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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Metallurgical aspects influencing the resistance to steam oxidation and fracture toughness of select advanced replacement alloys for LWR core internals

Life extension of the existing nuclear reactors imposes accumulated damages, such as higher fluences and longer period of corrosion, to structural materials, which would result in significant challenges to the traditional reactor materials such as type 304 and 316 stainless steels. Advanced alloys with superior radiation resistance will increase safety margins, design flexibility, and economics for not only the life extension of the existing fleet but also new builds with advanced reactor designs. The Electric Power Research Institute (EPRI) teamed up with Department of Energy (DOE) to initiate the Advanced Radiation Resistant Materials (ARRM) program, aiming to develop and test degradation resistant alloys from current commercial alloy specifications by 2021 to a new advanced alloy with superior degradation resistance in light water reactor (LWR)-relevant environments by 2024. Corrosion resistance in water environment is one of the fundamental properties required for LWR core internal materials. High-temperature steam oxidation tests are not only an accelerated life testing method to uncover potential failure modes in a short period of time, but also an approach to evaluate materials’ resistance to accidental scenarios. Coupons, prepared from fourteen candidate alloys that were selected under the ARRM program, were exposed to 1 bar full steam with ~10 part-per-billion oxygen content at 600 and 650°C for up to 5,000 h, which were weighed at 500-h intervals. Ni-base superalloys are an important class of alloys for reactor applications. Alloys 690, 725, and X- 750 were three of the selected Ni-base superalloys exposed to the steam tests. This report summarizes the metallurgical aspects, such as alloy thermodynamics and the nature of the oxides and the diffusivities of primary elements, and their effects on oxidation behavior of the three alloys. In addition to monitoring mass change, microstructures of the 5000h-exposed samples of alloys 690, 725, and X-750 were characterized using scanning and transmission electron microscopy and energy dispersive x-ray spectroscopy. Together with thermodynamic calculations, the scale constitution and its exfoliation behavior were discussed. Based on experimental and theoretical values, a new model was proposed to quantitatively estimate the metal thickness loss of the alloys. Alloy X-750 was found to have the best resistance to steam oxidation with the least metal thickness loss (<1 μm), which were slightly superior to alloy 690. Alloy 725 exhibited the worst resistance to steam oxidation with the greatest metal thickness loss, e.g., ~2.5 μm at 650°C, which is nearly three times of the metal thickness losses of alloys 690 and X-750 at 650°C. The greatest metal thickness loss of alloy 725 might be attributable to its high Mo content. Photos of the fracture toughness tested samples of eight alloys are presented, which will be correlated with their fracture toughness results and planned tensile test results to select representative alloy samples for detailed microstructural characterization to reveal their microstructure and properties relationships.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Testing and Expertise for Marine Energy (TEAMER) Program Support: MRE Dynamic Seals Performance Investigation (CRADA Final Report)

This TEAMER project allows NREL to use and augment a custom special-purpose testing system to perform accelerated-life testing of rotating seals for use in the Marine Renewable Energy (“MRE”) industry. The requirements of this industry are different from most applications including marine, and relevant performance information is lacking. In order to achieve low costs with extremely effective and reliable operation over long periods deployed underwater, more study of the best seals and arrangements of seals must be performed. By developing a rigorous framework for such testing, NREL hopes to greatly improve understanding of the relevant factors and provide significant data to the industry. Further, this work can inform standards developments for this critical component of MRE systems, leading to maturation and improved acceptance of the industry in commerce.

16 TIDAL AND WAVE POWER↗
DOE OSTI2016

TU-H-BRA-06: Characterization of a Linear Accelerator Operating in a Compact MRIGuided Radiation Therapy System

