Thermal storage unit comprising: - a receptacle comprising orifices (42; 44) allowing a heat-transfer fluid to be introduced into and extracted from the said receptacle, and - a stack of bricks preferably made of a material which at 25°C has a specific heat capacity higher than 600 J.°C -1.kg -1, the said bricks being arranged in the said receptacle in the form of superposed strata (46; 46'), each stratum having lower (47a; 47a') and upper (47b; 47b') large faces and defining a plurality of ducts (48; 48') each opening via lower (49a; 49a') and upper (49b; 49b') openings onto the said lower and upper large faces respectively, the stack comprising a pair of strata made up of a lower stratum and an upper stratum which is superposed on the said lower stratum, the said pair of strata, referred to as "passage strata pair", being such that: - the upper and lower large faces of the said lower stratum and of the said upper stratum, respectively, are separated from one another in such a way as to define a passage placing an upper opening of a lower duct of the said lower stratum in fluidic communication with at least one lower opening, that is entirely offset with respect to the said upper opening, of at least one upper duct of the said upper stratum, - the lower large face of the upper stratum closes off, at least in part, the said upper opening, referred to as "closed-off upper opening", when the said upper opening is observed, along its axis, from the said lower duct, the said bricks being shaped and configured in such a way that the said stack has a void volume fraction less than or equal to 60%, more than 20% by number of the upper openings of the said lower stratum being closed-off upper openings, more than 20% by number of the pairs of superposed strata of the stack being each a said passage strata pair. - a receptacle comprising orifices (42; 44) allowing a heat-transfer fluid to be introduced into and extracted from the said receptacle, and - a stack of bricks preferably made of a material which at 25°C has a specific heat capacity higher than 600 J.°C -1.kg -1, the said bricks being arranged in the said receptacle in the form of superposed strata (46; 46'), each stratum having lower (47a; 47a') and upper (47b; 47b') large faces and defining a plurality of ducts (48; 48') each opening via lower (49a; 49a') and upper (49b; 49b') openings onto the said lower and upper large faces respectively, the stack comprising a pair of strata made up of a lower stratum and an upper stratum which is superposed on the said lower stratum, the said pair of strata, referred to as "passage strata pair", being such that: - the upper and lower large faces of the said lower stratum and of the said upper stratum, respectively, are separated from one another in such a way as to define a passage placing an upper opening of a lower duct of the said lower stratum in fluidic communication with at least one lower opening, that is entirely offset with respect to the said upper opening, of at least one upper duct of the said upper stratum, - the lower large face of the upper stratum closes off, at least in part, the said upper opening, referred to as "closed-off upper opening", when the said upper opening is observed, along its axis, from the said lower duct, the said bricks being shaped and configured in such a way that the said stack has a void volume fraction less than or equal to 60%, more than 20% by number of the upper openings of the said lower stratum being closed-off upper openings, more than 20% by number of the pairs of superposed strata of the stack being each a said passage strata pair. - the upper and lower large faces of the said lower stratum and of the said upper stratum, respectively, are separated from one another in such a way as to define a passage placing an upper opening of a lower duct of the said lower stratum in fluidic communication with at least one lower opening, that is entirely offset with respect to the said upper opening, of at least one upper duct of the said upper stratum, - the lower large face of the upper stratum closes off, at least in part, the said upper opening, referred to as "closed-off upper opening", when the said upper opening is observed, along its axis, from the said lower duct,