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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Active region of a functionally integrated laser – modulator

A method for the functional integration of injection lasers and modulators of generated light in a single heterostructure with spatially displaced quantum wells in the conduction and valence bands, formed by the second-type heterojunctions, is proposed. The structures and energy band diagrams of the active regions of functionally integrated lasers – modulators with amplitude and frequency modulation are considered. A physical – topological model and a technique for numerical simulation of lasers – modulators is proposed. It is shown that the maximum modulation frequencies for the proposed heterostructures, in contrast to the same frequencies implemented under pump current modulation, are not limited by the duration of transients in the laser power supply circuit and the carrier lifetime in the laser active region but are determined by the photon lifetime in the cavity. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Compensation of residual amplitude modulation fluctuations in an optoelectronic system for laser radiation frequency stabilisation

Fluctuations of residual amplitude modulation in a scheme of laser frequency stabilisation by a Fabry – Perot cavity reduce the frequency stability of the laser systems intended for interrogating clock transitions of atoms and ions. The dependences of the residual amplitude modulation on a temperature of the waveguide-based electro-optical modulator used for modulating the radiation phase and on polarisation of the radiation are measured. The parameters are found, at which the influence of the residual amplitude modulation on the frequency stability is minimal. A system for active compensation is created, which reduces the contribution of fluctuations of residual amplitude modulation to the instability down to 2.1 × 10{sup −16}, which makes it possible to reach the thermal noise limit of a silicon cryogenic cavity. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Monthly modulation in dark matter direct-detection experiments

The signals in dark matter direct-detection experiments should exhibit modulation signatures due to the Earth's motion with respect to the Galactic dark matter halo. The annual and daily modulations, due to the Earth's revolution about the Sun and rotation about its own axis, have been explored previously. Monthly modulation is another such feature present in direct detection signals, and provides a nearly model-independent method of distinguishing dark matter signal events from background. We study here monthly modulations in detail for both WIMP and WISP dark matter searches, examining both the effect of the motion of the Earth about the Earth-Moon barycenter and the gravitational focusing due to the Moon. For WIMP searches, we calculate the monthly modulation of the count rate and show the effects are too small to be observed in the foreseeable future. For WISP dark matter experiments, we show that the photons generated by WISP to photon conversion have frequencies which undergo a monthly modulating shift which is detectable with current technology and which cannot in general be neglected in high resolution WISP searches.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Packaging of an 8-kV Silicon Carbide Diode Module with Double-Side Cooling and Sintered-Silver Joints

Packaging innovations are needed for medium-voltage wide bandgap power semiconductor modules to enable their adaptation in grid applications. A unique challenge for packaging medium-voltage power modules is managing the trade-off between insulation demand and heat dissipation. The focus of this work was on developing a packaging innovation that improves the module heat dissipation and offers more flexibility to its insulation design. Two strategies were explored for the packaging of an 8-kV SiC diode rectifier module:(1) double-side cooling and (2) sintered-silver bonding. Double-side cooling was realized by using short metal posts rather than long and thin wire bonds for device interconnection, forming a low-profile package with devices sandwiched between two insulated metal substrates. Sintered-silver bonding enabled the devices to function reliably at over 250 °C. Simulations of the packaged module showed a low interconnect inductance of 2.67 nH and a 50% less heat transfer coefficient required to cool the chips. Prototypes of the module were fabricated, and preliminary electrical testing results validated the package design.

27 ARPA - Advanced Research Projects Agency-Energy↗
DOE OSTI2015

Quantifying Solar Cell Cracks in Photovoltaic Modules by Electroluminescence Imaging

This article proposes a method for quantifying the percentage of partially and totally disconnected solar cell cracks by analyzing electroluminescence images of the photovoltaic module taken under high- and low-current forward bias. The method is based on the analysis of the module's electroluminescence intensity distribution, applied at module and cell level. These concepts are demonstrated on a crystalline silicon photovoltaic module that was subjected to several rounds of mechanical loading and humidity-freeze cycling, causing increasing levels of solar cell cracks. The proposed method can be used as a diagnostic tool to rate cell damage or quality of modules after transportation. Moreover, the method can be automated and used in quality control for module manufacturers, installers, or as a diagnostic tool by plant operators and diagnostic service providers.

14 SOLAR ENERGY↗
DOE OSTI2016

Modeling Current Transfer from PV Modules Based on Meteorological Data

Current transferred from the active cell circuit to ground in modules undergoing potential-induced degradation (PID) stress is analyzed with respect to meteorological data. Duration and coulombs transferred as a function of whether the module is wet (from dew or rain) or the extent of uncondensed surface humidity are quantified based on meteorological indicators. With this, functions predicting the mode and rate of coulomb transfer are developed for use in estimating the relative PID stress associated with temperature, moisture, and system voltage in any climate. Current transfer in a framed crystalline silicon module is relatively high when there is no condensed water on the module, whereas current transfer in a thin-film module held by edge clips is not, and displays a greater fraction of coulombs transferred when wet compared to the framed module in the natural environment.

