Design And Performance Of Compound Planar Spotlight Based On

With the gradual depletion of fossil energy in our planet, the application of solar energy gains more attention, especially the electricity generation from solar cells.However the use of solar cells is limited due to the high cost of electricity generated from photovoltaic systems. The use of cheap optical concentrators in place of expensive of solar cells is regarded as one of effective way to lower the cost of electricity from a photovoltaic(PV) system. Compound parabolic concentrators,sharing the advantages of simple structure and no need of sophisticated sun-tracking device, are widely tested and used for concentrating radiation on solar cells.Considering the non uniformity of solar flux on solar cells and the difficulty of manufacturing CPC’s reflectors, the composite plane concentrator as the alternative of CPC(CPC-A) is suggested and studied in this work with the aims to investigate the design optimization of such concentrator and compare its optical performance with the CPC based on which CPC-A is designed.Firstly, the CPC-A with any number of plane is designed based on principle of identical acceptance half-angle of all planes, and the equivalent acceptance half-angle of CPC-A is calculated based on number of plane(N) and structural parameters of CPC. Then angular dependence of optical efficiency of CPC-A with different N is obtained based on ray-tracing analysis and the annual collectible radiation on the absorber of CPC-A is calculated based on solar geometry and monthly horizontal radiation for comparison with CPC. Results show that, with the increase in N, the optical performance of CPC-A is more close to that of CPC. In the case of the tilt-angle of CPC-A’s aperture being yearly adjusted two times at two tilts, the annual collectible radiation of CPC-A with N=5 is about 99% of that annually collected by CPC, whereas for CPC-A with N=2, the annual collectible radiation is more than 95%of that annually collected by CPC. Ray-tracing also indicates that the solar flux distribution on the absorber of CPC-A is more uniform as compared to CPC, thus CPC-A is more suitable to be used for concentrating radiation on solar cells.The design optimization of CPC-A with N=2 is also performed based on the design principle of maximizing the annual radiation collection. Results show that, for CPC-A with N=2, the design with the ratio of vertical height of the lower plane to that of CPC-A in between 0.3-0.3 is the best design with a maximum annual collectible radiation which is almost identical to that of the CPC-A designed based on design principle of identical acceptance half-angle of all planes, indicating that CPC-A designed based on the principle of identical acceptance angle can be regarded as to be the optimal design of CPC-A.In order to compare the performance of CPC-A and CPC for concentrating radiation on solar cells, CPC-A with N=2 and CPC(a? =20o) with identical geometrical concentration factor( ? 2.4) were fabricated and tested for concentrating radiation on crystal silicon solar cells. The experimental results showed that, the power output from both systems were almost identical for radiation incident at the angle less than the equivalent acceptance half-angle of CPC-A, otherwise, the power output from the PV system equipped with CPC-A was less than that from the one equipped with CPC. Therefore, to make the performance of CPC-A close to that of CPC, it is necessary to adjust the tilt-angle of east-west aligned CPC-A in a reasonable way, making solar rays always within its equivalent acceptance angle.