Experiments on a discretized 3D compound parabolic concentrator with a sensible heat storage

Abstract

A Compound Parabolic Concentrator (CPC) is investigated for capturing and focusing sun rays onto an absorber, for conversion of solar radiation to heat. CPCs are cost-effective as they do not need solar tracking, only requiring tilting of the concentrator at intermediate times during a day. In this study, a 3D CPC with reflecting surfaces is strongly simplified by using only two sets of 4 flat mirrors (upper and lower mirrors) arranged in such a way that they form a quadratic funnel. A cylindrical heat absorber made of aluminum is positioned at the base of the funnel and the system is insulated to reduce the heat losses from the system. The purpose of the heat storage is to accumulate heat at sufficient temperatures for cooking. The idea is that a concentrator can be positioned over the heat storage and be replaced by an insulating cover after the heat storage has been charged. Tests with a CPC system is presented here, with test results in outdoor conditions in Trondheim, Norway during the months of May and June. The heat storage reached temperatures of about 135 °C at solar radiation conditions of 500–700 W/m², higher temperatures are to be expected with improved insulation and at sun conditions closer to equator. Previous separate cooking tests have been successfully demonstrated on a similar cylinder for initial heat storage temperatures of 220 °C. A computational model which was tuned to the 220 °C case showed that even an initial temperature of 140 °C can be sufficient for boiling water although at modest amounts of about 1 l.