Studying the Impact of Shading on the Energy Characteristics of a Solar String

The impact of spectral distribution on photovoltaic power generation and its quantitative evaluation model

In hyperspectral remote sensing measurements, the spectral effective information extracted under different measurement light source conditions will produce differences, which in turn affects the robustness of the constructed models. Therefore, it is important to study the differences between hyperspectral estimation models under different measurement light source conditions to construct a general hyperspectral model of vegetation parameters under different light source conditions. In this paper, hyperspectral models are constructed from artificial and natural light sources, and the hyperspectral reflectance and the corresponding SPAD values of artificial and natural light sources under winter wheat, corn and tea tree were measured under the same time period and the same light measurement angle and height. The collected data were used to construct models for the four vegetation indices with better results after screening and to explore how to reduce model variability under different measured light source conditions. The results show that the difference between the artificial light source and natural light source models is significant (the coefficient of determination R2 is significantly different between the artificial light source and natural light source models), and the influence of different light sources on the construction of hyperspectral estimation models can be reduced by selecting vegetation indices. The linear regression equation model constructed by NDVI can effectively reduce the influence of different light sources on the construction of SPAD hyperspectral models and make the model more general. This study can provide new ideas and methods to investigate the differences in spectral models under different measurement light sources.

Bypass diodes are usually connected in PV modules to reduce the impact of partial shading. There are two configurations of the bypass diodes used in commercially available PV modules: non-overlapping bypass diodes, in which each diode is separately connected to a unique group of series PV cells, and overlapping bypass diodes, in which the diodes are connected to mutual PV cells. Because almost all PV studies are based on non-overlapping configuration, the effects of the diodes are well understood. On the other hand, a complete analysis for the effects of the overlapped bypass diodes on the performance of the PV module has not been yet systematically disclosed. Moreover, there is still no available mathematical formulation to model such PV modules without the use of circuit simulations. This paper first derives a mathematical modeling approach to simulate overlapped PV modules and then provides a comprehensive study and analysis for the effect of overlapped bypass diodes on the electrical response of PV module under a wide variety of possible shading levels to fully understand their effects and impact. Moreover, it reveals their effects on partial shading power losses, and on the hot spot formation, which both have not yet been investigated in the literature of overlapped PV modules. Their possible negative effects on the efficiency of micro inverters are also illustrated. The results are validated both using Matlab Simulink and experimentally.

In this study, a finite element model of a micro-satellite named X-SAT was developed to perform heat transfer analysis and design a passive thermal control scheme in the form of thermal coatings, film, and paints. To start with, the modeling philosophy and computational methodology were introduced along with the suitable assumptions made. A typical thermal control scheme was proposed and implemented using SINDA/G-NEVADA software. The sensitivity of the results to the software settings was then assessed. It was observed that the limits on the ray counts for Monte Carlo simulation in RENO and VEGAS routines play a vital role in deciding reliability of the results, especially the temperature gradients within solar panels. Subsequently, two types of solar panel designs, one with all-active solar strings and other with selectively active solar strings, were examined. When the panels with all-active type of solar cell strings were adopted, heat dissipation through shunt regulators posed a challenge for thermal control. Various scenarios for the second case with high-efficiency, selectively operable solar strings were also simulated. For both case studies, a sun-tracking mode and an overhead pass-imaging operation were considered for the worst hot and cold cases. The results showed that the switchable string design was preferable in terms of operational flexibility and thermal control.

<strong class="journal-contentHeaderColor">Abstract.</strong> By accounting for surface-based light source emissions and Top-of-Atmosphere (TOA) downward lunar fluxes, we adapted the Spherical Harmonic Discrete Ordinate Method (SHDOM) 3-dimentional (RTM) radiative transfer model (RTM) to simulate nighttime 3-D TOA radiances as observed from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night-Band (DNB) onboard the Suomi-NPP satellite platform. Used previously for daytime 3D applications, new SHDOM enhancements allow for the study of the impacts of various observing conditions and aerosol properties on simulated VIIRS-DNB TOA radiances. Observations over Dakar, Senegal, were investigated for potential applications and opportunities for using observed radiances containing VIIRS-DNB &lsquo;bright pixels&rsquo; from artificial light sources to conduct aerosol retrievals. We found that using the standard deviation (STD) of such bright-pixels provided a more stable quantity for nighttime aerosol optical depth (AOD) retrievals than direct retrievals from TOA radiances. Further, both the mean TOA radiance and STD of TOA radiances over artificial sources are significantly impacted by satellite viewing angles. Light domes, the enhanced radiances adjacent to artificial light sources, are strong functions of aerosol properties and especially aerosol vertical distribution, which may be further utilized for retrieving aerosol layer height in future studies. Through inter-comparison with both day- and night-time Aerosol Robotic Network (AERONET) data, the feasibility of retrieving nighttime AODs using 3-D RTM SHDOM over artificial light sources was demonstrated. Our study shows strong potential for using artificial light sources for nighttime AOD retrievals, while also highlighting larger uncertainties in quantifying surface light source emissions. This study underscores the need for surface light emission source characterizations as a key boundary condition, which is a complex task that requires enhanced input data and further research. We demonstrate how quality-controlled nighttime light data from the NASA&rsquo;s Black Marble product suite could serve as a primary input into estimations of surface light source emissions for nighttime aerosol retrievals.

