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31st European Photovoltaic Solar Energy Conference and Exhibition; 2193-2196, This paper describes the technical characteristics and simulates the performance of a 75MW PV plant that is planned by the Moroccan Office National d’Electrecité et de l’Eau potable (ONEE) at Tafilalt, in the South of Morocco. Simulations have been performed using SISIFO, and online and free-software simulator of PV systems.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2265-2270, Monitoring data of grid-connected photovoltaic installations provides a valuable source to follow the operation and performance of a PV facility. Main failure modes can be spotted from the analysis of only this data. Combining measured monitoring data with detailed simulation results however, provides additional information that can reveal more subtle problems or help to track down the source of a complex malfunction. In this paper we describe how such a comparison can be performed, that would allow the detection of different kinds of problems on the module, string and inverter level. After some general considerations on how to compare measured data to simulation results, including the corresponding uncertainties, we study how possible discrepancies can point to problems either with the monitoring, the operation or the simulation results. The level of detail in the monitoring data will determine how well this assignment can be done in an unambiguous way. A tool allowing this kind of analysis is currently being implemented in the PVsyst software and its capabilities to compare monitoring data to the simulation results are being expanded.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2249-2252, In the presented work we introduce a detailed description of the photovoltaic power station working in GRID - ON mode installed by EZ Company in Dukovany. The photovoltaic power plant was built as the first one in the Czech Republic. After seventeen years in service is an appropriate candidate for an analysis of defects occurred by aging and environmental influences. The aim of the submitted work is in terms of degradation of the photovoltaic modules and photovoltaic cells caused especially by aging and also in its possible future prevention of the most commonly defects that reduce the long-term performance of the PV power plants. Based on the obtained data were determined the functionality and efficiency of the photovoltaic plant during its lifetime. The measurements and subsequent comparison of the basic parameters with the parameters set by the manufacturer have shown information about the influence of aging of photovoltaic cells. Identified defects can be useful in follow-up work for a design of solar power plants with a requirement of the lowest decline in performance throughout the years of service.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1967-1971, The performance of the photovoltaics systems depends on the weather, specifically on the irradiance and temperature, features that reveal a 99 % of the system performance. The design of the photovoltaic system depends on the veracity, for this reason it is significant to put photovoltaics panels in different locations. This research shows an analysis on the influence and efficiency of irradiance and temperature in different locations in the central region of Colombia. The characterization of the solar energy potential (irradiance) is done in four locations of the central region of Colombia where different environmental conditions can be found, likewise it is intended to do a characterization of the room temperature of each place that affects the panel, and finally do a characterization of the panel efficiency under the irradiance and temperature conditions of the four places already set. Curves IV and PV were built for the three panels in each location, there were 743 measurements in total, an average of 62 measurements in each city. The systematization, analysis and results show efficiencies that allow us to classify the places and analyze the irradiance and temperature within the output of the power panel.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1807-1812, Potential-induced degradation (PID) is a critical failure mode in today’s photovoltaic (PV) system architecture with very large to catastrophic impact on PV-module performance and energy yield. Potential-induced shunting (PID-s) is one of the most severe types of PID leading to shunting of p-type silicon solar cells. Previously, the kinetics of PID-s was investigated in detail and a preliminary model was presented describing the progression of the shunt resistance (Rsh) of fielded modules. In this work Rsh measurements of mini modules that were exposed to field conditions and a high negative potential at an outdoor test site for one full year are presented and compared to model calculations. In addition the performance decrease of PID-s prone 60cell PV-modules installed on the negative end of a positively grounded module string is shown and the shunt progression simulated. The modeled Rsh progressions are in good qualitative agreement with the measured data. Nevertheless quantitatively there are clear differences between the measured and simulated Rsh progressions. In order to improve the calculation results the origin of these differences is analyzed.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2524-2528, Isothermal ageing is a widely used method in electronics to address the alleged long-term stability of soldered joints. Compared to common IEC 61215 module tests such as damp heat or thermal cycling it is relatively fast (< 90 h), does not require the lamination of a module and allows ribbon peel testing and metallographic analysis after the test. We study the mechanical and chemical solder joint properties after isothermal cell testing compared to thermal cycling and damp heat exposure of mini-modules. In this study solder joints of encapsulated Multi-Busbar (MBB) solar cells, which provide a multitude of single joints, are investigated after accelerated ageing tests. A special demountable one-cell-module setup enables chemical and mechanical characterization of solder joints after damp heat and thermal cycling tests. The observed fracture patterns are analyzed and designated to the degradation products characterized by Raman spectroscopy. Isothermal ageing and thermal cycling show non-chemical failure mechanisms caused by mechanical stress or intermetallic phase growth. The largest impact on contact adhesion and indicators for chemical degradation are found after damp heat testing. As opposed to the phenomenon of grid finger corrosion with 3BB cells reported in literature, where the EL measurement shows clear indication for a complete loss of electrical contacts and very low adhesion to the cell, the EL measurement of the DH aged MBB module shows that the electrical contact of the affected metallization is still intact compared to the initial EL image.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2348-2352, IEC 62817:2014 Ed.1 Design qualification standard for PV solar trackers, defines test procedures for the complete tracker system and its key components, with the objective of ensuring that parameters reported in the solar tracker specification sheet are measured and verified by consistent and accepted industry procedures. In this way, the costumers can have a point of comparison of characteristics and quality of solar trackers. In addition, IEC 62817:2014 Ed.1 defines a set of tests that identify the solar tracker designs that are likely to have early failures and are not suitable for being used as specified by the manufacturer. CENER, National Renewable Energy Centre of Spain, has developed a methodology to apply IEC 62817:2014 standard tests in order to assess and characterize photovoltaic solar trackers. Main points of interest and difficulties found are discussed in the paper.