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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Day-Ahead Probabilistic Forecasting of Net-Load and Demand Response Potentials with High Penetration of Behind-the-Meter Solar-plus-Storage

The goal of this project is to develop advanced methods for day-ahead net-load forecasting, by leveraging the state-of-the-art machine learning techniques. The developed models produce both point and probabilistic forecasts for a variety of use cases, and are versatile to work with different types of data sets. The innovation lies in the novel design of the architectures, leveraging the most recent advances in machine learning that have not been explored in power systems, accompanied by techniques in the broader artificial intelligence fields such as fuzzy systems. This project has achieved the following accomplishments: (1) preprocessing of over 10 data sets covering varying geographical regions, time horizons, and system levels, which form a robust foundation for training and evaluating forecasting models across a wide range of realistic grid scenarios; (2) development of an interactive web app that enables exploratory analysis of load and generation data, and supports better understanding of data trends, anomalies, and correlations, facilitating model development and stakeholder engagement; (3) implementation of over 10 benchmark models for point and probabilistic forecasting, which include a mix of conventional machine learning methods and state-of-the-art deep learning approaches, providing a comprehensive baseline for performance comparison and validation of the proposed models; (4) development of a fuzzy system based gradient boosting model, tailored for small (less than 3 years) data sets, which achieves a mean absolute percentage error (MAPE) of 4% for point forecasting and a 20% improvement in average pinball loss for probabilistic forecasting; (5) development of a Transformer (a state-of-the-art deep learning architecture) based neural network model, tailored for large (3 years or more) data sets, which achieves a MAPE of 2% for point forecasting and a 20% improvement in average pinball loss for probabilistic forecasting; (6) development of a methodology for quantifying DR potential, and extensions of the previous models for multi-target forecasting of net load and DR potential, which achieve a MAPE of 10% for DR potential.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2018

Experimental demonstration of voltage-matched two-terminal tandem minimodules

Mechanically stacked tandem solar cells are a potential near-term solution for increasing the efficiency of photovoltaic modules. Practical implementation requires an interconnection approach that maximizes efficiency and minimizes complexity and cost. Connecting the top and bottom cells in a voltage-matched configuration allows two-terminal modules to be fabricated without altering the cell design or processing methods. Here, we experimentally demonstrate two-terminal voltage-matched GaInP 2 / Si minimodules. The two-terminal minimodules performed just as well as four terminal configurations when voltage-matching requirements were met. The magnitude of the efficiency loss experienced by the voltage-matched minimodule when voltage-matched conditions were not met depends on whether the voltage was constrained by the GaInP 2 or Si cells. Monte Carlo simulations also indicate that the two-terminal voltage-matched tandems respond to small cell-to-cell parameter variations in a similar manner as four terminal tandems.

14 SOLAR ENERGY↗
DOE OSTI2024

In-situ and wavelength-dependent photocatalytic strain evolution of a single Au nanoparticle on a TiO 2 film

Photocatalysis is a promising technique due to its capacity to efficiently harvest solar energy and its potential to address the global energy crisis. However, the structure–activity relationships of photocatalyst during wavelength-dependent photocatalytic reactions remains largely unexplored because it is difficult to measure under operating conditions. Here we show the photocatalytic strain evolution of a single Au nanoparticle (AuNP) supported on a TiO 2 film by combining three-dimensional (3D) Bragg coherent X-ray diffraction imaging with an external light source. The wavelength-dependent generation of reactive oxygen species (ROS) has significant effects on the structural deformation of the AuNP, leading to its strain evolution. Density functional theory (DFT) calculations are employed to rationalize the induced strain caused by the adsorption of ROS on the AuNP surface. These observations provide insights of how the photocatalytic activity impacts on the structural deformation of AuNP, contributing to the general understanding of the atomic-level catalytic adsorption process.

