Probing carrier lifetimes in photovoltaic materials using subsurface two-photon microscopy
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14 SOLAR ENERGY↗
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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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Feasibility and Reliability of a Single Layer Polymeric PV Backsheet in White, Transparent, or Luminescent Concentrator Options
A single layer polymeric backsheet material has been evaluated for use in silicon PV modules and as a luminescent solar collector. Physical and optical properties of the backsheet have been examined after damp heat, thermal cycling, and UV exposure for two different polymeric grades and three different pigment options including white, transparent, and photo-luminescent. As the importance of developing a white backsheet that is cost-effective, recyclable, and reliable is evident, the increased availability and use of bifacial cells is bound to increase the demand for transparent backsheets as well. In today's market, the cost of a clear backsheet is significantly higher than a white backsheet which is motivation for research and development of new material options in this field. Results from these extensive tests reveal the need for continued research in white pigments and positive results in transparent and luminescent backsheet options.
14 SOLAR ENERGY↗
Physics-Guided Machine Learning for Prediction of Cloud Properties in Satellite-Derived Solar Data
With over 20 years of high-resolution surface irradiance data covering most of the western hemisphere, the National Solar Radiation Database (NSRDB) is a vital public data asset. The NSRDB uses a two-step Physical Solar Model (PSM) that explicitly considers the effects of clouds and other atmospheric variables on radiative transfer. High-quality physical and optical cloud properties derived from satellite imagery are perhaps the most important data inputs to the PSM, representing the greatest source of radiation attenuation and scattering. However, traditional methods for cloud property retrieval have their own limitations and are unable to accurately predict cloud properties outside of nominal conditions. We introduce a physics-guided neural network that can accurately predict cloud properties when traditional methods fail or are inaccurate. Using this framework, we show reductions in relative Root Mean Square Error (RMSE) for Global Horizontal Irradiance (GHI) up to 13 percentage points for timesteps that previously had missing or low-quality cloud property data. We expect that this methodology will be effective in improving the quality of cloud property and solar irradiance data in the NSRDB.
cloud properties↗
The relevance of solar flares to astrophysics
The physical mechanisms associated with solar flares are reviewed. The relevance of flare mechanisms to other astrophysical phenomena is discussed. In this context, specific models of quasars and radio galaxies, Sco X-1 and gamma-ray bursts are examined.
Sturrock, P. A.↗
Scientific visualization tools for the ISTP project: Mission planning, data analysis and model interpretation
Visualization tools are being developed to meet the challenges of mission planning and data analysis presented by the International Solar-Terrestrial Physics (ISTP) program. ISTP encompasses a large number of spacecraft, multiple ground-based observatories, and several theoretical investigations, with the goal of understanding the global behavior of the solar wind/magnetosphere/ionosphere system. The tools include three-dimensional displays of key boundaries in geospace along with spacecraft trajectories, which can be animated and synchronized to universal time. Magnetic field models and MHD simulation results can be invoked to reveal the magnetic topology or to identify magnetic conjunctions between spacecraft and/or ground-based facilities. Simultaneous displays of satellite trajectories, spacecraft-borne observations, and model predictions are available to facilitate data processing and interpretation efforts. The current status of these tools is described, and their implementation at the ISTP Science Planning and Operations Facility and distribution to the entire ISTP community are discussed.
Peredo, M.↗
ISTP Global Geospace Science. Energy transfer in geospace
Solar-terrestrial physics concerns the study of the generation, flow, and dissipation of mass, momentum, and energy between the Sun and the Earth. Mass, momentum, and energy are carried by charged particles that compose the solar wind. When the solar wind reaches the Earth, some solar-wind particles enter the magnetosphere; this coupling between the solar wind and the Earth means that the solar wind can influence the Earth's upper atmosphere. As the first step in addressing the behavior of this solar-terrestrial system, the Global Geospace Science (GGS) Initiative will use the Wind and Polar satellites, provided by NASA, and the Geotail satellite provided by the Japanese Institute of Space and Astronautical Science (ISAS), to perform simultaneous and closely coordinated measurements of the key geospace regions and will add data from equatorial missions. Magnetic field and particle changes that occur when particles are energized during auroral events will be monitored. The intention behind the GGS Initiative is to understand the physical mechanisms and various regions controlling the transport of mass, momentum, and energy in geospace. A summary of the GGS Initiative is presented.
