System for large scale energy storage in a power generation system comprising: i) a circulating fluidized bed combustor (40, 52) with a first pipe (1, 18) for supplying a fuel and a second pipe (2, 19) for supplying a comburent through a gas distributor, the circulating fluidized bed combustor (40, 52) being connected to ii) a first cyclone (41, 53) for separating the resulting hot flue gas (12, 22) and the hot solids stream (11, 23) circulating to the circulating fluidized bed combustor (40, 52) iii) a first device (44, 55) for splitting solid streams falling by gravity from the first cyclone (41, 53) directing the solids from the first cyclone (41,53) a) towards the circulating fluidized bed combustor (40, 52) through a third pipe (3, 21), b) towards a higher temperature silo (43, 58) that receives higher temperature solids through a fourth pipe (4, 24), directing the solids from the higher temperature silo (43, 58) to a first fluidized bed heat exchanger (42, 61), and c) towards a lower temperature silo (47, 57) for storing lower temperature solids from a second fluidized bed heat exchanger (45, 56), the lower temperature silo (47, 57) connected to the second fluidized bed heat exchanger (45, 56) by means of a fifth pipe (5, 30) and connected to the circulating fluidized bed combustor (40, 52) by means of a sixth pipe (6, 31), and iv) a first solid control device (48, 60) for controlling the feed of the higher temperature solids from the higher temperature silo (43, 58), and v) a second control device (49, 62) for controlling the feed of the lower temperature solids from the lower temperature silo (47, 57) to the circulating fluidized bed combustor (40, 52). i) a circulating fluidized bed combustor (40, 52) with a first pipe (1, 18) for supplying a fuel and a second pipe (2, 19) for supplying a comburent through a gas distributor, the circulating fluidized bed combustor (40, 52) being connected to ii) a first cyclone (41, 53) for separating the resulting hot flue gas (12, 22) and the hot solids stream (11, 23) circulating to the circulating fluidized bed combustor (40, 52) iii) a first device (44, 55) for splitting solid streams falling by gravity from the first cyclone (41, 53) directing the solids from the first cyclone (41,53) a) towards the circulating fluidized bed combustor (40, 52) through a third pipe (3, 21), b) towards a higher temperature silo (43, 58) that receives higher temperature solids through a fourth pipe (4, 24), directing the solids from the higher temperature silo (43, 58) to a first fluidized bed heat exchanger (42, 61), and c) towards a lower temperature silo (47, 57) for storing lower temperature solids from a second fluidized bed heat exchanger (45, 56), the lower temperature silo (47, 57) connected to the second fluidized bed heat exchanger (45, 56) by means of a fifth pipe (5, 30) and connected to the circulating fluidized bed combustor (40, 52) by means of a sixth pipe (6, 31), and a) towards the circulating fluidized bed combustor (40, 52) through a third pipe (3, 21), b) towards a higher temperature silo (43, 58) that receives higher temperature solids through a fourth pipe (4, 24), directing the solids from the higher temperature silo (43, 58) to a first fluidized bed heat exchanger (42, 61), and c) towards a lower temperature silo (47, 57) for storing lower temperature solids from a second fluidized bed heat exchanger (45, 56), the lower temperature silo (47, 57) connected to the second fluidized bed heat exchanger (45, 56) by means of a fifth pipe (5, 30) and connected to the circulating fluidized bed combustor (40, 52) by means of a sixth pipe (6, 31), and iv) a first solid control device (48, 60) for controlling the feed of the higher temperature solids from the higher temperature silo (43, 58), and v) a second control device (49, 62) for controlling the feed of the lower temperature solids from the lower temperature silo (47, 57) to the circulating fluidized bed combustor (40, 52).