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8th World Conference on Photovoltaic Energy Conversion; 83-87, Aluminium doped zinc oxide (AZO) is an interesting transparent conductive oxide (TCO) for silicon heterojunction (SHJ) solar cells to replace indium tin oxide (ITO) to enable cost reduction and omit the use of the limited global indium reserve. However, AZO layers have a much higher sheet resistance and lower damp heat stability compared to ITO. This work shows that the AZO stability can be improved by using an ITO capping layer, which is also decreasing the sheet resistance of the AZO/ITO layer stack compared to a pure AZO layer. Here, high rate rotatable magnetron sputtering was used to deposit AZO and ITO films. Under these conditions ITO capped AZO layers deposited on a-Si/p can result in lower fill factors. It will be shown that heating before sputtering and introduction of a thin ITO layer between AZO and a-Si/P avoid the fill factor decrease and lead to fill factors above 80%. The properties of the solar cells with the ITO/AZO/ITO layer stack are comparable to those solar cells with the pure ITO reference layer. Similar solar cell properties with the same ITO/AZO/ITO layer stack on the a-Si/n of the front side have been achieved. Furthermore, the TCO materials costs of ITO, AZO/ITO and ITO/AZO/ITO layers stacks for industrial manufacturing are discussed.

8th World Conference on Photovoltaic Energy Conversion; 803-806, The interconnection technology for solar cells is an important component in the PV module production - not only for module reliability but with respect to the sustainability of the PV industry as well. We are proposing the interconnection technology “TECC Wire” (TECC=Thermoplastically and Electrically Conductive Coating) which is a new low-temperature method – and which avoids the usage of any rare or hazardous materials. As rare or critical materials in the PV industry are rated such as silver, bismuth, lead and indium because global resources are considered to be too limited or too expensive for the terawatt production level. And the usage of lead does not comply with the RoHS (Restriction of Hazardous Substances) directive. Although PV modules are still exempt from this directive, efforts to avoid using lead as a solder alloy are consensus in the industry. TECC-Wire is conceptually an improved stage of the multi-busbar or multi-wire concept. However, it allows to further reduce the consumption of silver for the solar cells metallization, and it even enables the vision of totally eliminating silver from solar cell production. The TECC wires have a similar copper core that is typically used for multi-busbar soldering of solar cell – but it is coated with an electrically conductive adhesive instead of a solder alloy. The filler material to achieve the electrical conductivity is based on non-silver particles. The recently built semi-automated stringing machine attaches the TECC wires precisely and in a defined manner. It allows us to build and test standard module configurations. The long-term reliability tests have already passed 3x IEC requirement. After 3000h damp heat test the degradation of the small modules is below 5%. In thermal cycling test the results after TC600 are around 5% for different solar cells. The peel strength is about 1.5 N/mm contact area over the entire solar cell – which is comparable to a solder joints. The homogeneity of the peel strength along the entire surface of the solar cells is remarkable, as the wires adhere to any surface and not only to the printed fingers.

8th World Conference on Photovoltaic Energy Conversion; 708-711, A new approach is presented to determine the angular response of PV modules outdoor, using a dual axis solar tracker and a reference module with known angular response. The method is based on measuring Isc data for both sample and reference module, rotating both modules away from the sun to vary the angle of incidence from 0-90 °. From these data, the Incident Angle Modifier (IAM) curve is calculated. Thanks to the quick rotation (< 1 min), no temperature sensors are needed. For outdoor calibration of reference (mini-)modules, a 1.2 m long tube is used, in which the reference module is rotated while the tube is tracking the sun. In this way, the IAM curve can be determined without diffuse light disturbance. Using such a reference module, IAM curves were determined for several modules. In particular, a mini-module previously measured indoor at PI-Berlin was measured, the maximum difference between the two curves was 1.1%. Compared to the outdoor IAM measurement of PV modules in IEC 61853-2, the method above requires less equipment/sensors and is faster. The method is also accurate, the use of a reference module and the calculation method ensure correction for the varying diffuse irradiation across the sky.

