TL;DR: The IES–UPM observations on 200 affected photovoltaic modules are presented, as well as electroluminescence, peak power rating and operating voltage tests have been carried out, and hot-spots temperature gradients larger than 20 °C are proposed as rejecting conditions for routine inspections under contractual frameworks.
Abstract: The hot-spot phenomenon is a relatively frequent problem occurring in current photovoltaic generators. It entails both a risk for the photovoltaic module’s lifetime and a decrease in its operational efficiency. Nevertheless, there is still a lack of widely accepted procedures for dealing with them in practice. This paper presents the IES–UPM observations on 200 affected photovoltaic modules. Visual and infrared inspection, as well as electroluminescence, peak power rating and operating voltage tests have been carried out. Thermography under steady state conditions and photovoltaic module operating voltage, both at normal photovoltaic system operating conditions, are the selected methods to deal in practice with hot-spots. The temperature difference between the hot-spot and its surroundings, and the operating voltage differences between affected and non-affected photovoltaic modules are the base for establishing defective criteria, at the lights of both lifetime and operating efficiency considerations. Hot-spots temperature gradients larger than 20 °C, in any case, and larger than 10 °C when, at the same time, voltage operating losses are larger than the allowable power losses fixed at the photovoltaic module warranties, are proposed as rejecting conditions for routine inspections under contractual frameworks. The upper threshold of 20 °C is deduced for temperate climates from the basic criterion of keeping absolute hot-spot temperatures below 20 °C.
Abstract: In this paper, the effect of dust on electrical and thermal behavior of photovoltaic panels is investigated. For this aim, several types of dusts are considered. Which leads to different panel behaviors in the thermal, optical and electrical aspects. Indeed, it has been shown that light transmission varies with dust type. Laboratory tests using various instruments such as microscope, spectrophotometer, I-V photovoltaic modules analyzer and data logger equipped with thermocouples are carried out. The obtained results show that variations on the physical parameters (grain size and type), level of light transmission and the glazing temperature lead to change in performance of photovoltaic panel (PV). The experimental observed behaviors were in accordance with the results obtained using the Energy2D computer simulation code of the thermal behavior applied to the glazing and PV module (Glass, EVA, Cell, Frame and Tedlar).
Abstract: A new bypass strategy for monocrystalline and polycrystalline solar panels allowing significant hot spot temperature reduction in both partial and full shading conditions is presented. The approach relies on a series-connected power MOSFET that subtracts part of the reverse voltage from the shaded solar cell, thereby acting as a voltage divider. Differently from other active bypass circuits, the proposed solution does not require either a control logic or power supply and can be easily substituted to the standard bypass diode. The operation of the new circuit is described with reference to the shading condition prescribed by the EN 61215 qualification procedure. Experiments performed on two commercial solar panels have shown that the shaded cell can be cooled up to 24 °C with respect to the case in which the standard bypass diode is adopted.
Abstract: Hot spotting is a reliability problem in photovoltaic (PV) panels where a mismatched cell heats up significantly and degrades PV panel output power performance. High PV cell temperature due to hot spotting can damage the cell encapsulate and lead to second breakdown, where both cause permanent damage to the PV panel. Therefore, the design and development of a hot spot mitigation technique is proposed using a simple, low-cost and reliable hot spot activation technique. The hot spots in the examined PV system is detected using FLIR i5 thermal imaging camera. Several experiments have been studied during various environmental conditions, where the PV module P-V curve was evaluated in each observed test to analyze the output power performance before and after the activation of the proposed hot spot mitigation technique. One PV module affected by hot spot was tested. The output power increased by approximate to 3.6 W after the activation of the hot spot mitigation technique. Additional test has been carried out while connecting the hot spot PV module in series with two other PV panels. The results indicate that there is an increase of 3.57 W in the output power after activating the hot spot mitigation technique.