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1902-1906, Cocktail sequential test for module endurance is investigated. Distinction of testing result is identified among P-multi, P-mono front contact and N-mono back contact module. We perform different types of cocktail sequence and compare for the correlation of degradation to test sequential order. [DH-HF] sub-sequence shows more severe synergy effect than [TC-HF] sub-sequence does. P-multi module suffers more damage in HF test, while Pmono is prone to be UV damaged. Back contact module owns excellent reliability especially when POE is instead of EVA encapsulation material. Faults and failure modes by cocktail sequential test are similar to those observed in the field, and it refers a possible methodology approach to simulate module reliability during PV system operation.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1624-1628, The purpose of the work is the evaluation of Tigo Optimizer benefits on the performances of a thin film PV plant. The experimental activity consists in a side by side test of two strings (with and without Tigo optimizers) to compare their energy yield in different operating conditions. The activity has the aim to test and assess the best solutions to increase the performances and reduce LCOE of PV plants, minimizing mismatch effect that can be caused by several factors. The first results of the experimental activity show a gain in the sub-field with Tigo optimizers in a range of 2- 4%. In order to assess potential benefit of Tigo optimizers on a utility-scale application, an analysis on existing PV plants has been carried out, from which the real mismatch measured on field has been estimated; finally an economical analysis has been carried out to evaluate the conditions of the PV plants, in terms of potential gain, in which the installation of the optimized solution can be a convenient investment.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1556-1559, The effect of fast-varying weather conditions on (simplified-) models on simulated solar cell temperature and energy yield prediction is investigated. The models have first been calibrated with indoor measurement data. We focus especially on short-term behavior (second to minute level). Frequency response analyses show that the solar cell temperature is mainly influenced by high-frequency illumination conditions, while the effect of highly varying wind on the solar cell temperature is more limited. For a period with highly varying weather, energy yield is calculated to illustrate the effect of the parameters in the model on the overall energy yield outcome.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1598-1601, Monitoring of distributed solar power sources is required for the correct evaluation of the system performances as well as the possible maintenance actions. The use of micro-converter based solutions, especially in BIPV systems, enables not only the maximization of the energy harvested from solar panels, but also the possibility to monitor the entire system with a resolution down to the micro-converter level. Typically all these devices have an built in electronic able to perform at least measures on the outputted power and energy. The accuracy of available measurements often is not declared on the manufacturer’s datasheets, as well as the way the different measures are performed. This aspect is addressed and investigated in this article by defining a test protocol based on the reference standard EN50530. By means of an experimental campaign over 5 micro-converter devices of different manufacturers the measures performed by the built in electronic of the different devices will be compared with those one performed by a reference acquisition system for different operative conditions of use.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1775-1779, Bifacial PV modules are able to convert solar irradiation from both surfaces. Therefore, larger amounts of produced energy are expected – compared to standard (monofacial) modules. Today, bifacial modules are offered by an increasing number of manufacturers, and marketing material sometimes promises quite optimistic bifacial gains. Reports on bifacial PV systems are also found in the literature, but mainly for test setups or small PV systems only. For large PV installations (as known with standard PV modules), realistic bifacial gains still need an assessment. Currently, none of the widely utilized PV system simulation tools is able to predict the rear surface contribution of bifacial modules accurately. Therefore, our approach combines simulation tools from different fields of (solar) energy technology, the lighting and daylighting domain and the PV system simulation domain. In this way, we are able to deal with solar geometry, sky radiance distribution, scene geometry, surface properties, PV module properties and wiring scheme without any need for severe approximations in the model definition. Using this tool, we calculated realistic yield values for a number of system configurations. The results are discussed with respect to their bifacial gain in relation to space requirements (expressed by ground cover ratio), mounting options and ground albedo. Reasonable ranges for expectable gains from bifacial modules and PV systems are given in the conclusion of this contribution

31st European Photovoltaic Solar Energy Conference and Exhibition; 1667-1674, Most photovoltaic (PV) string inverters have the hardware capability to measure at least part of the current-voltage (I-V) characteristic curve of the PV strings connected at the input. However, this intrinsic capability of the inverters is not used, since I-V curve measurement and monitoring functions are not implemented in the inverter control software. In this paper, we aim to show how such a functionality can be useful for PV system monitoring purposes, to detect the presence and cause of power-loss in the PV strings, be it due to shading, degradation of the PV modules or balance-of-system components through increased series resistance losses, or shunting of the PV modules. To achieve this, we propose and experimentally demonstrate three complementary PV system monitoring methods that make use of the I-V curve measurement capability of a commercial string inverter. The first method is suitable for monitoring single or independent PV strings, and is based on evaluating the ratio of certain operation points on the string I-V curve. The second method is applicable to PV systems with identical strings, and is based on monitoring and inter-comparison of string I-V curve parameters. For PV systems with non-identical strings, or when all strings can be affected by faults, we propose to use in-plane irradiance and module temperature measurements, and a performance model of the PV strings, to predict the optimal string I-V curve parameters, and then perform the inter-comparison with the measured values, to identify the cause of the faults.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1915-1919, In comparison with the evaluation of hail events in the field, a quantitative analysis of hail impact dependent of mass and velocity of the ice balls has been started. Glass breakage and star cracks of the solar cells are the typical failure modes of hail events in the field and in the lab. We found that the location of the hail impact on the PV module is a key parameter for both failures due to different stresses and strains of the glass after the hail impact. Hail tests according to IEC 61215 (Clause 10.17) [1] and VKF (Swiss hail protection register) [2] were performed with different PV module types to analyze the effect of strong hail impacts

