A thermal energy storage system, comprising: an ice brick, which comprises a tube which has the shape of an elongated hollow body, wherein the ice brick has at least one inlet and at least one outlet for a first fluid; and a plurality of capsules (715, 114) having a second fluid therein, wherein the plurality of capsules (715, 114) is arranged inside the ice brick; wherein: the first fluid is a heat transfer fluid for exchanging heat with the second fluid; the second fluid is a phase-change medium; wherein each capsule (715, 114) has a shape of a plate and an arrangement of the plurality of capsules (715, 114) inside the ice brick is such that the capsules (715 114) form a plurality of stacks of capsules (715, 114); characterized in that: the capsules (715, 114) comprise a filing nozzle; the capsules (715, 114) comprise oval protrusions arranged such that the flow path of the first fluid which passes by the capsule (715 114) is provided in a meander pattern in at least a part of the flow path characterized by the direction of the flow being regularly changed; the capsules (715, 114) comprise ridges (250, 252) such that the capsules are arranged to provide a gap as flow channel for the first fluid between the capsules (715, 114); wherein an average length of the actual flow path of the first fluid from a front end of the ice brick to the back end of the ice brick is larger than a length of the ice brick, and wherein the protrusions are arranged such that they overlap each other in the general flow direction of the flow. an ice brick, which comprises a tube which has the shape of an elongated hollow body, wherein the ice brick has at least one inlet and at least one outlet for a first fluid; and a plurality of capsules (715, 114) having a second fluid therein, wherein the plurality of capsules (715, 114) is arranged inside the ice brick; wherein: the first fluid is a heat transfer fluid for exchanging heat with the second fluid; the second fluid is a phase-change medium; wherein each capsule (715, 114) has a shape of a plate and an arrangement of the plurality of capsules (715, 114) inside the ice brick is such that the capsules (715 114) form a plurality of stacks of capsules (715, 114); characterized in that: the capsules (715, 114) comprise a filing nozzle; the capsules (715, 114) comprise oval protrusions arranged such that the flow path of the first fluid which passes by the capsule (715 114) is provided in a meander pattern in at least a part of the flow path characterized by the direction of the flow being regularly changed; the capsules (715, 114) comprise ridges (250, 252) such that the capsules are arranged to provide a gap as flow channel for the first fluid between the capsules (715, 114); wherein an average length of the actual flow path of the first fluid from a front end of the ice brick to the back end of the ice brick is larger than a length of the ice brick, and wherein the protrusions are arranged such that they overlap each other in the general flow direction of the flow. the first fluid is a heat transfer fluid for exchanging heat with the second fluid; the second fluid is a phase-change medium; wherein each capsule (715, 114) has a shape of a plate and an arrangement of the plurality of capsules (715, 114) inside the ice brick is such that the capsules (715 114) form a plurality of stacks of capsules (715, 114); characterized in that: the capsules (715, 114) comprise a filing nozzle; the capsules (715, 114) comprise oval protrusions arranged such that the flow path of the first fluid which passes by the capsule (715 114) is provided in a meander pattern in at least a part of the flow path characterized by the direction of the flow being regularly changed; the capsules (715, 114) comprise ridges (250, 252) such that the capsules are arranged to provide a gap as flow channel for the first fluid between the capsules (715, 114); wherein an average length of the actual flow path of the first fluid from a front end of the ice brick to the back end of the ice brick is larger than a length of the ice brick, and wherein the protrusions are arranged such that they overlap each other in the general flow direction of the flow. the capsules (715, 114) comprise a filing nozzle; the capsules (715, 114) comprise oval protrusions arranged such that the flow path of the first fluid which passes by the capsule (715 114) is provided in a meander pattern in at least a part of the flow path characterized by the direction of the flow being regularly changed; the capsules (715, 114) comprise ridges (250, 252) such that the capsules are arranged to provide a gap as flow channel for the first fluid between the capsules (715, 114); wherein an average length of the actual flow path of the first fluid from a front end of the ice brick to the back end of the ice brick is larger than a length of the ice brick, and wherein the protrusions are arranged such that they overlap each other in the general flow direction of the flow.