14 SOLAR ENERGY↗
DOE OSTI2014

THE EFFECTS OF INITIAL ABUNDANCES ON NITROGEN IN PROTOPLANETARY DISKS

The dominant form of nitrogen provided to most solar system bodies is currently unknown, though available measurements show that the detected nitrogen in solar system rocks and ices is depleted with respect to solar abundances and the interstellar medium. We use a detailed chemical/physical model of the chemical evolution of a protoplanetary disk to explore the evolution and abundance of nitrogen-bearing molecules. Based on this model, we analyze how initial chemical abundances provided as either gas or ice during the early stages of disk formation influence which species become the dominant nitrogen bearers at later stages. We find that a disk with the majority of its initial nitrogen in either atomic or molecular nitrogen is later dominated by atomic and molecular nitrogen as well as NH{sub 3} and HCN ices, where the dominant species varies with disk radius. When nitrogen is initially in gaseous ammonia, it later becomes trapped in ammonia ice except in the outer disk where atomic nitrogen dominates. For a disk with the initial nitrogen in the form of ammonia ice, the nitrogen remains trapped in the ice as NH{sub 3} at later stages. The model in which most of the initial nitrogen is placed in atomic N best matches the ammonia abundances observed in comets. Furthermore, the initial state of nitrogen influences the abundance of N{sub 2}H{sup +}, which has been detected in protoplanetary disks. Strong N{sub 2}H{sup +} emission is found to be indicative of an N{sub 2} abundance greater than n{sub N{sub 2}}/n{sub H{sub 2}}>10{sup −6} in addition to tracing the CO snow line. Our models also indicate that NO is potentially detectable, with lower N gas abundances leading to higher NO abundances.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Guidelines for Phase Change Material Selection Based on a Holistic System Model

Concentrating solar power (CSP) has potential to increase the amount of renewable energy on electric grids and reduce global carbon emissions, in particular because of its capability to incorporate inexpensive thermal energy storage. To realize this potential, development of latent heat storage with phase change materials (PCMs) is attractive because of its high energy density and low material cost. Research in this area has identified many promising materials, and has developed effective storage system designs that could be used to deploy PCMs. However, the field has lacked a rigorous methodology to select the optimal material for a particular CSP system. To address this need, here we present a holistic model that evaluates all important influences of PCM properties on the performance and cost of an entire CSP plant. We apply this model to over 100 of the most widely considered candidate materials, including both salts and metals. We quantify the relative value of each PCM property, and identify leading materials for application in CSP systems. This method and our results may aid future efforts to develop latent heat storage by providing a more informed view of how material selection impacts an entire CSP system.

14 SOLAR ENERGY↗
DOE OSTI2016

Transmissive concentrator multijunction solar cells with over 47% in-band power conversion efficiency

Transmissive concentrator multijunction (TCMJ) solar cells with over 47% in-band power conversion efficiency (PCE) have been designed and realized. These TCMJ solar cells have been characterized under 1 sun and concentrated 500 sun solar spectra, showing that the PCE for in-band light (photon energies above the cell’s lowest bandgap) can reach up to 47.6% (29.5% for the full solar spectrum). Temperature coefficients of electrical parameters (V oc , J sc , FF) have been derived from measurements within the temperature range of 20°C to 130°C, showing linear variations versus temperature change. Here, optical measurements demonstrate that the cells show 76.5% solar-weighted optical transmission for the out-of-band light (photon energy below the cell’s lowest bandgap). This TCMJ solar cell exhibits promising spectrum splitting capability, which has potential for use in hybrid photovoltaic-solar thermal applications.

14 SOLAR ENERGY↗
NASA NTRS1976

Interconnnect and bonding technologies for large flexible solar arrays

Thermocompression bonding and conductive adhesive bonding are developed and evaluated as alternate methods of joining solar cells to their interconnect assemblies. Bonding materials and process controls applicable to fabrication of large, flexible substrate solar cell arrays are studied. The primary potential use of the techniques developed is on the solar array developed by NASA/MSFC and LMSC for solar electric propulsion (SEP) and shuttle payload applications. This array is made up of flexible panels approximately 0.7 by 3.4 meters. It is required to operate in space between 0.3 and 6 AU for 5 years with limited degradation. Materials selected must be capable of enduring this space environment, including outgassing and radiation.

