Damp Heat Test Research Articles

A Custom High-Throughput Optical Mapping Instrument for Accelerated Stress Testing of PV Module Materials

The performance and integrity of photovoltaic (PV) modules and materials may be assessed through optical characterizations. We have developed a custom optical mapping instrument (OMI) to improve measurement throughput time, facilitate automated measurements, allow for localized specimen examination, obtain spatial information relative to commercial benchtop spectrophotometer instruments, and provide automated data analysis. Both the key components and the methods used to improve the measurements are described. The measurement precision for the OMI is benchmarked for hemispherical transmittance relative to a previous round-robin study for commercial spectrophotometers. In addition to the unique instrument developed in this study, new insights have emerged from the examination of specimens from previous experiments, including: the depletion of the UV absorber is revealed for specimens beyond a certain size after artificial ultraviolet (UV) weathering; an optical degradation by internal haze formation is confirmed following Damp Heat (85 °C/85% relative humidity) testing; the better uniformity of the wear pattern for falling sand abrasion is used to select the DIN 52348 fixture over the ASTM D968 fixture; and the greater local (in the order of millimeters) heterogeneity of surface contamination in the soiling-prone location of Dubai relative to Kuwait. The results of the UV study have already been used to improve the standardized weathering of encapsulants. The example for Damp Heat testing is given to increase awareness of a degradation believed to be ubiquitously occurring in safety and design-type qualification testing of PV modules.

Glass vs. Backsheet: Deconvoluting the Role of Moisture in Power Loss in Silicon Photovoltaics With Correlated Imaging During Accelerated Testing

Moisture ingress is an established issue for photovoltaic module durability. Durability studies that probe moisture effects typically evaluate performance losses at the module level, attributing global power losses to the overall humidity condition of the test environment while leaving local module behavior unknown. We leverage our recently published water reflectometry detection method and biased photoluminescence imaging to spatially correlate moisture content and cell performance over 2500 h of damp heat testing. These tests, carried out on glass–glass and glass–backsheet mini-modules at multiple temperatures and humidities, reveal two dominant modes of local cell performance loss—acute finger interruptions and cell-wide “background” series resistance increase. Finger interruptions occur earliest in glass–glass modules and at dry conditions. We do not observe any signs of contact corrosion at the front side in either module types. Still, glass–backsheet modules show a unique increase in series resistance at high humidities, suggesting a mechanism at the back contact. Overall, our results point to the humidity level of installation climate as a driving variable in selection of the bottom module layer.

Development and testing of light-weight PV modules based on glass-fibre reinforcement

In this paper we report on our approach on integrating c-Si PV into lightweight structures, in particular towards vehicle integration. To this end we want to get rid of the (bulk weight of the) glass but seek a suitable replacement in terms of mechanical stability. First we elaborate on the most basic standards and norms that VIPV products should relate to in terms of (thermo-)mechanical testing. Then, for the experimental part, 2 concepts are investigated. In a first approach, we reinforced the encapsulant with glass fibre material, while in a second one we applied a dedicated glass-fibre-reinforced sheet as a replacement of the backsheet. In both cases we stay as close as possible to using commercially available material. For each approach we elaborate the testing that has been carried out: thermal cycling, vibrations, mechanical shock and hail impact. On a final note, we point out some initial damp heat testing results, that are a particular challenge for light-weight modules without glass.

Raman spectroscopic analysis of encapsulants in aged photovoltaic modules

The aging of an encapsulation material of a random copolymer of ethylene and vinyl acetate (EVA), in outdoor-exposed (OE) crystalline-silicon (c-Si) photovoltaic (PV) modules was investigated through nondestructive Raman spectroscopy. The effect of water vapor (WV) on the Raman spectra of EVA encapsulants in c-Si PV modules was also investigated after long-term damp-heat (DH) tests at 85 °C and 85 % relative humidity. The EVA encapsulants in the long-term OE modules showed two different shapes and intensities of broad Raman spectra due to the increased intensity of the fluorescence background (FB). The encapsulants at the center of c-Si solar cells in the long-term OE modules showed a high intensity of FB, which increased with the exposure time. On the other hand, the Raman spectra of the encapsulant at the edge of the c-Si solar cells resembled those of the DH-exposed (DHE) modules, with a similar shape and lower intensity of FB than at the center. The spectral results indicate that the encapsulants at the edge were affected by WV, similar to the same as the DHE condition. The DHE-type Raman spectra for the EVA encapsulants at the edge of c-Si solar cells in OE modules show that the acetic acid may be formed from the EVA encapsulants by WV, resulting in corrosion of finger electrodes on c-Si solar cells and consequently diminishing the performance of the modules.

