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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Nexus of thermal resilience and energy efficiency in buildings: A case study of a nursing home

Extreme weather events become more frequent and severe due to climate change. Although energy efficiency technologies can influence thermal resilience of buildings, they are traditionally studied separately, and their interconnections are rarely quantified. This study developed a methodology of modeling and analysis to provide insights into the nexus of thermal resilience and energy efficiency of buildings. In this work, we conducted a case study of a real nursing home in Florida, where 12 patients died during Hurricane Irma in 2017 due to HVAC system power loss, to understand and quantify how passive and active energy efficiency measures (EEMs) can improve thermal resilience to reduce heat-exposure risk of patients. Results show that passive measures of opening windows and doors for natural ventilation, as well as miscellaneous load reduction, are very effective in eliminating the extreme dangerous occasions. However, to maintain safe conditions, active measures such as on-site power generators and thermal storage are also needed. The nursing home was further studied by changing its location to two other cities: San Francisco (mild climate) and Chicago (cold winter and hot summer). Results revealed that the EEMs' impacts on thermal resilience vary significantly by climate and building characteristics. The study also estimated the costs of EEMs to help stakeholders prioritize the measures. Passive measures that may not save energy may greatly improve thermal resilience, and thus should be considered in building design or retrofit. Findings from this study indicate energy efficiency technologies should be evaluated not only by their energy savings performance but also by their influence on a building's resilience to extreme weather events.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Porous condensers can double the efficiency of membrane distillation

Among membrane distillation (MD) configurations, air gap MD (AGMD) has superior energy efficiency at high salinity. However, flooding of the gap prevents optimal thin gap depths as water removal is a challenge. To address these challenges, this work provides the first analysis of efficiency enhancement via porous wicking conductive condensers in MD. To do so, we examined performance with experiments and comprehensive thermo-fluid numerical models; we find that the porous wick condenser significantly improves thermal efficiency, gain output ratio (GOR), and flux. MD experiments show that the porous copper foam improves the thermal efficiency of air gap membrane distillation up to 40 % and water flux up to 144 %. Numerical modeling shows the porous copper foam improves the GOR of membrane distillation in high salinity by 98.7 %, outperforming air gap MD, permeate gap MD, and conductive gap MD. Furthermore, the optimized thickness and permeability of porous condensers significantly help eliminate the risk of flooding in AGMD.

42 ENGINEERING↗
DOE OSTI2020

Boosting energy efficiency of Li-rich layered oxide cathodes by tuning oxygen redox kinetics and reversibility

In developing electrode materials for next-generation Li-ion batteries, significant efforts have been given to the energy, power density and cycling stability, with much less (if any) attention paid to the energy efficiency – arguably, the most important practical measure for large-scale applications. This is particularly true for the oxygen-redox active electrodes, such as Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , the notorious energy-inefficient cathode that has an extremely high capacity but comes with large voltage hysteresis and voltage decay. Herein, we report the rational design of an energy-efficient Li-rich layered cathode along with high energy, power density and cycling stability enabled by tuning oxygen redox activity. Specifically, the target material Li 1.12 Ni 0.22 Co 0.13 Mn 0.52 O 2 exhibits an ultrahigh energy efficiency at 1 C (90.6%), high capacity (> 200 mAh g -1 ) with 98.9% retention and less than 150 mV decay at the extended 200 cycles. Overall, through direct comparison between the material and Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , we show that the compositional change, although slightly, greatly improves the oxygen redox kinetics and reversibility, thereby boosts energy efficiency. The findings offer a strategy to narrow the gap between scientific interest and practical application of oxygen-redox chemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of molar expansion ratio of fuels on engine efficiency

Fuel properties have a strong impact on the efficiency of internal combustion engines. Contrary to other physical and thermochemical fuel properties, the molar expansion ratio is normally ignored. Molar expansion ratio is the ratio of number of moles of the products to the reactants. In this work, the impact of the fuel’s molar expansion ratio on engine efficiency is investigated. Findings are based on simulations of a spark ignition engine using different fuels (standard fuels and user-defined fuels) and different dilution ratios. Simulations without heat transfer and friction were performed first. The combustion then takes place at top dead center with a very short combustion duration to approach the ideal Otto cycle. The heat transfer and friction were then added step by step. From this analysis, it could be concluded that the heat loss and friction work decrease as molar expansion ratio increases. The gross indicated and brake thermal efficiencies thus increase. User-defined fuels with different molar expansion ratio, but the same physical and thermochemical properties were then employed. The simulated results showed that the brake thermal efficiency increases by around 1.15% with an increase in molar expansion ratio of 0.02 compared to a fuel with a molar expansion ratio of unity. Lastly, the simulation was also done with air and exhaust gas recirculation dilution.

