Ex situ bismuth doping for efficient CdSeTe thin-film solar cells with open-circuit voltages exceeding 900 mV
We dope CdTe solar cells with Bi after the device structure is completed using a solution process.
CdTe solar cell↗
SEARCH · Engineering Papers
Results for “MV”
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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Local Structural Disorder in Metavanadates MV 2 O 6 (M = Zn and Cu) Synthesized by the Deep Eutectic Solvent Route: Photoactive Oxides with Oxygen Vacancies
Metavanadates MV 2 O 6–δ (M = Zn and Cu) are synthesized by using a deep eutectic solvent (DES), a mixture of hydrogen bond donor and acceptor, as a reaction medium. Dissolution of stable binary metal oxides in a DES followed by a heat treatment yields phase-pure vanadates. According to in situ powder X-ray diffraction, ternary phases (α-Zn 2 V 2 O 7 and β-Cu 2–x V 2 O 7 , x ~ 0.27) are intermediates in the reaction pathway taken. Identifying a polymorphic phase transformation temperature for CuV 2 O 6 as well as the narrow temperature range between formation and decomposition for both metavanadates allows for tackling the challenge of the synthesis of these materials. The oxygen vacancy introduced by the DES route is accompanied by the formation of reduced V 4+ and Cu + in the oxide matrix, based on X-ray photoelectron spectroscopy. These oxygen vacancies modify the vibrational modes in the corresponding Raman spectra and are also responsible for broad optical absorptions in the 1.8–1.1 eV range. The optical band gaps of the materials are found at 1.8 eV (CuV 2 O 6 ) and 2.2 eV (ZnV 2 O 6 ), approximately 0.1–0.3 eV below the values reported in the literature. The reduced band gaps and sub-band gap photon absorption are key features of the oxygen-deficient metavanadates. Surface photovoltage spectroscopy reveals that all the synthesized vanadates are n-type materials with electrons as the majority charge carriers, and photoelectrochemical measurements confirm photoanodic currents for methanol oxidation. Furthermore, these results provide insight into the synthesis and structure–property relationship of the metavanadates for their potential use as photoanodes.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Control of Grid-Connected Multiport MV Power Electronics Energy Hub: Preprint
In this paper a new concept of multiport modular medium-voltage power electronics hub (M3PE-HUB) is introduced for future power grid. The goal for this project is to design, develop, and demonstrate foundational technologies and capabilities for multiport power electronics energy hubs that can serve as intelligent devices to coordinate and control several different sources and loads. In this paper, the architecture of the controller, the central controls, and its verification is presented.
controls↗
Hosting Capacity Improvement Method Using MV–MV Solid-State-Transformer
As a large number of distributed generations are connected to the distribution system, research on the hosting capacity is actively being conducted. In particular, various methods, such as smart inverter functionality, co-located energy storage systems (ESS), and the use of on-load tap changers (OLTC), have been proposed to improve the hosting capacity. In this paper, a method to improve the hosting capacity by utilizing a solid-state transformer (SST) and its unique control capability is proposed. Lastly, the proposed method is verified in the distribution system of the Republic of Korea using the OpenDSS program.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Modular HF Isolated MV String Inverters Enable a New Paradigm for Large PV Farms
The “Modular HF Isolated MV String Inverters Enable a New Paradigm for Large PV Farms” project focuses on exploring alternative power converter and system-level plant configurations to achieve the lowest cost and highest energy output for a given solar plus storage (e.g., PV + battery) plant, including the use of medium voltage (MV) collection while taking into account detailed models of all elements. To realize this objective, four approaches were utilized (i) employ a novel Medium Voltage String Inverter (MVSI) topology (soft switching solid state transformer – S4T) to convert 1000 Vdc to 4.16 kVac; (ii) plant collection using standard, low-cost overhead MV distribution network; (iii) enable energy storage integration without additional converter cost to achieve dispatchability of the PV resource; and (iv) provide advanced functionality (autonomous operation, track ISO signals for dynamic balancing and ancillary services, and PV farm operation as a virtual grid resource). Subsequently and in alignment with the previously mentioned approaches, the project was structured in five efforts (i) S4T MVSI simulation and design; (ii) system analysis and storage optimization; (iii) financial analysis; (iv) power converter prototype build and test; and (v) regulatory and commercial impact study. The outcomes provided by each effort can be summarized as follows (i) Project explored the use of MV AC distribution architecture for hybrid PV+storage utility-scale PV farms; (ii) Detailed loss and LCOE analysis for AC and DC side BESS architecture, including multiple converter topologies, as well as for proposed MVSI/MDCT systems; (iii) MVSI was built and holds promise but needs lower-cost high-voltage Si-C devices, which does not seem possible in the near term; (iv) MDCT provides a simpler modular building block – validated through HIL and farm level modeling, simulation and experimental validation; (v) 300 kVA MDCT prototype built and tested, technology is being commercialized; and (vi) Regulatory model of utility building PV plants, where PV panels are treated as DC generation (IPP), seems viable and can allow improved grid integration.
