Experimental studies on evacuated tube collector with in-built energy storage - Waste car engine oil as sensible heat storage medium

Solar air heating collectors fluctuate in their output due to the fluctuations in the incident solar radiation. The performance of the collectors could be improved by integrating an energy storage mechanism inside the collector itself, to provide a constant heat output. Thermic oil is generally used as energy storage medium for medium temperature applications. The objective of the present work is to check the feasibility of using waste car engine oil (WCEO) in place of Servotherm medium (STM) as energy storage medium to maintain the constant heat output. Three evacuated tube collectors (ETCs) are used in the study, each fixed with a U -pipe heat exchanger at the centre of ETC. One of the ETCs is filled with WCEO in the space available inside the tube as ESM to compare the performance with the ETC filled with STM as energy storage medium and the ETC without any energy storage medium. Constant air supply of 1.47 kg/h was admitted to all the three ETCs. Experiments were carried out for a period of one week and the data was analysed for two different days, one with less fluctuations and another day with more fluctuations of solar irradiation. The ETCs with energy storage medium could supply hot air up -to 23:30 h with more than or equal to 10 degree celsius whereas ETC without energy storage medium could not supply hot air beyond 17:30 h.