42 ENGINEERING↗
DOE OSTI2020

Adapting Optimal Velocity Tracking Control to Account for WEC Constraints and Power-Take-Off Efficiencies: Preprint

Wave energy converters (WECs) come in many different forms, from point absorbers, oscillating water columns, to bulge wave devices. This paper focuses on the control of point absorber WECs, which typically have a narrow-banded frequency response and, therefore, control is well placed to improve the energy capture of such WECs. The acausal nature of the control problem means that theoretically optimal control is almost impossible to achieve inpractice; however optimal velocity tracking (OVT) offers a simple and robust approximation to optimal control that can achieve better power capture than passive linear damping methods, albeit with necessarily higher force demands. OVT is a form of impedance matching and the magnitude of the power-take off (PTO) force demand is often not linearly proportional to the WEC velocity, which can lead to PTO force and speed combinations far from the optimalPTO efficiency. The highly non-linear PTO force and speed to efficiency mapping can, without remedial measures, severely diminish the effectiveness of OVT techniques. In this paper, limits to the movement and force of the PTO are demonstrated, allowing OVT to be more easily applied in practice. The effect of PTO efficiency is explored, and a potential solution to the problem of adapting control to account for efficiency is presented. Both aspects of the work presented highlight the requirement for co-design of the WEC, PTO, and controller.

conversion efficiency↗
DOE OSTI2020

Ultrahigh coulombic efficiency electrolyte enables Li||SPAN batteries with superior cycling performance

Raising the coulombic efficiency of lithium metal anode cycling is the deciding step in realizing long-life rechargeable lithium batteries. Here, we designed a highly concentrated salt/ether electrolyte diluted in a fluorinated ether: 1.8 M LiFSI in DEE/BTFE (diethyl ether/bis(2,2,2-trifluoroethyl)ether), which realized an average coulombic efficiency of 99.37% at 0.5 mA cm -2 and 1 mAh cm -2 for more than 900 cycles. This electrolyte also maintained a record coulombic efficiency of 98.7% at 10 mA cm -2 , indicative of its ability to provide fast-charging with high cathode loadings. Morphological studies reveal dense, dendrite free Li depositions after prolonged cycling, while surface analyses confirmed the formation of a robust LiF-rich SEI layer on the cycled Li surface. Moreover, we discovered that this ether-based electrolyte is highly compatible with the low-cost, high-capacity SPAN (Sulfurized polyacrylonitrile) cathode, where the constructed Li||SPAN cell exhibited reversible cathode capacity of 579 mAh g -1 and no capacity decay after 1200 cycles. A cell where a high areal loading SPAN electrode (>3.5 mAh cm -2 ) is paired with only onefold excess Li was constructed and cycled at 1.75 mA cm -2 , maintaining a coulombic efficiency of 99.30% for the lithium metal. Computational simulations revealed that at saturation, the Li-FSI complex forms contact ion pairs, with a first solvation shell comprising DEE molecules, and a second solvation shell with a mix of DEE/BTFE. This study provides a path to enable high energy density Li||SPAN batteries with stable cycling.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Neutron detection efficiency of the Neutron dEtector with Xn Tracking (NEXT)

An efficient neutron detection system with good energy resolution is required to correctly characterize decays of neutron-rich nuclei where β-delayed neutron emission is a dominant decay mode. The Neutron dEtector with Xn Tracking (NEXT) has been designed to measure β-delayed neutron emitters. By segmenting the detector along the neutron flight path, NEXT reduces the associated uncertainties in neutron time-of-flight measurements, improving energy resolution while maintaining detection efficiency. Detector prototypes are comprised of optically separated segments of a neutron-gamma discriminating plastic scintillator coupled to position-sensitive photomultiplier tubes. In this work we discuss how the first performance studies of this detector showed that high intrinsic neutron detection efficiency could be achieved while retaining good energy resolution. The results from the efficiency measurements using neutrons from direct reactions are presented

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Tin–Lead Alloying for Efficient and Stable All-Inorganic Perovskite Solar Cells