<strong class="journal-contentHeaderColor">Abstract.</strong> By accounting for surface-based light source emissions and Top-of-Atmosphere (TOA) downward lunar fluxes, we adapted the Spherical Harmonic Discrete Ordinate Method (SHDOM) 3-dimentional (RTM) radiative transfer model (RTM) to simulate nighttime 3-D TOA radiances as observed from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night-Band (DNB) onboard the Suomi-NPP satellite platform. Used previously for daytime 3D applications, new SHDOM enhancements allow for the study of the impacts of various observing conditions and aerosol properties on simulated VIIRS-DNB TOA radiances. Observations over Dakar, Senegal, were investigated for potential applications and opportunities for using observed radiances containing VIIRS-DNB &lsquo;bright pixels&rsquo; from artificial light sources to conduct aerosol retrievals. We found that using the standard deviation (STD) of such bright-pixels provided a more stable quantity for nighttime aerosol optical depth (AOD) retrievals than direct retrievals from TOA radiances. Further, both the mean TOA radiance and STD of TOA radiances over artificial sources are significantly impacted by satellite viewing angles. Light domes, the enhanced radiances adjacent to artificial light sources, are strong functions of aerosol properties and especially aerosol vertical distribution, which may be further utilized for retrieving aerosol layer height in future studies. Through inter-comparison with both day- and night-time Aerosol Robotic Network (AERONET) data, the feasibility of retrieving nighttime AODs using 3-D RTM SHDOM over artificial light sources was demonstrated. Our study shows strong potential for using artificial light sources for nighttime AOD retrievals, while also highlighting larger uncertainties in quantifying surface light source emissions. This study underscores the need for surface light emission source characterizations as a key boundary condition, which is a complex task that requires enhanced input data and further research. We demonstrate how quality-controlled nighttime light data from the NASA&rsquo;s Black Marble product suite could serve as a primary input into estimations of surface light source emissions for nighttime aerosol retrievals.

<strong class="journal-contentHeaderColor">Abstract.</strong> By accounting for surface-based light source emissions and Top-of-Atmosphere (TOA) downward lunar fluxes, we adapted the Spherical Harmonic Discrete Ordinate Method (SHDOM) 3-dimentional (RTM) radiative transfer model (RTM) to simulate nighttime 3-D TOA radiances as observed from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night-Band (DNB) onboard the Suomi-NPP satellite platform. Used previously for daytime 3D applications, new SHDOM enhancements allow for the study of the impacts of various observing conditions and aerosol properties on simulated VIIRS-DNB TOA radiances. Observations over Dakar, Senegal, were investigated for potential applications and opportunities for using observed radiances containing VIIRS-DNB &lsquo;bright pixels&rsquo; from artificial light sources to conduct aerosol retrievals. We found that using the standard deviation (STD) of such bright-pixels provided a more stable quantity for nighttime aerosol optical depth (AOD) retrievals than direct retrievals from TOA radiances. Further, both the mean TOA radiance and STD of TOA radiances over artificial sources are significantly impacted by satellite viewing angles. Light domes, the enhanced radiances adjacent to artificial light sources, are strong functions of aerosol properties and especially aerosol vertical distribution, which may be further utilized for retrieving aerosol layer height in future studies. Through inter-comparison with both day- and night-time Aerosol Robotic Network (AERONET) data, the feasibility of retrieving nighttime AODs using 3-D RTM SHDOM over artificial light sources was demonstrated. Our study shows strong potential for using artificial light sources for nighttime AOD retrievals, while also highlighting larger uncertainties in quantifying surface light source emissions. This study underscores the need for surface light emission source characterizations as a key boundary condition, which is a complex task that requires enhanced input data and further research. We demonstrate how quality-controlled nighttime light data from the NASA&rsquo;s Black Marble product suite could serve as a primary input into estimations of surface light source emissions for nighttime aerosol retrievals.

