Effects of geometrical parameters of a dish concentrator on the optical performance of a cavity receiver in a solar dish‐Stirling system

Dish‐Stirling concentrated solar power (DS‐CSP) system is a complex system for solar energy‐thermal‐electric conversion. The dish concentrator and cavity receiver are optical devices for collecting the solar energy in DS‐CSP system; to determine the geometric parameters of dish concentrator is one of the important steps for design and development of DS‐CSP system, because it directly affects the optical performance of the cavity receiver. In this paper, the effects of the geometric parameters of a dish concentrator including aperture radius, focal length, unfilled radius, and fan‐shaped unfilled angle on optical performance (ie, optical efficiency and flux distribution) of a cavity receiver were studied. Furthermore, the influence of the receiver‐window radius of the cavity receiver and solar direct normal irradiance is also investigated. The cavity receiver is a novel structure that is equipped with a reflecting cone at bottom of the cavity to increases the optical efficiency of the cavity receiver. Moreover, a 2‐dimensional ray‐tracking program is developed to simulate the sunlight transmission path in DS‐CSP system, for helping understanding the effects mechanism of above parameters on optical performance of the cavity receiver. The analysis indicates that the optical efficiency of the cavity receiver with and without the reflecting cone is 89.88% and 85.70%, respectively, and former significantly increased 4.18% for 38 kW XEM‐Dish system. The uniformity factor of the flux distribution on the absorber surface decreases with the decreases of the rim angle of the dish concentrator, but the optical efficiency of the cavity receiver increases with the decreases of the rim angle and the increase amplitude becomes smaller and smaller when the rim angle range from 30° to 75°, So the optical efficiency and uniformity factor are conflicting performance index. Moreover, the unfilled radius has small effect on the optical efficiency, while the fan‐shaped unfilled angle and direct normal irradiance both not affect the optical efficiency. In addition, reducing the receiver‐window radius can improve the optical efficiency, but the effect is limited. This work could provide reference for design and optimization of the dish concentrator and establishing the foundation for further research on optical‐to‐thermal energy conversion.     

Experimental analysis of a two‐axis tracking system for solar parabolic dish collector

In this paper, an attempt has been made to develop a two‐axis tracking system for solar parabolic dish concentrator and experimentally evaluated the performance of the tracking system. In this proposed design, the sensor design uses the illumination produced by the convex lens on the apex of a pyramid to align the dish in‐line with the sun. The change in incident angle of the solar rays on the lens surface shifts the area of illumination from the apex of the pyramid towards its faces. Photodiodes placed on the faces of the pyramid are used as the sensitive elements to detect the movement of the sun. The sensor output is fed to a microcontroller‐based system to drive the stepper motor on the basis of the programmed algorithm such that it receives normal incidence of sunlight on the sensor. To evaluate the performance of the proposed system, a conventional available 1‐W photovoltaic (PV) panel is placed at the focal point to measure the short circuit current and open circuit voltage. With respect to the conventional solar PV panel, it is observed that the positioning accuracy of the proposed tracking system enhances the short circuit current of 0.11 A by 86%. Thus, the proposed tracking system can be used in a stand‐alone parabolic dish with concentrating PV module as the focal point for further studies.     

Experimental investigation of ice‐chamber for melting of ice based on Scheffler solar concentrator for high altitude regions

This experimental analysis was performed with the aim to melt the ice into hot water at very high altitude regions such as Leh Ladakh. Three different designs of ice‐chamber were used to melt the ice with direct heating in minimum time. The radiations were focused on the receiver with the help of 1 m² Scheffler solar concentrator exposed to the atmospheric situations of NIT Kurukshetra. The Scheffler solar concentrator was fabricated with fiber‐reinforced plastic material. The fabrication process is discussed in detail. The results obtained from the design showed that the ice frozen at ?5°C completely melted, converting into water. The maximum temperature of water attained in the ice‐chamber with receiver 1 (circular plate with fins), 2 (CPC with fins), and 3 (copper crucible) was 57.7°C, 64.3°C, and 67.4°C, respectively.     