Cesium containing all-inorganic perovskites have received considerable interest in photovoltaics research because of their potential for improved stability compared to their organic-inorganic hybrid counterparts. However, the inorganic perovskites studied thus far still suffer from lower power conversion efficiency and long-term instability, due to an unfavorable bandgap and either phase instability or air-sensitivity. Herein, A strategy to mitigate these concerns is investigated by alloying tin and lead on the B site to form tin-lead alloyed low-bandgap (~1.34 eV) inorganic CsSn 0.3 Pb 0.7 I 3 perovskites. Solar cells made using this material in an inverted full-structured architecture with a PEDOT:PSS hole transport materials (HTM) attain power conversion efficiency (PCE) up to 9.41% (stabilized PCE 7.23%). Furthermore, a simple HTM-free device without PEDOT:PSS layer is demonstrated more stable than the full-structured device and exhibits a PCE of 7.60% (stabilized PCE 7.31%) – the highest efficiency to date for an inorganic perovskite with a bandgap below 1.40 eV. This simplified device structure shows good reproducibility and stability. Finally, this work provides a possible route for fabricating low-cost, high stability devices with competitive efficiencies.

14 SOLAR ENERGY↗
DOE OSTI2022

Organic Photovoltaic Efficiency Predictor: Data-Driven Models for Non-Fullerene Acceptor Organic Solar Cells

In the design of organic solar cells, there has been a need for materials with high power conversion efficiencies. Scharber’s model is commonly used to predict efficiency; however, it exhibits poor performance with new non-fullerene acceptor (NFA) devices, since it was designed for fullerene-based devices. In this work, an empirical model is proposed that can be a more accurate alternative for NFA organic solar cells. Additionally, many screening studies use computationally expensive methods. A model based on using semiempirical simplified time-dependent density functional theory (sTD-DFT) as an alternative method can accelerate the calculations and yield a similar accuracy. The models presented in this paper, termed organic photovoltaic efficiency predictor (OPEP) models, have shown significantly lower errors than previous models, with OPEP/B3LYP yielding errors of 1.53% and OPEP/sTD- DFT of 1.55%. As a result, the proposed computational models can be used for the fast and accurate screening of new high-efficiency NFAs/donor pairs.

14 SOLAR ENERGY↗
DOE OSTI2020

Bilayer Anion-Exchange Membrane with Low Borohydride Crossover and Improved Fuel Efficiency for Direct Borohdyride Fuel Cell

The development of membranes with low fuel crossover and high fuel efficiency is a key issue in direct borohydride fuel cells (DBFCs). In previous work, we produced a poly(vinyl alcohol) (PVA)-anion-exchange resin (AER) membrane with a low fuel crossover and a low fuel efficiency by introducing Co ions. In this work, a bilayer membrane was designed to improve the fuel efficiency and cell performance. The bilayer membrane was prepared by casting a PVA-AER wet gel onto the partially desiccated Co-PVA-AER gel. The bilayer membrane showed a borohydride permeability of 1.34 × 10 –6 cm 2 ·s –1 , which was even lower than that of the Co-PVA-AER membrane (1.98 ×10 –6 cm 2 ·s –1 ) and the PVA-AER membrane (2.80 × 10 –6 cm 2 ·s –1 ). The DBFC using the bilayer membrane exhibited a higher fuel efficiency (37.4%) and output power (1.73 Wh) than the DBFCs using the Co-PVA-AER membrane (33.3%, 1.27 Wh) and the PVA-AER membrane (34.3%, 1.2 Wh). Furthermore, the DBFC using the bilayer membrane achieved a peak power density of 327 mW·cm –2 , which was 2.14 times of that of the DBFC using the PVA-AER membrane (153 mW·cm –2 ). Finally, the drastic improvement benefited from the bilayer design, which introduced an interphase to suppress fuel crossover and avoided unnecessary borohydride hydrolysis.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Carbon Electrode with Sputtered Au Coating for Efficient and Stable Perovskite Solar Cells

Halide perovskite solar cells (PSCs) represent a low-cost and high-efficiency solar technology. However, most of the highly efficient PSCs need a noble electrode, such as Au, through thermal evaporation. Here it is reported that a sputtered Au electrode on a PSC could damage the organic hole transport layer (HTL) and the perovskite layer. Here, we report a simple, yet effective sputtered gold nanoparticle decorated carbon electrode to fabricate efficient and stable planar PSCs. The sputtered Au layer on the doctor-bladed coated carbon electrode can be directly applied to the perovskite semicells by mechanical stacking. By optimizing the gold thickness, a power conversion efficiency (PCE) of 16.87% was obtained for the composite electrode-based PSC, while the reference device recorded a PCE of 12.38%. The composite electrode-based device demonstrated 96% performance retention after being stored under humid conditions (50-60%) without encapsulation for ~100 h. This demonstrates a promising pathway toward the commercialization of large-scale manufacturable sputtered electrodes for the PSC solar module.