Purpose: To describe the performance of a linear accelerator operating in a compact MRI-guided radiation therapy system. Methods: A commercial linear accelerator was placed in an MRI unit that is employed in a commercial MR-based image guided radiation therapy (IGRT) system. The linear accelerator components were placed within magnetic field-reducing hardware that provided magnetic fields of less than 40 G for the magnetron, gun driver, and port circulator, with 1 G for the linear accelerator. The system did not employ a flattening filter. The test linear accelerator was an industrial 4 MV model that was employed to test the ability to run an accelerator in the MR environment. An MR-compatible diode detector array was used to measure the beam profiles with the accelerator outside and inside the MR field and with the gradient coils on and off to examine if there was any effect on the delivered dose distribution. The beam profiles and time characteristics of the beam were measured. Results: The beam profiles exhibited characteristic unflattened Bremsstrahlung features with less than ±1.5% differences in the profile magnitude when the system was outside and inside the magnet and less than 1% differences with the gradient coils on and off. The central axis dose rate fluctuated by less than 1% over a 30 second period when outside and inside the MRI. Conclusion: A linaccompatible MR design has been shown to be effective in not perturbing the operation of a commercial linear accelerator. While the accelerator used in the tests was 4MV, there is nothing fundamentally different with the operation of a 6MV unit, implying that the design will enable operation of the proposed clinical unit. Research funding provided by ViewRay, Inc.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Experimental Aging and Lifetime Prediction in Grid Applications for Large-Format Commercial Li-Ion Batteries

Due to the growth of electric vehicle and stationary energy storage markets, the production and use of lithium-ion batteries has grown exponentially in recent years. For many of these applications, large-format lithium-ion batteries are being utilized, as large cells have less inactive material relative to their energy capacity and require fewer electrical connections to assemble into packs. And especially for stationary energy storage systems, where energy delivered is the only revenue source, the economics of these battery systems is highly dependent on cell lifetime. However, testing of large-format lithium-ion batteries is time consuming and requires high current channels and large testing chambers, making information on the performance of commercial, large-format lithium-ion batteries hard to come by. Here, accelerated aging test data from four commercial large-format lithium-ion batteries is reported. These batteries span both NMC-Gr and LFP-Gr cell chemistries, pouch and prismatic formats, and a range of cell designs with varying power capabilities. Accelerated aging test results are analyzed to examine both cell performance, in terms of efficiency and thermal response under load, as well as cell lifetime. Cell thermal response is characterized by measuring temperature during cycle aging, which is used to calculated a normalized thermal resistance value that may help estimate both cell cooling needs or to help extrapolate aging test results to different thermal environments. Cell lifetime is evaluated qualitatively, considering simply the average calendar and cycle life across a range of conditions, as well as quantitatively, using statistical modeling and machine-learning methods to identify predictive aging models from the accelerated aging data. These predictive aging models are then used to investigate cell sensitivities to stressors, such as cycling temperature, voltage window, and C-rate, as well as to predict cell lifetime in various stationary storage applications. Results from this work show that cell lifetime and sensitivity to aging conditions varies substantially across commercial cells, necessitating testing for specific cell formats to make quantitative lifetime predictions. That being said, all commercial cells tested here are predicted to reach at least 10-year lifetimes for stationary storage applications. Based on the aging test results and modeling, some cells are expected to be relatively insensitive to temperature and use-case, making them suited for simple use cases with little or no thermal management and simple controls, while the lifetime of other cells could be extended to 20+ years if operated with thermal management and degradation-aware controls.

battery↗
DOE OSTI2016

Degradation in PV Encapsulant Strength of Attachment: An Interlaboratory Study Towards a Climate-Specific Test

Reduced strength of attachment of the encapsulant resulting from the outdoor environment, including ultraviolet (UV) radiation, may decrease photovoltaic (PV) module lifetime by enabling widespread corrosion of internal components. To date, few studies exist showing how the adhesion of PV components varies with environmental stress. We have conducted an interlaboratory experiment to provide an understanding that will be used to develop climatic specific module tests. Factors examined in the study included the UV light source (lamp type), temperature, and humidity to be proposed for use in accelerated aging tests. A poly (ethylene-co-vinyl acetate) (EVA) formulation often used in veteran PV installations was studied using a compressive shear test - to quantify the strength of attachment at the EVA/glass interface. Replicate laminated glass/polymer/glass coupon specimens were weathered at 12 institutions using a variety of indoor chambers or field aging. Shear strength, shear strain, and toughness were measured using a mechanical load-frame for the compressive shear test, with subsequent optical imaging and electron microscopy of the separated surfaces.