14 SOLAR ENERGY↗
DOE OSTI2018

Correction for Metastability in the Quantification of PID in Thin-Film Module Testing

A fundamental change in the analysis for the accelerated stress testing of thin-film modules is proposed, whereby power changes due to metastability and other effects that may occur due to the thermal history are removed from the power measurement that we obtain as a function of the applied stress factor. In this work, initial thermal treatment of the module is performed before application of the independent variable stress of system voltage so that any temperature-dependent processes (e.g., diffusion) that affect the module power are largely activated beforehand. Secondly, the power of reference modules normalized to an initial state-undergoing the same thermal and light exposure history but without the applied stress factor such as humidity or voltage bias-is subtracted from that of the stressed modules. For better understanding and appropriate application in standardized tests, the method is demonstrated and discussed for potential-induced degradation testing in view of the paralleloccurring but unrelated physical mechanisms that can lead to confounding power changes in the module.

14 SOLAR ENERGY↗
DOE OSTI2021

Representative Modules for Accelerated Thermal Cycling and Static Load Testing

In this work, we explore the influence of module size on the rate of interconnect solder bond thermomechanical fatigue (TMF) damage and the probability of cell fracture. For the solder bond TMF damage evaluation, structural mechanics models of crystalline silicon PV models are created to solve with the Finite Element Method. For the probability of cell fracture evaluation, Weibull analysis and weakest link theory are employed to resolve the probability of crystalline silicon PV cell fracture when measured as bare cells and when stressed in reduced- and full-sized modules. Results conclusively demonstrate that the rate of solder bond TMF damage is independent of module size, interconnect location across the cell and cell location across the module and that smaller, representative, modules must be loaded to a much higher level than their parent full-sized modules to achieve an equivalent driving force for cell fracture.

accelerated testing↗
DOE OSTI2022

Fast External Quantum Efficiency Measurements of Photovoltaic Modules

The external quantum efficiency (EQE) or associated spectral response is widely used to evaluate the performance of photovoltaics, light emitting diodes, photodetectors, photodiodes, semiconductor lasers, laser-induced refrigeration of solids etc. For photovoltaic (PV) devices, The EQE is used to determine the spectral mismatch correction that is used to convert a performance measurement from a non-ideal simulator spectrum to a standard spectrum in PV device calibrations. Moreover, EQE can provide important insight into the physics of a PV device. For instance, the EQE shape can be used to infer mechanisms limiting the performance of the device. However, EQE measurements of full-size PV modules remain a challenge in the PV community due to rare availability of reliable module QE measurement tools worldwide and the size and complexity of module architecture that comprises several cells connected in strings (series or/and parallel). Here, we use a customized nondestructive tool made of high-power light emitting diodes to perform high-throughput EQE measurements on PV modules. Circuit simulations show that the measurement system can safely be used to measure both crystalline silicon and thin film-based PV modules with series connected cells without the risk of damage through reverse bias. In addition, EQE mapping combined with electroluminescence show a strong correlation and provide a way to determine both spatial non-uniformity of the spectral response and defects/degradation effects across the module.

PV module↗
DOE OSTI2018

A Contribution to the Theory of the Interaction of Transient Radiation of a Charged Particle with Periodically Modulated Anisotropic Magnetodielectric Filling of a Waveguide

Transient radiation of a charged particle in a waveguide with modulated anisotropic magnetodielectric filling is considered. It is assumed that the particle moves with a constant velocity perpendicularly to the axis of the waveguide the filling of which is periodically modulated by the harmonic law. Wave equations for the transverse electric (TE) and transverse magnetic (TM) fields in the waveguide have been obtained. Analytical expressions have been obtained for fields in the waveguide in the first approximation by small modulation indices of waveguide filling. Energies of transient radiation of a charged particle have been calculated in the region of weak (nonresonance) interaction between the radiation and modulation waves, in particular, in the case of a rectangular waveguide. It has been shown that radiation energies at the zero harmonic in the region of weak interaction do not depend on the modulation indices and are proportional to the modulation indices in the first power at the plus and minus first harmonics. The mechanism of the appearance of Cherenkov radiation has been analyzed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Graphene metamaterial modulator for free-space thermal radiation