14 SOLAR ENERGY↗
DOE OSTI2024

Catalytic Resonance Theory: Turnover Efficiency and the Resonance Frequency

Programmable catalysts exhibiting forced oscillation in the free energy of reacting surface species were simulated to understand the general mechanisms leading to efficient use of the input energy. Catalytic ratchets with either positive or negative adsorbate scaling exhibited oscillation conditions of both high and low turnover efficiency, yielding catalytic turnover frequencies either close to or significantly lower than the applied catalyst oscillation frequency, respectively. The “effective rate”, defined as the product of the catalytic turnover frequency and the turnover efficiency (ηTOE), was limited via two catalytic mechanisms: a leaky catalytic ratchet existed when molecules repeatedly traversed backward through the catalytic transition state upon catalyst oscillation, while a catalytic ratchet with low surface participation exhibited reduced formation of a gas-phase final product due to low surface product coverage. Furthermore, a single applied frequency yielding a maximum effective catalytic rate defined as the “resonance frequency” provided maximum combined benefit for catalytic rate and efficiency.

25 ENERGY STORAGE↗
DOE OSTI2022

Quantum efficiency of InGaN–GaN multi-quantum well solar cells: Experimental characterization and modeling

InGaN-based multi-quantum well (MQW) solar cells are promising devices for photovoltaics (e.g., for tandem solar cells and concentrator systems), space applications, and wireless power transfer. In order to improve the efficiency of these devices, the factors limiting their efficiency and stability must be investigated in detail. Due to the complexity of a MQW structure, compared with a simple pn junction, modeling the spectral response of these solar cells is not straightforward, and ad hoc methodologies must be implemented. In this paper, we propose a model, based on material parameters and closed-formula equations, that describes the shape of the quantum efficiency of InGaN/GaN MQW solar cells, by taking into account the layer thickness, the temperature dependence of the absorption coefficient, and quantum confinement effects. We demonstrate (i) that the proposed model can effectively reproduce the spectral response of the cells; in addition, (ii) we prove that the bulk p-GaN layer absorbs radiation, but the carriers photogenerated in this region do not significantly contribute to device current. Finally, we show that (iii) by increasing the temperature, there is a redshift of the absorption edge due to bandgap narrowing, which can be described by Varshni law and is taken into account by the model, and a lowering in the extraction efficiency due to the increase in recombination (mostly Shockley–Read–Hall) inside the quantum wells, which is also visible by decreasing light intensity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Improved wall-plug efficiency of III-nitride tunnel junction micro-light-emitting diodes with AlGaN/GaN polarization charges

The electrical performances of III-nitride blue micro-light-emitting diodes (µLEDs) with different tunnel junction (TJ) epitaxial architectures grown by metalorganic chemical vapor deposition are investigated. A new TJ structure that employs AlGaN is introduced. The current density–voltage characteristic is improved by incorporating AlGaN layer above the n-side of the TJ layer, and the effects of the AlGaN/GaN superlattices is examined. Based upon the data from band diagram simulation, net positive polarization charge is formed at the AlGaN/GaN interface, which results in a reduction in tunneling distance and increase in tunneling probability. Moreover, similar electrical improvement is observed in various device dimensions and is independent of operating current density, suggesting that AlGaN/GaN biaxial tensile strain or current spreading is not the main contribution for the improvement. Finally, the effects on the efficiency performances are determined. While the maximum external quantum efficiency of the TJ devices remains identical, the wall-plug efficiency of µLEDs is enhanced significantly by the proposed AlGaN-enhanced TJ design. This work reveals the possibility of energy efficient TJ contact with high transparency in the visible wavelength range.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Low-efficiency-droop c -plane InGaN/GaN light-emitting diodes through the use of thick single quantum wells and doped barriers