Source record↗
SOLAR SPECTRAL IRRADIANCE, SOLAR ACTIVITY, AND THE NEAR-ULTRA-VIOLET
The previous calculations of the Solar Spectral Irradiance (SSI) by the Solar Radiation Physical Modeling, version 2 system, are updated in this work by including new molecular photodissociation cross-sections of important species, and many more levels and lines in its treatment of non-LTE radiative transfer. The current calculations including the new molecular photodissociation opacities produce a reduced over-ionizaton of heavy elements in the lower chromosphere and solve the problems with prior studies of the UV SSI in the wavelength range 160–400 nm and now reproduce the available observations with much greater accuracy. Calculations and observations of the near-UV at 0.1 nm resolution and higher are compared. The current set of physical models includes four quiet-Sun and five active-region components, from which radiance is computed for ten observing angles. These radiances are combined with images of the solar disk to obtain the SSI and Total Solar Irradiance and their variations. The computed SSI is compared with measurements from space at several nm resolution and agreement is found within the accuracy level of these measurements. An important result is that the near-UV SSI increase with solar activity is significant for the photodissociation of ozone in the terrestrial atmosphere because a number of highly variable upper chromospheric lines overlap the ozone Hartley band.
79 ASTRONOMY AND ASTROPHYSICS↗
Solar Energetic Particle Spectrometer (SEPS)
An outstanding problem of solar and heliospheric physics is the transport of solar energetic particles. The more energetic particles arriving early in the event can be used to probe the transport processes. The arrival direction distribution of these particles carries information about scattering during their propagation to Earth that can be used to test models of interplanetary transport. Also, of considerable importance to crewed space missions is the level of ionizing radiation in the interplanetary medium, and the dose that the crew experiences during an intense solar particle event, as well as the risk to space systems. A recent study concludes that 90% of the absorbed dose results from particles in the energy range 20-550 MeV. We will describe a new compact instrument concept, SEPS, that can cover the energy range from 50-600 MeV with a single compact detector. This energy range has been difficult to cover. There are only limited data, generally available only in broad energy bins, from a few past and present instruments outside Earth s magnetosphere. The SEPS concept can provide improved measurements for this energy range and its simple light-weight design could be easily accommodated on future missions.
Christl, Mark J.↗
Coronal Spectral Diagnostics: The Coronal Solar Magnetic Observatory (COSMO)
Understanding and predicting the major phenomena taking place in the solar corona, such as flares and Coronal Mass Ejections (CMEs), the heating and evolution of the solar atmosphere, and the acceleration of the solar wind, are fundamental challenges to predict our own star. These challenges are related to the solar magnetism and to the physical properties of solar plasmas: meeting them requires two types of measurements: A. Spectrally resolved, simultaneous observations of the entire corona in multiple spectral lines emitted by chromospheric to hot coronal plasmas at high spatial resolution and cadence for long periods of time; and B. Coronal magnetic field measurements.
Enrico Landi↗
Report from magnetospheric science
By the early 1990s, magnetospheric physics will have progressed primarily through observations made from Explorer-class spacecraft, sounding rockets, ground based facilities, and shuttle based experiments. The global geospace science (GGS) element of the International Solar Terrestrial Physics program, when combined with contributions to the ESA Cluster mission and ground based and computer modeling programs, will form the basis for a major U.S. initiative in magnetospheric physics. The scientific objectives of the GGS program involve the study of energy transport throughout geospace. The Cluster mission will investigate turbulence and boundary phenomena in geospace, particularly at high latitudes on the dayside and in the region of the neutral sheet at geocentric distances of about 20 earth radii on the night side of the earth. The current state of knowledge is reviewed and the goals of these missions are briefly discussed.