Source record↗
NASA NTRS1997

Advanced Ion Propulsion Technology for Solar System Exploration

The use of ion propulsion for deep-space missions is becoming a reality with the flight next year of the ion propelled Ner Millenium Deep Space 1 Spacecraft. This event is already stimulating the call for improved ion propulsion technologies, a trend which is expected to continue. This paper describes the examination of advanced solar electric propulsion technologies to determine their potential benefits for projeted near and mid-term solar system exploration missions.

Ion↗
DOE OSTI2014

Final Report-- A Novel Storage Method for Concentrating Solar Power Plants Allowing Storage at High Temperature

The main objective of the proposed work was the development and testing of a storage method that has the potential to fundamentally change the solar thermal industry. The development of a mathematical model that describes the phenomena involved in the heat storage and recovery was also a main objective of this work. Therefore, the goal was to prepare a design package allowing reliable scale-up and optimization of design.

14 SOLAR ENERGY↗
DOE OSTI2024

Impact of Temperature and Optical Error on the Combined Optical and Thermal Efficiency of Solar Tower Systems for Industrial Process Heat: Preprint

Concentrating solar thermal (CST) power towers can provide high flux concentrations at commercial scale. As a result, CST towers exhibit potential for high-temperature solar industrial process heat (SIPH) applications. However, at higher operating temperatures, thermal radiation losses can be significant. This study explores the trade-off between thermal and optical losses for SIPH applications using a collection of three case studies at operating temperatures that range from 900-1,550 degrees C. We assume blackbody radiation to represent the thermal losses at the receiver and we use ray tracing to estimate the optical losses. The results show the impact of process temperature on the maximum attainable system efficiency, as well as the higher flux concentration requirements as the temperature increases.

concentrating solar power↗
NASA NTRS1979

Epitaxial silicon growth for solar cells

The epitaxial procedures, solar cell fabrication, and evaluation techniques are described. The development of baseline epitaxial solar cell structures grown on high quality conventional silicon substrates is discussed. Diagnostic layers and solar cells grown on four potentially low cost silicon substrates are considered. The crystallographic properties of such layers and the performance of epitaxially grown solar cells fabricated on these materials are described. An advanced epitaxial reactor, the rotary disc, is described along with the results of growing solar cell structures of the baseline type on low cost substrates. The add on cost for the epitaxial process is assessed and the economic advantages of the epitaxial process as they relate to silicon substrate selection are examined.

Daiello, R. V.↗
DOE OSTI2017

Observational Signatures of Transverse Magnetohydrodynamic Waves and Associated Dynamic Instabilities in Coronal Flux Tubes

Magnetohydrodynamic (MHD) waves permeate the solar atmosphere and constitute potential coronal heating agents. Yet, the waves detected so far may be but a small subset of the true existing wave power. Detection is limited by instrumental constraints but also by wave processes that localize the wave power in undetectable spatial scales. In this study, we conduct 3D MHD simulations and forward modeling of standing transverse MHD waves in coronal loops with uniform and non-uniform temperature variation in the perpendicular cross-section. The observed signatures are largely dominated by the combination of the Kelvin–Helmholtz instability (KHI), resonant absorption, and phase mixing. In the presence of a cross-loop temperature gradient, we find that emission lines sensitive to the loop core catch different signatures compared to those that are more sensitive to the loop boundary and the surrounding corona, leading to an out-of-phase intensity and Doppler velocity modulation produced by KHI mixing. In all of the considered models, common signatures include an intensity and loop width modulation at half the kink period, a fine strand-like structure, a characteristic arrow-shaped structure in the Doppler maps, and overall line broadening in time but particularly at the loop edges. For our model, most of these features can be captured with a spatial resolution of 0.″33 and a spectral resolution of 25 km s{sup −1}, although we do obtain severe over-estimation of the line width. Resonant absorption leads to a significant decrease of the observed kinetic energy from Doppler motions over time, which is not recovered by a corresponding increase in the line width from phase mixing and KHI motions. We estimate this hidden wave energy to be a factor of 5–10 of the observed value.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Potential to Improve the Value of U.S. Geothermal Electricity Generation Through Flexible Operations

