Performance improvement of a desiccant based cooling system by mitigation of non-uniform illumination on the coupled low concentrating photovoltaic thermal units

Abstract

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.