Burch, J. L.↗
Energy Loss in Organic Photovoltaics: Nonfullerene Versus Fullerene Acceptors
The energy loss experienced by organic photovoltaics (OPVs) is the difference between the lowest photogenerated exciton energy of a donor or acceptor and the open circuit energy. It sets a fundamental limit to the open-circuit voltage and hence the efficiency of OPVs. This loss can be as large as 0.7 eV for fullerene acceptors, although nonfullerene acceptors (NFAs) reduce this to ≤0.6 eV. Here, we systematically quantify the relationship between charge transfer energy loss (ΔE CT ), nonradiative recombination loss, exciton binding energy, and intra- and intermolecular electron-phonon couplings. Density functional theory and comprehensive quantum mechanical modeling are used to associate molecular volume, effective conjugation length, and the nonbonding character of molecules to these types of energy losses. Nonradiative recombination in donor-NFA heterojunctions is quantified by the charge transfer state emission quantum yield and its Frank-Condon shift. Our analytical results are consistent with measurements where ΔE CT is varied between 0 and 0.6 eV using a variety of fullerene derivatives and thiophene-based NFAs paired with donor molecules. Furthermore, molecular design rules to decrease the energy loss in OPVs derived from our analysis are provided.
14 SOLAR ENERGY↗
Using the standard solar model to constrain solar composition and nuclear reaction 𝑆 factors
While standard solar model (SSM) predictions depend on approximately 20 input parameters, SSM neutrino flux predictions are strongly correlated with a single model output parameter, the core temperature 𝑇 𝑐 . Consequently, one can extract physics from solar neutrino flux measurements while minimizing the consequences of SSM uncertainties, by studying flux ratios with appropriate power-law weightings tuned to cancel this 𝑇 𝑐 dependence. Here, we reexamine an idea for constraining the primordial C + N content of the solar core from a ratio of CN-cycle 15 O to pp-chain 8 B neutrino fluxes, showing that non-nuclear SSM uncertainties in the ratio are small and effectively governed by a single parameter, the diffusion coefficient. We point out that measurements of both CN-I cycle neutrino branches— 15 O and 13 N 𝛽-decay—could, in principle, lead to separate determinations of the core C and N abundances, due to out-of-equilibrium CN-cycle burning in the cooler outer layers of the solar core. Lastly, we show that the strategy of constructing “minimum uncertainty” neutrino flux ratios can also test other properties of the SSM. In particular, we demonstrate that a weighted ratio of 7 Be and 8 B fluxes constrains a product of S-factors to the same precision currently possible with laboratory data.
Serenelli, Aldo↗
The relationship between hard and soft X-ray bursts observed by OSO 7
The paper reviews the observations of solar X-rays in the range 1-100 keV made by the solar X-ray instrument on board the OSO-7 satellite and explores the relationship between the hard and soft X-ray components in order to glean some information on the physics of solar flares. Some of the results are as follows: The growth of the soft X-ray emission in a burst must be due to the addition of new hot material to the flare plasma. The anticorrelation between cooling time and maximum plasma temperature gives new evidence to support conduction as the principal cooling mechanism of the hot flare plasma. Observations of hard X-ray emission from bursts which occurred behind the limb indicate that hard X-ray emission comes at least in part from considerable heights in the corona.
Datlowe, D. W.↗
Magnetic Fields and Flows in Open Magnetic Structures
Open magnetic structures connect the solar surface to the heliosphere and are thus of great interest in solar-terrestrial physics. This talk is primarily an observational review of what is known about magnetic fields and particularly flows in such regions with special focus on coronal holes and origins of the fast solar wind. First evidence of the connection between these two features was seen in correlations of Skylab data with in situ measurements of the solar wind soon after the discovery of coronal holes, which are now known to emanate from unipolar magnetic regions at the photosphere. Subsequently many observations of have been made, ranging from oscillations in the underlying photosphere and chromosphere, to possible beginnings of the solar wind as observed by Doppler shifts in high chromospheric and transition-region lines, to coronagraphic time-lapse studies of outward-moving blobs of material which perhaps trace elements of solar-wind plasma. Some of the many unresolved and controversial issues regarding details of these observations and their association with the solar wind will be discussed.