We proposed and demonstrated a new metamaterial architecture capable of high speed modulation of free-space space thermal infrared radiation using graphene. Our design completely eliminates channel resistance, thereby maximizing the electrostatic modulation speed, while at the same time effectively modulating infrared radiation. Experiment results verify that our device with area of 100 × 120 µm 2 can achieve a modulation speed as high as 2.6 GHz. We further highlight the utility of our graphene metamaterial modulator by reconstructing a fast infrared signal using an equivalent time sampling technique. The graphene metamaterial modulator demonstrated here is not only limited to the thermal infrared, but may be scaled to longer infrared and terahertz wavelengths. Our work provides a path forward for realization of frequency selective and all-electronic high speed devices for infrared applications.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Bottom-Up Cost Analysis of a High Concentration PV Module; NREL (National Renewable Energy Laboratory)

We present a bottom-up model of III-V multi-junction cells, as well as a high concentration PV (HCPV) module. We calculate $0.65/Wp(DC) manufacturing costs for our model HCPV module design with today’s capabilities, and find that reducing cell costs and increasing module efficiency offer the promising pathways for future cost reductions. Cell costs could be significantly reduced via an increase in manufacturing scale, substrate reuse, and improved manufacturing yields. We also identify several other significant drivers of HCPV module costs, including the Fresnel lens primary optic, module housing, thermal management, and the receiver board. These costs could potentially be lowered by employing innovative module designs.

$/W↗
DOE OSTI2015

In-Situ Measurement of Power Loss for Crystalline Silicon Modules Undergoing Thermal Cycling and Mechanical Loading Stress Testing: Preprint

We analyze the degradation of multi-crystalline silicon photovoltaic modules undergoing simultaneous thermal, mechanical, and humidity stress testing to develop a dark environmental chamber in-situ measurement procedure for determining module power loss. From the analysis we determine three main categories of failure modes associated with the module degradation consisting of: shunting, recombination losses, increased series resistance losses, and current mismatch losses associated with a decrease in photo-current generation by removal of some cell areas due to cell fractures. Based on the analysis, we propose an in-situ module power loss monitoring procedure that relies on dark current-voltage measurements taken during the stress test, and initial and final module flash testing, to determine the power degradation characteristic of the module.

14 SOLAR ENERGY↗
DOE OSTI2025

In‐Scribe Silane Bonding for Mechanical Reinforcement of Perovskite Photovoltaic Modules

Despite the extraordinary rise in power conversion efficiency over the last decade, metal halide perovskite (MHP) photovoltaics remain more mechanically fragile than other PV technologies. In this work, the scribe area, created by the monolithic interconnection of thin-film solar cells, is used to extrinsically reinforce the mechanical robustness of packaged MHP solar modules. In contrast to the epoxy-based chemistries often leveraged in the MHP literature, silane-grafted polyolefin encapsulants are designed to form strong covalent bonds to oxide surfaces, specifically to glass and the transparent conductive oxide at the base of the scribe line. Pseudo-modules encapsulated with silane-grafted polyolefin are measured with more than an order-of-magnitude enhancement infracture energy from 0.27 ± 0.01 J·m −2 (no scribes) to 5.97 ± 0.42 J·m −2 (scribes perpendicular to delamination directioncovering ≈2.2% of the module area). The silane-grafted polyolefin retains strong adhesion even after undergoing an accelerated IEC 61215 thermal cycling test consisting of 250 cycles. We find that the in-scribe bonding allows perovskite modules to have adhesion strength comparable to commercial c-Si and CdTe technologies with only 5% reduction in the active module area. This manufacturing-compatible approach offers a practical solution to address the mechanical integrity challenges in MHP solar modules, regardless of cell architecture.

14 SOLAR ENERGY↗
DOE OSTI2018

Evaluating and predicting molecular mechanisms of adhesive degradation during field and accelerated aging of photovoltaic modules

Extending photovoltaic (PV) module lifetimes beyond 30 years is a goal of significant priority. A challenge that must first be addressed, however, is the development of a predictive reliability model that captures the synergy of terrestrial stressors on module degradation, particularly at encapsulant interfaces. Using a metrology designed specifically for PV modules, a comprehensive study of the widely used ethylene vinyl acetate encapsulant was performed in which encapsulant adhesion was evaluated as a function of environmental stressors (UV exposure, temperature, and humidity) for modules aged both under accelerated lab and internationally located field conditions for months to nearly 3 decades. Mechanical and chemical characterization methods are combined with fundamental polymer reaction engineering to unravel the degradation processes active at the molecular scale that lead to encapsulant delamination. An analytical and modular model framework is put forward enabling the prediction of long-term PV module durability, starting from fundamental principles at the molecular level and explicitly accounting for bond rupture events in the bulk encapsulant and at the encapsulant interfaces. Successful parameter tuning to adhesion data indicates a dominant occurrence of deacetylation, β-scission, and hydrolytic depolymerization, respectively. The model contributes to the longstanding challenge of predicting module lifetimes in any geographic location while minimizing time-consuming and costly aging studies.

