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Coupling sky images with radiative transfer models: a new method to estimate cloud optical depth
摘要： A method for retrieving cloud optical depth (τc) using a UCSD developed ground-based sky imager (USI) is presented. The radiance red–blue ratio (RRBR) method is motivated from the analysis of simulated images of various τc produced by a radiative transfer model (RTM). From these images the basic parameters affecting the radiance and red–blue ratio (RBR) of a pixel are identified as the solar zenith angle (θ0), τc, solar pixel angle/scattering angle (?s), and pixel zenith angle/view angle (?z). The effects of these parameters are described and the functions for radiance, Iλ (τc, θ0, ?s, ?z), and RBR(τc, θ0, ?s, ?z) are retrieved from the RTM results. RBR, which is commonly used for cloud detection in sky images, provides non-unique solutions for τc, where RBR increases with τc up to about τc = 1 (depending on other parameters) and then decreases. Therefore, the RRBR algorithm uses the measured I meas (?s, ?z), in addition to RBRmeas (?s, ?z), to obtain a unique solution for τc. The RRBR method is applied to images of liquid water clouds taken by a USI at the Oklahoma Atmospheric Radiation Measurement (ARM) program site over the course of 220 days and compared against measurements from a microwave radiometer (MWR) and output from the Min et al. (2003) method for overcast skies. τc values ranged from 0 to 80 with values over 80, being capped and registered as 80. A τc RMSE of 2.5 between the Min et al. (2003) method and the USI are observed. The MWR and USI have an RMSE of 2.2, which is well within the uncertainty of the MWR. The procedure developed here provides a foundation to test and develop other cloud detection algorithms.
关键词： sky imager,cloud optical depth,solar forecasting,radiative transfer model,red–blue ratio
更新于2025-09-04 15:30:14
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Photometric magnetic-activity metrics tested with the Sun: application to <i>Kepler</i> M dwarfs
摘要： The Kepler mission has been providing high-quality photometric data leading to many breakthroughs in the exoplanet search and in stellar physics. Stellar magnetic activity results from the interaction between rotation, convection, and magnetic field. Constraining these processes is important if we want to better understand stellar magnetic activity. Using the Sun, we want to test a magnetic activity index based on the analysis of the photometric response and then apply it to a sample of M dwarfs observed by Kepler. We estimate a global stellar magnetic activity index by measuring the standard deviation of the whole time series, Sph. Because stellar variability can be related to convection, pulsations or magnetism, we need to ensure that this index mostly takes into account magnetic effects. We define another stellar magnetic activity index as the average of the standard deviation of shorter subseries which lengths are determined by the rotation period of the star. This way we can ensure that the measured photometric variability is related to starspots crossing the visible stellar disc. This new index combined with a time-frequency analysis based on the Morlet wavelets allows us to determine the existence of magnetic activity cycles. We measure magnetic indexes for the Sun and for 34 M dwarfs observed by Kepler. As expected, we obtain that the sample of M dwarfs studied in this work is much more active than the Sun. Moreover, we find a small correlation between the rotation period and the magnetic index. Finally, by combining a time-frequency analysis with phase diagrams, we discover the presence of long-lived features suggesting the existence of active longitudes on the surface of these stars.
关键词： M dwarfs,Solar activity,Stellar activity,Asteroseismology
更新于2025-09-04 15:30:14
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Effect of TiO<sub>2</sub>-rGO heterojunction on electron collection efficiency and mechanical properties of fiber-shaped dye-sensitized solar cells
摘要： It is demonstrated that the incorporation of graphene materials into oxide-based photoanodes can greatly increase the photoelectrochemical devices’ performances. In this work, reduced graphene oxide (rGO) has been incorporated into P25-TiO2 nanoparticle (NP) based photoanodes for fiber-shaped dye-sensitized solar cells (FDSSCs). Results showed that the rGO nanosheets have been uniformly dispersed within P25 nanoparticle layers. And as expected, the incorporation of rGO increased the FDSSCs’ short current density from 8.344 to 12.935 mA cm-2, open circuit voltage from 0.775 to 0.798 V, resulting into their power conversion efficiency (PCE) from 3.940% to 5.364%. This large increasement in PCE could be due to two aspects, i.e., the improved electron transport properties via rGO and the enhanced separation of photogenerated hole-electron pairs via rGO-TiO2 heterojunction. Furthermore, the incorporation of rGO can also make the FDSSCs have good mechanical properties, which is very crucial for their future applications in smart wearable electronics. In addition, based on our analysis, a possible rGO/multi-NP coupling enhancement mechanism was proposed.