31st European Photovoltaic Solar Energy Conference and Exhibition; 2185-2189, Photovoltaic generators (PVG) suffer from short-term intermittency of output power. With significant penetration of PV this intermittency can lead to power systems instability and power quality problems. Energy storage systems (ESS) can be used to compensate PV power fluctuations in order to mitigate these problems. In this paper ESS behavior, control and sizing have been investigated to mitigate instabilities caused by PV power plants operating in Northern European conditions through simulations that utilize measurements from the Tampere University of Technology (TUT) Solar PV power station research plant. Continuous synchronized measurements have been recorded with the irradiance and PV module temperature sensor network with a 10 Hz sampling frequency since June 2011. The ESS capacity and power requirements are derived from the simulations for different PVG sizes and PV power ramp rate (RR) limits. The results show how both capacity and power requirements decrease as functions of the RR limit and the PVG size. Also, interesting differences have been noticed compared to similar studies done in Southern European climate, which indicate that the operational climate of the PVG can have an effect on ESS sizing.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2128-2131, Intraday photovoltaic power production forecasting benefits to various energy stakeholders (grid operators, virtual power plant managers, electricity traders and other balance responsible parties). Solar irradiance forecast at this scale cannot be accurately produced using current weather models. Stochastic evolution of cloud cover is better represented by the extrapolation of cloud patterns observed by images from geostationary meteorological satellites. Soleksat is an integrated solution to produce global horizontal irradiance (GHI) up to 6 hours in advance using images from any geostationary satellite all over the world. Its architecture is based on geographic web servers. It enables a convenient flexibility for end-users requiring spatially distributed data. Soleksat input data can originate from any source respecting the standard of Open Geospatial Consortium without software modification. GHI forecast accuracy has been assessed by comparison with ground measurements located. Soleksat is able to forecast GHI with a relative RMSE smaller than 40% for a time horizon up to 4.5 hours.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2179-2184, In this paper, the performance of several large-scale Spanish photovoltaic plants is presented. 20 installations, totalling more than 90 MW, are analysed for a period of up to 4 years. We suggest a procedure to assure the consistency of the data coming from the field and a method of calculating the energy availability rate of the installations, both of them in a way that is independent of the operator of the plant. The operational results are final yields of more than 1,500 kWh/kW for static installations and more than 2,100 kWh/kW for a 2-axis tracking configuration; average performance ratios of 0.8 and energy availabilities of more than 99.5%, with no significant differences between static and tracking systems. Because of the large size and wide location distribution of this sample, we consider these results representative of the performance of large scale PV plants in Spain.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1842-1846, In this paper, we collected 177 multi-crystalline silicon modules which had been installed in Hainan Province of China, where the modules had been operating under typical subtropical climates for 23 years (1986-2008). The modules were measured by ISES in Guangzhou in 2009 and very low power degradation (relative decay of 6.8% in average) was detected. To understand how long these modules continue operation, 144 modules with a mean degradation rate of 4% were selected to re-install a small on-grid system and monitored since Oct, 2010. Their outdoor performance were quite comparable with other c-Si PV modules installed recently in southern China. The modules were re-measured in 2014, an average degradation of 5.4% in relative to their original power was found. Two test results showed that the modules’ degradation mainly caused by decrease of current Im and Isc. The result demonstrated excellent reliability of silicon wafer-based PV modules, indicating that the potential lifetime of modules over 30-year with degradation

31st European Photovoltaic Solar Energy Conference and Exhibition; 2420-2423, Every year, more than 2.2GW of commercial photovoltaic (PV) systems are installed worldwide. Approximately 30% of these are mounted on flat rooftops. PV systems that are mounted on flat rooftops have two special requirements: they need to add as little weight as possible to the building and be exposed to as little wind load as possible. The paper analyses the impact of wind on a new racking system developed for PV modules for flat rooftops. Computational Fluid Dynamics (CFD) simulation was used to examine the impacts of wind loads on a rooftop mount system. Wind tunnel testing was also carried out on a model representing this rooftop racking system to further verify the results of the CFD simulation. Testing results indicate that the external section of the PV array will experience a greater wind load compared to its internal section. Calculations performed using the drag coefficient of the Trinamount III D10 racking system demonstrates the advantages of this design under high wind loading. The light weight racking system presents a tilt angle of 10 degrees and includes an optimized wind diffuser to protect the structure against high-wind events. The attributes of robustness and light weight, coupled with its simplicity of installation and packaging make the Trinamount III D10 racking system a fast installing, non-penetrative PV mounting system very well suited for applications on flat rooftops.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1587-1591, Building Integrated and Building Attached Photovoltaic (BIPV, BAPV) systems may suffer from lower performance than predicted as a result of unwanted partial shading. New system architectures have been proposed to optimize performance. The common approach of these new architectures is to track the Maximum Power Point (MPP) of every solar module individually. A simulation model is developed to quantify the benefits and drawbacks of different PV system architectures. The model includes a shading evaluation of the installation with means of 3D modeling, irradiance calculations, PV cell modelling and finally an empirical power conversion model. The energy yield of three leading architectures is confirmed (string inverter, power optimizer, micro inverter) for clear and partial shading conditions by means of an outdoor field test. Results show that there is a clear benefit for MLPE systems at higher irradiance when partial shading is present. The analysis method can be used by PV installers and system designer to determine which is the optimal system architecture for maximum energy yield especially when partial shading is present.