8th World Conference on Photovoltaic Energy Conversion; 1099-1104, In this work we give an overview of the module monitoring results achieved within the H2020 funded project called HighLite. A dedicated online monitoring platform has been developed for the project to group and treat the data from all partners with homogeneous procedures. Monitoring of advanced prototype modules developed in the project and based on various cells and interconnection approaches, like silicon-heterojunction (SHJ)-shingle, TopCon-shingle, cut interdigital back-contact cells (cut-IBC) are reported. We describe key learnings from monitoring modules for various applications including building-applied PV (BAPV) and building-integrated PV (BIPV). Annual energy yield up to 1900 kWh/kWp is expected in Cadarache (France) based on HighLite PV technology. Temperature corrected performance ratios are used for a ranking of the new technologies against the reference PERC modules.

38th European Photovoltaic Solar Energy Conference and Exhibition; 533-537, The EU crystalline silicon (c-Si) PV manufacturing industry has faced strong foreign competition in the last decade. To strive in this competitive environment, the EU c-Si PV manufacturing industry needs to focus on highly performing c-Si PV technologies and on reducing environmental impact (lower CO2 footprint, improved sustainability, recyclability, etc.). In this work, we give an overview of the latest results achieved within the H2020 funded project called HighLite which addresses the work programme LC-SC3-RES-15-2019: Increase the competitiveness of the EU PV manufacturing industry. We report the progress made when implementing novel layers and processes in existing pilot-lines producing high-efficiency n-type silicon heterojunction (SHJ) cells with a shingle layout and interdigitated back-contact (IBC) cells with passivated contacts. In particular, we present the work done together with several industrial partners towards innovative production equipment for assembly of cut-cells into PV modules. Finally, we explain key learnings made so far when tailoring c-Si PV modules for various applications including building-applied PV (BAPV), building-integrated PV (BIPV) and vehicle-integrated PV (VIPV).

38th European Photovoltaic Solar Energy Conference and Exhibition; 814-819, For years, photovoltaic systems have been successfully installed on a large scale on open spaces as well as on (BAPV) and on buildings (BIPV). For the applications, PV modules in the classic glass-backsheet or glass-glass design are mostly used because their properties are well known. For BIPV and further on for automotive applications (VIPV) it makes sense to reduce the weight of the modules in order not to overload the building’s loadbearing capacity statics as well as for vehicles to minimize their energy consumption. One approach for weight reduction is by replacing glass with polymer materials. The light coupling on typical PV modules is largely optimized by means of an anti-reflective coating (ARC) on the front glass. This has not yet been done for polymer front sheets, but this paper will take the first step and characterize different lightweight approaches based on polymer front sheets with different solar cell types (SHJ, IBC) for their skewing behavior and then give an evaluation of the electrical yield for angle-dependent installation as well as for different locations.

38th European Photovoltaic Solar Energy Conference and Exhibition; 761-764, Lightweight photovoltaic (PV) modules are the key technology to access new markets such as industrial buildings and mobile applications. In this work we investigate methods to reduce the weight of a module while still being able to withstand mechanical loads according to IEC 61215. Finite element modelling (FEM) shows that increasing stiffness of the backsheet has more impact on the stress of the solar cells and displacement of the module under mechanical load than increasing the encapsulants stiffness. Therefore, two approaches are evaluated to increase the Young’s modulus and hence stiffness: Firstly, laminating glass fiber layer onto the rear side of a module and secondly laminating honeycomb structures into the module. The results show that an increase in Young’s modulus by glass fiber layers or honeycomb structures are sufficient to provide a significant rigidity to show a similar displacement during mechanical load tests as conventional module setups. Therefore, embedded glass fibers or honeycomb structures in the backsheet can be used to achieve lightweight modules with thinner or even without front glass. Additionally, backsheets with embedded glass fibers may be a viable option for modules with thinner front glass which currently require a rear glass.

38th European Photovoltaic Solar Energy Conference and Exhibition; 1574-1578, While PV is poised to become the leading renewable energy source in the EU and globally, both in terms of capacity and net output, its low spatial power density poses challenges in its effective use and distribution. One of the emerging use-cases for PV power is in electromotive applications, ranging from automotive (Vehicle integrated PV – VIPV – for cars, buses, trucks), rail-transportation (urban and extra-urban rail) and marine (recreational boats and sea- and inland waterway transport). Each of these has a particular topology, both of proximity to stationary PV, energy density of storage, and available surface area for mobile PV (which integrates VIPV with fixed PV assets dedicated to vehicle fleet electricity supply). In order to maximize benefit the entire PV Value chain in these applications, we identify the individual importance of several necessary components in planning and operational intelligence, and provide relevant examples based on current and emerging technology as well as an integrative framework for the modeling of these and related value chains based on energy flow modeling.

