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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Detection and Localization of Damaged Photovoltaic Cells and Modules Using Spread Spectrum Time Domain Reflectometry

The operating efficiency of photovoltaic (PV) plants can be improved if damaged or degraded modules can be detected and identified. Currently, string-level power electronics can detect problems with modules or cabling but not locate them, which would facilitate addressing these issues. Here, we investigate the ability of spread spectrum time domain reflectometry (SSTDR) to both detect and locate/identify damaged cells and modules within a series-connected PV string. We tested the ability of SSTDR to detect and locate single-cell mini-modules and full-sized PV modules, which were intentionally damaged by impacts with a hammer (breaking the glass and damaging the silicon below) or by cutting through some or all busbars. Damage to the glass and silicon of cells was detected and located within a small string of minimodules. Busbar damage was detectable only if an open was created by cutting through all intercell busbars. Furthermore, physical impact damage to the glass and silicon of a full-sized PV module could be detected, but further development of signal processing is needed to achieve localization of such damaged modules within a string.

14 SOLAR ENERGY↗
DOE OSTI2025

Field Aging of Photovoltaic Module Packaging Materials: DuraMAT Field Module Library

To understand and develop models for silicon photovoltaic module degradation, accelerated testing is often used, however, outdoor field testing is necessary for validation. Outdoor field testing publications are often limited by the lack of a pristine, control module to compare the fielded module to. In this work, commercially available modules were purchased from seven different manufacturers for outdoor fielding then destructive characterization to investigate packaging material degradation on

14 SOLAR ENERGY↗
DOE OSTI2024

Energy Yield Loss Due to LETID

This presentation presents an open-source LETID model part of the PVDegradationTools, which can calculate solar modules degradation due to Light and Elevated Temperature (LETID).

degradation↗
DOE OSTI2020

Fill Factor Loss in Fielded Photovoltaic Modules Due to Metallization Failures, Characterized by Luminescence and Thermal Imaging

Understanding the causes of photovoltaic module failure in the field can be achieved using spatially-resolved imaging tools in combination with current-voltage (IV) characterization. We evaluate 23 field-degraded modules by comparing their IV characteristics with module images obtained by electroluminescence, photoluminescence, UV-fluorescence, and dark lock-in thermography. We identify primarily metallization failures (metallization series resistance, solder point heating, broken fingers, disrupted interconnects) in these modules that has led to a severe drop in the fill factor and up to 35% power loss over only 2 years of deployment.

14 SOLAR ENERGY↗
DOE OSTI2020

System-level performance and degradation of 21 GWDC of utility-scale PV plants in the United States

We assess the performance of a fleet of 411 utility-scale (i.e., >5 MWAC and ground-mounted) photovoltaic (PV) projects totaling 21.1 GWDC (16.3 GWAC) of capacity, which achieved commercial operations in the United States from 2007 to 2016. This fleet of projects contributed more than 50% of all solar electricity generated in the United States in 2017. Using detailed information on individual project characteristics, in conjunction with modeled irradiance data, we assess the extent to which actual first-year performance has lived up to both modeled and stated expectations. We then analyze system-level performance degradation in subsequent years by employing a “fixed effects” regression model to statistically isolate the impact of age on system performance. We find that this fleet of utility-scale PV projects has generally lived up to ex ante expectations for first-year performance but that subsequent system-level degradation—found to be −1.3%/year (±0.2%)—has, on average, been worse than both ex ante expectations (commonly −0.5%/year) and results from past studies (ranging from −0.8%/year to −1.0%/year). We emphasize that −1.3%/year is a system-level estimate that captures more than just module degradation (e.g., including soiling, balance of plant degradation, and downtime for maintenance and/or other events). A side analysis of a variety of project characteristics suggests that system-level degradation rates tend to be of lower magnitude among newer projects and larger projects and at sites with lower long-term average temperatures.

