.Sc. and has worked in silicon solar cell and module research for many years. He joined Yingli in 2006, where he is currently the general manager of the Technology Center. He has extensive experience in lab to fab transference, as well as in cell and module mass production.

In recent years, potential-induced degradation (PID) has been recognized as a serious reliability issue for large PV systems, potentially causing efficiency losses of more than 90%, and even failures [1–4]. Such large decreases in efficiency may require the modules in the system to be replaced after just a few years’ operation. This has motivated a substantial research effort in the PV community, leading to a better understanding of the phenomenon, as well as to a range of mitigation strategies. A recent publication by Luo et al. gives a comprehensive overview of this research [5].

Potential induced degradation (PID): a test campaign at module level

By J. Carolus, Hasselt University and imec vzw; M. Daenen, Hasselt University and imec vzw

Potential induced degradation (PID) of photovoltaic (PV) modules gets a lot of attention since 2010 when Solon published their findings about a degradation mechanism in their PV modules caused by high potential differences. When multiple PV modules are connected in series, a potential difference up to 1000 V or at some places even 1500 V is created between the cell and the grounded frame. This electrical field causes a leakage current and ion diffusion. PID is a multi-level degradation with causes and solutions at cell, module and system level. A test campaign was conducted within the frame of a feasibility study for pidbull, a curing technology for PID developed by pidbull nv. 80 PV modules were characterized whereof 49 PV modules were stressed and cured for PID. The selected set of PV modules was composed of 49 different module types of 33 brands. The test was done according to the foil-method, as described by the standard in progress IEC 62804. However, to apply higher stressing and curing rates, the modules were tested with an aluminium foil inside a climate chamber for 96 hours. After the stress test, only 22% of the tested modules passed the 5% loss criteria as described by IEC 62804. In other words, 78% out of a set of today's most installed PV modules in Flanders are PID sensitive. Remarkable is that only 16 out of the 49 PV modules have less than 20% PID after the stress test. Additionally, a linear trend for PID reversibility was shown for modules with a stress level of less than 85%. The modules which lost more than 85% due to PID showed a lower recovery rate or in worst case didn’t recover at all.

Technical progress in high-efficiency solar cells and modules

By Rulong Chen, Xi Xi, Jie Zhou, TingTing Yan & Qi Qiao, Wuxi Suntech Power Co., Ltd

This paper focuses on the technical progress of high-efficiency crystalline silicon solar cells and modules, specifically with regard to passivated emitter and rear cell (PERC) processes, module description and light induced degradation (LID) data. Through appropriate optimizations of the solar cell and module processes, the cell efficiency achieved in mass production is 21.3%, with module power exceeding 300W. To solve the LID problem, hydrogenation technology developed by UNSW is used, bringing the cell LID rate down to below 1%.

Quo vadis bifacial PV?

By Radovan Kopecek & Joris Libal, ISC Konstanz

This paper presents a summary of the status of bifacial PV in respect of the technology in mass production, the installed PV systems, and the costs relating both to module production (cost of ownership – COO) and to electricity (levelized cost of energy – LCOE). Since the first bifacial workshop, organized by ISC Konstanz and the University of Konstanz, in 2012, many things have changed. Bifacial cells and modules have become cost effective, with installed systems now adding up to more than 120MWp and the technology becoming bankable. Large electricity providers have recognized the beauty of bifacial installations, as the lowest costs per kWh are attainable with these systems. The authors are sure that by the end of 2017, bifacial PV systems amounting to around 500MWp will have been installed, and that by 2025 this type of system will become the major technology in large ground-mounted installations.

PID –1,500V readiness of PV modules: Some solutions and how to assess them in the lab

By Benoit Braisaz1, Benjamin Commault2,3, Nam Le Quang4, Samuel Williatte4, Marc Pirot2,3, Eric Gerritsen2,3, Maryline Joanny2,3, Didier Binesti1, Thierry Galvez4, Gilles Goaer4 & Khalid Radouane, 1EDF R&D, ENERBAT, F-77250 Moret sur Loing; 2Univ. Grenoble Alpes, INES, Le Bourget du Lac; 3CEA, LITEN, Le Bourget du Lac; 4EDF ENR PWT, Bourgoin-Jallieu; 5EDF EN, La Défense, France

Even though it is now more than five years since potential-induced degradation (PID) began to proliferate, and despite the fact that solutions are under development, it is currently still the most discussed mode of degradation associated with cracking in PV modules.