Highly crystallized tungsten doped indium oxide film stabilizes silicon heterojunction solar cells in sodium environment

High-efficient silicon heterojunction (SHJ) solar cells are ideal bifacial devices. In this application context, Na + ions induced degradations from encapsulation soda-lime glass are of significance. We conducted accelerated Na + ions aging experiments at 85 °C, 85% relative humidity without encapsulation to simulate damp heat test in soda-lime glass for SHJ solar cells. It is found that Na + ions accelerated the formation of metal In and In(OH) 3 or InOOH in damp heat condition, which destroyed the capping metal oxide, i.e., tungsten doped indium oxide (IWO). Interestingly, it demonstrates that the device stability is highly dependent on the crystallinity of IWO films. IWO films with large grains are more resistive to Na + ions erosion, and consequently, account for the enhanced device stability of SHJ solar cells. We believe this work provides a guide for designing more reliable bifacial SHJ solar cells installed in hot climates and coastal areas. • Accelerated Na + ions aging experiments are performed to simulate damp heat test in soda lime glass for SHJ solar cells. • Na + ions diffuse to a-Si:H layers via the grain boundaries of IWO. • Highly crystallized IWO films are more likely to resist the diffusion and erosion of Na + ions. • This work provides a guide for designing more reliable bifacial SHJ solar cells installed in hot climates.

28.2%-efficient, outdoor-stable perovskite/silicon tandem solar cell

<h2>Summary</h2> Stacking perovskite solar cells onto crystalline silicon bottom cells in a monolithic tandem configuration enables power-conversion efficiencies (PCEs) well above those of their single-junction counterparts. However, state-of-the-art wide-band-gap perovskite films suffer from phase stability issues. Here, we show how carbazole as an additive to the perovskite precursor solution can not only reduce nonradiative recombination losses but, perhaps more importantly, also can suppress phase segregation under exposure to moisture and light illumination. This enables a stabilized PCE of 28.6% (independently certified at 28.2%) for a monolithic perovskite/silicon tandem solar cell over ∼1 cm² and 27.1% over 3.8 cm², built from a textured silicon heterojunction solar cell. The modified tandem devices retain ∼93% of their performance over 43 days in a hot and humid outdoor environment of almost 100% relative humidity over 250 h under continuous 1-sun illumination and about 87% during a 85/85 damp-heat test for 500 h, demonstrating the improved phase stability.

Smart Glass Coatings for Innovative BIPV Solutions

The glossy appearance of the cover glass of a photovoltaic module is mainly responsible for giving the module a mirroring effect, which is often disturbing in the case of building integrated photovoltaic (BIPV) façade applications. In this work, an innovative approach is presented to reduce the glare of BIPV modules by applying surface coatings to the front glass of the module. Three different glass coating technologies, applied on the outer surface of the photovoltaic module, were investigated: inkjet printing, screen printing, and sol-gel spray coating. The coatings, applied by these technologies in three different colours (grey, anthracite, and terracotta), were characterized with respect to their adhesion, light transmission, and reflection. Their chemical and physical stability after stress impact (condensed water resistance and chemical resistance against acids and salt-fog) was also investigated. The durability of these coatings was further evaluated after performing environmental simulations with artificial sunlight (xenon weathering) on coated glass. Additionally, accelerated aging tests (damp-heat testing, temperature cycling) were performed on the test modules to assess their performance stability. For those coatings, where no stress-induced changes in colour or the optical appearance of the module surface were detected, the potential for the architectural integration of the modules into building facades is high. A minimum glare of less than 0.1% of the specular reflection could be achieved. On the basis of the results of the optical characterization and the durability tests, grey screen-printed BIPV solar modules were installed in a demonstrator test façade. The high electrical performance, resulting in only a 10–11% performance decrease compared to the noncoated reference modules, perfectly showed the suitability of screen-printing in future applications for coloured and glare-reduced BIPV installations.