Geothermal power plants have typically been operated as baseload plants. The recent expansion of wind and solar power generation creates a potential opportunity to increase the value of geothermal generation through flexible operations. In recent years, California’s wholesale electricity markets have exhibited frequent, short-term periods of negative pricing, indicating that additional flexibility would be valued in the market. Here, we examine local nodal hourly price records at all geothermal plants located in the western United States. We describe how the frequency and temporal characteristics of negative pricing episodes have changed over recent years. Based on these price series, we calculate the value of multiple strategies of flexible operations. Additionally, we use the estimates of future prices, developed through a capacity-expansion model and a dispatch model, to explore how the value of such flexible operations might change along with further penetration of variable renewable power sources. Based on the historical pricing records, we find that simple curtailment of operations during negative pricing episodes could increase the average energy value by 1–2 dollars per MWh and that allowing for increased production during limited high-priced hours, in addition to curtailment during negative priced hours, could potentially double the increase in value (up to 4 dollars per MWh). The forward-looking simulations indicate reduced values of flexibility from geothermal power despite higher penetrations of variable renewable energy. This result highlights the possibility that increasing flexibility options throughout the system may counteract the influence of increased variable renewable energy deployment.

15 GEOTHERMAL ENERGY↗
DOE OSTI2014

ON THE FREQUENCY OF POTENTIAL VENUS ANALOGS FROM KEPLER DATA

The field of exoplanetary science has seen a dramatic improvement in sensitivity to terrestrial planets over recent years. Such discoveries have been a key feature of results from the Kepler mission which utilizes the transit method to determine the size of the planet. These discoveries have resulted in a corresponding interest in the topic of the Habitable Zone and the search for potential Earth analogs. Within the solar system, there is a clear dichotomy between Venus and Earth in terms of atmospheric evolution, likely the result of the large difference (approximately a factor of two) in incident flux from the Sun. Since Venus is 95% of the Earth's radius in size, it is impossible to distinguish between these two planets based only on size. In this Letter we discuss planetary insolation in the context of atmospheric erosion and runaway greenhouse limits for planets similar to Venus. We define a ''Venus Zone'' in which the planet is more likely to be a Venus analog rather than an Earth analog. We identify 43 potential Venus analogs with an occurrence rate (η{sub ♀}) of 0.32{sub −0.07}{sup +0.05} and 0.45{sub −0.09}{sup +0.06} for M dwarfs and GK dwarfs, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRSDate not supplied