Passive thermal management of the lithium‐ion battery unit for a solar racing car

In this study, a three‐dimensional numerical model is developed to investigate the thermal and electrical characteristics of 18 650 lithium‐ion battery cells that are used in the solar racing car of Dokuz Eylül University, i.e., SOLARIS. The Newman, Tiedemann, Gu, and Kim (NTGK) battery model of ANSYS Fluent software is implemented to resolve the coupled multiphysics problem. In the analysis, only the discharging period of the battery is considered. Before going through parametric studies under variable weather conditions, time‐wise variations of the cell temperature and the battery voltage are evaluated both experimentally and numerically under two different ambient conditions of 0°C and 25°C. Comparative results revealed that reasonable predictions are achieved with the current battery model, and the difference between the predicted battery surface temperature and experimental data is less than 1°C. Following the model validation, the battery performance is numerically examined by applying the battery model to a real race procedure of SOLARIS. Phase change materials (PCMs) with different amounts and melting temperatures are implemented around the batteries, and transient analyses are conducted under real weather conditions. The current study aims to keep the battery temperature of a solar racing car above a certain limit to prevent the overcooling and maintain higher charging capacity. Implementation of PCM with a melting temperature of 26°C yields 3.15% of capacity increment, and such a performance improvement corresponds to 15.51 Wh of extra energy that can be extracted from an individual battery.     

A closed‐loop proposal for hydrogen generation using steel waste and a prototype solar concentrator

An economically viable and environmental‐friendly method of generating PEM grade hydrogen has been proposed and is by the reaction of certain metals with steam, appropriately called ‘metal–steam reforming’—MSR. The drawbacks of conventional processes (hydrogen and carbothermic reduction schemes) are overcome by resorting to solution‐based reduction schemes and are made economically feasible using iron oxides from steel industry's mill‐scale waste. A novel aqueous‐based room temperature technique using sodium borohydride (NaBH₄) as the reducing agent has been developed that produces highly active nanoscale iron particles (～40 nm). By using hydrazine as an inexpensive and, compared with NaBH₄, more stable reductant, body centered cubic iron particles with ～5 nm edges were obtained via solvothermal process under mild conditions from acid digested mill‐scale waste. The nanoscale zerovalent iron (nZVI) powder showed improved kinetics and greater propensity for hydrogen generation than the coarser microscale iron. The rate constants for the MSR were obtained for all the reduction schemes employed in this work and are given by k_hydrogen=0.0158 min^?1 k_carbon=0.0248 min^?1 k_{sodiumborohydride}=0.0521 min^?1 and k_hydrazine=0.1454 min^?1, assuming first order kinetics. Another innovative effort converted the magnetite waste directly into nZVI under solvothermal conditions, thus obviating the sluggish and time‐consuming acid dissolution step. This particular aspect has significant ramification in terms of time and cost of making the iron precursor. To initiate and sustain the somewhat endothermic MSR process, a solar concentrator consisting of a convex polyacrylic bowl with reflective aluminum coating was fabricated and evaluated. This unique combination of mill‐scale waste as iron source, hydrazine as reductant, mild process conditions and solar energy as the MSR actuator obviates several drawbacks plaguing the grand scheme of producing and delivering pure and humidified H₂ to a PEMFC stack. Copyright © 2008 John Wiley & Sons, Ltd.     

Mirror rearrangement optimization for uniform flux distribution on the cavity receiver of solar parabolic dish concentrator system

The nonuniform and high‐gradient solar radiation flux on the absorber surface of solar dish concentrator/cavity receiver (SDCR) system will affect its operational reliability and service lifetime. Therefore, homogenization of the flux distribution is critical and important. In this paper, 2 mirror rearrangement strategies and its optimization method by combining a novel ray tracing method and the genetic algorithm are proposed to optimize the parabolic dish concentrator (PDC) so as to realize the uniform flux distribution on the absorber surface inside the cavity receiver of SDCR system. The mirror rearrangement strategy includes a mirror rotation strategy and mirror translation strategy, which rotate and translate (along the focal axis) each mirror unit of the PDC to achieve multipoint aiming, respectively. Firstly, a correlation model between the focus spot radius and mirror rearrangement parameters is derived as constraint model to optimize the PDC. Secondly, a novel method named motion accumulation ray‐tracing method is proposed to reduce the optical simulation time. The optical model by motion accumulation ray‐tracing method and optimization model of SDCR system are established in detailed, and then, an optimization program by combining a ray‐tracing code and genetic algorithm code in C++ is developed and verified. Finally, 3 typical cavity receivers, namely, cylindrical, conical, and spherical, are taken as examples to fully verify the effectiveness of these proposed methods. The results show that the optimized PDC by mirror rearrangement strategies can not only greatly improve the flux uniformity (ie, reduce the nonuniformity factor) and reduce the peak local concentration ratio of the absorber surface but also obtain excellent optical efficiency and direct useful energy ratio. A better optimization results when the PDC is optimized by mirror rotation strategy at aperture radius of 7.0 m, focal length of 6.00 m, and ring number of 6; the nonuniform factor of the cylindrical, conical, and spherical cavity receivers is greatly reduced from 0.63, 0.67, and 0.45 to 0.18, 0.17, and 0.26, respectively; the peak local concentration ratio is reduced from 1140.00, 1399.00, and 633.30 to 709.10, 794.00, and 505.90, respectively; and the optical efficiency of SDCR system is as high as 92.01%, 92.13%, and 92.71%, respectively. These results also show that the dish concentrator with same focal length can match different cavity receivers by mirror rearrangement and it can obtain excellent flux uniformity.     