Abstract: Towards tackling the evident practical challenges of fault detection and diagnosis for PV modules, especially in large-scale installations, this paper proposes two different techniques for advanced inspection mapping of PV plants; aerial triangulation and terrestrial georeferencing. The former uses data of aerial thermal/visual imagery of operating PV modules, obtained by an unmanned aerial vehicle (UAV), to generate static “inspection maps”, in the form of true orthophoto mosaics. On the other hand, georeferencing is used to associate terrestrial thermal/visual imagery, obtained at distinct positions in a PV plant, with geographic data. By such way, inspection is based on a dynamic virtual map of the installation. Both mapping techniques were tested in two grid-connected PV systems, of a total installed power of 70.2 KWp. Several defective modules were easily and accurately detected, typically as abnormal temperature profiles, in the infrared (IR) spectrum. In addition, specific thermal image patterns of operating modules, were validated and quantified by additional diagnostic measurements, and were assigned to possible fault types. On the basis of the experience feedback, the potential of the proposed techniques and their limitations, for further application to PV plants of larger scale, are also discussed.
Abstract: Hot spotting is a reliability problem in photovoltaic (PV) panels where a mismatched cell heats up significantly and degrades PV panel output-power performance. High PV cell temperature due to hot spotting can damage the cell encapsulate and lead to second breakdown, where both cause permanent damage to the PV panel. Therefore, the development of two hot-spot mitigation techniques is proposed using a simple and reliable method. PV hot spots in the examined PV system were inspected using the FLIR i5 thermal imaging camera. Multiple experiments have been tested during various environmental conditions, where the PV module $I - V$ curve was evaluated in each observed test to analyze the output-power performance before and after the activation of the proposed hot-spot mitigation techniques. One PV module affected by the hot spot was tested. The output power during high irradiance levels is increased to approximately 1.26 W after the activation of the first hot-spot mitigation technique. However, the second mitigation technique guarantees an increase in the power up to 3.97 W. An additional test has been examined during the partial shading condition. Both proposed techniques ensure a decrease in the shaded PV cell temperature; thus, there is an increase in PV output power.
Abstract: The influence of temperature and wavelength on electrical parameters of crystalline silicon solar cell and a solar module are presented. At the experimental stand a thick copper plate protected the solar cell from overheating, the plate working as a radiation heat sink, or also as the cell temperature stabilizer during heating it up to 80°C. A decrease of the output power (−0.65%/K), of the fill-factor (−0.2%/K) and of the conversion efficiency (−0.08%/K) of the PV module with the temperature increase has been observed. The spectral characteristic of the open-circuit voltage of the single-crystalline silicon solar cell is also presented. It is shown that the radiation-rate coefficient of the short-circuit current-limit of the solar cell at 28°C is 1.2%/(mW/cm2).
Abstract: A conventional photovoltaic module has been prepared with the purpose of accessing its cells either individually or associated. Measurements of every cell and of the whole module have been performed in direct and reverse bias, with the objective of documenting the scattering in cell parameters, working point of the cells and shading effects. Several shading profiles have been tested, and the influence of the reverse characteristic of the shaded cell in module output is stressed.
TL;DR: Findings of PV plant evaluations carried out during last years are presented, showing the possible degradation of PV modules and hidden manufacturing defects.
Abstract: The fast growth of PV installed capacity in Spain has led to an increase in the demand for analysis of installed PV modules. One of the topics that manufacturers, promoters, and owners of the plants are more interested in is the possible degradation of PV modules. This paper presents some findings of PV plant evaluations carried out during last years. This evaluation usually consists of visual inspections, I–V curve field measurements (the whole plant or selected areas), thermal evaluations by IR imaging and, in some cases, measurements of the I–V characteristics and thermal behaviours of selected modules in the plant, chosen by the laboratory. Electroluminescence technique is also used as a method for detecting defects in PV modules. It must be noted that new defects that arise when the module is in operation may appear in modules initially defect-free (called hidden manufacturing defects). Some of these hidden defects that only appear in normal operation are rarely detected in reliability tests (IEC61215 or IEC61646) due to the different operational conditions of the module in the standard tests and in the field (serial-parallel connection of many PV modules, power inverter influence, overvoltage on wires, etc.).
"Experimental observations on hot-sp..." refers background in this paper
...Fortunately, they can be easily detected through IR inspection, which has become a common practice in current PV installations (Auer et al., 2007; Botsaris and Tsanakas, 2010; Buerhop et al., 2011a,b,2012; Hoyer and Buerhop, 2008; Kasemann et al., 2009; King et al., 2000; Muñoz et al., 2011)....
...It can be observed that power dissipation at a hot-spot can vary nearly an order of magnitude depending on the defective cell (Alonso-García and Ruiz, 2006; Alonso-García et al., 2003; Herrmann et al., 1997,1998; Muñoz et al., 2011)....
