Search

37th European Photovoltaic Solar Energy Conference and Exhibition; 1542-1547, On the road to more photovoltaic (PV) energy production, high-throughput and non-disruptive maintenance routines are needed to ensure a reliable long-term performance of PV plants. Additionally, a method that allows a quantitative assessment of silicon PV module performance solely by measuring cell temperatures via infrared thermography (IR) is more easily applicable in a high-throughput fashion using e.g. unmanned aerial vehicles (UAVs) than measuring each module individually. We introduced a mathematical framework to determine power losses of modules from IR images. The method makes use of the fact that, in a steady state closed system, energy that is not converted into electrical power has to be dissipated as heat. In this contribution, we reduce this method to practice by analysing the electrical performance of four PV modules with temperature anomalies at two different sites, which are equipped with a power monitoring system by the company Sunsniffer for validation. We present an analytical expression for the power-temperature-relationship, and discuss influences of convection and how to correct for them. We find that power predictions often deviate less than 3% from the monitoring data and confirm our theoretical considerations, allowing power loss to be quantified. Cases with larger deviations show that some influences are yet to be better understood and more data is needed.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1287-1289, In this paper a dataset consisting of 2,426 solar cells extracted from high-resolution electroluminescence (EL) images is used for automated defect probability recognition. The collected images contain both functional and defective solar cells with varying degrees of degradation both in monocrystalline and polycrystalline solar modules. The images were labeled by expert who categorized the solar cells by the likelihood of a defect within each image. The labeled images can be used for development of computer vision and machine learning methods for automatic detection of different defects, like cracks, fracture interconnects, PID, and cell quality and for the purpose of predicting the power efficiency loss.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1396-1398, The proposed new PV system concept is based on several AC modules that are connected in series using inductive power transfer. These modules include a cell matrix that is connected to a module integrated DC/AC inverter. The high frequency AC current flows through the primary side planar coil generating a magnetic flux. Outside of the PV module, there is a clamp including ferromagnetic material for the magnetic circuit that caries the magnetic flux to the secondary winding. The magnetic flux induces an AC current in the secondary winding, which is formed by the common cable. An AC/AC converter is placed at the end of the PV module strings to generate the 50 Hz and to connect the PV power plant to the electricity grid. This new PV system concept is a fundamentally new approach of the electricity transmission in the field of PV system technology. It is not restricted to the replacement or optimisation of an individual system component, but it requires the continuing development of the PV module construction and the contactless connection technology to the common cable. The proposed inductive power transfer per each PV module opens up a complete new field for the PV system technology.

35th European Photovoltaic Solar Energy Conference and Exhibition; 2069-2074, In contrast to research photovoltaic (PV) systems, commercial PV systems are usually not equipped with sophisticated weather metrology and quite frequently even lack an irradiance sensor. Still, the determination of their degradation rate is of paramount importance for the plant owners. This paper compares various approaches to determine the degradation rates of commercial MW-scale PV systems from such “non-ideal” data sets as they are frequently obtained from monitoring data. In particular, the use of model-based irradiance and temperature data is evaluated and several novel methods for data filtering are introduced. It is investigated, for which weather conditions the use of externally weather station data is superior to on-site data. By reducing the data set to mostly sunny conditions, reliable DRs can be determined. Furthermore, the data scattering can be reduced significantly so that sudden performance drops or changes in the DRs become visible, which were previously masked by scattering and data drifts. These results demonstrate that significantly different DRs and uncertainties are obtained depending on the method of data filtering. Hence, care must be taken, when deriving DRs from “non-ideal” monitoring and weather data and when comparing DRs determined by different methods.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1554-1558, PV-modules with precracked solar cells are frequently present in PV-plants as current inspection methods reveal. How these modules perform in the future is still unknown. Uniform static loading tests characterize short-term performance well, as presented previously (EUPVSEC 2017). In order to simulate long-term stability, the application of alternating loads, comparable to wind gusts, is important. The load cycle is fed into the improved mechanical loading test-setup by a PLC whilst recording EL-images simultaneously and measuring IV-curves. For the first time, module performance for long-term stability with 100,000 cycles are presented. The results show that with an increasing number of cycles and pressure, the EL-intensity distribution of cracked cells changes but the performance loss is rather small. These findings correlate with analysis of field-exposed modules.