37th European Photovoltaic Solar Energy Conference and Exhibition; 1027-1032, In the last recent years the photovoltaic module design becomes more and more in the research focus to increase the module efficiency. Thereby the optimising of cell interconnection plays a major role since it affects the serial resistance and the power output at higher irradiation levels. A novel interconnection approach is the shingling of solar cell. In this work we characterised and studied the long term stability of commercial shingled pv modules. For its we created a special test sequence for shingled panels. Our results are focused on the low-light performance and compared that to outdoor measurements. As well as the mechanical stability by applying different stress tests. This paper ends in a weak-point-analysis of currently available shingled pv panels with different electrical layouts.

37th European Photovoltaic Solar Energy Conference and Exhibition; 1531-1535, In this study we address the issue of whether the field of robotics can supply the necessary technology readiness level (TRL) growth necessary to address the EU's Strategic Energy Technology (SET) roadmap targets for maintenance cost reductions in PV plants. The SET is a stakeholder-driven roadmap which shapes EU policy on, among others, PV sector growth, including measurable targets for performance, risk management and cost containment in different categories, including aspects of maintenance such as cost of diagnostics / failure analysis and quality control, lifetime and yield over lifetime. In the European context, with relatively rigid labor markets placing an inherent premium on night-time operations, 24-hour O&M automation is likely to play a leading role in meeting these targets. Moreover, in a global context robots can offer intensive maintenance in inhospitable and remote environments, where robot teams may integrate both multi-modal sensing and repair/cleaning action. We therefore investigate different maintenance needs and related actions, their relative frequency vs. age of installation and TRL levels of robotic solutions for each of these, where applicable, along with a prognosticated timetable of TRL / market penetration increases in each category the SET roadmap over the 5-10 year horizon.

36th European Photovoltaic Solar Energy Conference and Exhibition; 1860-1864, Over the past few years electricity generation costs for PV technology have dropped massively. Since, at the same time, PV module efficiencies have increased significantly, the market for building-applied PV systems has dramatically changed and in many countries it has become a de facto standard to use PV as the main source for the building´s energy needs. Because the power output of PV systems is fluctuating along with solar irradiation, advanced energy storage and management systems are necessary to cover the building energy demand on a stable basis. This paper presents a novel ‘gray-model’ approach to the estimation the forecast of PV energy systems. It is based on machine learning for solar irradiance forecasting and physical-mathematical models to simulate the PV system itself. The paper presents a comparison between simulated and real-life energy production data of a sample PV system.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1230-1235, When planning a photovoltaic system or being responsible for its maintenance, many issues have to be considered. In order to minimize any kind of risks the properties of the module technology must be well understood. One of the major potential risks is damage due to partly shading of PV modules. In such conditions the shaded solar cells are operating in reverse bias and thus can heat up significantly. In extreme situations such a high temperature gradient may occur that it can cause glass breakage - especially at thin-film modules where not fully-tempered glass can be used. In all module testing standards only stationary shadowing situations are investigated. However, during daytime also short-term shadowing situations can occur, e.g. through cleaning or inspection of modules, and therefore such situations must also be considered as certain module designs or technologies can be sensitive for this. This paper presents measurements before and after near field shadowing of two different types of thin-film modules. The effect of short-term shading on the IV curves at different irradiance levels as well as image-based electroluminescence analysis were carried out. Finally, the initial and after near-field shadowing IV curves where used to simulate the performance ratio for different locations. The paper will end up in a discussion about the influence of near-field shadowing on the performance ratio at thin film modules

