Thermal energy storage concept with high energy storage density

A sensible heat storage apparatus comprising

• a heat transfer fluid (HTF) tank comprising an HTF;
• a core container that is adapted to be at least partially submerged in the HTF when the HTF is present within said HTF tank;
• and
• a heater positioned within the core container;
• wherein said core container is adapted to be at least partially filled with a core material and which comprises an inner thermal insulation wall defining an internal volume of the core container adapted to contain said core material and wherein said sensible heat storage apparatus is adapted such that the core material and the HTF are switchably thermally connected,
• wherein the inner thermal insulation wall comprises a switchable vacuum insulation element of which the thermal conductivity can be controlled in the range of 1 mW/m/K to 4000 mW/m/K by decreasing or increasing a pressure in the switchable vacuum insulation element such that the inner thermal insulation wall can be switched between an active heat conductor and a heat insulator,
• wherein the heater is adapted to heat the core material to a temperature of more than 500° C.,
• wherein the HTF tank comprises an outer thermal insulation wall that is at least partially surrounding the HTF, and
• wherein the HTF is adapted to absorb heat that is lost by heat leakages from the core material when the inner thermal insulation wall functions as a heat insulator to reduce heat loss from the sensible heat storage apparatus.