Conception, realization and testing of a novel solar collector

Abstract

The system proposed in this article is a collector made up of hemispherical concentrators. The prototype consists of four reflecting bowls covered with 8 mm glass in which 42 L of sunflower oil circulates. The oil being the absorber itself is heated by the hot spots resulting from the concentration of the spherical reflectors. So the proposed collector stands against usual collectors by canceling the black plate absorber and by assuming that the hot spots heating process is a better way of heating a fluid in natural convection while keeping the permanent positioning advantage. The aim of the first series of tests was to confirm that the hot spots could better heat the oil, which was assessed by the oil excess temperature with the ambient reaching 32 $°$C for a maximum irradiation value of 970 W m${}^{-2}$. The second series of tests was carried out on the same collector heating a 60 L water tank in indirect heat transfer mode, resulting in an average daily efficiency of 86.30%. The annual daily effective heat gain was estimated at 6.21 MJ for a receptive surface area of 0.39 m² and an average irradiation value of 506 W m${}^{-2}$. 73.02% of this heat gain was allocated to water. In conclusion, direct heating of a liquid by hot-spots is effective. The proposed collector, while operating entirely in passive mode and retaining the convenience of flat plate collectors, has shown competing performances with them and can also be approved as an ICS after key actions against its drawbacks.