14 SOLAR ENERGY↗
DOE OSTI2021

Electrochemical Degradation Modes in Bifacial Silicon Photovoltaic Modules

Motivated by the rapidly rising deployment of bifacial monocrystalline-silicon photovoltaics (PV), we investigate the durability of various PV module packaging configurations with transparent coverings on both the front and rear sides of the module. We use a series of bifacial passivated emitter and rear cell (p-PERC) mini-modules with systematically varying outer cover materials (glass/glass, G/G, or glass/transparent backsheet, G/TB) and encapsulant chemistries (poly [ethylene-co-vinyl acetate], EVA; or polyolefin, POE). We study degradation modes over 1,000 hours of combined damp heat (DH) exposure and high system voltages that can cause potential-induced degradation (PID) under positive, zero, or negative 1,000 V cell-to-frame bias. We analyze the degradation modes using a combination of current-voltage measurements, impedance spectroscopy, external quantum efficiency, and spatially resolved luminescence and thermal imaging. Our results highlight various types of degradation including shunting, enhanced recombination, and series resistance increases, and we use spatially resolved characterization to separately identify the localized effects. We show that multiple PID and moisture-ingress degradation modes severely affect EVA-containing modules, with previously reported PID processes under negative-bias DH and a unique observation of rear-side surface recombination in G/EVA/G modules under positive-bias DH. We observe significantly less degradation in POE-containing modules, where the G/POE/G configuration exhibits minimal degradation under all stress conditions that we employ.

14 SOLAR ENERGY↗
DOE OSTI2024

Field‐representative evaluation of PID‐polarization in TOPCon PV modules by accelerated stress testing

Abstract Potential‐induced degradation‐polarization (PID‐p) can reduce module power, but how to project the extent to which PID‐p may occur in field conditions considering the factors of system voltage, condensed moisture, temperature, and illumination has not been clarified. Using tunnel oxide passivated contact (TOPCon) modules, this work demonstrates a method to test full‐size crystalline silicon PV modules for PID‐p to provide field‐representative results. In initial screening tests with positive or negative 1000 V electrical bias applied at 60°C for 96 h using Al foil electrodes on the glass surfaces, the module type exhibited reversible PID‐p only on the front face when the cell circuit was in negative voltage potential. No PID was detected on the rear after testing in either polarity. We then evaluated the PID‐p sensitivity on the front side under different UV irradiances while maintaining the glass surface wet to estimate real‐world susceptibility to PID‐p. The magnitude of the observed behavior was fit using a previously developed charge transfer and depletion by light model. Whereas power loss with −1000 V applied to the cell circuit at 60°C for 96 h in the dark was about 30%, testing the module front under 0.051 W·m −2 nm −1 at 340 nm UVA irradiation using fluorescent tubes, the mean degradation was only 3%. When the modules were tested in the dark for PID‐p with in situ dark current–voltage (I‐V) characterization, the thermal activation energy for degradation was 0.71 eV; for recovery in the dark, it was 0.58 eV. Whereas recovery from the degraded state at 60°C in the dark without voltage bias was 5% absolute in 38 h, rapid recovery of about 5% absolute was observed with 1000 W·s/m 2 exposure at 25°C using a flash tester.

14 SOLAR ENERGY↗
DOE OSTI2019

Power distribution and BER in indoor VLC with PPM based modulation schemes: a comparative study

Visible light communication (VLC) uses an intensity-modulation and direct-detection scheme to transmit data. The light source utilized in VLC structures is constantly switched on and off rapidly, resulting in flickering. Furthermore, most of illumination systems exclude dimming support to permit customers to dim the light source to the desired stage. Therefore, the modulation scheme for information transmission in VLC should consist of flicker mitigation and dimming manage abilities. Double inverse pulse position modulation (DIPPM), sub-carrier pulse position modulation (SC-L-PPM), and M-ary variable pulse position modulation (M-VPPM) are recommended for minimizing the flicker issues and supporting an excessive degree of dimming for VLC systems. In this paper, a comparison is introduced between DIPPM, SC-L-PPM, and M-VPPM according to error performance and bit rate. In addition, a simulation is carried out to measure the optical power distribution for a LED lamp in an indoor room topology for each modulation technique. The obtained results indicated that SC-L-PPM is the best choice regarding the bit error rate (BER) and optical power distribution compared to the other two schemes. A 10{sup −6} BER is achieved with a very low power requirement at L = 8, while a remarkable power distribution of 1.5–6.5 dBm is observed from 3 × 5 × 5 m{sup 3} room corners to the center, respectively. According to the bit rate, it is noticed that, M-VPPM is the most efficient one compared to the two other schemes. It achieves 2.3 × 10{sup 7} bps at a signal to noise ratio (SNR) of 22 dB and M = 8.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