2020 PV Reliability Workshop: February 27, 2020 Proceedings
These are the proceedings from the Feb. 27, 2020 Photovoltaic Reliability Workshop (PVRW) 2020 Conference.
41 EE - Solar Energy Technologies Office (EE-4S)↗
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2020 PV Reliability Workshop: February 25, 2020 Proceedings
These are the proceedings from the Feb. 25, 2020 Photovoltaic Reliability Workshop (PVRW) 2020 Conference.
41 EE - Solar Energy Technologies Office (EE-4S)↗
Solar photovoltaic waterless soiling monitoring systems and methods
A system for evaluation of soiling of solar photovoltaic (PV) modules may comprise a first pair of solar PV modules exposed to the elements, a second pair of solar PV modules enclosed within a protective housing having a glass cover; a component coupling the glass cover to the protective housing. The component may be configured to displace the glass cover for a limited period of time to temporarily expose the second pair of solar PV modules to the atmospheric elements.
14 SOLAR ENERGY↗
Benchmarks of Global Clean Energy Manufacturing, 2014-2016
Benchmarks of Global Clean Energy Manufacturing provides an assessment of the global state of clean energy manufacturing over 3 years from 2014 to 2016. Four technologies were examined - wind turbine components (blade, tower, nacelle), crystalline silicon (c-Si) solar photovoltaic (PV) modules, light-duty vehicle (LDV) lithium-ion battery (LIB) cells, and light-emitting diode (LED) packages for lighting and other consumer products. The analysis looked along each technology's manufacturing supply chain, including processing raw materials, producing required subcomponents, and assembling final products. Manufacturing supply chains were evaluated across 13 economies that are the primary manufacturing hubs for these technologies. This Highlights summary report features key findings across the manufacturing supply chains.
42 ENGINEERING↗
Degradation in Photovoltaic Encapsulant Transmittance: Results of the Second PVQAT TG5 Artificial Weathering Study
The optical degradation of encapsulants from ultraviolet (UV) radiation has historically resulted in a significant loss in performance throughout the life of a photovoltaic (PV) module. IEC test methods have recently been developed to screen for PV encapsulants prone to loss in optical performance. The present study was performed to benchmark polymeric packaging materials relative to IEC 62788-1-4 (covering the measurement of optical transmittance) and IEC 62788-1-7 (on the durability of transmittance), provide feedback toward improvement of the methods, and develop insight regarding optical degradation. Contemporary materials were examined, including: poly(ethylene-co-vinyl acetate) (EVA), thermoplastic polyolefin (TPO), polyolefin elastomer (POE), and polyvinyl butyral (PVB) encapsulants; a poly(ethene-co-tetrafluoroethene)/poly(ethylene terephthalate) (ETFE/PET) transparent backsheet; and a polystyrene (PS) working reference material. The use of silica-, specialty-, and rolled-glass was also compared in laminated coupons. Specimen size was separately examined from 2.5 cm to 12.5 cm. Weathering was performed with a xenon source, using IEC TS 62788-7-2 methods A2, A3, A4, and A5 (chamber temperature of 55 Degrees C, 65 Degrees C, 75 Degrees C, or 85 Degrees C), respectively. Characterizations were made using a UV-VIS-NIR spectrophotometer (transmittance and reflectance, with and without an integrating sphere), a UV-VIS fluorescence spectrophotometer, a camera, and an optical microscope. Performance was analyzed, including solar weighted transmittance, yellowness index, UV cut-off wavelength, and haze (scattering). Separate Arrhenius analyses were performed to assess retention of transmittance and changes in yellowness index. The activation energy for both characteristics was found to range from 15 kJ?mol-1-80 kJ/mol-1, with an average of 48 kJ/mol-1, similar to the average of 45 kJ/mol-1 identified in the previous international PV Quality Assurance Task Force (PVQAT) Task Group 5 (TG5) study of more traditional encapsulants. The separate degradation modes of discoloration and scattering were distinguished in the encapsulants using a comprehensive spectral characterization. Based on these results, the IEC 62788-1-7 pass/fail criteria of 5% change in transmittance was confirmed to identify a known bad encapsulant.
