Photovoltaic failure and degradation modes
TL;DR: In this article, the extensive photovoltaic field reliability literature was analyzed and reviewed, and inconsistencies in degradation mode identification were discussed to help guide future publication on this subject, and future work was prioritized based upon information assembled from recent installations.
Abstract: The extensive photovoltaic field reliability literature was analyzed and reviewed. Future work is prioritized based upon information assembled from recent installations, and inconsistencies in degradation mode identification are discussed to help guide future publication on this subject. Reported failure rates of photovoltaic modules fall mostly in the range of other consumer products; however, the long expected useful life of modules may not allow for direct comparison. In general, degradation percentages are reported to decrease appreciably in newer installations that are deployed after the year 2000. However, these trends may be convoluted with varying manufacturing and installation quality world-wide. Modules in hot and humid climates show considerably higher degradation modes than those in desert and moderate climates, which warrants further investigation. Delamination and diode/j-box issues are also more frequent in hot and humid climates than in other climates. The highest concerns of systems installed in the last 10 years appear to be hot spots followed by internal circuitry discoloration. Encapsulant discoloration was the most common degradation mode, particularly in older systems. In newer systems, encapsulant discoloration appears in hotter climates, but to a lesser degree. Thin-film degradation modes are dominated by glass breakage and absorber corrosion, although the breadth of information for thin-film modules is much smaller than for x-Si. Copyright © 2017 John Wiley & Sons, Ltd.
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TL;DR: Recent progress in addressing stability, how to allow mass production, and how to maintain uniformity of large-area films are reviewed, and the remaining challenges along the pathway to their commercialization are discussed.
Abstract: BACKGROUND Perovskite solar cells (PSCs) have attracted intensive attention because of their ever-increasing power conversion efficiency (PCE), low-cost materials constituents, and simple solution fabrication process. Initiated in 2009 with an efficiency of 3.8%, PSCs have now achieved a lab-scale power conversion efficiency of 23.3%, rivaling the performance of commercial multicrystalline silicon solar cells, as well as copper indium gallium selenide (CIGS) and cadmium telluride (CdTe) thin-film solar cells. Thousands of articles related to PSCs have been published each year since 2015, highlighting PSCs as a topic of intense interest in photovoltaics (PV) research. With high efficiencies achieved in lab devices, stability and remaining challenges in upscaling the manufacture of PSCs are two critical concerns that must be addressed on the path to PSC commercialization. ADVANCES We review recent progress in PSCs and discuss the remaining challenges along the pathway to their commercialization. Device configurations of PSCs (see the figure) include mesoscopic formal (n-i-p) and inverted (p-i-n) structures, planar formal and inverted structures, and the printable triple mesoscopic structures. PCEs of devices that use these structures have advanced rapidly in the case of small-area devices (~0.1 cm 2 ). PSCs are also attracting attention as top cells for the construction of tandem solar cells with existing mature PV technologies to increase efficiency beyond the Shockley-Queisser limit of single-junction devices. The stability of PSCs has attracted much well-deserved attention of late, and notable progress has been made in the past few years. PSCs have recently achieved exhibited lifetimes of 10,000 hours under 1 sun (1 kW/m 2 ) illumination with an ultraviolet filter at a stabilized temperature of 55°C and at short-circuit conditions for a printable triple mesoscopic PSCs. This irradiation is equivalent to the total irradiation of 10 years of outdoor use in most of Europe. However, within the PSC community, standard testing protocols require further development. In addition, transparency in reporting standards on stability tests needs to be improved; this can be achieved by providing both initial photovoltaic performance and normalization parameters. The upscaling of PSCs has also progressed steadily, leading to PSC mini-modules, standard-sized modules, and power systems. PV companies have set out to manufacture large-area PSC modules (see the figure), and a 110-m 2 perovskite PV system with screen-printed triple mesoscopic PSC modules was recently debuted. Studies of these increased-area modules and systems will promote the development of PSCs toward commercialization. PSC research is expanding to cover fundamental topics on materials and lab-sized cells, as well as to address issues of industrial-scale manufacturing and deployment. OUTLOOK The PV market has been continuously expanding in recent years, bringing opportunities for new PV technologies of which PSCs are promising candidates. It is imperative to achieve a low cost per watt, which means that both efficiency and lifetime need improvement relative to current parameters. The efficiency gap between lab cells and industrial modules has seen impressive reductions in crystalline silicon; PSCs must similarly enlarge module areas to the panel level and need to achieve lifetimes comparable to those of legacy PV technologies. Other improvements will need to include industry-scale electronic-grade films, recycling methods to address concerns regarding lead toxicity, and the adoption of standardized testing protocols to predict the operation lifetime of PSCs. Modules will need to endure light-induced degradation, potential-induced degradation, partial-shade stress, and mechanical shock. The field can benefit from lessons learned during the development of mature PV technologies as it strives to define, and overcome, the hurdles to PSC commercial impact.
1,160 citations
TL;DR: The perovskite cells are a promising new material for low-cost, high-efficiency photovoltaics as discussed by the authors, however, there remains uncertainty as to whether materials with the required stability can be found within the associated material system and whether the presence of Pb in highly soluble form will limit commercial application.