The Effect of Temperature on the Preservation of Volatile-Rich Lunar Samples

Introduction. The Moon’s south pole is a high-priority target for human exploration and scientific study. This interest is, in part, due to the presence of Permanently Shadowed Regions (PSRs), which could contain high concentrations of unique volatiles at cryogenic temperatures [1]. Returned samples from PSRs may include a unique combination of rocks, regolith, and volatile species, providing unprecedented insights into the history of the Solar System and the potential for resource utilization on the Moon. However, because PSR samples are cryogenic up-on collection, lunar polar sample return will eventually require cold stowage for the journey from the Moon to Earth. Without cold stowage, PSR sample return will likely result in phase changes and chemical reactions within the volatile component of the sample, which would negatively impact the resulting scientific studies of those samples. This abstract summarizes the initial results from an ongoing characterization of analog PSR samples at a range of temperatures, with the goal of defining the temperatures needed for a flight cold stowage freezer. Background. Based on remote sensing observations of the Moon [2], south polar PSRs range in temperature from ~120K for small and/or shallow PSRs to ~20K at the most extreme locations in large, deep PSRs. A range of volatiles have been hypothesized to exist at the surface or subsurface of the lunar poles [3-5 and others]. This hypothesis was verified when the LCROSS mission impacted the <50-K PSR in the crater Cabeus, detecting a range of volatiles from water to low condensation temperature species such as H2S and methane [6]. Species such as H2S and ammonia (also detected by LCROSS) are also highly reactive, and increase the likelihood of chemical reactions at elevated (non-cryogenic) temperatures. At the Johnson Space Center’s Planetary Exploration and Astromaterials Research Laboratory (JSC-PEARL), we have developed a volatile-bearing lunar simulant that incorporates several of the species detected by LCROSS [Table 1] mixed cryogenically with the USGS Lunar Highlands Type (LHT) regolith simulant. The new volatile-regolith simulant will be used to assess the degree of sample alteration at room temperature, -20°C, -80°C, and -196°C (liquid nitro-gen), over a two-week period. Room temperature samples represent those likely to be returned during initial missions without cold stowage, -20°C provides an analog to Apollo cold curated samples, -80°C is the temperature of multiple flight payload freezers (e.g., MELFI), and -196°C is analogous to lunar PSRs. Two weeks is an approximation of the time between sample collection and Earth return for initial Artemis missions. Over this period of time, sample head-space gases will be analyzed using a Universal Gas Analyzer (UGA, a type of mass spectrometer) coupled with a Baratron pressure sensor. After testing, the regolith component of the simulant will be purged of volatiles and preserved for future electron beam and/or FTIR analysis. Experimental Procedure. Volatile-regolith simulants will be produced as an initial homogenous batch; this batch will then be distributed into aliquots (gas chromatography/GC vials or cryo vials), ensuring that each sample has the same starting composition and conditions [Fig. 1]. In addition to the “full” simulant shown in Table 1, less complex simulant compositions will be used as baseline and control samples [Table 2]. Aliquots will be produced in triplicate for each simulant composition, storage temperature, and date of sampling. Headspace gases in all Day 0 samples will be analyzed by the UGA immediately. Cold storage samples for future analytical days will be placed in freezers appropriate to their target temperatures (-20°C, -80°C, -196°C). For ambient-temperature samples, regolith and regolith-water samples will be stored in a fume hood, while the full simulant will be stored in a sealed Parr vessel for safety; no other simulants (RWCM/ RWCM+) will be stored at ambient temperature for this test. Samples will be analyzed by UGA in this manner on each Analysis Day outlined in Table 2. Analytical Data. The UGA measures the partial pressures in a single sample aliquot over a set mass range of 0-105 atomic mass units (AMU) [Figure 2]; this set range was selected to slightly exceed the mass of the highest-mass expected reaction product (H2SO4). The Baratron complements the UGA by measuring the total pressure in the headspace of a sample vial. Coupled together, the quantitative abundances of gases will be monitored throughout the test. UGA analyses of the triplicate samples for each storage temperature, day, and simulant composition will be averaged, and standard deviations for each will be calculated. The compositions of starting species (shown in Table 1) will be characterized as a function of time, and the presence of any new compounds (reaction products) will be monitored as well. Total pressures will be recorded for each sample analysis, and any samples that show signs of leakage (e.g., a significant reduction in pressure or simulant volatiles) will be discarded. Anticipated Results. Testing is planned to begin in January 2022. The resulting data will allow compositional and phase changes in the volatile component of the simulants to be determined. Both the reduction in initial compounds and the addition of reaction products are expected to be observed. In addition, the relative efficacy of the different temperatures at pre-serving the initial composition of the simulants will be quantified. Finally, the regolith component of each sample will be argon-purged and stored in a controlled environment for future laboratory analysis. Compositional and morphological changes in the regolith are expected for samples above 0°C. This test will be repeated three times over the course of 2022. Understanding the effect of temperature on both the volatile and regolith components of analog lunar materials will allow requirements for a cold stowage freezer to be developed. The implementation of cold stowage for lunar polar missions will maximize the preservation of returned samples, enabling ground-breaking lunar and Solar System volatiles science for decades to come.