<strong class="journal-contentHeaderColor">Abstract.</strong> By accounting for surface-based light source emissions and Top-of-Atmosphere (TOA) downward lunar fluxes, we adapted the Spherical Harmonic Discrete Ordinate Method (SHDOM) 3-dimentional (RTM) radiative transfer model (RTM) to simulate nighttime 3-D TOA radiances as observed from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night-Band (DNB) onboard the Suomi-NPP satellite platform. Used previously for daytime 3D applications, new SHDOM enhancements allow for the study of the impacts of various observing conditions and aerosol properties on simulated VIIRS-DNB TOA radiances. Observations over Dakar, Senegal, were investigated for potential applications and opportunities for using observed radiances containing VIIRS-DNB &lsquo;bright pixels&rsquo; from artificial light sources to conduct aerosol retrievals. We found that using the standard deviation (STD) of such bright-pixels provided a more stable quantity for nighttime aerosol optical depth (AOD) retrievals than direct retrievals from TOA radiances. Further, both the mean TOA radiance and STD of TOA radiances over artificial sources are significantly impacted by satellite viewing angles. Light domes, the enhanced radiances adjacent to artificial light sources, are strong functions of aerosol properties and especially aerosol vertical distribution, which may be further utilized for retrieving aerosol layer height in future studies. Through inter-comparison with both day- and night-time Aerosol Robotic Network (AERONET) data, the feasibility of retrieving nighttime AODs using 3-D RTM SHDOM over artificial light sources was demonstrated. Our study shows strong potential for using artificial light sources for nighttime AOD retrievals, while also highlighting larger uncertainties in quantifying surface light source emissions. This study underscores the need for surface light emission source characterizations as a key boundary condition, which is a complex task that requires enhanced input data and further research. We demonstrate how quality-controlled nighttime light data from the NASA&rsquo;s Black Marble product suite could serve as a primary input into estimations of surface light source emissions for nighttime aerosol retrievals.

Characterization of solar photovoltaic modules powered by artificial light for use as a source for smart sensors

Shadow or partial shading is a bad phenomenon that affects the performance of photovoltaic (PV) systems in producing energy. Shadows can be caused by moving clouds, building shadows, tree shadows, bird droppings or dust covering the surface of solar panels. Therefore, this study was conducted to determine the effect of installing bypass diode on the output power of a partially closed solar panel based on three configurations of the solar module arrangement namely, a configuration without using bypass diode, two solar modules with one bypass diode, and one solar module with one bypass diode. Furthermore, the three configurations were tested with a shadow pattern scenario is 12.5% to 100% of solar panel area using Matlab software. The result shows the I-V and P-V characteristics when experiencing shading 12.5% - 100%. The peak power value or maximum power value of the one solar module configuration with one bypass diode is greater than the two solar module configuration with one bypass diode and the configuration without using a bypass diode. Different from shadow conditions 100% the effect of installing bypass diode on the configuration of two solar modules with one bypass diode and the configuration of one solar module with one bypass diode the resulting power is the same as the configuration without using a bypass diode, which is 179.2 W.

In this work, we demonstrate that partial shading of one solar cell in a state-of-the-art monocrystalline photovoltaic module with three bypass diodes results in hot cells with critical peak temperatures of 164 $^\circ$ C. We examine two solar modules in the IEC 61215-2 MQT 09 hot-spot endurance test, one with 367.3 W $_\text{P}$ featuring 72 full-cells and the other with 388.6 W $_\text{P}$ featuring 144 half-cells. For the solar module with 72 solar cells, we measure a maximum temperature of 164 $^\circ$ C, which results in a degradation of the encapsulation material and increases the risk of solar module failure. The high temperature results from the hot cell effect due to the power dissipation in the reverse-biased solar cell caused by partial shading. Our experiments show that the half-cell solar module is advantageous in terms of solar cell shading compared to the full-cell solar module. Although the half-cell solar module has a higher power output than the full-cell solar module, we measure a cooler peak temperature of 150 $^\circ$ C. However, under certain shading conditions, the half-cell solar module can exhibit similar temperatures as the full-cell solar module. Based on our experimental results, we develop an electrical and a thermal model to predict the temperature of novel high-power solar modules with solar cells from larger silicon wafer formats in case of partial cell shading. Our predictions consider the trends of further increasing solar cell and module efficiencies, larger silicon wafer formats, and larger solar modules. We simulate a maximum peak temperature of 176 $^\circ$ C at the solar module's surface, which significantly increases the risk of solar module failure. Our results show that new high-power solar modules employing solar cells that are made from larger silicon wafer formats need a new protection against overheating. Three bypass diodes per solar module are no longer sufficient.

