As photovoltaic penetration of the power grid increases, accurate predictions of return on investment require accurate prediction of decreased power output over time. Degradation rates must be known in order to predict power delivery. This article reviews degradation rates of flat-plate terrestrial modules and systems reported in published literature from field testing throughout the last 40 years. Nearly 2000 degradation rates, measured on individual modules or entire systems, have been assembled from the literature, showing a median value of 0·5%/year. The review consists of three parts: a brief historical outline, an analytical summary of degradation rates, and a detailed bibliography partitioned by technology. Copyright © 2011 John Wiley & Sons, Ltd.

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Photovoltaic Degradation Rates—an Analytical Review

Faults in any components (modules, connection lines, converters, inverters, etc.) of photovoltaic (PV) systems (stand-alone, grid-connected or hybrid PV systems) can seriously affect the efficiency, energy yield as well as the security and reliability of the entire PV plant, if not detected and corrected quickly. In addition, if some faults persist (e.g. arc fault, ground fault and line-to-line fault) they can lead to risk of fire. Fault detection and diagnosis (FDD) methods are indispensable for the system reliability, operation at high efficiency, and safety of the PV plant. In this paper, the types and causes of PV systems (PVS) failures are presented, then different methods proposed in literature for FDD of PVS are reviewed and discussed; particularly faults occurring in PV arrays (PVA). Special attention is paid to methods that can accurately detect, localise and classify possible faults occurring in a PVA. The advantages and limits of FDD methods in terms of feasibility, complexity, cost-effectiveness and generalisation capability for large-scale integration are highlighted. Based on the reviewed papers, challenges and recommendations for future research direction are also provided.

Fault detection and diagnosis methods for photovoltaic systems: A review

The objective of this paper is to introduce the integration of the diverse factors that affect the performance of Photovoltaic panels and how those factors affect the performance of the system. Those factors include: environmental, PV system, installation, cost factors as well as other miscellaneous factors. Each of these factors is further classified into novel subcategories along with the reduction/increase effects of some factors on the system output. Solar irradiance, module temperature, dust accumulation, shading and soiling factors are some of the environmental concerns that have major effects. Panel's I-V characteristics, inverter, battery and panel efficiencies, panel material, atomic structure and band-gap energy are some of the system factors. As for the installation factors, cable characteristics, angle of inclination, mismatch effects, fixed/tracking PV mechanisms as well as MPPT are crucial to consider. Concerning the cost factors, the cables and the overall system costs are to be taken into consideration especially during payback period calculations. Other miscellaneous factors have a role in affecting the performance of the system such as degradations in the PV panel, panel resistances, performance ratio, maintenance and cleaning, sizing of the system as well as the surface area of the panel. The study results shall help both practitioners and researchers in having an inclusive overview about the several factors that can have an effect on the performance of the PV panels by removing the burden of having to search several studies under each category of factors. Moreover, researchers can build on this study by researching new ways to decrease the effect of certain factors which can further enhance the performance of the system. On the other hand, practitioners can introduce new systems that can be physically implemented in our daily lives to hinder the effect of factors negatively affecting PV panels’ performance.

An integrated review of factors influencing the perfomance of photovoltaic panels

As any energy production system, photovoltaic (PV) installations have to be monitored to enhance system performances and to early detect failures for more reliability. There are several photovoltaic monitoring strategies based on the output of the plant and its nature. Monitoring can be performed locally on site or remotely. It measures production, focuses also on verification and follow-up of converter and communication devices' effective operation. Up to now, some faults diagnosis methods for PV components and systems have been developed. However, given the evolution of PV installations, more advanced monitoring techniques are continuously under investigation. In this paper, major photovoltaic system failures are addressed. Then techniques for photovoltaic monitoring proposed in recent literature are overviewed and analyzed to point out their differences, advantages and limits.

Fault detection and monitoring systems for photovoltaic installations: A review

Automatic classification of defective photovoltaic module cells in electroluminescence images

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.

Review of Failures of Photovoltaic Modules

Temperature cycling tests are part of the IEC 61215 qualification testing of crystalline silicon (c-Si) PV modules for
evaluating PV module degradation caused by the impact of thermo-mechanically induced stresses. The defined
temperature gradient and the cycle time by far exceed the actual impact of natural weathering, however. As a
contribution to comparisons between laboratory testing and natural weathering our work provides data from standard
temperature cycling tests as defined in IEC 61215 and extended from 200 (standard) to 800 cycles. The results of these
tests for seven commercial c-Si PV modules from various manufacturers are compared with results from identical
module types exposed outdoors in different climates for a period of 3 years. Degradation effects are evaluated with
respect to changes in output power, changes in insulation properties and with respect to interruptions in the electrical
interconnection circuits such as cell interconnects. Temperature gradients obtained at the different exposure locations are
used to model the thermo-mechanical stress arising from the mismatches of the thermal expansion coefficients of the
employed materials.

PV module degradation caused by thermomechanical stress: real impacts of outdoor weathering versus accelerated testing in the laboratory

PV Reliability (Cluster II): Results of a German Four-Year Joint Project - Part II, Results of Three Years Module Weathering in Four Different Climates -

During the past 3 years crystalline PV modules fabricated by various German manufacturers have been exposed to
outdoor conditions in four different climates: warm moderate climate (Cologne, Germany), tropical climate (Serpong,
Indonesia), cold high mountain climate (Zugspitze, Germany) and arid conditions (Sede Boqer, Israel) Annual
inspections and measurements examined the degradation of these modules with respect to electrical performance,
mechanical condition and visible alterations We give a detailed report of the results after 3 years of weathering, along
with the outlook for an extension to new worldwide test locations and for the enhancement of measurement options for
long-term characterizations

F. Reil

Papers

Review of Failures of Photovoltaic Modules

PV module degradation caused by thermomechanical stress: real impacts of outdoor weathering versus accelerated testing in the laboratory

PV Reliability (Cluster II): Results of a German Four-Year Joint Project - Part II, Results of Three Years Module Weathering in Four Different Climates -

Results of 3 Years' PV Module Weathering in Various Open-Air Climates