Development of a CPC with low thermal losses

• Published in: Solar & wind technology 1987, Vol.4 (2), p.157-162
• Main Authors: Fasulo, A., Odicino, L., Perello, D.
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Exact sciences and technology; Natural energy; Solar energy; Solar thermal conversion
• ISSN: 0741-983X
• DOI: 10.1016/0741-983X(87)90043-9

Presented here is an energy balance of a compound parabolic concentrator (CPC) of 0.5 m 2 surface area, built with parabolas made of glass, in the Solar Energy Laboratory of Universidad Nacional de San Luis. Firstly, the total thermal losses of the CPC are determined experimentally and then their conductive, convective and radiative components are found, for temperatures between 60 and 150°C. With the purpose of appreciating better the effects of the last two kinds of losses, use is made of different receivers. With each of them the performance of the CPC operating under solar radiation is measured and then the energy balance is carried out. On the basis of the results obtained with the first CPC, a second was constructed with low thermal losses. For this, the cover of dull black paint on the receiver was replaced by a selective surface—black chrome on dull nickel—which has an absorptance of 0.9 (for 0.2 μm ⩽ λ ⩽ 2 μm) and an emittance, ϵ = 0.2 for λ ⩾ 2 μm. Furthermore, a study of the trajectory of the rays in the interior of the CPC is carried out and the best transversal profile for an anticonvective surface, to be place 2.5 cm above the receiver, is determined. The first results that were obtained are presented here, for losses and effectiveness. A valuable improvement in the performance of the device can be noticed. In the best CPC an efficiency η equal to 0.16 is obtained for a mean temperature of 126°C for the fluid in the collector and an ambient temperature of 11°C.