Jones, Harrlson P.↗
The Origins of Plasmas in the Earth's Neighborhood (OPEN) program
The nature and objectives of the OPEN program are overviewed. The Origins of Plasmas in the Earth's Neighborhood program was conceived in 1979 and proposed as a major new initiative to study the energetics of the earth's space environment by the end of the 1980s. The objectives of OPEN have been integrated into the Global Geospace Study (GGS) segment to the International Solar-Terrestrial Physics (ISTP) program now being planned jointly by NASA, ESA, and Japan. The goals will be to develop a global understanding of the flow of energy from the sun through the earth's space environment above the neutral atmosphere and to define the cause and effect relationships between the plasma physics processes that link different regions of this dynamic environment. A network of four spacecraft will be used, each one carrying an instrument complement to characterize the composition and behavior of the upstream solar wind, the high-altitude polar magnetosphere, the equatorial magnetosphere, and the comet-like geomagnetic tail. Multispectral cameras will also be carried to image polar auroras at ultraviolet, visible and X-ray wavelengths. Experimentalists and theorists on the international team will participate.
Alexander, J. K.↗
Solar models with enhanced energy transport in the core
The discrepancy between the observed and computed flux of solar neutrinos can be eliminated if the temperature gradient in the core of the model, and hence its central temperature, is reduced. This could in principle be accomplished by reducing the core opacity; alternatively, it has been proposed that a fraction of the energy transport in the solar core results from the motion of hypothetical particles (the so-called WIMPs). The resulting changes in solar structure have measurable effects on the frequencies of the solar 5-minute oscillations. Here, models are considered where the opacity in the solar core has been decreased in a manner which roughly simulates the effects of the WIMPs. The analysis of the models and their frequencies provides insight into the consequences of modifications to the physics of solar models. In particular, it is found that models with the observed neutrino flux are inconsistent with observations of low-degree solar oscillations.
Christensen-Dalsgaard, J.↗
Ferroelectric barium titanate derivatives containing Mo and Mg for transparent photovoltaic applications
Using first-principles methods, we investigate the electronic properties of the [Ba(Mo 1/2 ,Mg 1/2 )O 3 ] x -[BaTiO 3 ] 1-x solid solution derived from barium titanate as a potential candidate to be used in photovoltaic devices. Focusing on the bandgap and its origin, we study the effect of different possible Mo and Mg contents, arrangements, and phases of [Ba(Mo 1/2 ,Mg 1/2 )O 3 ]x-[BaTiO 3 ] 1-x . We find that [Ba(Mo 1/2 ,Mg 1/2 )O 3 ] 0.25 -[BaTiO 3 ] 0.75 is a viable candidate for use in transparent photovoltaics due to its energy bandgap of 2.6 eV in the rhombohedral phase. In all cases, [Ba(Mo 1/2 ,Mg 1/2 )O 3 ]x-[BaTiO 3 ] 1-x materials exhibit spontaneous polarization that allows the exploitation of the bulk photovoltaic effect and in principle may allow high power conversion efficiency exceeding the Shockley-Queisser limit for these materials.
14 SOLAR ENERGY↗
IMP-8 Magnetometer Experiment
IMP-8 (IMP-J) was launched by NASA on October 26, 1973 to measure the magnetic fields, plasmas, and energetic charged particles (e.g., cosmic rays) of the Earth's magnetotail and magnetosheath and of the near-Earth solar wind. IMP-8, the last often IMP (Interplanetary Monitoring Platform) or AIMP (Anchored-IMP) spacecraft launched in 10 years, operated until October 7, 2006, in a near-circular, 35 Earth Radii, 12-day orbit. It was an important adjunct to the International Solar Terrestrial Physics program, provided in-ecliptic, one Astronomical Unit baseline data for the deep space Pioneer, Voyager and Ulysses missions, and built a long-time-series database useful in understanding long-term solar processes .
Szabo, Adam↗