35th European Photovoltaic Solar Energy Conference and Exhibition; 2001-2004, Potential induced degradation (PID) is still a severe problem in many PV-installations and a huge financial risk for investors and plant-owners if not detected early. In previous investigations it was shown that thermography, conducted with handheld or drone mounted IR-cameras, is a fast and reliable tool to detect PID affected PV-modules on site and estimate their remaining electrical power during normal plant operation. In this work we show how to improve the sensitivity of IR- and various other imaging techniques by using the characteristic behavior of PID affected cells regarding the different excitation forces, i.e. solar irradiance for IR- and electric current for DLIT- and EL-measurements. Furthermore, we address the implications of this specific behavior by simulating the energy yield of several PID affected PV-strings based on real monitoring data for two inspected sites and suggest carrying out the measurements on site- and under failure- relevant conditions rather than standard test conditions.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1147-1151, EL-imaging is a valuable tool to analyze PV-modules for the presence of cracked cells. Normally, these inspections are done in air-conditioned labs or at cool nights outdoors. However, the PV-modules are supposed to generate energy outdoors in the field. Therefore, they operate at significantly elevated temperatures which are much higher than the temperatures at the inspection time. In order to investigate the temperature influence on the performance of precracked PV-modules, EL-images and IV-curves were recorded of warm and mechanically loaded modules. The study illustrates that the performance of cracked cells changes with temperature and pressure. There is the tendency that modules at elevated temperatures perform better than those at low temperatures under the same loading situation.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1177-1181, In this paper, the temperature-induced performance losses of eight different photovoltaic (PV) module technologies under various real weather conditions are analyzed. Therefore, the electrical performance data of one year gathered at the ZAE Bayern’s PV test plant in Arzberg, Germany was correlated to on-site weather data and module temperature measurements. By classifying the measurement days into distinct weather categories an in-depth analysis of the weather- and technology-dependent performance is realized in this study. For each weather category, the different PV technologies are ranked with respect to their electrical yield. Subsequently, the temperature behavior of the technologies is analyzed for each of the categories in order to investigate, in how far the temperature-related yield losses are responsible for the weather-dependent performance differences that are observed for the different technologies. This analysis shows that the performance behavior is one of the main causes for the performance differences that are observed. However, it also becomes clear that further losses due to differences in spectral and / or angular sensitivity or weak light performance also influence the performance significantly. In the future, the results of this study will support system designers in choosing the appropriate PV technology for a given site based on the local climate conditions.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1931-1936, Potential induced degradation (PID) causes severe damage and financial losses even in modern PVinstallations. In Germany, approximately 19% of PV-installations suffer from PID and resulting power loss. This paper focuses on the impact of PID in real installations. The analysis focuses exemplarily on a 314 kWp PV-system in the Atlantic coastal climate. Infrared (IR)-imaging is used for identifying PID without operation interruption. Historic electric performance monitoring data for several years are analyzed on system and string level. Additionally, punctually measured module string current-voltage (I-V)-curves are considered. The data sets are combined for understanding the PID behavior of this PV plant. The number of PID affected cells within a string varies strongly between 1 to 22% with the string position on the building complex. A PID-resistance which correlates to the defined PID-defect-ration is presented. Finally, indicators for the reliable determination of PID is given.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2320-2324, First statistical evaluation of IR-inspections of PV-plants reveals that 81% of the installed PV-plants show IR-abnormalities. More than 140 PV-plants with more than 200,000 PV-modules were inspected and evaluated statistically. Main IR-abnormalities or failures in modules and string installations are analyzed, respectively. The average failure rate for PV-modules is about 6% and for module strings approximately 1%. The differentiation based on the installation type reveals that small residential installations relatively seen show more defective modules than large field installations. A first estimation of the missed income by not detecting and maintaining major module and plant failures yield a missed income of about 100 Mio. EUR considering the PV-systems installed in Germany. IR-imaging is a valuable method to give fast and reliable information about the actual quality and failure rate in inspected PV-installations.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1037-1040, We demonstrate a novel two-step method for accurate determination of the complex refractive indices of phosphor materials in particulate form. The real part of the refractive index is first measured at a number of selected wavelengths using the Becke Line method; the results are interpolated over a broader wavelength range using Sellmeier's equations. The imaginary part of the refractive index is extracted from measured optical characteristics of polymer layers embedded with phosphor particles; a specialized numerical simulation tool is employed for this purpose. Finally, using the determined complex refractive indices, we numerically investigate the potential of luminescent down-shifting applied to thin-film solution-processed solar cells. We study the influence of the main properties of luminescent down-shifting layers filled with phosphor particles, and indicate the gains in the solar cell performance that can be obtained using this approach.