关键词： fiber-shape,heterojunction,dye-sensitized solar cells,titanium dioxide,reduce graphene oxide (rGO)
更新于2025-09-04 15:30:14
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Properties of Co‐Evaporated RbInSe <sub/>2</sub> Thin Films
摘要： The formation of an Rb-containing In-Se compound at the surface of Cu(In, Ga)Se2 (CIGS) thin films is assumed to be part of the mechanism of RbF post-deposition treatments (PDTs) performed on these absorber layers. Alkali-PDTs have acquired attention lately as they significantly enhance the efficiency of CIGS solar cells. In this contribution the formation of various phases during the RbF-PDT has been investigated. The results indicate that RbInSe2 is the most probable phase to form. Combining theoretical and experimental investigations, fundamental properties of a thermally co-evaporated RbInSe2 thin film are reported in order to serve as reference values in further studies.
关键词： CIGSe thin film solar cells,crystal structure,RbInSe2 deposition,defect calculation,electronic structure
更新于2025-09-04 15:30:14
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Analysis of stakeholder roles and the challenges of solar energy utilization in Iran
摘要： Growing energy demand, rising greenhouse gas emissions and the depletion of fossil fuels necessitates the development of renewable energy sources. In order to improve renewable energy utilization, it is necessary to determine the most important factors influencing energy strategy. The energy system of Iran is highly dependent on fossil fuels; however, Iran has a high potential for solar energy development and several policies are being pursued by the government to develop power generation by renewable energy resources. This study presents and discusses several important parameters of energy policy and security which make the installation of photovoltaic (PV) systems crucial for the future. Installation of solar PV will improve energy security, foster job creation and reduce environmental problems. It also introduces and investigates those institutions and organizations involved in developing renewable energies, especially solar energy. These include the Ministry of Energy and universities, both of which play key roles in the development of solar energy.
关键词： Iran,Triple Helix,energy policy,solar energy
更新于2025-09-04 15:30:14
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The reliability of solar energy generating system with inverters in series under common cause failure
摘要： With the shortage of nonrenewable energy, renewable energy resources play an important role in practice. One of the most promising renewable energy is viewed as solar energy resources due to its cleanliness and the inexhaustibility. However, the quantitative assessment method on the reliability of a complicated solar energy generating system has been a considerable challenge. In this paper, we propose a Markov model to imitate a solar energy generating system with inverters in series, unreliable by-pass change-over switches, and common cause failure. Employing the renewal point technique and the Semi-Markov process theory, we build the quantitative reliability models of the system. Further, we develop a new algorithm to obtain the explicit form solution of reliability indices. An example illustrates that the proposed models and the algorithm are e?cient and concise.
关键词： Common cause failure,Switch failure,Micro-inverters,Reliability,Solar energy generating system
更新于2025-09-04 15:30:14
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Effective quenching and excited-state relaxation of a Cu(I) photosensitizer addressed by time-resolved spectroscopy and TDDFT calculations
摘要： Homogenous photocatalytic systems based on copper photosensitizers are promising candidates for noble metal free approaches in solar hydrogen generation. To improve their performance, a detailed understanding of the individual steps is needed. Here, we study the interaction of a heteroleptic copper (I) photosensitizer with an iron catalyst by time-resolved spectroscopy and ab initio calculations. The catalyst leads to rather efficient quenching of the 3MLCT state of the copper complex, with a bimolecular rate being about three times smaller than the collision rate. Using control experiments with methyl viologen, an appearing absorption band is assigned to the oxidized copper complex demonstrating that an electron transfer from the sensitizer to the iron catalyst occurs and the system reacts along an oxidative pathway. However, only about 30% of the quenching events result in an electron transfer while the other 70% experience deactivation indicating that the photocatalytic performance might suffer from geminate recombination.
