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This paper deals with approximate analytical solutions to the two-region one-dimensional model describing the charging process of stratified thermal storage tanks with variable inlet temperature as well as momentum-induced mixing. The inlet temperature, which is allowed to increase arbitrarily except that it always remains higher than (or equal to) the temperature at the tank top, is broken down into step changes and intervals of continuous change. Assuming that each continuous interval can be approximated as a finite number of piecewise linear functions, there is admitted an analytical solution for the perfectly mixed region. Based on the principle of superposition, the temperature profiles in the plug flow region (assuming both semi-infinite and adiabatic ends) are successfully derived, in terms of well-defined functions. The effect of the end condition proves to be negligible under the practical operating conditions. For a quadratic variation of inlet temperature, the approximate solution modeled on a moderate number of pieces agrees well with the corresponding closed-form solution.

Abstract Cadmium selenide (CdSe) nanoparticles were synthesized in aqueous medium using mercaptopropionic acid (MPA) as the stabilizer at the temperature 100 °C. Air stable sodium selenite (Na2SeO3) was used as the selenium source. The synthesized particles were used to co-sensitize the TiO2 nanotubes with N3 dye. Ex-situ linker assisted method was used to sensitize the nanotubes by CdSe nanoparticles. Electrochemical anodization technique was employed to prepare TiO2 nanotubes in the presence of hydrogen fluoride (HF) as electrolyte. A solar cell was fabricated using co-sensitized TiO2 nanotubes by N3 dye/CdSe nanoparticles as the anode and platinum coated fluorine doped tin oxide (FTO) electrode as the cathode. Polysulphide ( S 2 - / S x 2 - ) mixture was used as the electrolyte. UV–Visible, SEM, AFM and TEM analysis were used to characterize the synthesized particles and TiO2 nanotubes.

Abstract Maximally concentrating collectors include the class of ideal concentrating collectors, but are a more general class offering many more practical possibilities. By evaluating such configurations using the concept of maximal flux concentration, based upon average radiation flux concentration over the acceptance angle, clear ray trace comparisons may be made between different collector configurations. These comparisons allow the most effective configuration to be selected for a given application. An example of a comparatively simple and practical two-stage concentrator having equal or better maximal performance than previous work for high rim angle primaries is given. This uses an unusual straight section of reflector and allows rays to cross from one reflector segment of the secondary to another. Versions which allow concentration up to 90% of maximal are described, as are versions achieving 80% with high collection efficiency. Use of the 1 sin θ max geometrical concentration criterion based upon aperture ratios is suggested to be inappropriate for comparisons.

Abstract The technological and economic impact of design changes in thermal energy storage of concentrated solar power (CSP) systems is assessed. It is shown that the system costs change with the types of storage tanks and also that the operation temperature is limited by the thermal properties of the thermal storage medium. In addition, the cost of energy can be substantially reduced by replacing the conventional power cycle with more advanced power cycles, such as a supercritical carbon dioxide power cycle. Using two types of thermal storage tanks and two thermal storage media, cases are generated incorporating combinations of the design options. A sensitivity analysis is used to investigate the impacts of each technological improvement. The results of this work will contribute to predicting the impact of research and improving the economics of the CSP system.

Abstract Seasonal solar thermal energy storage (SSTES) has been investigated widely to solve the mismatch between majority solar thermal energy in summer and majority heating demand in winter. To study the feasibility of SSTES in domestic dwellings in the UK, eight representative cities including Edinburgh, Newcastle, Belfast, Manchester, Birmingham, Cardiff, London and Plymouth have been selected in the present paper to study and compare the useful solar heat available on dwelling roofs and the heating demand of the dwellings. The heating demands of space and hot water in domestic dwellings with a range of overall heat loss coefficients (50 W/K, 150 W/K and 250 W/K) in different cities were calculated; then the useful heat obtained by the heat transfer fluid (HTF) flowing through tilted flat-plate solar collectors installed on the dwelling roof was calculated with varied HTF inlet temperature (30 °C, 40 °C and 50 °C). By comparing the available useful heat and heating demands, the critical solar collector area and storage capacity to meet 100% solar fraction have been obtained and discussed; the corresponding critical storage volume sizes using different storage technologies, including sensible heat water storage, latent heat storage and various thermochemical sorption cycles using different storage materials were estimated.

Abstract The cooperative effect of hybrid Au-Ag nanoparticles and organic-inorganic cathode interfacial layers to advance the power conversion efficiency (PCE) of regio regular (rr) P3HT:PCBM based polymer solar cells (PSCs) are systematically demonstrated. In this work initially, two types of plasmonic nanoparticles (NPs), namely, citrate stabilized gold (AuNPs) and silver (AgNPs) were separately synthesized and then physically blend together with three different volume ratio [AuNPs + AgNPs (25:75), AuNPs + AgNPs (50:50) and AuNPs + AgNPs (75:25)]. These three blended NP solutions were then mixed together in the PEDOT:PSS (20 v/v %) hole extraction layer (HEL) to form three new NPs doped HEL and their effect on the rr-P3HT:PCBM based PSCs were systematically analyzed. For dual organic-inorganic cathode interfacial layers, two organic hole blocking materials, BPhen and BCP were used for enhanced charge collection in combination with LiF:Al as conventional cathode electrode. The collective effect of hybrid NPs with the dual cathode interfacial layers was examined with two varying active polymer blends, rr-P3HT:PC61BM and rr-P3HT:PC71BM. It has been found that the PCE increases considerably for both the active blend systems, with PEDOT:PSS + [AuNPs:AgNPs (25:75)] + BCP:LiF:Al as the modified cathode electrode. This is due to suitable electronic energy level matching of BCP:LiF:Al and active blend with the excellent surface plasmon property of the AuNPs:AgNPs (25:75) in the UV–Visible region compared to AuNPs:AgNPs (50:50) and AuNPs:AgNPs (75:25). Devices having configuration PEDOT:PSS + [AuNPs:AgNPs (25:75)] as HEL, rr-P3HT:PC71BM as active blend and BCP:LiF:Al provided PCE, ɳmax = 5.71% with Jsc = 16.44 mA/cm2, Voc = 0.58 V, FF = 60% and device with rr-P3HT:PC61BM as active blend layer was showing as PCE, ɳmax = 5.31% with Jsc = 14.77 mA/cm2, Voc = 0.58 V and FF = 62% with the same PEDOT:PSS + [AuNPs:AgNPs (25:75)] layer and BCP:LiF:Al. These results conclusively described a very simple technique in which the cooperative effect of plasmonic hybrid metals nanoparticles and dual cathode interfacial layers outstandingly enrich the PCE and in general the complete nature of rr-P3HT:PCBM based PSCs.

Abstract A general procedure for determining the optimum geometry of a reflector-augmented solar collector which produces a desired pattern of flux-augmentation is described. The example used for illustration is a stationary collector whose winter performance is to be improved. Consideration both a flat-plate collector with a bottom reflector and one with a top reflector led to distinct differences in their optimum configuration and performance being identified. Since either systems can be used to augment winter flux, a criterion for selecting the appropriate system is given. This criterion is based on the displacement in collector tilt from latitude inclination.