Experimental Study of a Stationary Hot Air Solar Collector Built with Hemispherical Concentrators and Enhanced with Fresnel Lenses

Abstract

Aims: This paper is about a solar collector made of hemispherical concentrators. This collector is sun tracking free, and used for natural convection. Lenses are used on top of each concentrator to improve its efficiency.
 Study Design: The Solar collector is made of hemispherical concentrators with Fresnel lenses axially-centered to those concentrators and placed on top of each one of them. Those concentrators are covered with a 4 mm glass for a greenhouse effect. The concentrators generate hot spots that heat the inside air. There is no need for receivers at the hot spots.
 Methodology: from Inlet to outlet, temperatures are measured as well as inlet air speed, which allow the efficiency evaluation.
 Results: Although those measurements were conducted in a cloudy period, temperature difference from the inlet to the outlet was around 55°C to 65°C. This result is superior to previous studies of the same system without lenses which gave temperature difference around 35°C to 45°C. It is sharply superior to that of usual black-painted convective system with fined plates that gives a temperature difference of around 20°C to 25°C.
 Conclusion and Perspectives: The global efficiency calculated using measurement values reaches 56%. This is far greater compared to previous black plate systems’ efficiency of 29%, giving an efficiency increase of 93%, but expected knowing that we are using a concentration system for convection.