14 SOLAR ENERGY↗
Structure and phase transitions in niobium and tantalum derived nanoscale transition metal perovskites, Ba(Ti,MV)O3, M=Nb,Ta
The prospect of creating ferroelectric or high permittivity nanomaterials provides motivation for investigating complex transition metal oxides of the form Ba(Ti, MV)O3, where M = Nb or Ta. Solid state processing typically produces mixtures of crystalline phases, rarely beyond minimally doped Nb/Ta. Using a modified sol-gel method, we prepared single phase nanocrystals of Ba(Ti, M)O3. Compositional and elemental analysis puts the empirical formulas close to BaTi0.5Nb0.5O3−δ and BaTi0.5Ta0.5O3−δ. For both materials, a reversible temperature dependent phase transition (non-centrosymmetric to symmetric) is observed in the Raman spectrum in the region 533–583 K (260–310 °C); for Ba(Ti, Nb)O3, the onset is at 543 K (270 °C); and for Ba(Ti, Ta)O3, the onset is at 533 K (260 °C), which are comparable with 390–393 K (117–120 °C) for bulk BaTiO3. The crystal structure was resolved by examination of the powder x-ray diffraction and atomic pair distribution function (PDF) analysis of synchrotron total scattering data. It was postulated whether the structure adopted at the nanoscale was single or double perovskite. Double perovskites (A2B′B″O6) are characterized by the type and extent of cation ordering, which gives rise to higher symmetry crystal structures. PDF analysis was used to examine all likely candidate structures and to look for evidence of higher symmetry. The feasible phase space that evolves includes the ordered double perovskite structure Ba2(Ti, MV)O6 (M = Nb, Ta) Fm-3m, a disordered cubic structure, as a suitable high temperature analog, Ba(Ti, MV)O3Pm-3m, and an orthorhombic Ba(Ti, MV)O3Amm2, a room temperature structure that presents an unusually high level of lattice displacement, possibly due to octahedral tilting, and indication of a highly polarized crystal.
Chemistry↗
Monte Carlo simulation of shielding designs for a cabinet form factor preclinical MV–energy photon FLASH radiotherapy system
Purpose: A preclinical MV-energy photon FLASH radiotherapy system is being designed at Stanford and SLAC National Accelerator Laboratory. Because of the higher energy and dose rate compared to conventional kV-energy photon laboratory-scale irradiators, adequate shielding in a stand-alone cabinet form factor is more challenging to achieve. We present a Monte Carlo simulation of multilayered shielding for a compact self-shielding system without the need for a radiation therapy vault. Methods: A multilayered shielding approach using multiple alternating layers of high-Z and low-Z materials is applied to the self-shielded cabinet to effectively mitigate the secondary radiation produced and to allow the device to be housed in a Controlled Radiation Area outside of a radiation vault. The multilayered shielding approach takes advantage of the properties of high-Z and low-Z radiation shielding materials such as density, cross-section, atomic number of the shielding elements, and products of radiation interactions within each layer. The Monte Carlo radiation transport code, FLUKA, is used to simulate the total effective dose produced by the operation. Results: The multilayered shielding designs proposed and simulated produced effective dose rates significantly lower than monolayer designs with the same total material thickness at the regulatory boundary; this is accomplished through the manipulation of the locations where secondary radiation is produced and reactions due to material properties such as neutron back reflection in hydrogen. Borated polyethylene at 5 wt% significantly increased the shielding performance as compared to regular polyethylene, with the magnitude of the reduction depending upon the order of the shielding material. Conclusions: The multilayered shielding provides a path for shielding preclinical FLASH systems that deliver MV-energy bremsstrahlung photons. Furthermore, this approach promises to be more efficient with respect to the shielding material mass and space claim as compared to shielded vaults typically required for clinical radiation therapy with MV photons.