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2561-2564, In recent years there has been extensive research on the topic of micro cracks. Marc Koentges delivered ground breaking work several years ago. Especially his simulation and theory of the possible power loss caused by micro cracks serves as a basis for the analysis and evaluation of micro cracks. What has been missing in the past is information about the probability that the possible power loss occurs under normal outdoor operating conditions. PV lab build a 30 kW power plant equipped with 130 multi crystalline Si-modules 6” 60 cell which have been sorted out due to severe micro cracks. All PV modules have been preselected: they have been sorted out from a power plant project after EL screening due to severe micro cracks (either number of cracked cells per module or highly damaged cells). So the investigation basically focuses on a worst-case scenario. The plant has been put into operation before winter 2011. In spring 2014 and 2015, after three resp. four winters, the modules have been inspected again with STC-power measurement and EL imaging. The data is analyzed on cell and on module level. On cell level every cell is characterized by the type of micro crack, the percentage of potentially isolated area and of isolated area. The analysis compares the development of the micro crack status of the different types of cracks with respect to isolated areas and potential power loss. Approximately 200 cells in four categories have been specifically selected for detailed monitoring and analysis. Changes in number of cracks, crack-shape and isolated areas were investigated. 17,2% of the number of the areas which have been endangered to become isolated have really been electrically separated from the live circuit.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2575-2578, Since short-circuit of bypass diodes of PV module causes output reduction and hotospot of PV module, we have to detect the failure as soon as possible. However, since existing detection technology is affected by environmental conditions, we propose new detection technology for identifying position of failure using DC power source and infrared camera. In this detection method, since surface temperature of cells connected to noramal bypass diode is different from that of cells connected to short-circuit bypass diode, we can find difference of those temperature with infrared camera. The theoretical merit of this technology is that detection results is not affected by environmental condition such as irradiation, so on. As the first step of study, we conducted indoor and outdoor tests and we found the failure position in a minute with 20% current of Isc under the indoor test. However, it was difficult to find the failure position under outdoor test more than indoor test. Because environment condition affects the surface temperature of PV modules. Therefore, we have to clear proper curent and time to find failure positions at the next study.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1972-1975, As Photovoltaics (PV) has been recognized as one of the major renewable energy sources to be used on a large scale to contribute to solving the energy challenges faced by South Africa, one of the most fundamental questions is which technology is best to deploy in specific areas in order to achieve the highest energy yield. This paper reports on the energy yield monitoring of various PV technologies operating under different deployment configurations at the Outdoor Research Facility (ORF) at the Nelson Mandela Metropolitan University, Port Elizabeth. I-V characteristic data measured with a high temporal resolution was used to directly compare the performance and device parameters of the various PV technologies under varying meteorological conditions. In addition, the energy yield and performance trends at high temporal resolution based on the I-V characteristics and meteorological conditions is discussed. Preliminary results confirm the benefit of energy yield gain by utilizing single-axis tracking and application of an appropriate module cleaning routine to reduce the effects of soiling.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2557-2560, Module hot spot is the crucial reliability issue for massive PV deployment as a major renewable electricity source. We carry out the statistic analysis from 3.8 million modules over 1GW capacity during the first five-year system operation. There are total 49 faulty hot spot modules spreading out in 9 of over 1,250 global project sites with 12.9ppm failure rate. Around 73.5% of failure contribution is due to system install sector. Most faults due to module and cell sector occur within first two year operation. Main failure modes include hot cell, burning from cell edge and burnt backsheet, while 69.4% portion of the root cause results from cell cracking induced by frame damage during system construction. Other root causes are also investigated by detail inspection, and the correlation is established between analysis result and failure mode. In cell level, experiments validate that increasing shunt resistance and reducing reversed current effectively suppress module hot spot temperature. In addition, suggestion for preventing hot spot risk is provided for each sector respectively through whole PV value chain.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2012-2016, This paper presents a numerical analysis of using a water layer as an optical solar spectrum splitter for concentrated and non-concentrated Photovoltaic/Thermal systems (CPVT and PVT) based on ray-tracing technique using OPTISWORKS software. In the proposed approach, the water is to be circulated above the PV module to extract the heat from PV module and to act as a spectrum splitter to the solar radiation. This effect of different water layer thicknesses (2.5 – 30 mm) on the radiation received by the PV cell and the radiation absorbed by the water layer was investigated. Results showed that the optical filter has low transmittance of UV radiation and hence good absorption efficiency (over 99%). The filter transmittance of IR radiation decreased with the increase in water layer thickness to reach 50%. Also, for VIS radiation, as the water layer increases, the transmittance of VIS radiation decreases from 92% with water layer of 2.5 mm to 50% with water layer of 30 mm thickness. Additionally, the overall radiation output of the optical filter is presented showing optical efficiency of 74.5% but this radiation considers mainly of VIS lights beneficial to the PV.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1804-1806, The Photovoltaic Laboratory (PV LAB) at Bern University of Applied Sciences BFH in Burgdorf, Switzerland, developed its own remotely-controlled IR Multicopter Drone. The aim was to economically optimise the quality-control of predicted energy yields from PV-installations in the Swiss PV monitoring network as operated by the PV LAB since the 1990s. The work is carried out within the SCCER FURIES project and in collaboration with Swiss industry partners. The drone system was assembled in a Bachelor thesis and extensively tested on the PV LABs own roof-top PV-installation. Application to two large Swiss PV-installations (football stadium “Stade de Suisse“, Bern / 1.3 MWp and open-field “Mont Soleil” in the Jura Mountains / 554.5 kWp) confirmed the economic benefit of remotely-controlled drone inspection as compared to manual thermographic examination. The IR Multicopter Drone now allows a rapid thermal survey of operating PV-modules at all installations in the Swiss PV monitoring network. As the system is electric, it offers an added value for thermal inspection of PV-installations where no disturbing emissions are allowed. This is a requirement at the world’s highest research facility at Jungfraujoch (3 454 m asl) where the PV LAB measures the longest energy yield record from PV in the Swiss Alps.