Concept of Cold Energy Storage for Superconducting Flywheel Energy Storage System

A superconducting flywheel energy storage (SFES) system is an energy storage device with unprecedented small kinetic energy loss by utilizing diamagnetic levitation property of superconductor. The system, therefore, is expected to be one of the most promising candidates in the application of renewable energy field such as PV (photovoltaic) or wind energy development where the power generation is intermittent. An innovative concept to store cold thermal energy as well as kinetic energy in the SFES system is proposed in this paper to decrease required cooling energy during the energy storage period. We have found that the cooling energy can be considerably decreased by the suggested cooling concept. The methodology of cold thermal energy storage is introduced, and the experimental validation is carried out. A specially designed thermosiphon is adopted as a thermal bridge between the high temperature superconductor (HTS) bulks and the cold head of cryocooler, and the working fluid of the thermosiphon is utilized as the thermal energy storage material. Solid nitrogen is generated in the thermosiphon by surplus electricity, and then the mock up HTS bulks are successfully cooled around 64 K by the existence of solid nitrogen even though the implemented cryocooler is turned off.