Heat Loss Prediction from Solar LFR linear evacuated surface receiver with variable 2-stage concentrated flux
A numerical study has been carried out to analyse the thermal performance of the receiver system of solar Linear Fresnel Reflector (LFR) module. Realistic flux conditions obtained by the optical analyses are applied as the boundary condition to the circumference of the absorber. Heat losses caused by convection as well as radiation from the parabolic secondary receiver are investigated under evacuated and non-evacuated annular region between the absorber and the glass tube. The investigation has been carried out to determine the heat loss by varying the annular gap between the absorber tube and the protective glass.
Design and production of a 2.5 kWe insulated metal substrate-based densely packed CPV assembly
The original design of a new 144-cell concentrating photovoltaic assembly is presented in this paper. It is conceived to work under 500 suns and to generate about 2.5 kWe. An insulated metal substrate was selected as baseplate, in order to get the best compromise between costs and thermal performances. It is based on a 2mm thick aluminum plate, which is in charge of removing the heat as quick as possible. The copper pattern and thickness has been designed accordingly to the IPC Generic Standard on Printed Board Design and to the restrictions of fit a reflective 125x primary optics and a 4x secondary refractive optics. The original outline of the conductive copper layer has been developed to minimize Joule losses by reducing the number of interconnections between the cells in series. Multijunction solar cells and Schottky bypass diodes have been soldered onto the board as surface mounted components. All the fabrication processes are described. This board represents a novelty for the innovative pattern of the conductive layer, which can be easily adapted to be coupled with different optics geometries and to allocate a different number of cells. The use of an IMS as baseplate will give an experimental contribution to the debate about the exploitability of this kind of substrates in CPV. This board is being characterized indoor and outdoor: the results will be used to improve the design and the reliability of the future receivers.
Characterization of various two-phase materials based on thermal conductivity using modified transient plane source method
This paper presents the thermal conductivity of various two-phase materials using modified transient plane source (MTPS) technique. The values are determined by using commercially available C-Therm TCi apparatus. It is specially designed for testing of low to high thermal conductivity materials in the range of 0.02 to 100 Wm-1K-1 within a temperature range of 223-473 K. The results obtained for the two-phase materials (solids, powders and liquids) are having an accuracy better than 5%. The transient method is one of the easiest and less time consuming method to determine the thermal conductivity of the materials compared to steady state methods.
Numerical investigation of micro-channel based active module cooling for solar CPV system
Concentrating photovoltaic (CPV) technology is one of the fastest growing solar energy technologies achieving higher electrical conversion efficiencies. The increase in temperature of solar CPV cell significantly reduces the performance; the efficiency of a CPV system can be improved by introducing effective thermal management or cooling system. This paper presents the design and numerical analysis of a heat sink based on micro-channels for efficient cooling of a commercial high concentration photovoltaic (HCPV) cell. A combinatory model of an array of micro-channels enclosed in a wide parallel flow channel design is developed. The optimized geometry of the micro-channel heat sink was found by using commercial CFD software ANSYS 13. Based on numerical simulations, it is found that the optimum configuration of micro-channel with 0.5mm width and aspect ratio of 8. The micro-channels provided high heat transfer over heat generations spots and parallel flow channels resulted in lower pressure drop. The temperature rise across the micro-channel is estimated as10K in CPV module of 120 × 120 mm2 and with a pressure drop of 8.5 kPa along a single channel with six such channels in each modules at a flow rate of 0.105 liter/s. © 2014 The Authors.
Optical study of a 3-D elliptical hyperboloid concentrator
The optical performance of a solar concentrator is mostly depends on the geometry of the concentrator profile. In the present paper, work focuses on the optical efficiency of 3-D Elliptical Hyperboloid Concentrator (3-D EHC) using Optis™ Ray-trace software. An extensive theoretical prediction, using a 3-D ray tracing technique has been adopted in the current investigation to calculate the optical efficiency of a novel 3-D EHC. The effect of source angle (from +90° to -90°) on the optical efficiency of a 3-D EHC is reported. Due to the wide acceptance angle of the Elliptical Hyperboloid solar Concentrator, the optical efficiency was found to be 87% for a concentration ratio of 18x. Due to the three-dimensional nature of the Elliptical hyperboloid solar concentrator, the optical efficiency and the concentration ratio are also a function geometric parameters such as the ratio of the concentrator height to each of the receiver's major and minor axes; a parametric study of these variables has also been conducted The aperture length was fixed for all simulations. Results presented also show the distribution of the concentrated radiant energy over the receiver/absorber. For the range of parameters investigated, an optimum design is presented.