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1738-1743, Photovoltaic modules are the key component of any solar power plants. Their long-term performance and availability are responsible for the electrical yield and thus for the profitability of the power plant. To minimise the failure risk, extensive module quality investigations should be carried out already during their planning phase. One of a major module stress factor is the solar cell overheating when partly shaded, or if broken cells or inhomogeneous module soiling occurs. At these conditions, the local cell temperature exceeds the normal operating module temperature which can lead to a significantly reduction of the long-term stability. A standard hot spot test is part of the PV module product certification. Unfortunately, this testing procedure takes a quite long time and the cell leakage current is used for determining the worst case cell. Therefor only some cells are thermal stressed. These are the motivation to develop an advanced hot spot method called rapid thermal hot spot method for PV modules. This paper will describe the technical set-up, the simulation models and the comparison between measurement and simulation.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 2270-2276, PV modules in solar plants are exposed to changing shading conditions. Due to partial module shading, cells are forced to operate in their reverse bias, which potentially leads to hot spots. In extreme situations, the extraordinarily high temperature gradient may cause in glass breakage. As a consequence, the thermal stability of pv modules is an important safety issue, especially in overhead installations. Warranty issues might be another consequence. In this paper, the thermal hot spot stability of different commercial thin film technologies will be investigated under artificial light exposure. Realistic shading conditions are simulated by shading elements of field realistic shapes that are moved step wise over the module. From ir images the failure location will be derived and correlated to other investigation technologies, such as power measurements, visual inspection and electroluminescence. This work also presents a hot spot risk benchmark of the investigated thin film modules, and their consequences regarding reliability issues. This knowledge is important for all quality assurance activities along the pv value chain, in the field and in the laboratory, as well as for the process of standardization.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2485-2489, Infrared imaging is a powerful method to identify and to analyze solar cells or modules with relatively higher temperatures during flied inspections. Higher temperature values can be attributed to cell mismatches, shadowing or isolated fractures (i.e., reduction of the active cell area). In this paper, the consequences of higher thermal loads on the encapsulation and back sheet foils have been investigated. Typical pv-module foils were aged at defined temperatures and periodically the visual, the electrical isolation and the optical properties were analyzed. Finally, this paper shows a hot spot risk assessment for different encapsulation foils and back sheets materials.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2554-2556, Hot spots of crystalline silicon solar cells are a major failure mode for solar modules. Consecutive on our last year’s investigation where we showed that a comparison of (i) a simple hot spot test on bare cells in the dark to (ii) a hot spot test on module level with complete shaded cells gives a rather wide spread in temperature rise with non-perfect correlation. In this work we shortly recapitulate and present investigation where we varied the shading level of laminated solar cells with different reverse bias current levels. The data shows for each solar cell a worst case shading scenario that is dominated by the reverse bias current behavior. This finding is also supported by simulations that show a comparable maximal dissipated power for each investigated cell.

29th European Photovoltaic Solar Energy Conference and Exhibition; 3153-3156, Hot spots of crystalline silicon solar cells are a major failure mode for solar modules. In this work we try to answer the question how hot spot cells behave first in bare state and second after lamination. For this study bare cells are initially characterized and sorted by hot spot risk. An infrared camera is used to document temperature and size of the hot spot when applying a reverse voltage of -12 V. Prone cells are then built into modules and a special hot spot endurance test of the Photovoltaic Institute Berlin is performed where each cells gets shaded for 15 seconds. The comparison of both test methods show a low correlation between the hot spot behavior of bare cells and laminated cells. An extension of the shading time to up to 10 minutes proves that 15 seconds are sufficient to identify most of the severe hot spots. Finally possible sorting criterions for cell or module manufacturer are discussed.

29th European Photovoltaic Solar Energy Conference and Exhibition; 3209-3213, In PV applications solar modules are not always fully illuminated but occasionally partly shaded. In this case the partly shaded cells potentially operate in reverse bias of the current voltage characteristic. For this reason the cells heat up and in the worst case the polymer foils can melt. For studying the thermal stability of a module the standardized hot spot test can be applied. The standardized conditions of the hot spot test allow some degrees of freedom like the module temperature of the non shadowed module area. In this work, the influence of the module temperature and of the radiation level on the maximum hot spot temperature will be analyzed indoor. Then, an outdoor hot spot tests will performed. Finally, this paper will show a worst case comparison between the in- and outdoor hot spot test conditions.

28th European Photovoltaic Solar Energy Conference and Exhibition; 2972-2977, Photovoltaic modules are stressed in indoor climate chambers to determine long-term stability. Generally, aging tests are performed to study the loss of power and energy yield but not the operating stability in reverse bias. That should be analysed as well, because beyond the decrease of power, most of the stressed modules are also showing micro cracked cells. Therefore, this paper presents the electrical and thermal properties of partly shaded modules after aging tests. The tolerance of PV modules towards shading and reverse bias is studied as a function of long-term stability exposure of the modules and the aging of the materials – such as the influence of penetrating humidity. Finally, the paper presents a risk analysis of the hot spot stability of aged silicon crystalline photovoltaic modules and its materials.