Colorful Transparent Silicon Photovoltaics with Unprecedented Flexibility

AbstractIntegrated photovoltaics are regarded as next‐generation photovoltaic technologies that can generate electricity in urban areas with limited available land while also serving as aesthetic architectural elements. The criteria for integrating photovoltaics into buildings and electronic devices are flexibility, color tunability, efficiency, scalability, and stability. It is very challenging for integrated photovoltaics to demonstrate all‐around performance benefits because photovoltaic performances exist in a trade‐off relation, such as that between transparency and efficiency. Here, great all‐around transparent solar cells (TSC) featuring high flexibility and high transparency with color‐tunable solar cells are demonstrated. The TSCs exhibit an efficiency of 7.38% and 5.52% at the average visible transparencies of 45% and 60%, respectively. Moreover, by introducing a periodic hole array structure, the flexibility of TSCs is dramatically improved. The minimum bending radius decreases to 6 mm; it further decreases to 3 mm after PDMS embedding. The results of the numerical simulation show that the periodic hole array structure uniformly distributes the stress across the entire area as a self‐stress relief structure. The PDMS‐embedded TSCs demonstrate unprecedently high flexibility and long‐term stability without significant degradation even after cyclic bending deformations up to 1000 cycles and 1500 h of the standard damp heat test.

A Novel Accelerated Aging Test for Floats in a Floating Photovoltaic System

Countries around the globe have recently been actively developing a new type of solar power system known as the floating photovoltaic (FPV) system. The FPV system is advantageous in terms of efficiency and is economic; however, the environmental conditions on the surface of water are harsher than on the ground, and regulations or standards of the long-term durability of the float are insufficient. As a result, this study aims to investigate the durability of the float through three types of accelerated aging tests, including the damp heat test, the ozone-aging test, and the ultraviolet (UV) aging test. After the 7-day damp heat test (80 °C/95% RH), the results revealed that four groups of high-density polyethylene (HDPE) extrusion specimens neither produced more oxygen-containing functional groups, according to Fourier-transform infrared (FTIR) spectrum analysis, nor became more easily broken by the tensile test. Furthermore, more oxygen-containing functional groups were produced after the 7-day ozone-aging test (80 °C/95% RH/500 ppm) than the 17-day UV-aging test (60 °C/0% RH/60 kW·h·m−2). On the contrary, UV aging would make HDPE specimens harder and more brittle than ozone aging. To conclude, both ozone- and UV-aging tests can evaluate the durability of the float quickly and efficiently.

Improved reliability PERC PV modules with moth-eye nanostructured optical films using nano imprint lithography

In this study, a Moth-eye nanostructured optical film was studied to improve the reliability of the PERC PV module. Moth-eye nanostructures were composed of three types by using the Nano Imprint Lithography method and different process conditions. These are initial optical film, Moth-Eye structure (MES) optical film, and Improved Moth-Eye structure (I-MES) optical film. The I-MES film had a transmittance of 99%. Compared with the Initial film, transmittance increased by 4%. Also, PERC mini modules were manufactured using these three types of optical films and I-V analysis was performed. The Power output (Pmax) of the I-MES PV module is 4.324 W, which is a 5.5% increase compared to the Initial PV module. In addition, one of the IEC-61215 reliability Damp-heat test was conducted for 1000 h. The I-MES PV modules showed only a 0.8% degradation compared to the Initial PV modules, and it increased by 2.4% compared to the MES PV modules. These results indicate that they are suitable for increasing the long-term reliability of PV modules.

Experimental Research on Anti-rust Performance of Drive Train Oils Used in Construction Machinery

Based on the working conditions of transmissions and drive axles used in the construction machinery, and combined with the current testing requirements for the anti-rust performance of lubricants, this paper test the oils commonly applied in the drive train of the construction machinery through the copper corrosion, rust preventing test and damp-heat test. The results show that the damp-heat test acted as a dynamic corrosion test, its parameters are closer to the real working conditions and it can better investigate the corrosion performance of oils in different quality grades and provides a reference for the selection of drive train oils.

Study of Novel High-Density Modules with Negative Space between Solar Cells

High-density crystalline silicon modules have recently invoked large interest in PV industry due to its higher efficiency. However, high-density stacking of cells in this kind of module may have additional reliability problem, which might cause higher power loss during outdoor operation. Modules based on half-cut cells have been widely studied due to their higher power output compared with modules based on full cells. When a cell is half cut, its current level is half reduced. When it is 1/3 cut, its current level is decreased by 2/3. However, high-density modules based on 1/3-cut cells have rarely been studied. Therefore, in this work, damp heat (DH), thermal cycle (TC), UV irradiation and humidity freezing (HF) test were utilized to study the power degradation performance of these high-density modules fabricated with 1/3 cut cells. The obtained results show that these novel high-density modules with negative space between 1/3 cut cells have good reliability in various environmental conditions.

