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Results for “ground-reflected radiation”

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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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Albedo Data for Bifacial PV Systems

At the September 2018 Bifacial PV Workshop in Lakewood, CO, a better understanding of albedo values and characteristics was identified as a key need by both the PV and financial communities to better estimate performance and to reduce risk of bifacial PV systems. To meet this need, the U.S. Department of Energy (DOE) has initiated work with the National Renewable Energy Laboratory (NREL) to provide the following: A multi-year database of measured and quality assessed albedo values with temporal resolution of one hour or less for numerous locations and types of ground surfaces. Site metadata for each location (Pictures, instruments and calibration history, soil and vegetation types, etc.) Site albedo statistics for each location (diurnal profiles, monthly and annual means, interannual variability) Analysis of the spectral mismatch for bifacial PV modules of the ground-reflected radiation for anticipated deployment surfaces (using both measured and modeled spectral albedo data). Comparisons of the measured albedos with available satellite-derived MODIS albedo products to validate the MODIS albedo products for estimating bifacial PV system performance.

14 SOLAR ENERGY↗
NASA NTRS1977

Reduction of polarizing radiometer data

High-precision polarizing radiometers have been constructed for the measurement of the angular dependence of the intensity and polarization for atmospheric and ground-reflected radiation. When the data are fit with a form containing constant, first harmonic, second harmonic, and slope terms, excellent agreement with data taken with a polarizing radiometer may be obtained. A technique has been derived for rapid data reduction by using a single matrix which, when multiplied by the data values, produces the reduced values in the sense of a least-squares fit.

Walraven, R. L.↗
DOE OSTI2019

Albedo Data to Facilitate Bifacial PV System Planning

For mono-facial photovoltaic (PV) systems, the ground-reflected radiation typically comprises only 1% to 2% of the total radiation received by the PV module. Consequently, a rudimentary understanding of the ground albedo is adequate for predicting their performance. However, for bifacial PV modules where their benefit is determined by the additional radiation reflected by the ground to their backside, a better understanding of albedo values and characteristics is needed by both the PV and financial communities to better estimate performance and to reduce risk. This was identified as a key need at the 2018 Bifacial PV Workshop. Subsequently, the Department of Energy (DOE) has initiated work with the National Renewable Energy Laboratory (NREL) to provide albedo data for different locations and ground surfaces for both the simulation of bifacial PV systems and for summary information, including variations in albedo with respect to time of day, season, and year. This albedo data base will include data from measurement networks (SURFRAD and Ameriflux), and the PV industry is also asked to provide their albedo measurements and take part in a cooperative effort to provide an expansive and accurate data base of albedo values.

14 SOLAR ENERGY↗
DOE OSTI2020

Spectral Effects in Albedo and Rearside Irradiance Measurment for Bifacial Performance Estimation: Preprint

Albedo data are essential for accurate prediction of bifacial PV module performance. However, spectral response mismatch between PV modules and irradiance sensors used in albedometers can limit the accuracy of performance predictions. In order to provide quantitative assessment of this effect, we investigate via simulation the differences in spectrally responsive albedo measured with thermopile pyranometers and crystallinesilicon PV reference cells in comparison to a representative crystalline-silicon bifacial PV module for nine different representative ground surface materials. Calculations are performed using simulated solar spectra together with catalogued spectral reflectivity data distributed with the SMARTS simulation software. For the specific materials considered, the results show that albedo measurement using thermopile pyranometers could over or under-estimate the ground-reflected radiation usable by a bifacial PV module by up to 10%, versus only approximately 4% total range of variation for a PV reference cell.

Albedo↗
NASA NTRS1986

Passive Element Shapes Antenna Radiation Pattern

Parasitic waveguide element suppresses ground-reflected multipath radiation. Small section of waveguide placed in front of phased-array antenna operating at 850 MHz modifies radiation field by reducing power density parallel to and below ground plane without significantly affecting primary radiation at angles greater than 20 degrees above horizontal. Acts as parasitic radiator that shifts phase of portion of wavefront by approximately 180 degrees, causing partial cancellation in ground plane, thereby reducing radiation intensity in that direction by about 10 dB. Produces corresponding reduction in multipath radiation scattered from ground. Waveguide technique also used to decouple two nearby antennas.

Bonebright, M. E.↗
DOE OSTI2021

Influence of Diffuse and Ground-Reflected Irradiance on the Spectral Modeling of Solar Reference Cells

Thermal Energy Storage (TES) is a key component for solar thermal applications to bridge the gap between the demand for thermal energy and the supply of solar energy, whose availability depends on the time of day and season. Thus, cost-effective packed-bed thermal containers filled with a solid storage medium have been proposed for high-temperature sensible heat storage as materials are abundant and relatively cheap. Thus, it is necessary to investigate their performance and temperature profiles during the charge-discharge cycle. Several models are available for this purpose. Typically, the more detailed a model, the greater the computational effort required to solve it, and hence a time-efficient model is needed to prevent excessively long computation times for long-term analysis. At the more basic level, the common Hughes E-NTU model and the less realistic simplified Infinite-NTU model are very important for their less time and computational effort. In this paper, the appropriateness of employing the Infinite-NTU model was evaluated to investigate the performance of a typical and scalable rock-bed TES as a case study. The results presented provide a methodology to quickly test the validity of the model and predict the temperature profile for the case under study. Accordingly, such simple charge-discharge cycle thermal performance predictions are important to plan, design, and rapidly deploy a reliable and economical solar thermal system for the supply of valuable heat to high-temperature demanding applications of power generation and industrial processes as part of a rapid shift towards non-polluting renewable energy. Keywords: Solar Thermal, TES, Packed-bed, NTU model, Temperature profile

PV modeling↗