62 RADIOLOGY AND NUCLEAR MEDICINE↗
Clinical 6 MV X-Ray Facility Photo-Neutron/Fission Interrogations with TMFD Sensors
Detection of several targets (U, Be, D2O) of interest to national security has been achieved at Purdue University’s 6 MV (~104 R/h) X-Ray clinical linear accelerator (CLINAC), from photoneutron/fission induced neutron signatures using a Centrifugally Tensioned Metastable Fluid Detector (CTMFD). Traditional neutron detection schemes were saturated and ineffective under the intense (to ~104 R/h) photon environment; however, the CTMFD sensor technology was capable of measuring the relatively insignificant (~10-12x lower intensity) neutron field produced from 6 MeV-end point X-Ray beam interactions with the CLINAC components and surroundings. This is in stark contrast to published results based on conventional belief for immeasurable neutron dose in 6 MV CLINAC facilities. Photoneutron and photofission neutron production rates were detected and analyzed at various standoffs from the isocenter, with and without special nuclear material (SNM) related targets ranging in mass from 5 g of Be, to ~0.6 kg of UO2. It was confirmed that 6 MV X-Ray photons do result in measurable neutron dose above normal cosmic background. Additionally, in threshold mode, the CTMFD operating under a tensioned metastable pressure of -5bar, enabled conclusive rejection of background photoneutrons, while enabling the rapid detection of: Be, D2O, C and U targets within seconds to minutes while operating in and around 104 R/h photon fields.
Ozerov, Stepan↗
Hierarchical Distributed Optimal Power Flow of HV and MV Distribution Networks With Continuous and Discrete Devices
With large-scale distributed photovoltaics (PVs) being integrated into distribution networks (DNs), coordinated optimal power flow (OPF) of high voltage (HV) and medium voltage (MV) DNs should be investigated to optimally dispatch the distributed PVs and other network devices. Here, this paper presents a hierarchical distributed OPF method for HV and MV DNs with on-load tap changers, reactive power compensators, feeder switches and distributed PVs. A hierarchical master-slave control architecture is applied to implement coordinated OPF of two-layer DNs. The HV master problem and MV subproblems are transformed into mixed-integer convex problems respectively with second order cone programming and LinDistFlow approximation. Since there is no efficient distributed algorithm to solve such OPF models with integer subproblems, a novel distributed algorithm is proposed in this paper to efficiently solve the hierarchical coordinated OPF model with integer subproblems in a distributed manner. In the proposed algorithm, the coordinated OPF model is solved in a branch-and-bound framework, where in each branch node generalized Benders decomposition (GBD) algorithm is applied to decompose the coordinated OPF model into a master problem and relaxed subproblems and solves them iteratively to get optimal solution. The GBD optimal and feasible cutting planes generated in a branch node are proved to be valid for its descendants. Moreover, three acceleration techniques are introduced into the proposed algorithm to improve computational efficiency. Finally, the effectiveness and accuracy of the proposed method are verified via simulation tests in Jinzhai DNs of China.
42 ENGINEERING↗
A measurement of cosmic-ray positron and negatron spectra between 50 and 800 MV
A balloon-borne spark chamber magnetic spectrometer has been used to measure the spectra of cosmic-ray positrons and negatrons at energies between 50 and 800 MV. The data reported here were obtained during two flights from Fort Churchill, Manitoba, in July 1972. The present results indicate that the dominance of negatrons from primary sources, found in earlier experiments above 200 MV, extends down to at least 50 MV. Solar modulation of the positron component is found to be consistent with that of the total electron spectrum, assuming that the positron component is entirely attributable to collisions between cosmic-ray nuclei and the interstellar gas.
Daugherty, J. K.↗
Towards a 700 mV silicon solar cell
The key to improved silicon solar cell performance lies in increasing cell open circuit voltage. Not only does improved voltage direclty increase cell efficiency, but it also increases the limiting value of fill factor and decreases the temperature sensitivity of the cell. Limits on attainable open circuit voltage are not well defined. A thermodynamic limit of 850 mV exists for black body silicon cells, with 700 mV long regarded as a practical limit. This paper describes experimental work which has resulted in experimental devices with open circuit voltages approaching 700 mV. Values up to 694 (AM0, 25 C) have been demonstrated. The cells are similar in structure to conventional p-n junction cells, but particular attention is paid to passivating the entire top surface of the cell, including regions under the top contact.
Green, M. A.↗
Determination of the Three-Dimensional Morphology of ALH84001 and Biogenic MV-1 Magnetite: Comparison of Results from Electron Tomography and Classical Transmission Electron Microscopy
Dated at approximately 3.9 billion years of age, carbonate disks, found within fractures of the host rock of Martian meteorite ALH84001, have been interpreted as secondary minerals that formed at low temperature in an aqueous medium. Heterogeneously distributed within these disks are magnetite nanocrystals that are of Martian origin. Approximately one quarter of these magnetites have morphological and chemical similarities to magnetite particles produced by magnetotactic bacteria strain MV-1, which are ubiquitous in aquatic habitats on Earth. Moreover, these types of magnetite particles are not known or expected to be produced by abiotic means either through geological processes or synthetically in the laboratory. The remaining three quarters of the ALH84001 magnetites are likely products of multiple processes including, but not limited to, precipitation from a hydrothermal fluid, thermal decomposition of the carbonate matrix in which they are embedded, and extracellular formation by dissimilatory Fe-reducing bacteria. We have proposed that the origins of magnetites in ALH84001 can be best explained as the products of multiple processes, one of which is biological. Recently the three-dimensional (3-D) external morphology of the purported biogenic fraction of the ALH84001 magnetites has been the subject of considerable debate. We report here the 3-D geometry of biogenic magnetite crystals extracted from MV-1 and of those extracted from ALH84001 carbonate disks using a combination of high resolution classical and tomographic transmission electron microscopy (TEM). We focus on answering the following questions: (1) which technique provides adequate information to deduce the 3-D external crystal morphology?; and, (2) what is the precise 3-D geometry of the ALH84001 and MV-1 magnetites?