27th European Photovoltaic Solar Energy Conference and Exhibition; 1985-1990, The first experiences with potential induced degradation (PID) of silicon solar cells have been presented in literature since 1989 [1-4]. It has been shown that PID may cause power losses of more than 30% for modules out in the field. Critical issues on the cell level are the SiNx anti-reflective coatings (ARC), their deposition method, the emitter thickness and metallization (thus influencing the electrical series resistance). The leakage current was found as an indicator for the intensity of degradation. Moreover, different test methods to prove the stability or susceptibility of samples have been presented. In this paper we are showing the influence of the anti-reflection coating to provoke PID and the ability of silicon nitrite layers to prevent PID. For each layer structure, at least four different designs have been manufactured and tested for their stability against PID. To do so, it was necessary to find an appropriate test sequence, which would show polarization effects in an adequate time frame, while there is no standard procedure available that addresses this problem for the time being. Furthermore, it has been necessary to develop suitable reference samples to compare the results and to prove the repeatability of the test sequences. The experiment has been divided into two parts: The pre-evaluation has been realized with small onecell mini-modules to probe the adequate testing parameters and to analyze the leakage currents for various prone samples. During the second part, we also investigated the reversibility of PID - depending on the state of degradation of these samples - to check whether PID is one 100% reversible, or whether the degradation mechanism also shows an irreversible part.

27th European Photovoltaic Solar Energy Conference and Exhibition; 3511-3517, This paper is mainly focusing on electrochemical failure modes for silicon based technology frequently observed in field recently and referred to as so-called ‘snail tracks’. Suitable test sequences are presented for both failure provoking and for risk analysis for field panels already affected. Different field findings - referred to as ‘snail tracks’ - have been categorized with respect to their optical appearance. Relevance for power and yield issues in field has been investigated and correlated to underlying crack issue as well as additional corrosive phenomena. Affected field panels have been further characterized with respect to their isolation properties. Results for leakage current measurements as well as interfacial adhesion (glass/EVA) are presented. Material investigations have been conducted and bulk resistivity for different encapsulation materials (including different EVA types/suppliers) are presented.

27th European Photovoltaic Solar Energy Conference and Exhibition; 3553-3557, The hot spot stability is part of the product qualification test sequence of pv modules. Therein the major challenge is the selection of the cell with the highest hot spot risk. Currently, the electrical properties of the cells are used as selection criteria, e.g., the highest threshold currents at the point where the bypass diode turns “on” and/or cells with maximum and minimum values for the parallel resistance. The weak point of this procedure is, that the cells with a hot spot risk are not ranked by temperature, which may cause a hot spot event. The paper presents the results of a comparison between the electrical and thermal properties of shadowed solar cells in pv modules. Finally, an improved hot spot test sequence is presented that shows a better prediction probability for this specific module failure.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 4002-4006, The hot spot risk of crystalline silicon modules is the only reliability and safety issue, which is attributed to cell properties. The increased hot spot risk results from local shunts or deformations of the pn-junction, which might origin from inhomogeneities in the raw material of the waver or bad cell processing. This paper presents an overview of existing and new approaches for the hot spot analysis of crystalline silicon cells. Its aim is to provide a reliable, non-destructive and fast testing-scheme, that can be used for screening of large lots of finished modules or as a final test in the module production. Infrared-thermographs and dark-current measurements are used to forecast the probability of a destructive hot spot effect deriving from partial shading in the field. A new hardware set-up is proposed and its feasibility for an in-line production use is discussed. Finally, the ongoing discussion between different national reliability standards for the hot spot endurance test is commented.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 3321-3326, Photovoltaic devices increase in complexity and thus introduce new calibration challenges, largely being affected by deviations of test spectrum from natural spectra. Future energy rating standards will impose further challenges as one needs to simulate realistic sunlight spectra conditions. Generally only light intensity and module temperature can be varied in a solar simulator, which means that they do not provide the variability of environmental conditions and it maintains problematic to measure multi-junction solar cells. A solution to this is to use LEDs instead of the traditional light source in a simulator. Their unique characteristics allow precise intensity adjustment and the combination of a steady state with a flash solar simulator, thus providing high flexibility. With the LEDs availability in colours over the whole spectrum, the AM1.5G spectrum can be accurately represented with the benefit of an adjustable spectral output. CREST has designed and constructed an LED-based solar simulator prototype of which the hardware set-up as well as classification results and PV device and repeatability measurements are presented. Weaknesses of the prototype and their solutions have been indentified, and are currently being realised in the next stage of the development. Those are described in detail.