Experimental investigation of energy storage for an evacuated solar collector

This paper presents the results of an experimental study involving energy storage materials (paraffin wax and water) placed inside a new type of cylindrical evacuated solar collector system. The potential of this system to provide continuous hot water, even during short periods of low incident solar radiation, was investigated. Five cases, including a reference case, were studied experimentally and the performance of each was analysed. Of the materials studied, water was found to give best performance in terms of thermal storage and subsequent release of stored energy. Partial filling of the evacuated solar collector tubes with water gave greatest overall thermal efficiency for a cycle including two periods of no input energy under the test conditions employed.