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2096-2100, The increasing penetration of PV systems in the distribution network creates new opportunities but also raises several issues for the grid operation. New challenges, arising from the variable nature of solar energy generation, must be tackled in order to keep a stable and balanced power grid. In this study, short term variability in power output due to changing intensity of the cloud cover is assessed for its impact on energy delivery. Studies on this subject conclude that while there may be local variability, there is a strong reduction in that variability when the aggregate of several PV systems is taken into account, rather than just one PV system. The analysis shows that the aggregated effect of many geographically dispersed systems PV systems yields a smoothing effect that reduces the impact of local variability. We shortly present the theoretical background of the smoothing effect and the variability model of Hoff and Perez. In the following chapters, the model is demonstrated in three case studies for different regions and with different time and space resolution and one of a distributed generation system in Hawaii, USA. The current report shows the general validity of the model and suggests a simple global model for modelling variability of PV fleets. Both need further validations at more sites and in more regions to detect the strengths and limitations of the models and the worldwide usability.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2435-2438, In places where PV modules are most of the time exposed to solar irradiance larger than 1000 Wm-² (like Egypt and Northern Chile), the current at MPP (maximum power point) is significantly higher than the current measured at STC, which increases the electrical losses, especially for longer periods of exposure and has a measurable effect on the NOCT (normal operating cell temperature) of the module. In order to reduce these losses a conductive cell interconnection scheme or material with lower electrical resistance is required, meaning ribbons with larger cross section, half cut solar cells or solar cells with more busbars than 3. In this paper it is shown how the electrical losses of PV modules are affected by changing the ribbon cross-section, implementing multiple busbars or cutting the cells by half, considering the operating temperature at several irradiance levels. A first approach shows the 3BB halved-cell is a suitable choice for desert conditions.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1830-1834, In this work the performance stability of rear side passivated mc-Si solar cells and modules under carrier injection at different temperatures is investigated. Severe degradation levels of above 10% can be detected which cannot be explained by B-O complex formation or FeB pair dissociation. A high statistic of cells and modules degraded in lab and outdoor using material from different suppliers confirm the relevance of this new effect. LeTID (Light and elevated Temperature Induced Degradation) is a mc-Si bulk phenomena leading to a highly injection dependent degradation and features a regeneration phase after degradation. Characteristics of LeTID as a function of temperature and injection level are presented and a comparison between laboratory and outdoor tests is drawn. The time constant of this degradation mechanism accelerates with increasing temperature, however, the time span for degradation and regeneration of thousands of hours at relevant temperatures between 60-85°C demands for a solution on wafer material or processing side. LeTID can be significantly reduced by adapting the cell process and processing sequence.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1976-1979, The South African utility grid has been under severe pressure since 2008 due to, in part, lack of expansion planning, aging infrastructure and a continued need for unscheduled maintenance shut downs. Since then there has been a flooding of substandard, unregulated photovoltaic (PV) modules and balance of system (BOS) components onto the lower end of the domestic market. These modules and components are being sold with the assurance to provide electricity for domestic purposes, seemingly with no name plate rating of modules, system sizing assistance, installation guidelines or after sales service. We have discovered these claims to be misleading. In this regards, ten a-Si:H modules were obtained at a local hardware store and mounted at our outdoor research facility, SolarWatt Park, on a north facing test rig tilted to the latitude of the site, 34o. For the purpose of this study, the electrical performance of five of these modules was monitored. These measurements indicated a high variation in both measured and STC corrected values of up to 30%. Analysis of the observed degradation showed a significant 33–35% decrease in performance, which is unacceptable. Within 2–4 days of outdoor deployment, some modules even developed cracks on the front glass due to the cyclic daily thermal stresses. Furthermore, 3–D SEM coupled with EDX for structural evaluation have revealed the presence of hotspots and the presence of foreign organic substances in affected modules. FTIR analysis have also revealed that in addition to the a-Si:H bonds, foreign bonds such as C=N, N=O and C=H were present. These developed due to the degradation of the EVA. Comparative TGA analysis of the affected and non-affected regions has revealed high temperature volatization of the affected regions. This is attributed to the absence of ethyl-vinyl acetate (EVA), which has already been degraded by the localized heating caused by hotspot formation.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1959-1963, Nameplate, datasheet, instruction or user manual, markings and documentation: A lot of terms that are floating around while a manufacturer tries to get his product documentation done right. Based on existing standards actually this is very challenging since standards for one product sometimes require different information and it is not clear what is mandatory and what is voluntary information. IEC 61730, 61215/61646, 61853-1, EN 50380 and UL 4730, all provide some input on marking and documentation requirements. During the project formation and several discussions to update EN 50380 it turned out to be clear that there is a need for unified marking and documentation requirements. With the idea of the new EN 50380 nameplate and datasheet are well covered because they are part of the product markings and the documentation. The manufacturer should be able to choose what information to put on e.g. datasheet vs. user manual. It is only important that the product can be used safely in the end application. It sounds strange, but from a product safety and installation point of view performance does not really matter. Based on these more substantial changes it is much more difficult to compare EN 50380 with UL 4730. After giving several terms needed for the understanding and a detailed motivation for the changes to EN 50380, combined with some background of UL 4730 a more high level comparison of the standards will be given. This overview is provided as a table and compared directly to the more common, newly updated IEC safety standards. The nameplate is part of the product markings, here the PV module, and typically shows several ratings e.g. Pmax and Isc. Not only to create the nameplate some definitions are needed, but it is also important to be able to verify such parameters. Therefore the terms and definition sections discuss the impact of measurement uncertainties (MU), manufacturer tolerance (MT), binning of PV modules based on their performance determination but also laboratory terms like accuracy, repeatability and reproducibility. Words that on a first look basically mean the same, but they have small, but important differences. To understand those terms when evaluating the acceptance and pass criteria not only for the nameplate standards, but also for the upcoming revision of IEC 61215, is essential.