14 SOLAR ENERGY↗
DOE OSTI2024

Accelerated Irradiation and Qualification of Ceramic Nuclear Fuels

Accelerated neutron irradiation testing is an component of accelerated qualification of new nuclear fuels for light water reactor (LWRs), microreactors, and other special purpose reactors. The qualification and licensing of nuclear fuel is a lengthy process that can take 20-25 years to bring a new fuel into service. Accelerated fuel qualification combines both experimental and modeling work to expedite the total qualification time to 5-10 years timeframe. The experimental aspect of this is accelerated irradiation aims to reduce the total time needed for neutron irradiation to achieve targeted burnup, which can take years using conventional irradiation profiles. The data that results from this irradiation testing can then be entered into BISON models to develop robust and reliable performance simulations to ensure safe operation under normal and off normal conditions. This milestone focused on the fabrication of test articles for accelerated irradiation testing at the Advance Test Reactor (ATR).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Development of Accelerated Steady-state Test Capsule Experiments to Replicate EBR-II Fuel Behavior Using BISON Fuel Performance Analysis

Here in this work, BISON fuel performance calculations were performed to predict the fuel behavior of accelerated burnup U-Pu-Zr fuel, with temperature operation conditions of the fuel and the cladding mirroring conditions within EBR-II fuel pins. The temperature operating conditions within the FAST accelerated burnup rods were aimed at replicating EBR-II X447/X447A fuel surface and inner cladding surface temperatures. Due to the FAST capsule design, these temperatures can be replicated with fission rate densities being significantly increased. fuel performance modeling has not been assessed for novel experiments such as accelerated burnup utilizing the FAST capsule within ATR. This is an important step in understanding accelerated irradiation methods as many performance models are empirical models conforming to the results of PIE but do not always include physical models that would represent the changes in irradiation tests.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

CSP Optical Facilities at the National Renewable Energy Laboratory

The concentrating Solar Power (CSP) Optical Facilities at NREL comprise unique optical tools and facilities for testing and characterizing concentrating solar optical components. These facilities are maintained to aid researchers and industry efforts to reduce market barriers, improve the performance, reduce the cost, and improve the lifetime and reliability of CSP materials, components, subsystems, and integrated concepts, where accurate and timely characterization methods are needed. To reach this goal, NREL is committed to collaborating in ongoing and projected research needs for industry, academia, and government entities, in the development and characterization of low-cost, high-performance reflector and absorber materials in addition to their components-a key element in the conversion of concentrated sunlight into energy. To accomplish this mission, the core laboratory includes the Advanced Optical Materials Laboratory, indoor and outdoor accelerated weather testing tools, "Distant Observer" for parabolic troughs, the High Flux Solar Furnace, and the ultra-accelerated weather testing tools. This equipment enables to rapidly respond to new challenges with novel solutions that align with the goals of the Solar Energy Technology Office (SETO) at the U.S. Department of Energy. The goal of this paper is to present the state-of art-optical facilities available at NREL that can help support the research needs of the CSP community. Therefore, we review here the different components of the CSP Optical Facilities at NREL and highlight their characteristics and importance for the CSP community.

accelerated weather testing↗
DOE OSTI2023

Towards linking lab and field lifetimes of perovskite solar cells

Metal halide perovskite solar cells (PSCs) represent a promising low-cost, thin-film photovoltaic (PV) technology, with unprecedented power conversion efficiencies (PCEs) obtained for both single-junction and tandem applications. To push PSCs toward commercialization, it is critical, albeit challenging, to understand device reliability under real-world outdoor conditions where multiple stress factors (e.g., light, heat, humidity) coexist, generating complicated degradation behaviors. It is necessary to identify accelerated indoor testing protocols - which can correlate specific stressors with observed degradation modes in fielded devices - to quickly guide PSC development. Here, we use a state-of-the-art p-i-n PSC stack (with PCE up to ~25.5%) to show that indoor accelerated stability tests can predict our 6-month outdoor aging tests. Device degradation rates under illumination and at elevated temperatures are most instructive for understanding outdoor device reliability. Further, we also find that the indium tin oxide (ITO)/self-assembled monolayer (SAM)-based hole transport layer (HTL)/perovskite interface most strongly affects our device operation stability. Improving the ion-blocking properties of the SAM HTL increases averaged device operational stability at 50 degree C-85 °C by a factor of ~2.8, reaching over 1000 h at 85 °C and to near 8200 h at 50 °C with a projected 20% degradation, which is among the best to date for high-efficiency p-i-n PSCs.