durability↗
UV Degradation in Backsheets: A Ray-Tracing Irradiance Simulation Approach
Around 90% of current photovoltaic (PV) modules are less than ten years old. New PV technologies and materials are deployed without documented durability and performance histories. Accelerated testing attempts to capture degradation modes but can produce false results with such rapid deployment of new materials. Current testing assumes UV dosage on the rear of a module to be 10% of that incident on the front. We present a method to quantify degradation on PV backsheets in the field. We aim to evaluate if current acceleration factors for UV damage in chambers are properly estimating degradation for different PV site installations. The method leverages bifacial_radiance to ray-trace and evaluate irradiance on the front and the rear of the modules. Then an equation to estimate the relative degradation is proposed.
accelerated testing↗
Evaluation of Surface Crack Formation in Photovoltaic Backsheets Using Fragmentation and Finite Element Simulations: Preprint
Backsheet cracking is among the most commonly observed degradation modes of photovoltaic (PV) modules in the field. Cracks can reduce the ability of backsheets to fulfil their functions, for example, protection of the modules from the environment or electrical insulation. This work presents an evaluation of the degradation and cracking propensity of two backsheets during accelerated IEC TS 62788-7-2 A3 (International Electrotechnical Commission) aging with the fragmentation test: a co-extruded polyamide backsheet (AAA), and a laminated multilayer backsheet with a polyethylene terephthalate core and outer layer and ethylene vinyl acetate inner layer (PPE). Results show the surface embrittlement of the AAA outer layer during exposure. A longer time of exposure causes cracks to form at lower strains during stretching and creates deeper cracks. Accordingly, Young's modulus of the outer layer increases, as measured by cross-sectional nanoindentation. PPE exhibits cracking after exposure as well. While no similar increase of modulus or crack depth can be observed, the outer layer of PPE exhibits more obvious signs of erosion during exposure, including progressive morphological changes and thickness losses. A finite element model to simulate surface crack formation is devised, based on initially zero-thickness decohesion elements. Decohesion criteria define a critical stress, at which these elements grow, and cracks can begin to form. These criteria are obtained via parameter optimization by comparison between simulation and experiment. The model is used to interpret crack formation in both backsheets.
backsheet↗
Determining the Crosslinking and Degradation Reaction Kinetics in Photovoltaic Encapsulants Using Accelerated Aging: Preprint
Degradation of photovoltaic (PV) module encapsulant mechanical characteristics that lead to embrittlement and delamination remains a cause of failure in solar installations. A multiscale reliability model based on detailed molecular degradation reaction kinetics was previously published, connecting the encapsulant mechanical properties (elastic modulus, yield strength, and adhesion energy) to the degraded molecular structure and interfacial bond density to adjacent solar cell and glass substrates. The model, developed primarily for poly(ethylene-co-vinyl acetate) (EVA) encapsulants, remains to be experimentally validated. Determining the degradation and crosslinking kinetics of alternative encapsulants, such as polyolefin elastomer (POE) and EVA/POE/EVA composites (EPE), can further generalize the model. Importantly, the activation energy for crosslinking of fully cured PV encapsulant products from temperature or UV is presently unknown or unavailable. In this work, we subject EVA, POE, and EPE encapsulants to a set of accelerated aging conditions, varying the temperature, UV intensity, and relative humidity. We use DSC, FTIR, and Soxhlet extraction (gel content) to characterize the encapsulants' changing molecular structure. This allows for determination of the photochemical degradation and crosslinking kinetics of the encapsulants. Preliminary results show an increase in gel content (crosslinking) and a decrease in crystallinity of EVA, POE, and EPE encapsulants under hot-aerobic (90 deg C, 22% RH) and hot-anaerobic (90oC, sealed in N2 air) accelerated aging, even in the absence of UV and crosslinking initiating agents. For a least squares regression with an assumed first-order crosslinking kinetics, the crosslinking rate parameters were computed for the three encapsulants under hot-aerobic and hot-anaerobic aging conditions. FTIR analysis showed insignificant encapsulant degradation for hot-aerobic and hot-anaerobic aging, demonstrating the critical role of UV and moisture in accelerating degradation. Aging conditions with UV exposure and elevated humidity are presently in progress.
