Apparatus and method for energy storage

An energy storage apparatus comprising a first fluidic circuit containing a first phase change material, the first fluidic circuit including a first storage vessel and a first expander, and a second fluidic circuit containing a second phase change material having a boiling point greater than a boiling point of the first phase change material, the second fluidic circuit including a second storage vessel and a second expander. The energy storage apparatus further comprises a heat pump having a cold side heat exchanger thermally coupled to the first fluidic circuit and a hot side heat exchanger thermally coupled to the second fluidic circuit. The apparatus is operable in a charging mode, a storage mode following the charging mode, and a discharge mode following the storage mode. In the charging mode the heat pump is energised to cool the first phase change material and heat the second phase change material. In the storage mode the first phase change material is stored in the first storage vessel and the second phase change material is stored as a pressurised vapour in the second storage vessel. In the discharge mode vaporised first phase change material is expanded by the first expander, and/or the vaporised second phase change material is expanded by the second expander.