The invention provides a plant for production of energy, comprising any type of heat or energy source including but not limited to solar power sources, nuclear reactors, fossil fuel plants, wind power plants, tidal power plants, waste heat power plants and geothermal sources, operatively arranged at an input side of the plant, and heat delivery or energy production means such as turbine-electric generator sets, operatively arranged at a delivery side of the plant. The plant is distinctive in that it further comprises a thermal energy storage with integrated heat exchanger, comprising a solid state thermal storage material, a heat transfer fluid and means for energy input and output, wherein: the storage comprises at least one heat transfer container, solid state thermal storage material is arranged around the heat transfer container, the heat transfer container contains the heat transfer fluid and the means for energy input and output, so that all heat transferring convection and conduction by the heat transfer fluid takes place within the respective heat transfer container, the thermal energy storage with heat exchanger has been arranged inside thermal insulation, and the solid state thermal energy storage with heat exchanger, has been arranged between the input side and delivery side of the plant for storage and heat exchange of thermal energy, the storage is coupled directly or via an additional heat exchanger to the source and the storage is coupled directly or via an additional heat exchanger to the delivery side of the plant.