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.

复合抛物面聚光器（Compound Parabolic Concentrators, CPCs）凭借其可在宽角度范围内接收入射太阳辐射的特性，具备重要的应用价值。本文采用精准的太阳光线追踪分析方法，对太阳能复合抛物面聚光器开展光学与热力学分析。为此，基于改进的复合抛物面聚光器方程并考虑漫射辐射影响，针对不同几何聚光比（Ct）计算得到了该聚光器的光学效率。研究结果表明，当几何聚光比为1.63时，可实现最高的太阳辐射吸收效果。随后，将固定式真空管复合抛物面聚光器的出口温度（To）、能量效率与㶲效率（ηI和ηII）与两款不带聚光器的真空管太阳能集热器（集热管间距分别较大或较小）进行了对比。结果显示，复合抛物面聚光器集热器的平均入射太阳辐射量高于另外两款无聚光器的太阳能集热器。此外，在复合抛物面聚光器的有效反射角范围内，其能量效率高于其他两款集热器；而当入射角度较大时，其能量效率则低于或等于这两款无聚光器的太阳能集热器。