14 SOLAR ENERGY↗
DOE OSTI2025

Comparing Outdoor to Indoor Performance for Bifacial Modules Affected by Polarization-Type Potential-Induced Degradation

Bifacial photovoltaic (PV) modules have the advantage of using light reflected off of the ground to contribute to power production. Predicting the energy gain is challenging and requires complex models to do so accurately. Often, module degradation over time is neglected in models for the sake of simplicity or is underestimated. Comparing outdoor and indoor current–voltage (I–V) performance for bifacial modules is more challenging than for monofacial modules, as there are additional variables to consider such as rear albedo non-uniformity, cell mismatch, and their effects on temperature. This challenge is compounded when heterogeneous degradation modes occur, such as polarization-type potential-induced degradation (PID-p). To examine the effects of PID-p on I–V predictions using an empirical data-driven approach, 16 bifacial PERC modules are installed outdoors on racks with different albedo conditions. A subset is exposed to high-voltage biases of −1500 V or +1500 V. Outdoor data are traced at irradiance ranges of 150–250 W/m 2 , 500–600 W/m 2 , and 900–1000 W/m 2 . These curves are corrected using control module temperature, wire resistivity, and module resistance measured indoors. We examine several methods to transform indoor I–V curves to accurately, and more simply than existing methods, approximate outdoor performance for bifacial modules without and with varying levels of PID-p degradation. This way, bifacial performance modeling can be more accessible and informed by fielded, degraded modules. Distributions of percent errors between indoor and outdoor performance parameters and Mean Absolute Percent Errors (MAPEs) are used to assess method quality. Results including low-irradiance data (150–250 W/m 2 ) are discussed but are filtered for quantifying method quality as these data introduce substantial errors. The method with the most optimal tradeoff between low MAPE and analysis simplicity involves measuring the front side of a module indoors at an irradiance equal to plane-of-array irradiance plus the product of module bifaciality and albedo irradiance. This method gives MAPE values of 1–6.5% for non-degraded and 1.6–5.9% for PID-p degraded module performance.

14 SOLAR ENERGY↗
DOE OSTI2021

Local Resistance Measurement for Degradation of c-Si Heterojunction with Intrinsic Thin Layer (HIT) Solar Modules

Silicon heterojunction with intrinsic thin layer (or HIT) modules typically degrade at a rate of less than 1% annually in solar fields with dominant degradation in open-circuit voltage and some degradation in series resistance. However, detailed mechanisms can differ from module to module. Here, we study increases in local series resistance that occur over long-term field deployment, indicated by cell areas where the photoluminescence intensity does not degrade but the electroluminescence degrades significantly. To directly measure the local series resistance, we have cored out the local electroluminescence-degraded area, and we measured the sheet resistance by 4-point-probe and local nm-scale resistance using scanning spreading resistance microscopy (SSRM). The results by 4-point-probe show scattered sheet resistance that can be caused, for example, by nonuniform current paths through the transparent conductive oxide layer, the a-Si:H emitter, or the near-junction c-Si inversion layer. In contrast, the SSRM results indicate a relatively uniform and non-degraded resistivity on smaller nanometer spatial scales. SSRM is an atomic force microscopy-based two-terminal resistance mapping technique that measures the local resistance in nm-volume beneath the probe. The consistent resistances measured on the control and degraded samples can exclude the degradation of transparent conductive oxide resistance.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2022

Photovoltaic module antireflection coating degradation survey using color microscopy and spectral reflectance

Abstract Commercial antireflective coatings (ARCs) on photovoltaic (PV) module glass can improve module power by 2.5%–3.0%, but their long‐term field performance requires additional study. In this paper, we investigate ARC performance on fielded modules using two nondestructive techniques: reflectance spectroscopy and RGB microscopy, finding a large variation in coating durability and performance. For new coatings, the fleet average nominal power enhancement is 2.8%. This power enhancement is observed to degrade at approximately −0.05%/year absolute over the first 8 years of fielding in arrays that are not regularly cleaned. Interferometry and imaging results imply that coating loss for these modules is due to slow chemical thinning of the initial 125 nm thick coating by 1.4 to 5.0 nm/year. Due to the physics of interference coatings, the performance loss is projected to accelerate as the coating is further thinned, resulting in a coating lifetime (time to 80% of initial performance) of 7.5 to 25 years. At the higher 5.0 nm/year coating loss rates, we estimate that −0.14%/year power degradation of the module can be attributed solely to ARC degradation over the first 20 years. Extreme coating loss is observed on some modules where after 8 years fielding, the coating can be completely removed with a single wet wipe with a lens tissue. A case study is also presented comparing ARC and noncoated modules installed at a single site in 2013. We find that the ARC modules have a 2.6% higher soiling power loss than the noncoated modules; this exceeds the ARC power enhancement of 2.4% and leads to the surprising conclusion that the ARC lowers production for modules in this location due to increased soiling. These results demonstrate that RGB microscopy is a powerful, field‐capable, and quantitative characterization technique for assessing degradation of PV module ARCs.

