US Patent 8656712 Energy storage

Apparatus (10) for storing energy, comprising: compression chamber means (24) for receiving a gas; compression piston means (25) for compressing gas contained in the compression chamber means; first heat storage means (50) for receiving and storing thermal energy from gas compressed by the compression piston means; expansion chamber means (28) for receiving gas after exposure to the first heat storage means; expansion piston means (29) for expanding gas received in the expansion chamber means; and second heat storage means (60) for transferring thermal energy to gas expanded by the expansion piston means. The cycle used by apparatus (10) has two different stages that can be split into separate devices or combined into one device.