14 SOLAR ENERGY↗
DOE OSTI2015

Synthesis and Characterization of Mixed-Conducting Corrosion Resistant Oxide Supports

An extensive search and evaluation of electrochemically stable catalyst supports (including metal oxides like RuO2-SiO2, RuO2-TiO2, and ITO was perfomed during the 4 years of the project. The suports were also catalyzed by deposition of Pt and tested for its performance and electrochemical stability in RDE and fuel cell experiments. For testing the electrochemical stability and fuel cell performance of the catalysts and supports, we have employed the protocols in use at the Department of Energy and Nissan Technological Center North America (NTCNA). The use of such procedures allows a precise and reproducible estimation of the performance and stability of the materials and permits comparisons among laboratories and DOE funded projects. RuO2-SiO2 catalyst supports showed no loss in surface area during start-stop stability tests that were performed by cycling the electrode potential between 0 V to 1.8 V for 1000 cycles. Catalyzed support (40% Pt/RuO2-SiO2; 1:1 mole ratio) were tested in a PEFC, resulting in a current density of 750 mA/cm2 at 0.6 Volts, and a maximum power density of 570 mW/cm2. Measurements were conducted at 80 ºC with 75% relative humidity of the inlet gases (H2/O2); Pt loadings were 0.4 mg/cm2 at the cathode and 0.2 mg/cm2 at the anode. Start-stop stability tests for support and catalyzed support performed in RDE and PEFC set-ups have confirmed RuO2-TiO2 support stability. The beginning of life performance was exactly equal to end of life performance (in an MEA that has been subjected to severe start-stop cycling for 10,000 start/stop cycles between 1 V to 1.5 V). This result was in sharp contrast to baseline Pt/C catalyst that showed significant performance deterioration after accelerated stability tests. The Pt/TRO showed minimal loss in performance upon exposure to start-stop cycles. The loss in cell voltage at 1 A/cm2 at 100% RH was almost 700 mV for Pt/C whereas it was only ca. 15 mV for Pt/TRO. 40% RH data (of inlet gases) revealed a similar trend in terms of stability – exceptional stability for Pt/TRO as opposed to very poor stability for Pt/HSAC. These observations were attributed to the much higher stability of the TRO support compared to Carbon. The carbon dioxide concentration in the cathode exit stream during the accelerated degradation test with Pt/TRO (start-stop protocol) was extremely low (between 3 to 10 ppm of CO2). In contrast, the CO2 emission levels from a conventional Pt/C catalyst were found to be approx. 200 ppm. This observation was a clear indicator that the main source of carbon being oxidized to carbon dioxide in an MEA was the carbon catalyst support, and not the gas diffusion layer or the graphite flow fields. Indium tin oxide (ITO) was also evaluated as a catalyst support for PEFCs. Pt/ITO was very stable under start-up/shutdown accelerated degradation protocol (RDE tests in perchloric acid). The ECSA change was less than 4% over 10,000 cycles. The load cycling accelerated protocol (from 0.6 to 0.95 V vs. RHE) resulted in a loss of approximately 34% of the initial ECSA after 10,000 cycles. However, fuel cell testing resulted in a very low performing catalyst. XPS spectroscopy was employed to investigate the changes in the catalysts occuring during fuel cell operation. It was observed a shift of In 3d5/2 and In 3d3/2 peaks towards higher binding energies. This can be explained by the formation of hydroxides or oxy-hydroxides in the surface of the catalyst. O1s spectrum for Pt/ITO catalyst after being operated in the fuel cell, also confirmed the formation of significant amounts of surface hydroxides (12 to 16%). The presence of surface hydroxides in the catalyst increased the electrode resistivity affecting fuel cell performance. NTCNA performed a detailed analysis of transport phenomena (reactants and products to/from the Pt active sites) in both commercial catalyst and Pt/RTO (in order to have a better understanding at the basic level). The proton resistance (Rionomer) in Pt/C and Pt/RTO cathode catalyst layers were 150 and 12 mΩ-cm2, respectively. Pt/RTO catalyst layer has about an order or magnitude lower proton transfer resistance than Pt/C catalyst layer. Since the ionomer/support ratio that was used in formulating the ink for both catalysts was the same (0.9), it is expected that the volumetric coverage of ionomer of both catalysts will be significantly different due to the disparity in the surface areas (Pt/C had ~ 800 m2/g, while Pt/RTO had ~ 50 m2/g). The differences in the ionomer volumetric coverage and the ionomer film thickness may explain the significantly higher proton conductivity in the Pt/RTO catalyst layer when compared to Pt/HSAC. It is therefore very important to optimize the ionomer loadings when synthesizing new catalyst supports (and never rely on values for carbon-based commercial catalysts). Finally, NTCNA has elaborated a cost model for non-carbon support materials considering their durability benefits. Material costs for production of Pt/ RuO2-TiO2 electrodes were compared to Pt/C. RuO2-TiO2 support was more expensive than carbon but the total material cost was still dominated by platinum cost. Though ruthenium is considered a precious metal, its cost is far less than platinum. It should also be noted that ruthenium only makes up 38% of the mass of the support, while the rest is inexpensive TiO2. After considering the durability advantages of Pt/RTO, cost model showed that even with almost double the Pt loading (0.35 vs 0.18 mgPt/cm2), Pt/RTO ($22.7/kWnet) is only slightly more expensive than Pt/C ($21.9/kWnet).