Karin, Todd↗
DOE OSTI2021

Ultrasonic Characterization of Ethylene Vinyl Acetate (EVA) Crosslinking for Quality Assurance and Lamination Process Control (US-Xlink)

Module makers strive to cut lamination processing times to enhance production throughput and reduce costs. If overdone, this might lead to poor EVA quality due to incomplete EVA crosslinking and a large concentration of potentially harmful reactants. Those deficiencies are frequently missed during production quality testing as initially their impact on power output is small. Additionally, the crosslinking agent is frequently inhomogeneously dispersed across the EVA foils such that local destructive characterization procedures such as differential scanning calorimetry (DSC), Soxhlet extraction, swelling methods, or mechanical tests provide only a limited amount of information. However, these defects and inhomogeneities can become considerably more important during field operation, dramatically reducing long-term power yield, and increasing LCOE. Examples of typical long-term module degradation modes relating to poor lamination process conditions include cell breakage, corrosion of the metallization, delamination, and local quality deficiencies. To provide reliable material characterization in a manufacturing setting, we devised a non-destructive technology that uses ultrasound to evaluate the quality of interface adhesion and the degree of crosslinking. As a calibration reference, DSC measurements were employed. Although the potential of ultrasonic approaches for this purpose has already been noted, those previous methods were generally limited to local qualitative measurements. Furthermore, variations in EVA thickness and temperature had a substantial impact on them. The solution we propose solves these limitations by employing ultrasonic absorption rather than relying solely on sound velocity data.

14 SOLAR ENERGY↗
DOE OSTI2024

Carbon Footprint Analysis of Floating PV Systems

This report, conducted by the Dutch research organization TNO, presents the first detailed life cycle inventory (LCI) analysis of operational floating photovoltaic (FPV) systems. The study, focusing on two operational systems in Western Europe, reveals that FPV systems on small inland water bodies can be a valuable complement to ground-mounted PV systems in terms of greenhouse gas emissions reduction. If PV module degradation is limited, these systems' carbon footprint is 3-4 times lower than the EU grid mix target for 2030. The report compares two FPV systems with different floater compositions (HDPE and steel/HDPE) to hypothetical ground-mounted systems, using comprehensive background data. The findings highlight the necessity for long-term monitoring and thorough environmental assessments. Josco Kester, a scientist at TNO, underscores the potential environmental benefits of these systems, which could enhance the adoption of renewable energy technologies.

14 SOLAR ENERGY↗
DOE OSTI2021

Reliability and Power Degradation Rates of PERC Modules Using Differentiated Packaging Strategies and Characterization Tools

The reliability, durability and lifetime performance of passivated emitter, rear cell (PERC) modules used in real-world PV power plants is a critical challenge underlying the rapid adoption and bankability of these PERC cells, whose high efficiency help reduce the levelized cost of electricity (LCOE). We propose a degradation-science study of PERC module degradation pathways, benchmarking them relative to known degradation mechanisms and pathways of the incumbent aluminum back surface field (Al-BSF) modules exposed to real-world and accelerated exposure conditions.