TL;DR: The international Task 13 expert team has summarized the literature as well as their knowledge and personal experiences on actual failures of PV modules, and introduces a signal transition method for the detection of defective circuits in installed PV modules.
Abstract: One key factor of reducing the costs of photovoltaic systems is to increase the reliability and the service life time of the PV modules. Today's statistics show degradation rates of the rated power for crystalline silicon PV modules of 0.8%/year Jordan11. To increase the reliability and the service life of PV modules one has to understand the challenges involved. For this reason, the international Task 13 expert team has summarized the literature as well as their knowledge and personal experiences on actual failures of PV modules. The target audience of this work is PV module designers, PV industry, engineering lines, test equipment developers, testing companies, technological research laboratories, standardisation committees, as well as national and regional planning authorities. In the first part, this document reports on the measurement methods which allow the identification and analysis of PV module failures. Currently, a great number of methods are available to characterise PV module failures outdoors and in labs. As well as using I-V characteristics as a diagnostic tool, we explain image based methods and visual inspection. For each method we explain the basis, indicate current best practice, and explain how to interpret the images. Three thermography methods are explained: thermography under steady state conditions, pulse thermography and lock-in thermography. The most commonly used of these methods is thermography under steady state conditions. Furthermore electroluminescence methods have become an increasingly popular standard lab approach for detecting failures in PV modules. 2A less common but easier to use method is UV fluorescence. This method can be used to detect module failures similar to those detected with thermography and electroluminescence techniques; however, the PV modules must be sited outdoors for at least one and a half years for the method to be effective. For visual documentation of module conditions in the field, we set up a standard which is now accepted and used by all authors documenting such tests. This standard format allows the documentation of visible module failures in standardised way and makes the data accessible for statistical evaluation. Furthermore we introduce a signal transition method for the detection of defective circuits in installed PV modules. All methods are linked to the PV module failures which are able to be found with these methods. In the second part, the most common failures of PV modules are described in detail. In particular these failures are: delamination, back sheet adhesion loss, junction box failure, frame breakage, EVA discolouration, cell cracks, snail tracks, burn marks, potential induced degradation, disconnected cell and string interconnect ribbons, defective bypass diodes; and special failures of thin-film modules, such as micro arcs at glued connectors, shunt hot spots, front glass breakage, and back contact degradation. Where possible, the origin of the failure is explained. A reference to the characterisation method is given to identify the failure. If available, statistics of the failure type in the field and from accelerating aging tests are shown. For each failure, a description of safety issues and the influence on the power loss is given, including typical follow-up failure modes. In the third part, new test methods are proposed for detection of PV module failures in the field. A special focus is made on mechanical tests because many problems have arisen in the last few years from the mechanical loading of modules. These mechanical loads occur during transportation and from snow loads on modules mounted on an incline. Furthermore, testing for UV degradation of PV modules, ammonia corrosion (sometimes found in roofs of stock breeding buildings) and potential induced degradation are described. The latter method caused some controversy within the international standardization committee until the finalization of this report because many alternative suggestions from different countries were proposed. The test methods are explained in detail, linked to failure descriptions and the results are compared to real failure occurrences, where possible. During a past Task 13 project phase, we recognised that the topic â��3.2 Characterising and Classifying Failures of PV Modulesâ�� is an important on-going subject in the field of PV research. The current review of failure mechanisms shows that the origin and the power loss associated with some important PV module failures is not yet clear (e.g. snail tracks and cell cracks). There are also still some questions as to how best to test for some types of failure (e.g. potential induced degradation and cell cracks). Furthermore, despite the fact that a defective bypass diode or cell interconnect ribbon in a PV module may possibly lead to a fire, very little work has been done to detect these defects in an easy and reliable way once installed in a PV system. However, there are research groups currently working on those topics in order to overcome these challenges. Therefore, it is planed to continue our in-depth review of failures of photovoltaic modules in an extension of the TASK 13 project.
"Experimental observations on hot-sp..." refers background or methods in this paper
...However, previous experiences do not allow a clear relation between module temperature and lifetime to be established (Osterwald and McMahon, 2009)....
...We propose to consider 85 °C, which is the maximum temperature of the thermal cycling tests described in the IEC-61215, as the maximum absolute PV module temperature for acceptance/rejection purposes (Osterwald and McMahon, 2009)....