"Passive thermal storage systems and methods comprising at least one thermal storage module for storing thermal energy in a predetermined temperature range, are disclosed. The thermal storage module comprises an FT unit and a Heat Storage (HS) unit at least partially filled with a first Phase Change Material (PCM). The HS unit comprises a container. The thermal storage module may be in the form of a stacked structure comprising the FT unit having a first wall with a first heat exchange surface and the HS unit having a second wall with a second heat exchange surface, the first and second heat exchange surfaces being in thermal contact with each other. The thermal storage system may be used to maintain the temperature of the payload of a temperature controlled container at a predetermined value or within a predetermined range."