08 HYDROGEN↗
DOE OSTI2024

An approach to combine neutron and ion irradiation data to accelerate material qualification for nuclear reactors

Next-generation nuclear power plants are generally characterized by higher operating temperatures, increased neutron fluences and energies, and distinct corrosive coolant environments versus the existing light water reactor fleet. Whether using existing materials in new environments, newly developed materials tailored for these environments, or new manufacturing methods, the traditional decades-long approach for materials qualification does not facilitate rapid deployment. Ion irradiation has demonstrated success in reproducing material microstructure and select property evolution resulting from neutron irradiation with three to four orders of magnitude reduction in time and cost, making it an ideal candidate for accelerated irradiation testing. Because microstructure has a large impact on bulk material properties, limited neutron irradiation data at lower damage levels can in principle be combined with accelerated ion testing results and modeling and simulation to form an accurate prediction of microstructure evolution and select properties under different neutron irradiation conditions and at higher damage levels. The objective of this work is to present a conceptual framework of specific steps to fulfill several technical challenges associated with qualifying materials for performance in radiation environments on an accelerated time frame. A brief review of the regulatory landscape for materials in nuclear environments is presented, followed by additional overviews to understand the current state of the art for correlation of materials properties across radiation environments using experimental and computational methodologies. Finally, the roles of academia, national laboratories, and industry in the advancement of this accelerated materials qualification framework are discussed as a path forward, with possible case studies presented.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Rapid assessment of the creep rupture life of metals: A model enabling experimental design

Prediction of the creep rupture life of engineering metals is critical for qualification and design of new materials. The use of long-term creep tests and the need to quantify the performance variability in a priori similar systems hinder the rapid creep assessment of a given material. Therefore, it is essential to develop methods that can extrapolate the long-term performance of alloys and the associated variability from short-term experiments. To this end, this study introduces a new model which enables the estimation of the rupture life of a material for a given stress and temperature. This model relies on two components. First, a new relation for the minimum creep rate (MCR) of materials is introduced. It includes a stress dependent stress exponent allowing the model to capture the variation of MCR across a wide range of temperatures and stresses. Second, employing the Monkman-Grant (MG) law, we establish a relation between stress, temperature and creep rupture life. Together, these two elements yield a new closed-form mathematical expression for the Larson Miller parameter as a function of stress and temperature. This expression captures the creep rupture time for many metals (Gr91, Copper, Gr122 and 347H) and compares favorably with alternate empirical approaches. The model is then used to assess the minimum duration of creep rates necessary to qualify the material up to 100000h. Furthermore, it is found that depending on the material system, creep tests as few as five limited to 5000 h for steels (Gr91, Gr122, 347H) and 100 h for copper are sufficient to model creep lifetimes. Finally, using a Bayesian inference-based approach to calibrate the model, we demonstrate that variability in rupture life can be captured via the quantification of the uncertainty in the model parameters and extrapolated from a limited number of short to moderately short creep tests; thereby paving the way for accelerated creep testing.