Salvador Ponce-Alcántara & Guillermo Sánchez,

By Salvador Ponce-Alcántara & Guillermo Sánchez,, Valencia Nanophotonics Technology Center – UPV, Spain

Conventional ribbons used for interconnecting solar cells in PV modules act like mirrors, causing a large proportion of incident light to be lost. Experimental results indicate that only around 5% of the perpendicular incident light on the connections can be reused; as a result, this area contributes very little, if at all, to the current generation.

Top 5 solar module manufacturers in 2016

By Mark Osborne, Senior News Editor

PV Tech can reveal the preliminary top 5 solar module manufacturers in 2016, based as usual on final shipment guidance from third quarter financial results.

Investigation of cell-to-module (CTM) ratios of PV modules by analysis of loss and gain mechanisms

By Hamed Hanifi, Charlotte Pfau, David Dassler, Sebastian Schindler, Jens Schneider, Marko Turek & Joerg Bagdahn Fraunhofer Center for Silicon Photovoltaics CSP, Halle; Anhalt University of Applied Sciences, Faculty EMW, Koethen, Germany

The output power of a solar module is the sum of the powers of all the individual cells in the module multiplied by the cell-to-module (CTM) power ratio. The CTM ratio is determined by interacting optical losses and gains as well as by electrical losses. Higher efficiency and output power at the module level can be achieved by using novel ideas in module technology. This paper reviews methods for reducing different optical and electrical loss mechanisms in PV modules and for increasing the optical gains in order to achieve higher CTM ratios. Various solutions for optimizing PV modules by means of simulations and experimental prototypes are recommended. Finally, it is shown that designing PV modules on the basis of standard test conditions (STC) alone is not adequate, and that, to achieve higher CTM ratios by improving the module designs in respect of environmental conditions, an energy yield analysis is essential.

Back-contact technology: Will we need it in the future?

By Radovan Kopecek, Joris Libal, Andreas Halm, Haifeng Chu, Giuseppe Galbiati, Valentin D. Mihailetchi, Jens Theobald & Andreas Schneider, International Solar Energy Research Center (ISC) Konstanz, Germany

The back-contact (BC) technology currently available on the market is considered to be either highly efficient but extremely expensive (interdigitated back contact – IBC – from SunPower) or, if cost-effective, not very efficient (metal wrap-through – MWT) compared with what is becoming today’s new standard: passivated emitter and rear contact (PERC) technology. Something in between, such as low-cost, high-efficiency IBC cells and modules, would therefore be desirable. This paper briefly describes the past, focuses on the present, and forecasts the possible future developments of BC technology in respect of efficiencies, costs and applications.

All about PID – testing and avoidance in the field

By Peter Hacke, Senior scientist, National Renewable energy Laboratory; Steve Johnston, National Renewable Energy Laboratory

Potential-induced degradation can cause significant power loss in modules if the appropriate precautions are not taken. In the first part of a new series in PV Tech Power on module failure, Peter Hacke and Steve Johnston assess the current state-of-the-art in detecting, avoiding and mitigating the worst effects of PID.

Reducing the electrical and optical losses of PV modules incorporating PERC solar cells

By Henning Schulte-Huxel, Robert Witteck, Malte Ruben Vogt, Hendrik Holst, Susanne Blankemeyer, David Hinken, Till Brendemühl, Thorsten Dullweber, Karsten Bothe, Marc Köntges & Rolf Brendel, Institute for Solar Energy Research Hamelin (ISFH), Emmerthal, Germa

The continual increase in cell efficiency of passivated emitter and rear cells (PERCs), as well as the optimization of the module processes, has led to significant advances in module power and efficiency. To achieve the highest module power output, one important aspect to consider is the optimization of the solar cell front metallization and the cell interconnection.

Positive cell-to-module change: Getting more power out of back-contact modules

By Bas B. van Aken & Lenneke H. Slooff-Hoek, ECN – Solar Energy, Petten, The Netherlands

Cell-to-module (CtM) loss is the loss in power when a number of cells are interconnected and laminated in the creation of a PV module. These losses can be differentiated into optical losses, leading to a lower photogenerated current, and resistive losses, leading to a decrease in fill factor. However, since the application of anti-reflection (AR) coatings and other optical ‘tricks’ can sometimes increase the Isc of the module with respect to the average cell Isc, the CtM loss in such cases needs to be expressed as a negative value, which gives rise to confusion. It is proposed to use the CtM change, where a negative value corresponds to a loss in current or power, and a positive value to a gain. In this paper, the CtM changes for back-contact modules utilizing a conductive foil are described and compared with other mature module technologies. A detailed analysis of the CtM change for a full-size metal-wrap-through (MWT) module is presented.