Abstract: The thermal storage apparatus contains a heat transfer fluid (102) and a thermal storage medium (101), being immiscible and of differing densities. The thermal storage apparatus comprises a vessel (100) for containing a layer of heat transfer fluid (102) in contact with a layer of thermal storage medium (101), and a charging loop (120) including an inlet nozzle (200) having a mouth The charging loop (120) is arranged to supply cool heat transfer fluid (102) into the vessel (100) directed at least partially into the layer of thermal storage medium (101) and the inlet nozzle (200) is shaped such that heat transfer fluid (102) flowing therethrough operatively draws thermal storage medium (101) into the mouth thereof. The thermal storage apparatus described provides good mixing of cooled heat transfer fluid (102) with thermal storage medium (101), minimal blockages in the charging loop (120) and allows good separation of the heat transfer fluid (102) and thermal storage medium (101).