Comparative study of Non -Tracking and Low Concentrating Photovoltaic systems Using Low -Cost Reflectors
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Date
2012-10-01
Authors
Hatwaambo, Sylvester
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Abstract
The traditional high concentrating photovoltaic systems have proved to be expensive as they use high grade silicon solar cells, highly specular reflecting materials and require tracking arrangements which are equally expensive. The problem of un-even illumination creates heat-sinks which have not been solved in high concentrating systems. This thesis addresses the problem of un-even illumination in low concentrating photovoltaic systems using low cost reflecting materials for low-cost electricity. The large module cells are replaced by small string modules and the highly specular materials are replaced with low-cost diffuse materials.Concentrating sunlight onto a solar module has an effect of hot-spot formation which reduces the fill factor and hence the efficiency of the photovoltaic system. To address this problem, diffuse reflectors with rolling marks either parallel or perpendicular to the plane of the module were tested in low Concentrating photovoltaic systems. The changes in the fill factor were monitored as different reflector materials were replaced within concentrator geometries. It was experimentally shown that diffuse reflectors gave better fill-factor than specular reflectors. It was further demonstrated that diffuse reflectors with rolling grooves aligned parallel to the plane of the module gave better fill-factor than
diffuse reflectors with rolling grooves aligned perpendicular to the plane of the module surface. In particular, the power increased by a factor of 2 in all reflector materials studied but the drop in the fill factor was 28% for rolling marks parallel to the plane of the module as compared to 30% for rolling marks perpendicular to the plane of the module. The parallel rolling marks (horizontal grooves) gave improved fill factor. Probably the rolling marks scattered the solar flux within the concentrator geometry at large angles and hence evenly illuminated the solar cell module area. The vertical grooves on the other hand had low angle scattering of the solar flux and could not spread the solar flux along the plane of the module. The vertical orientation of the grooves had similar performance as specular reflectors. Furthermore, the performance of the CPC geometry with semi-diffuse aluminium foil was under estimated due to construction errors as compared with anodized aluminium which gave a better performance as it was used as the base material. It was also verified that anodized aluminium, miro and rolled aluminium foil respectively, were the best reflector materials that withstood the environmental conditions.However, due to its low cost, the rolled aluminium foil was preferred for use in low concentrating photovoltaic systems.
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Non-Tracking Reflectors