J L Mitchell↗
DOE OSTI2019

Defect‐Tailoring Mediated Electron–Hole Separation in Single‐Unit‐Cell Bi 3 O 4 Br Nanosheets for Boosting Photocatalytic Hydrogen Evolution and Nitrogen Fixation

Abstract Solar photocatalysis is a potential solution to satisfying energy demand and its resulting environmental impact. However, the low electron–hole separation efficiency in semiconductors has slowed the development of this technology. The effect of defects on electron–hole separation is not always clear. A model atomically thin structure of single‐unit‐cell Bi 3 O 4 Br nanosheets with surface defects is proposed to boost photocatalytic efficiency by simultaneously promoting bulk‐ and surface‐charge separation. Defect‐rich single‐unit‐cell Bi 3 O 4 Br displays 4.9 and 30.9 times enhanced photocatalytic hydrogen evolution and nitrogen fixation activity, respectively, than bulk Bi 3 O 4 Br. After the preparation of single‐unit‐cell structure, the bismuth defects are controlled to tune the oxygen defects. Benefiting from the unique single‐unit‐cell architecture and defects, the local atomic arrangement and electronic structure are tuned so as to greatly increase the charge separation efficiency and subsequently boost photocatalytic activity. This strategy provides an accessible pathway for next‐generation photocatalysts.

Di, Jun↗
DOE OSTI2022

Review of Potential–Induced Degradation in Bifacial Photovoltaic Modules

Bifacial modules are increasingly deployed in the field and are expected to represent half of the market share within 10 years. Their rear structure differs from monofacial modules to allow additional light absorption. However, it brings new reliability challenges to address. In particular, the risk of potential-induced degradation (PID) is increased as both module sides are impacted. Different PID processes have been identified in the literature: shunting type (PID-s), polarization type (PID-p), Na penetration type, and corrosion type (PID-c). Their occurrence depends on the photovoltaic system configuration as well as the module's materials. Apart from PID-s, PID processes are not well understood and extensive research is needed to elucidate the PID scenario and underlying mechanisms. Herein, current knowledge about PID processes and their impact on the main bifacial modules in the market are gathered with the aim to guide future research. Bifacial module technologies and leakage current paths leading to PID are described. Indoor and outdoor PID testing methods are detailed. For each bifacial module technology, the PID processes are investigated with their indicators, mechanism and recovery process. Furthermore, PID-impacting factors and limitation solutions are finally reported and a state of the art on PID modeling is presented.

14 SOLAR ENERGY↗
DOE OSTI2019

Physical properties of RF magnetron sputtered GaN/n-Si thin film: impacts of RF power

GaN thin film was successfully produced on n-Si(100) substrate by RF magnetron sputter under different RF power. Experimental measurement techniques such as UV/Vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and Micro-Raman Spectroscopy were used to research effects of Radio Frequency power on physical properties of produced thin film. It has been found that produced thin film was polycrystalline structure with (100) and (110) planes of hexagonal GaN from X-ray diffraction measurement result. It also proved that increasing RF power gives rise to deterioration in crystal quality of GaN thin film. Reason of this deterioration was discussed. It has been achieved that increasing RF power has resulted in decreasing optical band gap energy of GaN thin film. Reasons for these changes in optical band gap energy were explained. It was seen that some thin films were grown as layer-plus-island mode (Stranski–Krastanov growth mode) and others were grown as layer-by-layer growth mode (Frank van der Merwe mode) from AFM analysis. It has been found that increasing RF power has resulted in improvement of surface morphology of thin film from field emission scanning electron microscopy analysis. However, reaching RF power to 125 W leads to start to deteriorate of surface of GaN thin film. The reasons for this have been discussed. E{sub 1}(TO) transverse optical phonon mode of hexagonal GaN with different intensity was detected from Micro-Raman Spectroscopy measurement. The reasons for this difference have been discussed. It was concluded that RF power has played a significant role in growing high quality GaN thin film. Morphological, structural, and optical properties of GaN thin film were enhanced by controlling RF power, making them a potential candidate for LED, solar cell, diode application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