Enhancing the performance of BICPV systems using phase change materials
Building Integrated Concentrated Photovoltaic (BICPV) systems have three main benefits for integration into built environments, namely, (i) generating electricity at the point of use (ii) allowing light efficacy within the building envelope and (iii) providing thermal management. In this work, to maintain solar cell operating temperature and improve its performance, a phase change material (PCM) container has been designed, developed and integrated with the BICPV system. Using highly collimated continuous light source, an indoor experiment was performed. The absolute electrical power conversion efficiency for the module without PCM cooling resulted in 7.82% while using PCM increased it to 9.07%, thus showing a relative increase by 15.9% as compared to a non-PCM system. A maximum temperature reduction of 5.2°C was also observed when the BICPV module was integrated with PCM containment as compared to the BICPV system without any PCM containment.
Enhancing ultra-high CPV passive cooling using least-material finned heat sinks
Ultra-high concentrating photovoltaic (CPV) systems aim to increase the cost-competiveness of CPV by increasing the concentrations over 2000 suns. In this work, the design of a heat sink for ultra-high concentrating photovoltaic (CPV) applications is presented. For the first time, the least-material approach, widely used in electronics to maximize the thermal dissipation while minimizing the weight of the heat sink, has been applied in CPV. This method has the potential to further decrease the cost of this technology and to keep the multijunction cell within the operative temperature range. The designing procedure is described in the paper and the results of a thermal simulation are shown to prove the reliability of the solution. A prediction of the costs is also reported: a cost of 0.151$/Wp is expected for a passive least-material heat sink developed for 4000x applications.
Optimization of woven jute/glass fibre-reinforced polyester hybrid composite solar parabolic trough collector
In the present work, structural analysis of 5.77m × 4m woven jute (J)/glass (G) fibre-reinforced polyester hybrid composite solar parabolic trough is carried out based on trough parameters to obtain the minimum RMS local slope deviation, termed as SDx value under gravity loading. The optimization is done by varying parameters viz. direction and size of reinforced conduits, stacking number and sequence of hybrid trough laminate at fibre orientation of Δθ=45° and Δθ=60° amongst the layers at 0° collector angle. The analysis revealed that the configuration in which the conduits are placed in both X and Y directions is preferred over other configurations to scale down the effect of wind loads. Furthermore it has been observed that laminate of the order [0°G/45°G/-45°J/90°J]s undergoes minimum surface deformation amongst all the other configurations at conduit reinforcement in both X and Y directions for a conduit thickness of 0.75 mm and radius of 10 mm and obtains the overall SDx value of 1.3492 mrad. The results shows that proposed trough model is very promising and evolves a cost effective system.
Optimization of the least-material approach for passive Ultra-High CPV cooling
The attention around Ultra-High CPV is increasing year by year, because of the potential cost-cutting achievable by increasing the concentration ratio. In these systems, an adequate thermal management becomes particularly important: cooling systems are required to be compact, reliable and efficient. In this work, the geometry of a passive heat sink for a 4000x CPV application is optimized to reduce the volume and the costs, limiting the effects on the thermal performance. The same approach is used to model the behavior of a UHCPV heat sink in New Orleans, LA (USA): the hourly cell temperatures are presented in the paper.
The design of a parabolic reflector system with high tracking tolerance for high solar concentration
A compact high concentrating photovoltaic (HCPV) module based on cassegrain optics is proposed; consisting of a primary parabolic reflector, secondary reflector and homogeniser. The effect of parabolic curvatures, reflector separation distance and the homogeniser's height and width on the tracking tolerance has been investigated for optimisation. In this type of HCPV, the addition of a solid transparent homogeniser to the two stage reflector design greatly improves the tracking tolerance. Optical simulation studies show high optical efficiencies of 84.82-81.89 % over a range of ± degree tracking error and 55.49% at a tracking error of ±1.5 degrees.