Reduced graphene oxide–titania nanocomposite‐modified photoanode for efficient dye‐sensitized solar cells

We report the successful application of reduced graphene oxide–titania (rGO–TiO₂) nanocomposite as an efficient photoanode for dye‐sensitized solar cell (DSSC). The DSSC assembled with the rGO–TiO₂‐modified photoanode demonstrated an enhanced solar to electrical energy conversion efficiency of 4.74% compared with the photoanode of DSSC composed with unmodified TiO₂ (2.19%) under full sunlight illumination (100 mW/cm², AM 1.5G) as a result of the better charge collection efficiency of rGO, which reduced the back electron transfer process. Influence of the rGO content on the overall efficiency was also investigated, and the optimal rGO content for TiO₂ was 0.5 mg. Further, the modification of rGO–TiO₂ on the compact layer TiO₂ surface led to an increase in efficiency to 5.83%. The superior charge collection and enhanced solar energy conversion efficiency of the rGO–TiO₂ nanocomposite makes it to be used as a promising alternative to conventional photoanode‐based DSSCs. Copyright © 2015 John Wiley & Sons, Ltd.     

Assessment of a low-cost gold-free metallization for III–V high concentrator solar cells

A gold-free metallization is proposed to be used as the grid contact in III–V concentrator solar cells. This metallization is based on the Cu/Ge system which has been reported to attain very low specific contact resistances on n-GaAs. In this letter, we show that metal layers with low resistivity (13 μΩ cm) can be obtained if the copper content in the alloy is around 28% in weight for a wide range of annealing temperatures (400–450 °C). Finally, this metallization has been used to manufacture single-junction GaAs high concentrator solar cells. Efficiencies of 26.2% at 1000 suns have been reached.     

Photoresponse of novel mixed metal chalcogenide MoSb2‐xCuxSe4/CdS thin film solar cells fabricated by CBD method using citric acid

In this present work, novel MoSb_2‐xCu_xSe₄ thin films were prepared for different copper concentrations (x = 0.0, 0.1, 0.2 and 0.3 M) by a simple chemical bath deposition method. XRD patterns revealed the phase conversion of orthorhombic Sb₂Se₃ into Cu₃SbSe₃ by the incorporation of copper content with successive peak shift towards higher angles. Average crystallite was found to be 8, 17 and 25 nm for 0.1, 0.2 and 0.3 M Cu content, respectively. Fourier transform infrared spectra witnessed the presence of functional groups in citric acid and metal oxide vibrations. Field emission scanning electron microscope analysis picturized the grain size growth with respect to Cu content. UV–Vis analysis showed higher absorption in the visible region, and band gap values were found to be 2.08 ? 1.69 eV. Hall effect studies confirm the p‐type nature of the material. The photocurrent analysis shows higher photoconversion efficiency of 1.196% for 0.3 M copper content. Copyright © 2017 John Wiley & Sons, Ltd.     

Novel Cu–carbon nanofiber composites for the counter electrodes of dye‐sensitized solar cells

Copper (Cu)‐catalyzed carbon nanofibers (CNFs) were used as an alternative of the conventional platinum‐noble‐metal‐based catalyst at the counter electrode (CE) of a dye‐sensitized solar cell (DSSC). The CNFs were grown on activated carbon microfiber powder (PACF) using chemical vapor deposition (CVD) and the Cu nanoparticles (NPs). The Cu NPs served simultaneous roles: (i) as the CVD catalyst for the growth of the CNFs; (ii) as an enhancer of the electrode conductivity; and (iii) as a catalyst for the reduction reaction. The Cu‐CNF composite was applied as a thin layer on the fluorine‐doped tin oxide glass using the simple doctor blade method. The prepared Cu‐NP‐dispersed PACF/CNF composite was characterized using various spectroscopic techniques, including scanning electron microscopy, Fourier transform infrared ray, X‐ray diffraction, Raman spectroscopy, and transmission electron microscopy. The electrochemical tests showed that the Cu‐PACF/CNFs had a high electrocatalytic activity and low charge transfer resistance (1.26 Ω cm²), using the cyclic voltammetry and electrochemical impedance spectroscopy measurements. The DSSC fabricated with Cu‐PACFs/CNFs exhibited a power conversion efficiency value of 4.36%, open circuit voltage of 0.75 V, short circuit current density of 11.12 mA cm^?2, and fill factor of 54%. The prepared transition metal–CNF composite was simple to develop and can potentially be used as an efficient catalyst at the CE of DSSCs. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and application of Fe3O4@nanocellulose/TiCl as a nanofiller for high performance of quasisolid‐based dye‐sensitized solar cells