Analytical Modeling of Diffusion of Moisture in Silicon Photovoltaic Module under Damp Heat Testing Condition

Analytical Modeling of Diffusion of Moisture in Silicon Photovoltaic Module under Damp Heat Testing Condition

Performance Evaluation of Photovoltaic Modules by Combined Damp Heat and Temperature Cycle Test

Standard damp heat (DH), temperature cycle (TC), and combined DH-TC tests were performed using monocrystalline Si 72-cell modules with a conventional ethylene vinyl acetate (EVA) encapsulant, and their module performance and electroluminescence images were investigated. During the DH test, a significant drop (~20%) in the maximum output power of the module was noticed, primarily because of the degradation of fill factor and an increase in series resistance at 5500 h of DH testing (DH5500), presumably due to the corrosion of metal electrodes by moisture ingress. Conversely, it was revealed that temperature cycling did not seriously degrade module performance until 1400 cycles. However, the combined DH5000-TC600 test suggested in this study, with a sequence of DH1000-TC200-DH1000-TC200-DH1000-TC200-DH2000, was confirmed to provide harsher conditions than the DH-only test by causing a 20% decrease in maximum output power (Pmax) after DH3000/TC400. Promisingly, we confirmed that the module with a polyolefin elastomer encapsulant showed better durability than the module with EVA even in the combined DH-TC test, showing a limited decrease in Pmax (~10%) even after the DH5500/TC600 test.

Silicon solar cells and modules with front contact paste containing copper‐based component

AbstractIn this article, we present the results of aging tests of silicon photovoltaic modules with a copper‐containing electrode deposited in one‐step screen printing method. For front metallization, a mixture of commercial silver paste with copper filler was used, where copper constituted 30% of total paste volume. The filler is based on copper particles about 1 μm of diameter covered with a protective coating layer based on nickel (CCu1) or nickel–silver (CCu2). For the first time, Si solar cells with screen‐printed front electrode containing massive copper with efficiency over 20% are reported. Aging tests included 2000 h of damp heat (DH) and 400 times of thermal cycling (TC) tests. TC results are very promising and provide slight deterioration of the electrical parameters of the modules with both CCu1 and CCu2. Greater decreases were found when performed DH tests, but it is worth pointing out that mainly fill factor (FF) and η have fallen while Voc and Isc did not change by more than 5% for both pastes. After 2000 h of the test, FF decreased by 28% for CCu1 and 37.4% for CCu2, whereas the efficiency deteriorated by 32% and 42.6% for CCu1 and CCu2. The electroluminescence (EL) and X‐ray photoelectron spectroscopy (XPS) measurements suggest that decrease in electrical parameters is a consequence of Cu corrosion caused by harmful products of the decomposed EVA laminating film.

Adhesive Reliability Study at the Encapsulant/Backsheet Interface of Solar Modules for Various Ethylene-Vinyl Acetate Copolymer White Films

White EVA film has recently been widely applied between the solar cells and the backsheet to improve the light reflection and gain more power. The peel strength between EVA layer and backsheet may decrease in damp heat environments. The decline in peel strength may vary for different EVA films as well as different match with backsheets. In this work, the weather resistance performance of four different white EVA films were comparatively studied with four different backsheets. Peel strength before and after the damp heat test for 1000h and 1500h was measured. For the interface with low initial peel strength, increase in bonding force was observed after the damp heat test. For the interface with high initial peel strength, degradation in bonding force may probably occur. These results suggest that a higher initial performance cannot always ensure a higher performance after degradation.

Damp heat resilient thermoplastic polyolefin encapsulant for photovoltaic module encapsulation