14 SOLAR ENERGY↗
DOE OSTI2020

Defect Kinetics and Control for Module Reliability

Potential induced degradation is currently one of the most important module degradation mechanisms. It has been suggested that stacking faults decorated with sodium from the module glass are responsible for this effect and authors have also shown the reversibility of this effect upon reverse biasing of the module. The importance of sodium in the failure mechanism is clear, however, little is known regarding the factors that control its diffusion into the wafer, making it nearly impossible to predict the performance of a given module and engineer it to be better. Sodium migration from module glass into silicon cells and the resulting module degradation is a clear example of how defect kinetics can determine overall module performance and long-term reliability. To the detriment of the industry and its bankability, no quantitative models yet exist to predict defect-assisted module degradation, limiting the progress in improving reliability. In particular, the understanding of defect behavior under high electric fields, under stresses imparted by encapsulation or temperature, and under real operating conditions over long periods of time is a crucial gap in the current state-of-the-art. In this work we developed a Defect-Device-Degradation model to predict defect behavior and its impact on device performance over the module operational lifetime using experimentally-determined defect parameterizations. The validated model will provide a platform for manufacturing process optimization across input materials and architectures to avoid deleterious defects upstream and enable enhanced module robustness.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Polarization Type Potential Induced Degradation under Positive Bias in a Commercial PERC Module: Preprint

Potential induced degradation of the polarization type (PID-p) can reduce module performance in a relatively short period of time. PID-p can occur at both voltage polarities, but most studies are focused on degradation under a negative bias. This paper uses commercial bifacial passivated emitter and rear contact (PERC) cells within a monofacial glass-backsheet module construction to evaluate the impact of PID-p under a positive bias on the front side. Using the aluminum-foil (Al-foil) method, the module was stressed for PID in an environmental chamber. After the stress, the maximum power (Pmax) showed a decline of 3.1% at 1000 W/m2 and 6.2% at 200 W/m2. Recovery under light was also investigated. Complete recovery was observed at high irradiance, while a partial recovery was seen at lower irradiance. The outcomes of this study can help in understanding PID-p degradation under a positive bias and its recovery under the light.

PERC↗
DOE OSTI2021

Designing Modules to Prevent Reverse Bias Degradation in Perovskite Solar Cells when Partial Shading Occurs

When a solar cell in a panel is shaded, the illuminated cells can place a large reverse bias on the shaded cell to attempt to force current through it. Although the panel can continue to produce power, the reverse bias can cause significant problems for the shaded cell. In the case of perovskite solar modules, Joule heating and irreversible electrochemical reactions will degrade the cell. Some photovoltaic technologies use bypass diodes to solve this problem. To prevent both a perovskite cell and an all-perovskite tandem cell from falling into reverse bias breakdown while shaded, no more than two cells per bypass diode are allowed, which is likely to be prohibitively expensive for many applications. Herein, how many solar cells can be protected by one bypass diode in single-junction and multijunction perovskite modules is explored. It is easier to incorporate bypass diodes into modules with singulated cells than with monolithic panels. It is shown that perovskite–silicon tandems can be protected with fewer bypass diodes than with single-junction perovskite modules. Furthermore, it is suggested that if bypass diodes cannot be feasibly incorporated, then the panels should be deployed in utility-scale power plants.

14 SOLAR ENERGY↗
DOE OSTI2020

Drivers for the cracking of multilayer polyamide‐based backsheets in field photovoltaic modules: In‐depth degradation mapping analysis

Abstract There is a lack of understanding on the root cause of cracking of photovoltaic (PV) backsheets due to the challenge of multilayer characterization and the complicated failure modes at the submodule level. In this work, the in‐depth degradation mapping of field‐exposed polyamide‐based (PA‐based) PV module backsheets was studied, with the major focus on the identification of underlying drivers for the through cracking (in between the solar cells). PV modules were retrieved from five different locations, comprising a variety of climates, including humid subtropical, hot‐summer Mediterranean, tropical savanna climate, and hot arid. A suite of microscale cross‐sectional characterizations, including chemical changes, fluorescence intensity, and modulus as a function of distance from the air surface of the backsheet, was performed. Results showed more advanced signs of degradation of the inner layer than the outer layer in the cracking region. Increases in the modulus were identified as the major indicator for the cracking. Moreover, a rudimentary test by immersion in acetic acid, which forms during photodegradation of the ethylene‐vinyl acetate copolymer (EVA) encapsulant, showed the first‐time direct evidence that acetic acid can largely accelerate the chemical degradation and facilitate the cracking of PA inner layer. This study suggests that the field cracking of PA‐based backsheet can be attributed to the combined effects of chemical degradation and physical reorganization (chemi‐crystallization) under cyclic thermomechanical stresses. Therefore, it is important to consider effects of local microclimates and interlayer infection to understand the heterogeneous nature of backsheet failures.