In this research, to optimize the surface of the photoanode, two different types of surface coatings were used and their effects on the photovoltaic parameters were investigated. Also, to compare the two different electrolytic systems based on liquid and gel‐state electrolyte, the novel magnetic core‐shell nanocellulose/titanium chloride (Fe₃O₄@)NCs/TiCl) nanocomposite was introduced into a polymeric system as a nanofiller to decrease the crystallinity of the polymer and enhance the diffusion of triiodide ions in quasisolid‐state dye‐sensitized solar cells (QS‐DSSCs). For this purpose, Fe₃O₄@)NCs/TiCl was synthesized by coprecipitation of Fe³⁺ and Fe²⁺ ions in the presence of nanocellulose and then used as magnetic support for bonding TiCl₄ to prepare QS‐DSSCs. Containing a 10.0 wt% magnetic nanocomposite, it displayed a higher apparent diffusion coefficient (D_app) for I₃^? ions (4.10 × 10^?6 cm²/s) than the gel polymeric electrolyte (GPE) did (1.35 × 10^?6 cm²/s). GPEs were characterized using various techniques including current density‐voltage curves, AC impedance measurements, and linear sweep voltammetry (LSV). The photovoltaic values for the short‐circuit current density (J_sc), open‐circuit voltage (V_OC), and fill factor (FF) and the energy conversion efficiency (η) of the novel Fe₃O₄@NCs/TiCl nanocomposite–based QS‐DSSCs were 14.90 mA cm^?2, 0.757 V, 64%, and 7.22%, respectively.     

Novel improvements in the sensitizers of dye‐sensitized solar cells for enhancement in efficiency—a review

In the present review article, we have focused our study on the novel improvements that have been brought about in the molecular design of various sensitizers for application in dye‐sensitized solar cells (DSSCs). The sensitizers based on noble metals such as ruthenium, osmium, and rhenium showed high efficiency, but their cost and complicated synthesis restrict their wide applications. Further, to reduce the cost of fabrication of DSSCs, researchers are focusing their interest in organic sensitizers. In this context, organic dyes have offered several possibilities, as by improving their molecular structure brings about improvement in the light harvesting ability of dyes, and with the help of such dyes, optimal DSSCs have been fabricated. Further, to reduce the cost of DSSCs, researchers are also focusing on natural sensitizers such as betacyanin and anthocyanin or chlorophyll, as natural sensitizers are easy to prepare, cost effective, and environmentally friendly. With the help of these natural sensitizers, eco‐friendly and more cost‐effective DSSCs can be fabricated. Thus, we found from our study that beside metal‐based sensitizers, organic and natural sensitizers also offer a vast potential for the optimization of efficiency in DSSCs. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization of the electrical energy consumption of a building for the dimensioning of a solar‐hydrogen energy system

The photovoltaic (PV) applications where the dimensioning is effected through the daily energy balance criteria obtained by the estimation of the energy consumption depending on the power and time of use of the electrical apparatus are limited to autonomous PV systems with well‐defined end use. Applications where one would like to electrify complex end use, such as office buildings, schools, hospitals, laboratories, residential units, etc., quantifying the daily energy consumption is difficult mainly due to two aspects. First, there will be great number of a variety of electrical appliances and second the proportionate electrical consumption of each one of them is unpredictable. For this reason it is necessary to establish a methodology that permits one to quantify precisely the daily energy consumption pattern to predict the energetic functioning of the PV system whose size may be determined by this procedure. In this work we describe a methodology for the energetic quantification of the installed equipments by using a Power Quality Analyzer to obtain the historical global energy consumption, daily energy consumption (kWh day⁻¹, kVAh day⁻¹) and the energy quality for the dimensioning of the PV system. Copyright © 2009 John Wiley & Sons, Ltd.