adhesion↗
Recycling lead and transparent conductors from perovskite solar modules
Abstract Perovskite photovoltaics are gaining increasing common ground to partner with or compete with silicon photovoltaics to reduce cost of solar energy. However, a cost-effective waste management for toxic lead (Pb), which might determine the fate of this technology, has not been developed yet. Here, we report an end-of-life material management for perovskite solar modules to recycle toxic lead and valuable transparent conductors to protect the environment and create dramatic economic benefits from recycled materials. Lead is separated from decommissioned modules by weakly acidic cation exchange resin, which could be released as soluble Pb(NO 3 ) 2 followed by precipitation as PbI 2 for reuse, with a recycling efficiency of 99.2%. Thermal delamination disassembles the encapsulated modules with intact transparent conductors and cover glasses. The refabricated devices based on recycled lead iodide and recycled transparent conductors show comparable performance as devices based on fresh raw materials. Cost analysis shows this recycling technology is economically attractive.
14 SOLAR ENERGY↗
From Modules to Atoms: Techniques and Characterization for Identifying and Understanding Device-Level Photovoltaic Degradation Mechanisms
This report documents how degraded modules are analyzed for the characterization of cell-level performance reduction. The primary degradation topics presented here are 1) potential-induced degradation, 2) defect metastability and impurity diffusion, and 3) partial-shading-induced reverse-bias breakdown. Imaging techniques, such as electroluminescence imaging, photoluminescence imaging, and lock-in thermography provide spatial information of full modules on the meter scale. Area of interest can then be imaged with higher spatial resolution by zooming in with fields of view near the mm scale. We document procedures for coring cell samples from selected regions of interest using mechanical drilling. The small samples are then of suitable size for various microscopic analyses using techniques such as scanning electron microscopy, time-of-flight secondary ion spectrometry, atomic force microscopy, electron beam induced current, transmission electron microscopy, and atom probe tomography, which can provide chemical, structural, and electrical characterization down to the atomic scale.
14 SOLAR ENERGY↗
User handbook for block IV silicon solar cell modules
The essential electrical and mechanical characteristics of block 4 photovoltaic solar cell modules are described. Such module characteristics as power output, nominal operating voltage, current-voltage characteristics, nominal operating cell temperature, and dimensions are tabulated. The limits of the environmental and other stress tests to which the modules are subjected are briefly described.
Smokler, M. I.↗
Block 5 documentation and solar modules
Design and fabrication of Spire Corporation's Block 5 photovoltaic flat plate module is reviewed. These modules exhibited power of about 70 watts under standard test conditions. Results of performance and environmental testing are provided.
Source record↗
Photovoltaic driven multiple quantum well optical modulator
Multiple quantum well (MQW) structures (12) are utilized to provide real-time, reliable, high-performance, optically-addressed spatial-light modulators (SLM) (10). The optically-addressed SLM comprises a vertical stack of quantum well layers (12a) within the penetration depth of an optical write signal 18, a plurality of space charge barriers (12b) having predetermined tunneling times by control of doping and thickness. The material comprising the quantum well layers has a lower bandgap than that of the space charge barrier layers. The write signal modulates a read signal (20). The modulation sensitivity of the device is high and no external voltage source is required. In a preferred embodiment, the SLM having interleaved doped semiconductor layers for driving the MQW photovoltaically is characterized by the use of a shift analogous to the Moss-Burnstein shift caused by the filling of two-dimensional states in the multiple quantum wells, thus allowing high modulation sensitivity in very narrow wells. Arrays (30) may be formed with a plurality of the modulators.
