A battery for storing thermal energy is comprised of: a tank having insulated walls and containing heat transfer fluid (HTF, 102); a plurality of tubes arranged vertically within the tank, each of the tubes being substantially filled with a phase change material (PCM, 110); and a plurality of diffusers (104, 105, 106) operatively connected to the tank constructed and arranged to enable flow of the HTF through a load heat exchanger and a liquid chiller heat exchanger characterized in that the battery comprises: a bottom diffuser from the plurality of diffusers (104, 105, 106) that is located in a lower portion of the tank and is connected to the load heat exchanger and adapted for transfer of cold HTF from the tank to the load heat exchanger; a top diffuser from the plurality of diffusers (104, 105, 106) that is located in an upper portion of the tank and is connected to the load heat exchanger and adapted for the return of hot HTF from the load heat exchanger to the tank; one or more diffusers from the plurality of diffusers (104, 105, 106) which one or more diffusers are located in an upper portion of the tank and connected to the liquid chiller and adapted for the transfer of hot HTF to the liquid chiller, which one or more diffusers may comprise the top diffuser being further connected to the liquid chiller and adapted for the transfer of hot HTF to the liquid chiller; and a further diffuser from the plurality of diffusers (104, 105, 106) located in a lower portion of the tank and connected to the liquid chiller and adapted for the transfer of cold HTF from the liquid chiller to the tank. a tank having insulated walls and containing heat transfer fluid (HTF, 102); a plurality of tubes arranged vertically within the tank, each of the tubes being substantially filled with a phase change material (PCM, 110); and a plurality of diffusers (104, 105, 106) operatively connected to the tank constructed and arranged to enable flow of the HTF through a load heat exchanger and a liquid chiller heat exchanger characterized in that the battery comprises: a bottom diffuser from the plurality of diffusers (104, 105, 106) that is located in a lower portion of the tank and is connected to the load heat exchanger and adapted for transfer of cold HTF from the tank to the load heat exchanger; a top diffuser from the plurality of diffusers (104, 105, 106) that is located in an upper portion of the tank and is connected to the load heat exchanger and adapted for the return of hot HTF from the load heat exchanger to the tank; one or more diffusers from the plurality of diffusers (104, 105, 106) which one or more diffusers are located in an upper portion of the tank and connected to the liquid chiller and adapted for the transfer of hot HTF to the liquid chiller, which one or more diffusers may comprise the top diffuser being further connected to the liquid chiller and adapted for the transfer of hot HTF to the liquid chiller; and a further diffuser from the plurality of diffusers (104, 105, 106) located in a lower portion of the tank and connected to the liquid chiller and adapted for the transfer of cold HTF from the liquid chiller to the tank. a bottom diffuser from the plurality of diffusers (104, 105, 106) that is located in a lower portion of the tank and is connected to the load heat exchanger and adapted for transfer of cold HTF from the tank to the load heat exchanger; a top diffuser from the plurality of diffusers (104, 105, 106) that is located in an upper portion of the tank and is connected to the load heat exchanger and adapted for the return of hot HTF from the load heat exchanger to the tank; one or more diffusers from the plurality of diffusers (104, 105, 106) which one or more diffusers are located in an upper portion of the tank and connected to the liquid chiller and adapted for the transfer of hot HTF to the liquid chiller, which one or more diffusers may comprise the top diffuser being further connected to the liquid chiller and adapted for the transfer of hot HTF to the liquid chiller; and a further diffuser from the plurality of diffusers (104, 105, 106) located in a lower portion of the tank and connected to the liquid chiller and adapted for the transfer of cold HTF from the liquid chiller to the tank.