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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.

Abstract Molten salts have high solidification temperatures, so they easily solidify in the receiver tube when the incident energy fluxes are very low due to clouds drifting and floating across the sky. Additional energy and time are then wasted to thaw the frozen solid with the salt freeze/thaw cycles eventually damaging the receiver. Therefore, operators need to adopt appropriate operating strategies to ensure that the salt remains molten during extended cloudy periods. The present study presents a thermo-hydraulic dynamic model of a molten salt receiver to investigate the heat transfer processes. The model is based on the Badaling 1 MWth receiver experiment with three experimental groups of tests modeled to validate the thermal hydraulic model in both the direct-filling mode and the S-type flow mode. The model results agree well with the experimental measurements with maximum relative errors of 0.4% for the outlet temperature and 0.9% for the surface temperatures. Then, a sensitivity analysis is conducted to better illustrate the flow distribution and surface temperatures, including the effects of the flow resistance, inlet temperature, cloudy duration, and valve abnormalities. Finally, the results indicate that the S-type flow mode should be used to prevent solidification for cloudy conditions.

Abstract A three-dimensional numerical model of a solar parabolic trough receiver–reactor (SPTRR) with methanol steam reforming reaction was developed. Based on this model, the characteristics of hydrodynamics, heat transfer and chemical reaction of SPTRR were studied. Also, the effects of non-uniform heat flux boundary condition, catalyst layout and mass flow rate on the performances of SPTRR were analyzed. The results showed that SPTRRs partially filled with catalyst have better comprehensive performance than those fully filled with catalyst, and the SPTRR with horizontal cylindrical segment shaped catalyst in the lower part of receiver tube is recommended to substitute the fully catalyst-filled SPTRR. The chemical energy conversion per unit pump power of the proposed partially catalyst-filled SPTRR is one order of magnitude larger than that of the fully catalyst-filled SPTRR, and the mean outer surface temperature and maximum outer surface temperature difference of the proposed partially catalyst-filled SPTRR can be as low as that of the fully catalyst-filled SPTRR, when the mass of the catalyst in the partially catalyst-filled SPTRR is 0.4 times as much as that in the fully catalyst-filled SPTRR.

Analytical method is used to obtain the geometrical shape for non-imaging secondary (NIS) mirror in the application of concentrated photovoltaic (CPV). It is discussed in beam down optical system, NIS presents advantages to eliminate dark image, to reduce the solar disc effect, to improve the uniformity of the illumination, etc. comparing to the imaging secondary. The authors have emphasized that the geometrical shape of optical components in non-imaging optics can generally be high order surfaces not restricted to the quadratic surface in imaging optics and mostly "CPC" in early developed non-imaging optics. This paper has discussed the general criteria and two practical approaches for designing NIS. We listed some of the examples in this paper to form NIS by rotating a segment of linear or quadratic or cubic curve around the central axis of primary reflector. The method to calculate the parameters of such segment is described. Although in present discussion, we are referring the usage in PV concentrator, the method is generally applied in other optical fields. (C) 2013 Elsevier Ltd. All rights reserved.

Abstract Molten salt is a major heat storage medium for medium–high temperature solar thermal power applications. The heat storage density and heat transfer efficiency of molten salt are important factors of solar thermal power efficiency. Recently, many studies have reported that molten salt nanofluid, which is formed by adding nanoparticles in molten salt, can remarkably enhance the specific heat capacity of molten salt. However, research on the forced convection heat transfer of molten salt nanofluid is inadequate. In this study, the forced convection heat transfer experiments were carried out in a circular tube of a previously reported promising molten salt nanofluid composed of KNO3–Ca(NO3)2 + 1 wt% of 20 nm SiO2 nanoparticles (K-C-Snm). Results showed that compared with its base pure molten salt, the K-C-Snm molten salt nanofluid exhibited substantially better forced convection heat transfer performance under the same working condition. The Nusselt number and the convective heat transfer coefficient of K-C-Snm molten salt nanofluid were 16.3% and 39.9% higher than its base pure molten salt, respectively. The experimental data of K-C-Snm molten salt nanofluid largely differed from the classical correlation equations. Hence, a new empirical heat transfer correlation equation was set for K-C-Snm molten salt nanofluid, and the deviation between the experiment data and new correlation was within ±7%.

Abstract Recently, organo–metal halide perovskites have attracted much attention of the scientific community relating to their successful application in the absorber layer of low-cost solar cells. However, enough is known about the material and device properties, to realize that much remains to be learned. In this study, a two-dimensional modeling of planar heterojunction perovskite solar cells was performed combining the optical and electrical responses to reveal the impact of the carrier diffusion length, the relative permittivity of absorber layer and the valence band offset of absorber/hole transport material (HTM). Simulation results presented a great dependence of power conversion efficiency (PCE) on the carrier diffusion length of perovskite layer. Meanwhile, to achieve high PCE, the frequency depended dielectric constant should not exceeded 40 and the double HTMs design was very effective to match the valence bands between the absorber and HTM.