Thermal energy storage system

A thermal energy storage system (1) comprising:

• a first container (2) for containing a phase change material,
• a jacket (4) connected to an exterior of the first container, wherein a space is formed between the jacket and a wall portion of the first container, the jacket having an inlet,
• a heating chamber (6) comprising a heating device, the heating chamber being in fluid communication with the inlet of the jacket,
• a second container (8) for containing a heat transfer fluid,
• a pump arrangement (10) provided in the second container for pumping the heat transfer fluid from the second container, via the heating chamber in which the heat transfer fluid is heated by the heating device, and to the said space formed between the jacket and the wall portion of the first container, in order to cause thermal energy to be transferred between the heat transfer fluid and the phase change material via said wall portion of the first container,
• wherein the heating chamber has a projecting portion (12) that extends through a wall (14) of the second container such that a connecting interface (16) between the pump arrangement and the heating chamber is located inside the second container, wherein if any heat transfer fluid leaks through the connecting interface it will remain in the second container.