Maserjian, Joseph↗
Photovoltaic power generation system with photovoltaic cells as bypass diodes
A photovoltaic power generation system that includes a solar panel is described herein. The solar panel includes a photovoltaic sub-module, which includes a group of microsystem enabled photovoltaic cells. The group includes a first string of photovoltaic cells, a second string of photovoltaic cells, and a differing photovoltaic cell. Photovoltaic cells in the first string are electrically connected in series, and photovoltaic cells in the second string are electrically connected in series. Further, the first string of photovoltaic cells, the second string of photovoltaic cells, and the differing photovoltaic cell are electrically connected in parallel. Moreover, the differing photovoltaic cell is used as a bypass diode for the first string of photovoltaic cells and the second string of photovoltaic cells.
14 SOLAR ENERGY↗
Photovoltaic response in pristine WSe{sub 2} layers modulated by metal-induced surface-charge-transfer doping
We obtained photovoltaic response in pristine multilayer WSe{sub 2} by sandwiching WSe{sub 2} between top and bottom metals. In this structure, the work-function difference between the top metal and WSe{sub 2} plays a critical role in generating built-in potentials and photovoltaic responses. Our devices with Zn as top metal exhibit photo-conversion efficiencies up to 6.7% under 532 nm illumination and external quantum efficiencies in the range of 40%–83% for visible light. This work provides a method for generating photovoltaic responses in layered semiconductors without detrimental doping or exquisite heterostructures, and also advances the physics for modulating the band structures of such emerging semiconductors.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Comparison of breakdown-voltage of contemporary and veteran photovoltaic backsheets
The ability of designated electrically insulating materials in a module, including the backsheet, to act as insulators is a key safety requirement for photovoltaic technology. The recently developed test standards IEC TS 62788-2 (including a method for direct-current breakdown-voltage) and IEC TS 62788-7-2 (for ultraviolet [UV] weathering) are examined for the first time together in this study. Thirty-six contemporary backsheets were compared using the breakdown-voltage test, before and after UV weathering, according to the recent A3 test condition. Twenty-eight backsheets, extracted from a variety of veteran photovoltaic modules, were also examined using the breakdown test. Additional characterizations were performed to interpret the breakdown-voltage results, including: surface and cross-sectional optical microscopy failure analysis; cross-sectional scanning electron (SEM) microscopy with EDS energy-dispersive X-ray spectroscopy (EDX) failure analysis; Fourier-transform infrared spectroscopy (FTIR) to identify the base resin and its chemical integrity; and differential scanning calorimetry (DSC) to identify phase transitions that might adversely affect degradation during weathering. The electrical insulation for the backsheets is discussed relative to: the industry safety requirement; features observed to facilitate the degradation of insulation; the validity of the artificial UV weathering test; the validity of the sheet geometry used for specimens in this study; and the validity of subsequent mechanical testing.
14 SOLAR ENERGY↗
Module of Laser-Radiation (λ = 1064 nm) Photovoltaic Converters
The results of a study and the development of a module designed for energy transmission via atmospheric channels are presented. The four-cell module based on single-junction metamorphic InGaAs/GaAs converters grown by metal-organic vapor-phase epitaxy has an open-circuit voltage of ~3 V. It is shown that the monochromatic efficiency (at a wavelength of 1064 nm) of this module is 31.5% under exposure to a Xe-lamp with a radiation power of 1.5 W/cm{sup 2}.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Moisture-temperature degradation in module encapsulants: The general problem of moisture in photovoltaic encapsulants
A general research approach was outlined toward understanding water-module interactions and the influence of temperature involving the need to: quantify module performance loss versus level of accumulated degradation, establish the dependence of the degradation reaction rate on module moisture and temperature levels, and determine module moisture and temperature levels in field environments. These elements were illustrated with examples drawn from studies of the now relatively well understood module electrochemical degradation process. Research data presented include temperature and humidity-dependent equilibrium leakage current values for multiparameter module material and design configurations. The contributions of surface, volume, and interfacial conductivities was demonstrated. Research directions were suggested to more fully understand the contributions to overall module conductivity of surface, volume, and interfacial conductivities over ranges of temperature and relative humidity characteristic of field environments.
Mon, G. R.↗