Systemic acquired resistance (SAR) is effectively inducible in greenhouse and certain artificial light sources cause non-optimal growth of tobacco plants. Therefore, the morphological characteristics, local and systemic resistance response of N. tabacum cv. ‘Xanthi’ nc plants (harbouring NN resistance genes) to tobacco mosaic virus (TMV) infection under three artificial light sources with different spectral distribution were compared with greenhouse conditions. Statistical analysis of data was carried out by R package (R Core Team, 2015). Generally, artificial light sources (especially fluorescent tube, and halogen lamp) decreased the local resistance response and caused substantial morphological and developmental differences as compared to greenhouse conditions when plants were kept during their entire life (lifelong experimental regime) under these conditions. On the contrary, no or much less differences were found when plants were transferred from greenhouse to artificial light sources only at six leaf stage (short experimental regime). While induction of systemic acquired resistance (SAR) frequently decreased TMV lesion size by about 50-60% under greenhouse conditions, two of the three artificial light sources, fluorescent tube and halogen lamp were substantially and significantly less effective under short experimental regime conditions (25-35%). A metal halide light source with similarity to sunshine’s spectral distribution, however, partially mimicked the effect of greenhouse conditions indicating the importance of light spectrum among other factors in SAR induction and prevention of distorted growth of plants. Consequently, the optimization of the effect of artificial light sources is an important factor in experimental design studying signal transduction and biochemistry of SAR.

One of the more common operational problems in a solar PV system string is the open circuiting of one or more diodes. Open circuit conditions are often created in solar PV strings by mechanical failure of circuit continuity over a period of time or else due to transient conditions like shadow effects which affect one or more cells in the string This affects the reliability of the system. The reliability of a solar photovoltaic (SPV) string can be modified by the use of bypass diodes across affected cells suffering an open circuit. Cells in the string that are enclosed between the ends of the bypass diode, if affected, will be bypassed and the chances of power continuity will be improved. In this paper, we attempt reliability evaluation of a single string of 6 solar PV cells in series using a single bypass diode that can enclose a variable number of cells of the string between its ends. We assume that only one cell is open circuited in the string. Monte Carlo simulations are used to evaluate the LOLP of the string with different bypass diode configurations. Next, we introduce a second bypass diode across the remaining cells not under the influence of the first bypass diode. The object is to examine if any improvements in the system reliability result. The results of the study appear to indicate that both types of bypass diode configurations result in almost identical reliability estimates although some configurations may prove to be better in terms of the LOLP estimates. The evaluation is done for three levels of load i.e. 90%, 80% and 70% of the rated power delivery of the string.

Indoor bifacial perovskite photovoltaics: Efficient energy harvesting from artificial light sources

The three main tasks of modern lighting design are to support the visual performance, satisfy color emotion (color quality), and promote positive non-visual outcomes. In view of large-scale applications, the use of simple and inexpensive RGB color sensors to monitor related visual and non-visual illumination parameters seems to be of great promise for the future development of human-centered lighting control systems. In this context, the present work proposes a new methodology to assess the circadian effectiveness of the prevalent lighting conditions for daylight and artificial light sources in terms of the physiologically relevant circadian stimulus (CS) metric using such color sensors. In the case of daylight, the raw sensor readouts were processed in such a way that the CIE daylight model can be applied as an intermediate step to estimate its spectral composition, from which CS can eventually be calculated straightforwardly. Maximal CS prediction errors of less than 0.0025 were observed when tested on real data. For artificial light sources, on the other hand, the CS approximation method of Truong et al. was applied to estimate its circadian effectiveness from the sensor readouts. In this case, a maximal CS prediction error of 0.028 must be reported, which is considerably larger compared to daylight, but still in an acceptable range for typical indoor lighting applications. The use of RGB color sensors is thus shown to be suitable for estimating the circadian effectiveness of both types of illumination with sufficient accuracy for practical applications.