Experimental evaluation of vitrified waste as solid fillers used in thermocline thermal energy storage with parametric analysis

•4 m3 Pilot-scale thermocline TES for CSP.•Asbestos contained waste as solid filler in TES outperofrm alumina: 9.7% better discharge efficiencies, 16% lower thermocline thickness during charge and 23% during discharge, a 7% better charge/discharge time ratio.•10% bigger solid filler diameter results a 2.2% wider thermocline thickness and 1.4% reduction in discharge efficiency after the optimum diameter.