A unit for storing and releasing thermal energy including: - a plurality of modular blocks , each block including: -- individualised elements for storing and releasing said thermal energy including at least one PCM, -- a body comprising: --- a chamber receiving elements of PCM, the chamber being defined within the outer walls of the body assembled by a bottom closing on one side the chamber, --- at least one communication passage between the chambers of the blocks, for the circulation of the fluid between two adjacent chambers, in heat exchange relationship with said elements in each chamber, - attachment means suitable for attaching together the blocks , such that said fluid can circulate between same via the communication passages, - and elements for the thermal management of the chambers, arranged around said chambers and at least some of which include a thermally insulating material , characterised in that : - each chamber is open on one side other than the bottom , for placing therein or removing therefrom said elements of PCM, and the modular blocks further individually include a sealing surface surrounding the open side of the chamber, for providing sealing in relation to the fluid, such that two adjacent modular blocks can be arranged with their chambers thereof face to face or back to back, the modular blocks being stacked along an axis , and the communication passages passing through the bottoms of the chambers , - and at least some of the elements for the thermal management of the chambers include a PCM . - a plurality of modular blocks , each block including: -- individualised elements for storing and releasing said thermal energy including at least one PCM, -- a body comprising: --- a chamber receiving elements of PCM, the chamber being defined within the outer walls of the body assembled by a bottom closing on one side the chamber, --- at least one communication passage between the chambers of the blocks, for the circulation of the fluid between two adjacent chambers, in heat exchange relationship with said elements in each chamber, -- individualised elements for storing and releasing said thermal energy including at least one PCM, -- a body comprising: --- a chamber receiving elements of PCM, the chamber being defined within the outer walls of the body assembled by a bottom closing on one side the chamber, --- at least one communication passage between the chambers of the blocks, for the circulation of the fluid between two adjacent chambers, in heat exchange relationship with said elements in each chamber, --- a chamber receiving elements of PCM, the chamber being defined within the outer walls of the body assembled by a bottom closing on one side the chamber, --- at least one communication passage between the chambers of the blocks, for the circulation of the fluid between two adjacent chambers, in heat exchange relationship with said elements in each chamber, - attachment means suitable for attaching together the blocks , such that said fluid can circulate between same via the communication passages, - and elements for the thermal management of the chambers, arranged around said chambers and at least some of which include a thermally insulating material , - each chamber is open on one side other than the bottom , for placing therein or removing therefrom said elements of PCM, and the modular blocks further individually include a sealing surface surrounding the open side of the chamber, for providing sealing in relation to the fluid, such that two adjacent modular blocks can be arranged with their chambers thereof face to face or back to back, the modular blocks being stacked along an axis , and the communication passages passing through the bottoms of the chambers , - and at least some of the elements for the thermal management of the chambers include a PCM . <EOS>