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1451-1456, Damaged modules, especially with existing cell cracks, are observed quite often in PV-installations. Little knowledge exists about the stability of such pre-cracked modules under real operating conditions. Previous investigations and existing standards focus on the degradation of new, defect-free modules. This work highlights a twofold approach for performance study of pre-cracked modules: 1) artificial stressing of 20 representative pre-cracked modules with a novel load test set-up simulating snow and wind loads, 2) simulating IV-curves of cracked cells. The experimental results are discussed with respect to field exposure data. EL-images of stressed PV-modules indicate that new cracks are only initiated once a certain threshold is exceeded. Below this threshold formerly unseen cracks open, as can be seen by small changes in the EL-intensity. Power measurements yield a strong power reduction at the loaded state. Due to the solar cell being under tension the cracks open and the separated areas lose their electrical contact. Considering a break resistance in the IVcurve, simulations lead to good agreement with the observed experimental results. It is highlighted that the electric contact after unloading for the previously unloaded module recovers visibly in the ELimage as well as in the power output. Simulating real weather (operating) conditions by moderate static loading tests reveals no measurable changes in the EL-images affecting the power output.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2274-2279, In this paper, a new metric for assessing the location-specific mechanical loads imposed by snow or wind gusts which a photovoltaic module can be expected to be exposed to at a given location is introduced. For demonstrating this general approach, two locations of moderate distance (~110km) in Northern Bavaria are compared. It is shown that even on moderate distances the expected loads differ by a factor of four or more highlighting the importance of location-specific requirements for PV modules. For assessing the loads, the historical weather data of the closest surrounding weather station is evaluated in order to deduce an expectation value for the site of interest. This data is analyzed with respect to the frequency and severity of the relevant weather events such that the annuality of a weather event of a given severity can be determined. Finally, the severity of an event corresponding to a single occurrence in 20 years, i.e. a standard product warranty, is chosen to represent the requirements of a location with respect to a certain parameter.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1010-1012, In spite of the steadily improved quality of co-evaporated Cu(In,Ga)Se2 absorber layers, the existence of local defects affecting the module performance in large area production can still be an issue. Generally, both, lateral composition gradients and point defects can be found in those layers. We show the necessity to separate these two influences and propose two measurement techniques in order to asses the effect of the material and the defects individually. In oder to quantify the theoretical defect-free open circuit voltage (Voc), given by the material composition, we used luminescence spectroscopy. The additional effect on the Voc originating from local defects was determined using dark lock-in thermography. The combination of both these methods enables a local prediction of a module’s Voc. In the following, we conduct an indepth analysis of the determination of the material composition and its impact on the resulting Voc.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 2036-2040, In recent years, remote-controlled unmanned air vehicles (UAV) have been used increasingly to attain aerial infrared (aIR) recordings of large photovoltaic (PV) power plants with which thermally suspicious PV modules can be identified and localized. But so far, aIR recordings are still analyzed mostly manually – a process which can be extremely time-consuming and error-prone. In this context, the performance of a module and defect detection algorithm for aIR images is evaluated as a function of the flying altitude. For this purpose, aIR recordings of a PV power plant are generated from six flying altitudes from 5 m to 30 m above ground level by means of a drone measurement system and used as data input for the image processing tool. The results indicate optimal flying altitudes for both module and defect detection. However, the most suitable flying altitude may be a compromise with further conditions. The findings of this work will advance future automatic monitoring and early detection systems.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 2021-2026, The on-site inspection of solar farms with infrared cameras from the air using unmanned aerial vehicles (UAVs) is called aIR-PV-check. Applying this method with a sophisticated image processing enables the quality control of installed thin-film PV-modules. Various module defects can be detected and visualized based on their elevated temperature. There are modules with cracks and ones affected by potential induced degradation PID. The IR-imaging data correspond well with EL-images and electrical data. Thus, modules with slightly elevated temperature - typical for PID modules - appear damaged in the EL-images as well as in their electrical behavior. Furthermore, modules with different power classes can be located. Therefore, IR-imaging is a fast and suitable technique to detect PID and other features in installed CIGS modules.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1837-1841, A fast and non-destructive failure inspection is essential to ensure the reliability of PV plants. This might only be achieved by using highly sensitive imaging techniques which can detect local electrical losses in solar modules. Here, EL imaging used for outdoor PV inspection gained large interest, since it can be used to characterize local cell damages, series resistances, and shunts in solar modules. However, currently available EL-cameras base on Si-CCD-detectors. Besides high spatial resolutions they exhibit long image integration times (IIT) of about 1 s for obtaining evaluable EL-images. To overcome this limitation we present, for the first time, an InGaAs camera which enables a complete EL-characterization of field-installed PV-modules with IITs between 1 ms and 20 ms. The short IITs result in frame rates of about 100 Hz which even offer the opportunity of recording dynamic EL-movies and daylight Electroluminescence Lock-In (ELLI) measurements. To test the outdoor applicability we compared EL-movies of the InGaAs camera with EL-images of a Si-CCD camera and show that all relevant power reducing cell failures (e. g. cracks) can be detected and characterized.