Lyu, Yadong↗
DOE OSTI2021

First principles modeling of polymer encapsulant degradation in Si photovoltaic modules

An outstanding issue in the longevity of photovoltaic (PV) modules is the accelerated degradation caused by the presence of moisture. Moisture leads to interfacial instability, de-adhesion, encapsulant decomposition, and contact corrosion. However, experimental characterization of moisture in PV modules is not trivial and its impacts can take years or decades to establish in the field, presenting a major obstacle to designing high-reliability modules. First principles calculations provide an alternative way to study the ingress of water and its detrimental effect on the structure and decomposition of the polymer encapsulant and interfaces between the encapsulant and the semiconductor, the metal contacts, or the dielectric layer. Here, we use density functional theory (DFT) computations to model single chain, crystalline and cross-linked structures, infrared (IR) signatures, and degradation mechanisms of ethylene vinyl acetate (EVA), the most common polymer encapsulant used in Si PV modules. IR-active modes computed for low energy EVA structures and possible decomposition products match well with reported experiments. The EVA decomposition energy barriers computed using the Nudged Elastic Band (NEB) method show a preference for acetic acid formation as compared to acetaldehyde, are lowered in the presence of a water solvent or hydroxyl ion catalyst, and match well with reported experimental activation energies. This systematic study leads to a clear picture of the hydrolysis-driven decomposition of EVA in terms of energetically favorable mechanisms, possible intermediate structures, and IR signatures of reactants and products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Module-Level Solutions For Degradation by Ionization Damage

After years of improving module efficiency while targeting mean degradation rates of 0.5 to 0.6 %/y for crystalline silicon technology, there is much evidence that the degradation rates are now increasing significantly. Contributing factors include:Radiation damage (UV-Light Induced Degradation): Trina solar: -4.5%/y degradation rate in Singapore, DOE National Laboratory Regional Test Centers showed degradation of -1% < r < -2%/y in crystalline silicon modules, Jinko Solar: -4% < r < -7% efficiency loss from 540 MJ/m-2 of UV-A light, ISFH: 15% relative power loss during of 1.8 GJ/m-2 UV exposure, attributed to H+. Electrical bias from positive system voltage (e.g., +1000 V, +1500 V) can drive ions and metallization through the encapsulation, NREL: Ion transport can affect the cell passivation, resulting in power loss of 5% to 40% in p-PERC+ (bifacial), NREL: Damage at cell rear with up to 17% power at cell fronts in n-PERT modules. Delamination can also occur due to cell surface reactions driven by light and bias.

module efficiency↗
DOE OSTI2021

Assessing UV-Induced Degradation in Bifacial Modules of Different Cell Technologies

Bifacial technology enables solar cells to offer higher power output and lower levelized cost of energy compared to their monofacial counterparts. Here, we examined the adverse effects of ultraviolet-induced degradation (UVID) on a variety of high-efficiency silicon wafer-based bifacial cell technologies, including silicon heterojunction (SHJ), interdigitated back contact (IBC), passivated emitter rear contact (PERC), and passivated emitter rear totally-diffused (PERT). Both the front and rear sides of bifacial cells without any encapsulation were exposed to an artificially accelerated UV exposure test. After 2000 h of UV irradiation, the bifacial cells exhibited greater power loss with backside exposure indicating potential sensitivity of the rear passivation to UV. The highest power degradation is observed in SHJ cells, followed by p-PERC and n-PERT cell technologies. The degradation in SHJ cells is attributed to the reduction in V oc and FF, while the degradation in p-PERC and n-PERT cells is correlated with a significant drop in I sc . This suggests that each cell type/make degrades via different degradation pathways.

bifacial cells↗