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1726-1732, This paper analyzes the cumulative grid feed-in behavior of distributed PV battery systems. Simulations with a time resolution of 1 s were performed to determine the impact of the feed-in limit and respective moving average interval on the power flows fed into the grid by spatially dispersed PV battery systems. The study focuses on the main question: What is the impact of different averaging intervals on the grid feed-in behavior of a distributed fleet of PV battery systems? The simulation results reveal that the peaks in the overall feed-in power can be mitigated by reducing the averaging interval from 10 min to 1 min or less.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2402-2407, In order for a PV system to offer ancillary services to the grid, it should be capable of maintaining active power reserves and controlling its output power. In this paper, such a power regulation technique is proposed, which is based on an improved algorithm to estimate the maximum available power when operating suboptimally. The method introduced employs the fundamental equation of the single-diode PV model and applies linear least squares curve fitting to provide the model parameters in an analytical and computationally efficient way. The effectiveness of the control strategy is validated through simulations in MATLAB/Simulink, recording the system’s response in irradiance/temperature variations and reserve command step changes, in both noiseless and noisy environment. Results show excellent dynamic response and increased accuracy and reliability compared to previous approaches.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1739-1743, In this article we investigate the impact of residential solar PV plants on energy losses in distribution networks and their impact on distribution transformers lifetime. Current guidelines in Denmark states that distribution transformers should not be loaded with more than 67% solar PV power to avoid accelerated loss of life. If a solar PV plant causes this limit to be exceeded, the particular owner has to pay for upgrading the transformer. Distribution Network Operators also charge an annual tariff from the solar PV plants to cover the expenses to keep the grid capacity available, the so called “Availability Tariff”. According to the Danish Energy Regulatory Authority, the Availability Tariff must cover the exact expenses, with energy savings etc. from the solar PV plants taken into consideration. Our conclusion is that a distribution network, which represents a typical residential network, can handle up to 110-120% of the transformer nominal ratings before the value of solar PV plants in the distribution network becomes negative. The results suggest that from a technical perspective the aforementioned limit can be increased from 67 to 100%

31st European Photovoltaic Solar Energy Conference and Exhibition; 1744-1747, We expose five pairs of thin-film photovoltaic modules including amorphous silicon, tandem micromorph silicon, two types of CIGS, and CdTe to outdoor conditions for one year. During outdoor exposure they are operated in individual maximum power points with periodic real-time performance measurements and frequent outdoor performance characterization and electroluminescence (EL) inspection. We observe module type specific metastability of performance and EL intensity and the correlation between the two. EL inspection reveals several inhomogeneities, many of which show dynamic character, such as general inhomogeneity redistribution, shunt formation and mitigation, scribing failure mitigation and bright spot formation. Some inhomogeneities are module type specific, while some are not. Despite the presence of dynamic inhomogeneities we predict that they are not responsible for all the observed performance changes and that performance changes arise from the more homogeneous changes on micro-level across the whole module.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1946-1951, Spectral tuning of solar simulators is a well-known procedure, used in the experimental practice for years with multi-junction cells for concentrating photovoltaics (CPV) and space photovoltaic (PV) applications. Multi-junction structures are also used in second generation thin-film PV modules (for example in a-Si:H compounds). A dedicated international standard procedure (IEC 60904-1.1) is in view of publication, describing the “how-to” for current-voltage characterization of multi-junction PV cells and modules: thereafter spectral tuning will need to become soon a widely diffuse practice in research, research-and-development and development-andproduction sites. With this in mind, the authors present here the upgrade of a Class AAA large area pulsed solar simulator to allow spectral tuning by means of a set of high power LEDs. They revise the spectral tuning procedure and show results on commercial modules. They give indications to quantify the new uncertainty contributions arising from the non-uniformity of spectral irradiance and from the spectral mismatch, which affects not only the shortcircuit current (which is the same as in single-junction devices), but also the fill factor and the open-circuit voltage in multi-junction devices.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2378-2380, Integration of Batteries at the input of central inverters of utility scale photovoltaic systems promise high power conversion efficiency and lower installation costs compared to AC-coupling. Unfortunately available maximum power point trackers for DC-coupling of the batteries only boost the voltage of the photovoltaic strings and are not able to operate the strings at the same voltage range of the battery. Depending on state of charge, the range of the battery voltage VBatt, approximated to 630 V VBatt 1000V, limits the voltage VString of photovoltaic strings to VString < 600V. Using a buck / boost converter to charge the batteries allows for VString < VBatt raising power conversion efficiency and has the possibility to reduce costs of the whole system compared to systems using boost converter MPPTs or AC-coupling of the batteries.