Thermoplastic polyolefin (TPO) is a non-crosslinking material used in photovoltaic module encapsulation. TPO thermal degradation and its weather stabilities are still not known. In this work, TPO laminates were prepared and subjected to extended damp-heat weather test. TPO encapsulant properties were studied and compared with the most commonly used encapsulant, Ethylene-Vinyl Acetate (EVA). Four times lower rate of transmittance loss and increment rate in the yellowness index values have been found for TPO compared to EVA laminate. Damp-heat induced degradation mechanism, and its components were studied using Raman and Fourier-transform-infrared (FTIR) spectroscopy. Raman spectra revealed that the carbonyl group loss rate at the edge is one order of magnitude higher than the center. FTIR has shown a higher rate of acetic acid and hydroxyl group formation in EVA as compared to the TPO. FTIR also demonstrated that TPO has a lower water absorption because of its nonpolar nature, whereas EVA shows more water absorption due to its polar nature. The rate of change in thermal properties of TPO and EVA encapsulants were studied through the heat-cool-heat cycle. A higher rate of increment in the degree of crystallinity is found for EVA as compared to the TPO encapsulant during the extended damp-heat acceleration test. This study helps to understand the TPO and EVA encapsulants degradation behavior, degradation components, and mechanism to the encapsulant researchers and PV module manufacturers when a PV module experiences the hot-humid conditions. This TPO may result in the industry adopting the different PV modules for fabricating.

Performance of PV modules using co-extruded backsheets based on polypropylene

Due to the general price pressure PV modules experienced in the last decade, a variety of alternative polymer materials and new backsheet designs were developed and introduced into the market, amongst others also extruded backsheets based on polypropylene (PP). The production of co-extruded films represents a backward integration of backsheet manufacturers, allowing for easy material and design modifications regarding additive formulation, fillers and geometry. The main objective of this paper was to describe the influence of the special properties of PP-based backsheets on the performance and reliability of PV modules. The higher reflectance of the PP backsheet compared to a reference polyester (PET) based laminate led to an increase in power output between 1.5 and 2.5%. Test modules using PP and PET backsheets were exposed to 3000 h of damp heat testing. No changes in power output for either of the test modules was observed. However, the selective permeation properties of PP backsheets prevent humidity from entering the module (similarly to PET based backsheets) but allow for significantly higher diffusion of acetic acid out of the PV module. Therefore, in contrast to test modules using Ethylene Vinyl Acetate (EVA) encapsulants and PET backsheets, no silver grid corrosion was observed for modules using PP backsheets. Co-extruded backsheets based on PP show great potential to be a valid replacement of standard PET based backsheets in PV modules. On the one hand, the PP backsheet so far proved excellent stability, exhibiting no severe material degradation after extended exposure to temperature, humidity and irradiation. On the other hand, its improved functional properties (optical properties; selective permeability) lead to increased performance and improved long-term stability of the tested PV modules.

Thermal and Damp Heat Stability of High‐Mobility In2O3‐Based Transparent Conducting Films Fabricated at Low Process Temperatures

High electron mobility of transparent conductive oxide (TCO) facilitates high conductivity at a moderate carrier density, resulting in an extension of the degree of transparency from visible to near‐infrared due to less free carrier absorption. These broadband TCO electrodes provide opportunities to improve the performance of optoelectronic devices. Herein, the thermal and damp heat stability characteristics of TCO films are described. It is found that the difference in the crystal growth method has a significant influence on the initial electrical properties and stability characteristics. Polycrystalline In2O3:Me (Me: W, Ce) films deposited at 200 °C exhibit a relatively high mobility of 70–80 cm2 V−1 s−1, are stable after a damp heat test, and improve the mobility of 110–140 cm2 V−1 s−1 after postannealing at temperatures greater than the deposition temperature. Conversely, solid‐phase crystallized In2O3:Me,H films prepared by postannealing amorphous films exhibit an extremely high mobility of 100–160 cm2 V−1 s−1; however, they exhibit reduced stability characteristics after the damp heat test and high‐temperature annealing process compared to the polycrystalline films. The deterioration of the electrical properties increases as the hydrogen content in the films increases. The results suggest that polycrystalline and solid‐phase crystallized films should be used properly, according to the device manufacturing processes.

Durable crystalline silicon photovoltaic modules based on breathable structure

The long-term durability of crystalline silicon (c-Si) photovoltaic (PV) modules was investigated by long-term damp-heat (DH) tests at 85 °C with 85% relative humidity. Breathable module structure using front or rear materials with low-barrier properties markedly improved the long-term DH resistance of c-Si PV modules. No corrosion of finger electrodes on c-Si solar cells occurred by diffusion of acetic acid, which was formed from an encapsulant of a random copolymer of ethylene and vinyl acetate (EVA) towards the outside of the modules by the breathable structure. Raman spectroscopy data indicated that degradation of the EVA encapsulants including additives (e.g. UV absorber) were suppressed by the usage of a breathable front film compared to a front cover glass used for the conventional modules. The breathable modules based on low-barrier components would improve the long-term photochemical and chemical durability of c-Si PV modules further to achieve 40 year operation.