Abstract: One of the most exciting developments in photovoltaics over recent years has been the emergence of organic–inorganic lead halide perovskites as a promising new material for low-cost, high-efficiency photovoltaics. In record time, confirmed laboratory energy conversion efficiencies have increased from a few percent to over 22%. Although there remains uncertainty as to whether materials with the required stability can be found within the associated material system and whether the presence of Pb in highly soluble form will limit commercial application, it is certain that these perovskite cells will remain the focus of concerted research efforts over the coming decade. The early history of the development of this technology leading to the first perovskite cells is documented as are significant recent developments.
300 citations
TL;DR: In this paper, the authors assess the global status of practice and knowledge for end-of-life management for crystalline silicon PV modules and recommend research and development priorities to facilitate material recovery and recycling of solar modules.
Abstract: Large-scale deployment of photovoltaic (PV) modules has considerably increased in recent decades. Given an estimated lifetime of 30 years, the challenge of how to handle large volumes of end-of-life PV modules is starting to emerge. In this Perspective, we assess the global status of practice and knowledge for end-of-life management for crystalline silicon PV modules. We focus in particular on module recycling, a key aspect in the circular economy of photovoltaic panels. We recommend research and development to reduce recycling costs and environmental impacts compared to disposal while maximizing material recovery. We suggest that the recovery of high-value silicon is more advantageous than the recovery of intact silicon wafers. This approach requires the identification of contaminants and the design of purification processes for recovered silicon. The environmental and economic impacts of recycling practices should be explored with techno–economic analyses and life-cycle assessments to optimize solutions and minimize trade-offs. As photovoltaic technology advances rapidly, it is important for the recycling industry to plan adaptable recycling infrastructure. The increasing deployment of photovoltaic modules poses the challenge of waste management. Heath et al. review the status of end-of of-life management of silicon solar modules and recommend research and development priorities to facilitate material recovery and recycling of solar modules.
141 citations
TL;DR: How a single gene affects the convergent evolution of a complex color pattern is unveiled, finding that regulatory changes of the gene agouti-related peptide 2 (agrp2) act as molecular switches controlling this evolutionarily labile phenotype.
Abstract: The color patterns of African cichlid fishes provide notable examples of phenotypic convergence. Across the more than 1200 East African rift lake species, melanic horizontal stripes have evolved numerous times. We discovered that regulatory changes of the gene agouti-related peptide 2 (agrp2) act as molecular switches controlling this evolutionarily labile phenotype. Reduced agrp2 expression is convergently associated with the presence of stripe patterns across species flocks. However, cis-regulatory mutations are not predictive of stripes across radiations, suggesting independent regulatory mechanisms. Genetic mapping confirms the link between the agrp2 locus and stripe patterns. The crucial role of agrp2 is further supported by a CRISPR-Cas9 knockout that reconstitutes stripes in a nonstriped cichlid. Thus, we unveil how a single gene affects the convergent evolution of a complex color pattern.
119 citations
TL;DR: It is evident that currently underappreciated degradation modes such as mechanical stability, high applied voltages and reverse bias, where especially hot spots could become problematic, must be considered in the coming years when evaluating the long-term stability of PSCs.
Abstract: Recently organic–inorganic perovskite solar cells (PSCs) have emerged as promising candidates for photovoltaics because of their relatively high efficiency and low processing costs. However, for possible commercialisation, long-term stability remains a key obstacle, especially when compared to silicon or GaAs. Thus, future research will significantly focus on stability. The most relevant industry standards for the stability of solar cells are issued by the International Electrotechnical Commission (IEC), summarized in the so-called IEC 61215 norm. The IEC 61215 is a series of very detailed, time-consuming and interconnected stress tests that provide accelerated aging conditions to extrapolate the potential long-term lifetime of a solar module. Established silicon, for example, passes the full IEC 61215. To gain the confidence of investors and customers, passing the full IEC 61215 is a necessary minimum requirement for the commercialization of perovskites. Interestingly, the IEC 61215 is not openly accessible which may be one reason why there are often references to outdated versions. To remedy this situation, we introduce and analyse the most current IEC 61215 stability standards for solar cells and to which degree perovskites have passed them. We then elaborate on the most pertinent challenges for the long-term stability of PSCs in the coming years. This includes less explored stability tests such as potential-induced degradation (IEC TS 62804-1) and ammonia corrosion (IEC 62716). From this, it is evident that currently underappreciated degradation modes such as mechanical stability, high applied voltages and reverse bias, where especially hot spots could become problematic, must be considered in the coming years when evaluating the long-term stability of PSCs.
117 citations
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TL;DR: In this paper, the degradation rates of flat-plate terrestrial modules and systems reported in published literature from field testing throughout the last 40 years have been analyzed, showing a median value of 0·5%/year.
Abstract: 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.
1,202 citations
TL;DR: In this article, the authors examined the data in several ways to minimize this bias and found median degradation for x-Si technologies in the 0.5-0.6%/year range with the mean in the 2.8-3.9%/month range.