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 2252-2254, Photovoltaic (PV) modules are often affected by defects caused by transport and installation or by field degradation due to environmental conditions. If a power reduction is observed in the inverter data, a detailed error cause analysis is often very cost-intensive even when using imaging methods like thermography or electroluminescence. We present a method to classify the defect type of PV modules only by evaluating the maximum power output (Pmpp) for different irradiances. Thereby, low parallel resistance, high series resistance and broken cells can be distinguished from each other. Simulations and consistent explanations confirm the experimental findings. The method works particularly well for parallel resistance problems like potential induced degradation (PID). Thus, this failure type can easily be diagnosed in modules. The method should also be applicable to data of module strings and to thermography-based failure analysis in field which will be investigated in the future.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 2027-2029, IR-thermography is a useful tool for the inspection of installed PV-modules. It is well-known that ambient conditions like irradiance and wind velocity have an influence on the measured temperatures. In this investigation, we study the influence of short-time changes of the electrical system, caused by the global maximum power point search algorithm of a grid-tie inverter, on IR-images. Considerable changes of the temperature difference at defects within seconds were detected. Therefore, we perform an experimental study with different types of inverters on a test facility at the ZAE Bayern and thermal simulations of the behavior of different types of module defects. Furthermore, we discuss the impacts on the defect temperature and make a proposal to avoid misinterpretation of IR-images of PV-modules affected by short-time changes of the electric system.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1815-1818, In the lifetime of photovoltaic (PV) modules, the quality and the stability of the encapsulation are important characteristics as they affect the electrical isolation as well as the weathering protection of the photovoltaic cells. One of the most commonly used encapsulation materials is ethylene vinyl acetate (EVA), which is crosslinked during the lamination process. The degree of crosslinking is decisive regarding the long-term stability of photovoltaic modules. Therefore, manufacturers look for technologies for inline evaluation of the EVA crosslinking degree. In this work, the authors present a new method to evaluate the crosslinking degree of EVA based on Raman spectral analysis. We found a direct correlation between the degree of crosslinking and the Raman peak at 1649 cm-1, which presumably originates from residual C=C double bonds in EVA.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 2016-2020, The on-site inspection of solar farms with infrared cameras from the air using unmanned aerial vehicles UAVs is called aIR-PV-check. A 2.4 MW PV-tracking system with more than 200 arrays was IR-inspected. 75% of the trackers had defective modules, which corresponds to more than 8% of the modules. Fairly high temperatures above 80°C were often measured at defects. The spatial distribution of the modules within the tracker plane was studied. Statistical data evaluation shows that more defective modules are found in the upper half. For the vertical failure distribution one maximum exists in the center, whereas for the horizontal dimension two maxima are present. One explanation may be the considerably high wind loads at the installation spot in context with the stiffness of the tracker system construction. It is shown that IR-inspection is a suitable method to reveal failures in tracking PVsystems where monitoring data fail for various reasons.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1548-1551, In this paper, the influence of the heat dissipated by a broken cell in a photovoltaic module on the encapsulation properties is investigated. Therefore, a combined study based on drone-based infrared thermography, electroluminescence and indentation tests of the mechanical properties of the encapsulant is presented. For the first time, direct evidence is given that the viscoelastic properties of the encapsulant are shifted towards increased stiffness and brittleness by the long-term presence of hot cells. Therefore, the dissipated heat may lead to a local damage of the encapsulant on the long-term, which in turn may trigger the degradation of the module due to insufficient encapsulation.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2612-2621, The decentralized character of the German Energiewende is most evident in the installation of more than half a million domestic rooftop solar systems. Their success story however has slowed down in the last two years because of frequent regulatory updates, anti-dumping measures, decreasing feed-in tariffs and little experience with the influence of electrical self-consumption. To make it even more complex solar battery systems were introduced to the market increasing the number of layout factors. In this paper we present a detailed techno-economic model to compute the profitability of different PV-battery-setups. All technical parameters as well as current German regulation and appropriate cost functions especially designed to small systems and derived from an extensive market survey are taken into account. Rates for self-consumption are determined by a continuous power flow simulation. All input data is assessed and uncertainties analyzed by means of a Monte Carlo Simulation. A sensitivity analysis finally identifies the parameters of highest influence. Optimizing self-consumption with batteries is close to being a business case for electro-chemical storage and this paper provides a detailed analysis of various setups and technologies.