Thomas-Keprta, Kathie L.↗
The hot white dwarf in the cataclysmic variable MV Lyrae
We have obtained the first far-ultraviolet spectrum of the novalike cataclysmic variable MV Lyrae using the Far Ultraviolet Spectroscopic Explorer. We also obtained contemporaneous optical light curves and spectra. All data are from a deep faint accretion state of MV Lyr.
hot white dwarf↗
Conversion of the LLNL/CAMS 1 MV biomedical AMS system to a semi-automated natural abundance 14C spectrometer: system optimization and performance evaluation
The Lawrence Livermore National Laboratory – Center for Accelerator Mass Spectrometry compact 1 MV biomedical accelerator mass spectrometer was repurposed and optimized for the semi-automated radiocarbon measurement of natural abundance environmental samples. Here we present results from 15 months of routine system operation and evaluate the system performance based on 30 sample wheels measured with consistent operating conditions over 7 months from August 2019 to March 2020. Additionally, the average measurement precision was 2.7 ± 0.7‰. System accuracy was assessed with measurements of 14 C-free materials, standard materials with 14 C-content spanning 0.5 to 1.5 F 14 C, and by comparison to split samples measured with the 10 MV AMS system. Overall, this system can routinely measure samples as small as 300 µgC and less than 33000 years without the need for size-specific correction protocols.
43 PARTICLE ACCELERATORS↗
The interplanetary scattering mean free path from 1 to 3 x 1000 MV
The paper reports a statistical study of published intensity-time profiles of proton and electron solar particle events from 1967 to 1974. The purpose of the study was to examine systematically the temporal and rigidity dependence of the interplanetary scattering mean free path from approximately 1000 to 3000 MV. The observed t-max, the time from release of particles at the sun to the time of maximum flux at the spacecraft, were interpreted in terms of a propagation model to obtain the average radial scattering mean-free path. This path (1) appears to be species independent when it is derived from proton and electron solar particle events, (2) varies less than a factor of 2 from solar maximum to solar minimum, and (3) is nearly rigidity independent below approximately 500 MV. The path values obtained at low rigidities are inconsistent with path values derived theoretically from the interplanetary magnetic field fluctuations.
Zwickl, R. D.↗
Soft X-ray emission from the vicinity of MV Lyr
Evidence for a soft X-ray source at the location of the nova-like variable star MV Lyr is presented. Data from the smallest field of view of the A2 experiment on board HEAO-1 in the range 0.18 to 2.5 keV reveals a source of 0.18 to 0.43 keV emission, designated H1901+43, with a count rate corresponding to a flux of 4 x 10 to the -12th erg/sq cm per sec if a spectral temperature of 3 x 10 to the 5th K is assumed. The two-dimensional error box of H1901+43 is observed to contain the UX UMa star MV Lyr, which is suggested as the only obvious candidate for the source of X-ray emission, in accordance with the observations of soft X-ray emission from other cataclysmic variables, notably AM Her, U Gem and SS Cyg.
Mason, K. O.↗
IUE and optical observations of MV Lyrae at intermediate and low states
Ultraviolet observations of MV Lyrae were obtained with the aid of the International Ultraviolet Explorer (IUE) spacecraft on 1979 December 2 when MV Lyr was at a normal low state and on 1980 December 8. The optical observations were obtained at Kitt Peak, Lick Observatory, and the University of Washington Observatory with various image-tube scanners and photometers. The photometric colors were found to be very blue at the very low state and at the normal low state. Robinson et al. (1981) have identified three components in their very low-state optical spectra. The significance of the observations is discussed.
Szkody, P.↗
MV-3 communication subsystem
The operational mobile VLBI data acquisition system (MV-3) requires that a voice link be established between the mobile data system and a fixed site. A communications subsystem was incorporated in the MV-3 design which consists of HF radio, VHF mobile radio telephone and conventional land line telephone. The HF antenna design was optimized for short and long range transmission using both inverted V and yagi antennas mounted on a self-supporting telescoping mast.
Parks, G. S.↗