The influence of gap losses on the optical, energy, and exergy efficiencies of the all-glassed evacuated tube compound parabolic concentrator (CPC) solar collectors

The compound parabolic concentrators (CPCs) are of importance due to their capability in absorbing the incident solar radiation in a wide limit. The present paper deals with the optical and thermodynamic analysis of a solar CPC applying the accurate solar ray-tracing analysis. To this end, the optical efficiency of the CPC was obtained for different geometric concentration ratios (Ct) based on the CPC modified equations and considering the diffuse radiation effects. The results demonstrated that the highest solar radiation absorption is obtained for Ct of 1.63. The outlet temperature (To), energy and exergy efficiencies (ηI and ηII) of the stationary evacuated tube CPC were compared with those of two different evacuated tube solar collectors without a concentrator (with large or low distance between the tubes). Based on the results, the average incident solar radiation of the CPC collector is higher than that of two other solar collectors without a concentrator. Besides, ηI of the CPC is higher than that of other collectors within the range of effective reflective angle of the CPC, while for the higher incident angles, ηI is lower than or equal to the other two collectors without a concentrator.