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1538-1548, As variable, non-dispatchable photovoltaic power continues to displace traditional generation assets, additional resources are needed to control bulk and local power systems. One highly versatile option for providing frequency and voltage stability is to incorporate Energy Storage Systems (ESSs) at the distribution-level. Deployment of these technologies is expected to increase rapidly as time-of-use pricing and self-consumption requirements become wide-spread and provide greater financial incentives. Japanese, European and American stakeholders are working on the standardization of interoperability certification protocols for many grid support functions to validate the Distributed Energy Resource (DER) operations and communications within the power system. Specifically, in this project, Smart Grid International Research Facility Network (SIRFN) laboratories—Sandia National Laboratories (SNL), Austrian Institute of Technology (AIT), Ricerca sul Sistema Energetico (RSE), and National Institute of Advanced Industrial Science and Technology (AIST) Fukushima Renewable Energy Institute (FREA)—are collaborating to create a concise set of test protocols for evaluating the ESS interoperability and functionality. First, a survey of grid-support standards and use cases from several countries was completed. Then the grid support functions were condensed to the unique set of ESS capabilities and organized by function, control signal requirements, and response requirements. From this list, draft certification protocols were written to enable advanced interoperable ESSs covering this range of capabilities to better support photovoltaic and renewable energy integration. An overview of the protocol development process along with preliminary ESS test results for four initial functions (active power, fixed power factor, volt-var, and frequency-watt) is presented. This work is expected to provide the basis of an international testing standard for ESS grid-support functions in the future.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2051-2056, Performance of a PV installation depends critically on the modules behaviour. That is the reason why a good estimation of energy production of a PV installation relies not only on the goodness of the module power characterization at standard test conditions, but also on the goodness of the characterisation of the module behaviour related to the variation of irradiance and temperature. So, it is closer to the reality running a simulation exercise of energy production with the actual values measured outdoors than with the values obtained from datasheets. This paper presents a device specifically implemented to measure outdoors the power of modules at standard test conditions, as well as their efficiency variation with irradiance and their temperature coefficients. Results of measurements with this device are also reported.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2545-2548, In this paper we have presented an overview of the recent reliability results obtained at ECN for foilbased p-MWT, and novel high-efficiency n-MWT and IBC back-contact modules. As deduced from extensive TC and DH testing on p-MWT modules, two alternative low-cost conductive back sheet foils were shown to improve the module reliability. Exposure to DH of the foil-based modules can cause Cu discoloration. This is observed for EVA and a number of alternative encapsulants, with moisture ingress and some specific interactions between encapsulant and Cu substrate playing a role. The n-MWT modules showed improved resistance to DH exposure as compared to n- Pasha (front-to-back tabbing) modules. TC300 and DH2000 tests were passed for frameless IBC Mercury 2x2 modules built using standard foil-based module manufacture process and standard module materials.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2482-2484, Moisture Vapour Transmission Rate (MVTR), also called Water Vapour Transmission Rate (WVTR) of air-side layer of PV Backsheets plays a significant role on the performance and durability of Backsheet and consequently on the reliability of the PV module. This study reveals that the performance and the reliability of photovoltaic modules are highly influenced by the MVTR of the air-side layer of Backsheet if the core layer of the Backsheet is Polyester based. The Backsheet manufactured using air-side Hydrolysed PET (HPET) layer having lower MVTR value shows less hydrolytic degradation of the core layer PET as compared to Backsheet made of Fluoro materials as air-side layers having higher MVTR value. Backsheets with air-side layer having lowest MVTR shows lowest degree of hydrolytic degradation irrespective of types of Backsheets. The Backsheet with structure HPET / PET / Priming layers shows better hydrolytic resistance than all remaining Fluoro based structures considered in the study. The Solar PV module having HPET / PET / Priming layer Backsheet showed lowest power loss (max 3%) up to damp heat 2500hrs. Whereas, the Modules made using Backsheet structure with Fluoro polymer as airside layer having higher MVTR value (Fluoro-2 / PET / Priming layer & Fluoro-3 / PET / Priming layer) showed more power loss ( >5%) after the DHT of 2500hrs. Cracking of core layer PET was observed in the modules made using Backsheets with Fluoro materials. Backsheet structure with Fluoro-1 polymer having lower MVTR value (Fluoro-1 / PET / Priming layer) showed power loss < 4 % after the DHT of 2500hrs. In this study we found that when Fluoro materials are used in the Backsheet as sir-side layer, it remains stable itself for a longer time but due to its poor moisture barrier, the core layer PET of the Backsheet gets hydrolysed faster with time. This phenomenon of hydrolysis reduces the mechanical strength of the core layer PET causing mechanical cracks. Once the cracks in the Backsheet are developed, it leaves almost no protection towards moisture ingress from climate to the module, causing rapid degradation in the cells and interconnects reducing the performance and the durability of the module.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2565-2568, Modules containing cells with small defects can still meet the reliability and energy output performance standard requirements set in IEC61215, as we show by a series of indoor and outdoor reliability and energy output performance tests. There seems to be no direct link between the presence of small defects within the modules and the performance degradation after reliability testing under the following two circumstances: First, the temperature difference, T, is mainly in the range of 9.6 – 30 in modules with defective cells (under short-circuit condition during outdoor exposure), and this is not much different from the T that a “normal” module experiences. Second, as long as the cell defects are kept to a small proportional area less than about 6%, there is no obvious relationship between the location of the defect detected by EL and the position of hot-spots detected with an IR camera. In addition, if the modules are maintained at the maximum power point, testing results show that there is a typical temperature difference of less than 5 under normal irradiance conditions, even for modules with small cell defects.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1789-1792, Infrared thermography is a valuable method for inspecting installed photovoltaics. Easily IR-inspections can be repeated without influencing the operational state. However, the ambient conditions may differ between the measurements. This fact makes the comparability of the results difficult. – Therefore, we studied the influence of differing ambient conditions on the characteristics and the temperature profile on areal and point-shaped defect sites in PV-modules. An especially developed measurement unit recorded simultaneously IR-images, weather data and electric module data. – The evaluated data show that areal cell defects behave linearly with the solar irradiance, while point-shaped defects (e. g. solder joints) exhibit a non-linear dependence.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1748-1752, Electroluminescence (EL) images taken from on-field measurements often suffer from optical and perspective distortion affecting the interpretation and quantification of the images taken. Methods to correct these distortions are presented as well as a method to assess the associated uncertainties. This method uses the uncertainty of pixel position as intermediate step. The influence of pixel deflection, re-projection error and depth-of-field blur is evaluated. Three different camera systems are compared regarding tilt angle dependence. The re-projection error and the camera’s focal length are identified as major influence on the resulting uncertainty. It was shown that EL images with sufficient quality can be recovered, from images taken at high perspective misalignments with tilt angles of about 50°.