关键词： Solar hydrogen generation,Time-resolved spectroscopy,Ab initio calculations,Copper photosensitizers,Electron transfer
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC) - Kota Kinabalu, Malaysia (2018.10.7-2018.10.10)] 2018 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC) - Mitigating the effect of partial shading by triple-tied configuration of PV modules
摘要： Partial shading is the phenomenon, which occurs when PV modules receive irregular irradiance on a PV array. Due to that, shaded PV modules are bypassed by diodes and significant reduction in power is experienced. To counter such problem, PV modules are connected in different configuration to provide alternative path for current to flow, so that the effect of partial shading is lessened and power attainment is improved. A comprehensive literature review suggests that several PV configurations are proposed namely simple-series (SS), parallel (P), series-parallel (SP), total-cross-tied (TCT), bridge-linked (BL) and honey-comb (HC). In this paper, a comprehensive review is presented to highlight the benefits and limitations of each scheme. To mitigate the limitation of other approaches, a new configuration named triple-tied (TT) is proposed. Several experiments are carried out using both MATLAB Simulink and hardware implementation to validate the performance of proposed configuration. Eleven different partial shading cases are used to analyze the output characteristics. Based on the results, the proposed TT configuration outperforms other PV configurations except TCT. However, in TT wiring connections are significantly reduced compared to TCT which makes it favorable in many large-scale PV applications.
关键词： PV Configuration,Maximum Power,Partial Shading,Solar,PV,Irradiance Mismatch
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE Energy Conversion Congress and Exposition (ECCE) - Portland, OR, USA (2018.9.23-2018.9.27)] 2018 IEEE Energy Conversion Congress and Exposition (ECCE) - Supervisory Control Architecture for Standalone Solar Photo- Voltaic Power Generation System
摘要： Solar Photo-Voltaic (SPV) based power generation system is an attractive alternative to diesel based counterparts for standalone or dual-mode AC micro-grids. Typically, a suitably sized battery-based energy storage system is required alongside PV that supplies power when solar energy and the grid are unavailable. In this work, a supervisory control architecture is proposed for the operation of such an SPV micro-grid system with battery storage. Three sub-modes of operation of the SPV converter, namely, Charger (CHGR), Maximum Power Point Tracking (MPPT) and Virtual Battery Emulation (VBE) modes are deployed to suitably control the system and manage power ?ow under varying conditions of battery voltage, load power, and solar insolation. The novel VBE mode emulates a parallel battery bank with the aid of the SPV converter and its appropriate control. This reduces the battery discharge and thus ensuring the extension of its cycle life. A ?nite state machine is presented that facilitates digital implementation of the proposed supervisory control scheme. Experimental results of various modes on a 1.2 kW SPV system prototype are presented for performance verification.
关键词： battery charging,buck converter,MPPT,Solar PV,battery emulation,supervisory control
更新于2025-09-04 15:30:14
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Efficiency of evacuated tube solar collector using WO3/Water nanofluid
摘要： The thermal performance of the evacuated tube solar collector with WO3/Water Nanofluid was studied in this paper. The WO3 nanoparticles were spherical with 90 nm diameter Three different volume fraction of WO3 nanoparticles of 0.014%, 0.028%, and0.042% were examined at several mass flux rates of 0.013 kg/s.m2, 0.015 kg/s.m2 and 0.017 kg/s.m2. The stability of the nanofluid was checked. Experiments were performed in Budapest, Hungary on the latitude of 47°280N and longitude of 19°030E. The results showed that the temperature difference of the fluid increased up to 21% with adding WO3 nanoparticles. The maximum heat gain at the solar irradiance of 900 W/m2 was raised up to 23% when WO3 nanoparticles were used. The proportion of the growth of the heat removable factor for nanofluids comparing to water at the same mass flux rate is between 1.05 and 1.16. The results indicated that the efficiency of the evacuated tube solar collector enhanced with more nanoparticles added. The thermal-optical efficiency of the evacuated tube solar collector reached 72.8%.
关键词： WO3/Water nanofluid,Solar collector,Efficiency,Evacuated tube
更新于2025-09-04 15:30:14