Refraction-Based Optical Design for Static Solar Concentrator

Abstract

The concentrated photovoltaic system (CPV) had advantage over the non-concentrated one in that they can generate more electricity per cell and thus reduce the overall energy price. However, the system was not suitable for the installments in individual house, small building, or remote places because it normally needed an active tracking component that requires frequent maintenance. Therefore, static concentrated photovoltaic system (SCPV) had been demonstrated as solution for maintenance problems of tracking system in CPV. Most static concentrators had been mainly designed by reflection mechanism. Thus, their low concentration ratio and manufacturing issues were obstacles for application in industry. In present study, more flexible and cheaper static concentrator for higher concentration ratio and seasonal variation was developed by non-imaging lens as the primary method of concentration. And a design optimization procedure was suggested. Two lenses system which consisted conventional concave lens and design convex lens having a lot of optimized prisms for non-imaging was a basic design element. The convex lens was designed by simple refraction and total internal reflection theory. Its width and angle of prisms in lens were optimized by ray-tracing method which was in-house code and system performance was evaluated by optimization approach how rays of all distributed angles enter systems simultaneously. Simulation method was validated by comparing simulation results and experimental data. Simple two lenses which were commercial convex lenses having different size and focal length was set in experiment. Simulation results are reasonably close to experiment one and mean absolute percentage error between simulation and experiment is less than 5%. Designed non-imaging lens help lights concentrate onto photovoltaic. It consists of many prisms whose shape is different. Concentration ratio varies seasonally and yearly average concentration ratio is 1.82. The maximum concentration ratio is 3.745 at vernal and autumnal equinox because sunlight perpendicularly enters system at these times. The maximum concentration ratio is quiet higher than yearly average concentration ratio. And the yearly average concentration ratio is higher than the previous SCPV. Therefore designed non-imaging lens has potential for effective concentration for peak power demand. Array system where several small-sized single systems are combined is considered. It can be applicable in practical situations. Array system is more benefit able than bulky single system in cost-wise and installment-wise. The yearly average concentration ratio of array system sharply increases. Its value is 2.33. Especially concentration ratio at the summer and winter solstices remarkably improve because a lot of sunlight reaches photovoltaic in the adjacent system. The yearly average concentration ratio of array system is within about 10% of the available maximum concentration ratio defining as thermodynamic. Semi-SCPV system whose meaning is that passively changing angle facing the a few times a year without dynamic tacking system is suggested for another practical model system. Two models for bi-yearly semi-SCPV are considered. In first model, system position change to maximize average concentration ratio. At the middle of between vernal equinox and summer solstices, position of SCPV change to receive sunlight perpendicularly and after about 6 month, position of SCPV change. At this time sunlight normally enter the system. The yearly average concentration ratio of first model is 3.6 and the maximum concentration ratio is 5.92. The concentration ratio is remarkably increased. And periodic variation for seasons of concentration ratio reduces. As a result, more energy provides during each season. A motivation of second model is to maximize concentration ratio for peak seasons like summer and winter. System is located at angles where sunlight perpendicularly enters system at summer and winter solstices. Its concentration ratio is the same as array system one. However, the maximum concentration ratio generates at summer and winter solstices as planned. Therefore second model can flexible concentrates sunlight for replying to peak power demand.