36 MATERIALS SCIENCE↗
DOE OSTI2012

A scintillator-based online detector for the angularly resolved measurement of laser-accelerated proton spectra

In recent years, a new generation of high repetition rate ({approx}10 Hz), high power ({approx}100 TW) laser systems has stimulated intense research on laser-driven sources for fast protons. Considering experimental instrumentation, this development requires online diagnostics for protons to be added to the established offline detection tools such as solid state track detectors or radiochromic films. In this article, we present the design and characterization of a scintillator-based online detector that gives access to the angularly resolved proton distribution along one spatial dimension and resolves 10 different proton energy ranges. Conceived as an online detector for key parameters in laser-proton acceleration, such as the maximum proton energy and the angular distribution, the detector features a spatial resolution of {approx}1.3 mm and a spectral resolution better than 1.5 MeV for a maximum proton energy above 12 MeV in the current design. Regarding its areas of application, we consider the detector a useful complement to radiochromic films and Thomson parabola spectrometers, capable to give immediate feedback on the experimental performance. The detector was characterized at an electrostatic Van de Graaff tandetron accelerator and tested in a laser-proton acceleration experiment, proving its suitability as a diagnostic device for laser-accelerated protons.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

New photomultiplier active base for Hall C Jefferson Lab lead tungstate calorimeter

A new photomultiplier tube active base was designed and tested. The base combines active voltage division circuit and fast amplifier, powered by the current flowing through voltage divider. This base is developed to upgrade older photomultiplier bases of Jefferson Lab lead-tungsten calorimeter (about ˜1200 crystals of PbWO{sub 4} from the PrimEx experimental setup). This is needed for the extension of detectors&#x27; rate capability to meet requirements of new Hall C proposal PR12-11-102 of measurements of the L/T separated cross sections and their ratio R = πL/πT in neutral-pion p(e,e'π0)p deep exclusive and p(p(e,e'π{sup 0})p)X semi-inclusive scattering regions. New active base is direct replacement of older passive base circuit without adding of additional power or signal lines. However, it extends detectors rate capability with factor over 20. Moreover, transistorized voltage divider improves detector&#x27;s amplitude resolution due to reduction of photomultiplier gain dependence from tube anode current. The PMT active base is the invention disclosed in V. Popov&#x27;s U.S. Patent No. 6,791,269, which successfully works over ten years in several Jefferson Lab Cherenkov detectors. The following design is a new revised and improved electronic circuit with better gain stability and linearity in challenge to meet requirements of new Hall C experimental setup. New active base performance was tested using fast LED light source and Pr:LuAG scintillator and gamma sources. Electronics radiation hardness was tested on JLab accelerator. Results of testing R4125 Hamamatsu photomultiplier tube in new active base are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Mitigation and Diagnosis of Pin-Hole Formation in Polymer Electrolyte Membrane Fuel Cells

In this work, we implement a calendering technique to flatten stray fibers within the gas diffusion media, thereby mitigating pin-hole formation in the hot-pressed MEAs. We have investigated the influence of calendering on the long-term durability for several types of gas diffusion electrodes (GDEs) using a combined chemical and mechanical accelerated stress test (AST). The calendered MEAs demonstrate an average AST lifetime improvement of 77% relative to the as-fabricated MEAs.

AMR↗
DOE OSTI2020

Prediction of Climate-Specific Degradation Rate for Photovoltaic Encapsulant Discoloration

Encapsulant discoloration is a well-known field degradation mode of crystalline-silicon photovoltaic modules, particularly in the hot climate zones. The discoloration rate is influenced by several weathering factors, such as UV light, module temperature, and humidity, as well as the permeability of oxygen into the module. Here, a rate dependence model employing the modified Arrhenius equations to predict the degradation rate for encapsulant discoloration in different climates is presented. Two modeling approaches are introduced, which utilize the field and accelerated UV testing degradation data in conjunction with the field meteorological data to determine the acceleration factor for encapsulant browning. A novel method of accelerated UV stress testing at three simultaneous module temperatures in a single environmental chamber test run is implemented to estimate the activation energy for browning. The test was performed on three field-retrieved modules to capture the wear-out failure mechanism. The degradation in short-circuit current Isc rather than maximum power is used as a decisive parameter for the discoloration analysis. Furthermore, the developed model has been used to predict the Isc degradation rate for the Arizona field characterized by a hot and dry climate and is validated against the field-measured value. It has also been applied to other climate types, e.g., the cold and dry climate of New York.

14 SOLAR ENERGY↗