Abstract: Published data on photovoltaic (PV) degradation measurements were aggregated and re-examined. The subject has seen an increased interest in recent years resulting in more than 11 000 degradation rates in almost 200 studies from 40 different countries. As studies have grown in number and size, we found an impact from sampling bias attributable to size and accuracy. Because of the correlational nature of this study we examined the data in several ways to minimize this bias. We found median degradation for x-Si technologies in the 0.5–0.6%/year range with the mean in the 0.8–0.9%/year range. Hetero-interface technology (HIT) and microcrystalline silicon (µc-Si) technologies, although not as plentiful, exhibit degradation around 1%/year and resemble thin-film products more closely than x-Si. Several studies showing low degradation for copper indium gallium selenide (CIGS) have emerged. Higher degradation for cadmium telluride (CdTe) has been reported, but these findings could reflect a convolution of less accurate studies and longer stabilization periods for some products. Significant deviations for beginning-of-life measurements with respect to nameplate rating have been documented over the last 35 years. Therefore, degradation rates that use nameplate rating as reference may be significantly impacted. Studies that used nameplate rating as reference but used solar simulators showed less variation than similar studies using outdoor measurements, even when accounting for different climates. This could be associated with confounding effects of measurement uncertainty and soiling that take place outdoors. Hotter climates and mounting configurations that lead to sustained higher temperatures may lead to higher degradation in some, but not all, products. Wear-out non-linearities for the worst performing modules have been documented in a few select studies that took multiple measurements of an ensemble of modules during the lifetime of the system. However, the majority of these modules exhibit a fairly linear decline. Modeling these non-linearities, whether they occur at the beginning-of-life or end-of-life in the PV life cycle, has an important impact on the levelized cost of energy. Copyright © 2016 John Wiley & Sons, Ltd.
351 citations
"Photovoltaic failure and degradatio..." refers background in this paper
...Numerous publications have focused on degradation rates were first summarized and analyzed by some of the authors and were recently updated; however, degradation modes were not discussed [4,5]....
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TL;DR: Different degradation modes are discussed and how some of these may cause approximately linear degradation within the measurement uncertainty while other degradation modes lead to distinctly non-linear degradation, aiding in predictions of what may be seen in other systems.
Abstract: Photovoltaic (PV) reliability and durability have seen increased interest in recent years. Historically, and as a preliminarily reasonable approximation, linear degradation rates have been used to quantify long-term module and system performance. The underlying assumption of linearity can be violated at the beginning of the life, as has been well documented, especially for thin-film technology. Additionally, non-linearities in the wear-out phase can have significant economic impact and appear to be linked to different failure modes. In addition, associating specific degradation and failure modes with specific time series behavior will aid in duplicating these degradation modes in accelerated tests and, eventually, in service life prediction. In this paper, we discuss different degradation modes and how some of these may cause approximately linear degradation within the measurement uncertainty (e.g., modules that were mainly affected by encapsulant discoloration) while other degradation modes lead to distinctly non-linear degradation (e.g., hot spots caused by cracked cells or solder bond failures and corrosion). The various behaviors are summarized with the goal of aiding in predictions of what may be seen in other systems. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.
116 citations
"Photovoltaic failure and degradatio..." refers background in this paper
...[3] Delamination was partitioned into major and minor categories, as minor delamination, such as shown in Figure 5(a) or (b) may not have much impact on the power production....
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...[3] Because most publications do not differentiate the cause for each hot spot, these potentially related degradation modes are presented in variations of green color....
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...Therefore, it is imperative to correlate not only the power loss curve, which may be nonlinear, but also the observed degradation modes and mechanisms from the field with the accelerated tests [3]....
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20 Jun 2010
TL;DR: In this paper, the performance and energy rating testbed (PERT) at the Outdoor Test Facility (OTF) at National Renewable Energy Laboratory (NREL) was used to compare 40 PV modules from different manufacturers for their long-term outdoor stability.
Abstract: As photovoltaic (PV) penetration of the power grid increases, it becomes vital to know how decreased power output may affect cost over time. In order to predict power delivery, the decline or degradation rates must be determined accurately. At the Performance and Energy Rating Testbed (PERT) at the Outdoor Test Facility (OTF) at the National Renewable Energy Laboratory (NREL) more than 40 modules from more than 10 different manufacturers were compared for their long-term outdoor stability. Because it can accommodate a large variety of modules in a limited footprint the PERT system is ideally suited to compare modules side-by-side under the same conditions.
85 citations
TL;DR: The extrapolative predictions inherent in the use of accelerated testing raise serious concerns, and the useof accelerated testing has many dangerous pitfalls, so potential users are warned about some of these pitfalls.
Abstract: Accelerated tests are used to obtain timely information on product life or performance degradation over time. Test units are used more frequently than usual or are subjected to higher than usual levels of accelerating variables like temperature and voltage. Then the results are used, through an appropriate physically-based statistical model, to make predictions about product life or performance over time, at the more moderate use conditions. The extrapolative predictions inherent in the use of accelerated testing raise serious concerns, and the use of accelerated testing has many dangerous pitfalls. This paper warns potential users about some of these pitfalls.
76 citations