Numerical modeling and performance assessment of elongated compound parabolic concentrator based LCPVT system
In this work, a non-imaging low concentrating 2.5X Compound Parabolic Concentrator (CPC) truncated to 1.7X has been explored. CPCs inherently form non-uniform distribution of flux on the PVT module which has been mitigated by the integration of optimized homogenizer referred to as Elongated CPC (ECPC). The study involves detailed optical, thermal, and electrical modeling of the ECPC based Low Concentrating Photovoltaic Thermal (LCPVT) system. Optical simulations provide insight into the flux distribution on the PVT panel surface, which is further coupled with a thermal and electrical model for precise prediction of the performance of the system. These models are validated experimentally with a 315 Wp solar panel integrated with ECPC based LCPVT system. Performance evaluation of the system has shown peak thermal efficiency of ∼40% at ΔT of 16 °C, peak electrical efficiency of 12%, and an overall peak exergy efficiency of 15% at 38 Liters per hour (LPH) flow rate. A comparison of outlet water temperature results obtained from the numerical model and experiments has shown an excellent match with a relative error of 4%. Results also show that the increase in mass flow rate from 22 LPH to 38 LPH improves the electrical efficiency by 3% however a drop in ΔT of 2–3 °C is observed.
Performance improvement of a desiccant based cooling system by mitigation of non-uniform illumination on the coupled low concentrating photovoltaic thermal units
A Low Concentrating Photovoltaic Thermal system typically employs compound parabolic concentrator to focus sunlight and enhance the quality of both thermal and electrical energy extracted. One of the major issues during this process is the introduction of non-uniform illumination on the photovoltaic panels which can cause hot-spots and significantly reduce both the reliability and the electrical output from this system. This non-uniform illumination can be mitigated by integrating homogenizers which are typically linear extensions to the compound parabolic concentrators profile also referred to as elongated compound parabolic concentrators. In this work, the performance of a 2.5× Elongated Compound Parabolic Concentrator truncated to 1.7× and connected to a desiccant based cooling system has been explored. For a detailed analysis of the system, a coupled 3-D optical, electrical, thermal and process efficiency model has been developed. A full-scale prototype of the modelled system is also fabricated using a 380-Watt peak photovoltaic panel. Experiments conducted on the developed system showed a peak outlet water temperature of 56 °C at a mass flowrate of 24 L per hour. Comparative studies between compound parabolic concentrators and elongated compound parabolic concentrators based low concentrating photovoltaic thermal system is also presented to showcase the overall improvement in the process efficiency due to the mitigation of non-uniformity. Using a 400 mm length of the homogenizer the spatial non-uniformity factor was found to drop from 0.5 to 0.29 under normal incidence angle and results in a rise of 12% in the electrical output when compared to a compound parabolic concentrators-based system. The coefficient of performance of the desiccant-based air-cooling system is found to increase by 50% when coupled with two series-connected elongated compound parabolic concentrators based low concentrating photovoltaic thermal system. The improvement in coefficient of performance is mainly because of thermal and electrical energy savings from the developed system amounting to 352 kWhe/year and 665 kWhth/year, respectively. Further, the mitigation of non-uniform illumination showed a performance improvement of 5% in the coefficient of performance of the air-cooling system compared to a compound parabolic concentrators-based system.
Optical and electrical performance investigation of truncated 3X non-imaging low concentrating photovoltaic-thermal systems
Compound Parabolic Concentrators (CPC) have non-uniform distribution of flux when integrated to a Photovoltaic-Thermal (PVT) module. The non-uniform distribution of flux deteriorates the electrical and thermal performance of the solar panel. To reduce this effect, optimized homogenizers are integrated to CPC of concentration ratio 3X truncated to 2.5X and 2X. The study aims to demonstrate the effect of integration of homogenizer on the electrical performance of the system. Optical simulations carried out for full scale model (1 m × 2 m solar PVT panel area) with homogenizers, referred as Elongated Compound Parabolic Concentrators (ECPC), showed a reduction in the peak local concentration of 55% and 66% for the 2.5X and 2X cases at normal angle of incidence. Optically coupled electrical simulations are carried out, which are further validated using a scaled down prototype tested under solar simulator. The experimental results show peak electrical efficiency of 13.9% (2X) and 13.6% (2.5X) for CPC and 14.1% (2X) and 13.9% (2.5X) for ECPC. Further, benefits of homogenizer are evident near half acceptance angle, when improvement in electrical efficiency by ~23 ± 2% and ~37 ± 2% is observed for ECPC of concentration ratio 2X and 2.5X in comparison to CPCs of similar configuration. In addition, the effect of temperature on electrical performance has also been studied by conducting experiments for actively cooled and uncooled condition. A reduction in 10% electrical efficiency is reported for uncooled condition compared to actively cooled condition.