Efficiency droop at high current densities is a problem for InGaN-based light-emitting diodes (LEDs), especially for conventional c-plane devices. The large internal electric fields in c-plane quantum wells (QWs) lead to an increase in the active region carrier density (n), causing the electrical efficiency droop onset to occur at low current densities. Here, we present an approach to reduce the internal electric fields (Eint) in c-plane QWs by placing doped p-type and n-type GaN barriers close to the QW. The reduced Eint also allows a thick QW active region design, which helps to lower n to further reduce the droop. The concept of using doped barriers to control Eint is explained using theory and device simulations. Following that, multiple series of thick single QW (SQW) LEDs were grown and characterized. Key parameters in the epitaxial design such as the doping levels and the relative position of the doped barriers were systematically studied and optimized. In conclusion, by using optimized doped barriers and a thick SQW, c-plane LEDs with a low-efficiency droop of 14% at 300 A/cm2 [with respect to the peak external quantum efficiency (EQE)] and a high peak EQE of 49% were demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

High efficiency, low cost, RF sources for accelerators and colliders

Accelerators for High Energy Physics (HEP) are large users of energy, much of it in the form of radiofrequency (RF) power to accelerate particles to very high energies. Proposed HEP projects will require even larger amounts of RF energy. Increasing concerns of the cost and availability of energy will require the HEP community to use energy as efficiently as possible. Successful transfer of HEP technology to the public and private sectors will be most effective if it is highly efficient. Historically, the HEP community has utilized available RF power sources, mainly in the form of vacuum tube technology, much of which was developed during the cold war or is otherwised used in the private sector. The private sector is moving to solid-state RF sources which do not exhibit the electrical efficiency that is needed for future HEP projects. Here we summarize the state of the development of a number of RF sources that promise efficiencies of 80% and above. We also outline future efforts that are needed to fully realize the potential of these sources.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Emerging inorganic solar cell efficiency tables (version 2)

Abstract This paper presents the second version of the efficiency tables of materials considered as emerging inorganic absorbers for photovoltaic solar cell technologies. The materials collected in these tables are selected based on their progress in recent years, and their demonstrated potential as future photovoltaic absorbers. The first part of the paper consists of the guidelines for the inclusion of the different technologies in this paper, the verification means used by the authors, and recommendation for measurement best practices. The second part details the highest world-class certified solar cell efficiencies, and the highest non-certified cases (some independently confirmed). The third part highlights the new entries including the record efficiencies, as well as new materials included in this version of the tables. The final part is dedicated to review a specific aspect of materials research that the authors consider of high relevance for the scientific community. In this version of the efficiency tables, we are including an overview of the latest progress in quasi one-dimensional absorbers, such as antimony chalcogenides, for photovoltaic applications.

14 SOLAR ENERGY↗
DOE OSTI2021

The genetic architecture of leaf stable carbon isotope composition in Zea mays and the effect of transpiration efficiency on leaf elemental accumulation

With increased demand on freshwater resources for agriculture, it is imperative that more water-use efficient crops are developed. Leaf stable carbon isotope composition, δ 13 C, is a proxy for transpiration efficiency and a possible tool for breeders, but the underlying mechanisms effecting δ 13 C in C 4 plants are not known. It has been suggested that differences in specific leaf area (SLA), which potentially reflects variation in internal CO 2 diffusion, can impact leaf δ 13 C. Furthermore, although it is known that water movement is important for elemental uptake, it is not clear how manipulation of transpiration for increased water-use efficiency may impact nutrient accumulation. Here, we characterize the genetic architecture of leaf δ 13 C and test its relationship to SLA and the ionome in five populations of maize. Five significant QTL for leaf δ 13 C were identified, including novel QTL as well as some that were identified previously in maize kernels. One of the QTL regions contains an Erecta-like gene, the ortholog of which has been shown to regulate transpiration efficiency and leaf δ 13 C in Arabidopsis. QTL for δ 13 C were located in the same general chromosome region, but slightly shifted, when comparing data from two different years. Our data does not support a relationship between δ 13 C and SLA, and of the 19 elements analyzed, only a weak correlation between molybdenum and δ 13 C was detected. Together these data add to the genetic understanding of leaf δ 13 C in maize and suggest that improvements to plant water use may be possible without significantly influencing elemental homeostasis.

59 BASIC BIOLOGICAL SCIENCES↗