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2057-2060, Two models to estimate the hourly energy produced by photovoltaic modules of different technologies under real operating conditions are presented. Traditional energy prediction models have shown limits for modules of amorphous technologies when the global radiation is mainly diffuse, because this type of modules is more sensitive to diffuse radiation. Additionally, traditional models do not take into account the spectral distribution of the incident radiation. That fact is a source of inaccuracy especially in photovoltaic technologies with a narrow spectral response such as amorphous silicon. Two models are proposed in this paper. One of them assumes that the energy produced by a module only depends on the incident irradiation and its working temperature. The other one is based on adding a variable that takes into account the spectral composition of solar radiation in the calculation of the energy produced. These models were estimated using hourly values. The hourly temperature of a module is obtained from the ambient temperature, solar irradiation and wind speed. The results obtained for modules of four different technologies, including thin film technologies, show the validity of proposed models.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1825-1829, Small leakage currents flow between the frame and the active cell matrix in photovoltaic (PV) modules under normal operation conditions due to the not negligible electric conductivity of the module building materials. Even if the leakage current is well below the ground-fault detection threshold, predominantly the DC part can cause significant electrochemical corrosion of cell and frame metals, potential-induced degradation (PID) of the shunting type or PID of the solar cells’ surface passivation. In general, it was found that the degradation rate has a high correlation with the leakage current density which is a strong function of position in large-area modules due to the voltage drop between the frame and the cells. In this work we measured material and surface conductivities and subsequently calculated the local leakage current density distribution in large-area PV modules in order to obtain quantitative insight into the local degradation. The shares of leakage currents through individual materials are discussed and, as an example, the width of the circumferential module area threatened by electrochemical corrosion was predicted under accelerated test conditions.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2261-2264, As a technique of maintaining and checking the solar photovoltaic power system, it is general that the amount of system power output is simulated from various weather conditions and the method for comparing it with an actual amount of PV power output. In that case, the check starts at field site afterwards when the actual measurement value of the amount of power output has decreased than the simurated value to some degree. Author proposed the advanced approach that measures the I-V curve to evaluate the I-V characteristic of the photovoltaic modules more accurately from 1st quadrant to 4th quadrant. The current flows from photovoltaic modules in the 1st quadrant and flows to PV in the 4th quadrant. This method has an advantage that I-V characteristic is evaluated more accurately because the data range of I-V curve increases1). In the present study, the effect was investigated how the I-V characteristic causes difference that the module was connected in the series, and the deteriorated module is contained with the string. The more accurate evaluation proved by measuring the I-V curve of each string to confirm accuracy by this advanced measurement method.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2119-2121, There are about 1.5 million photovoltaic systems in Germany. Private owners who cannot assign an operation and maintenance company due to economic reasons operate most of their systems on their own. Furthermore, monitoring systems are too complex or cannot be afforded by typical system owners. This is one reason that about 80 percent of the photovoltaic systems in Germany do not generate the yield that is technically possible. Therefore, we present an innovative web-application that allows system users and operators to monitor the actual status and profitability of their photovoltaic system. Also, they can get in contact with a specialized company, which can repair or maintenance the system in case of problems such as too small yield, damages or malfunctions. Our goal is the development of an application that is easy to use and designed for computers as well as mobile devices.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1980-1983, The aim of this paper is the use and validation of artificial intelligence techniques to predict the temperature of a thin-film module based on tandem CdS/CdTe technology. The cell temperature of a module is usually tens of degrees above the air temperature, so that the greater the intensity of the received radiation, the greater the difference between these two temperature values. In practice, directly measuring the cell temperature is very complicated, since cells are encapsulated between insulation materials that do not allow direct access. In the literature there are several equations to obtain the cell temperature from the external conditions. However, these models use some coefficients which do not appear in the specification sheets and must be estimated experimentally. In this work, a support vector machine and a multilayer perceptron are proposed as alternative models to predict the cell temperature of a module. These methods allow us to achieve an automatic way to learn only from the underlying information extracted from the measured data, without proposing any previous equation. These proposed methods were validated through an experimental campaign of measurements. From the obtained results, it can be concluded that the proposed models can predict the cell temperature of a module with an error less than 1.5 °C.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1764-1769, Bifacial solar cells convert photons into electricity on both their front and rear sides, which makes the assessment of solar resource trickier than for classical solar cells that are active on their front side only. Indeed, the solar irradiation received by the front side of the module is highly dependent on direct and diffuse irradiation and not to the same degree on ground-reflected irradiation. In a tilted configuration, the back side of the module hardly ever receives direct irradiation, thus increasing the importance of a good estimation of ground-reflected irradiation. A model has been developed with the Modelica language in a Dymola simulation environment in order to calculate the back-side solar irradiations received by the different modules in a PV installation. The simulation and experimental results prove that the albedo of the ground surface is of prime importance. However, the shadow of the PV installation on the ground also has a direct impact on the amount of electricity generated by the rear side. This paper assesses the relative impacts of several factors of importance in the design of a bifacial PV power plant such as elevation of structures, ground albedo, tilt angle and spacing between structures.