Conversion characteristics and coupling relationship of the quantity and quality of electricity-to-heat or -to-cold energy storage

Energy storage is a key technology for absorbing renewable energy and utilizing excess off-peak power resources. Electric heat/cold storage is one of the methods for large-scale energy storage. Aiming at electric heat/cold storage, a dimensionless analysis method is proposed to analyze the quantity and quality of stored energy and the coupling relationship between quantity and quality. The energy stored per unit electrical energy, maximum work potential, and maximum work potential of stored energy per unit electrical energy are used to evaluate the quantity, quality and comprehensive energy quality (CEQ) of stored energy, respectively. The unit storage energy quantity of direct electric heat storage can be 1, but its energy quality is constrained by the temperature resistance of the storage material. For electric cold storage, its energy quantity and quality are mutually restricted. There are equivalent points between the CEQs for direct heat storage and cold storage with the increase in energy quality. When the energy quality is lower than the equivalent points, the cold storage exchanges quality for quantity and its CEQ is greater than that of direct heat storage. Otherwise, the cold storage exchanges quantity for quality and its CEQ is less than that of direct heat storage. Taking liquid air energy storage (LAES) as an example, the actual CEQ of direct heat storage with the same quality is 1038% higher than that of LAES. Higherquality cold energy is stored at the expense of the energy quantity. An equivalent sharing of congeneric thermodynamic processes method is proposed to offset the effects of the reduction in the cold energy quantity on work potential when the cold energy exchanges quantity for quality.

Automated summary

Energy storage is crucial for absorbing renewable energy and utilizing excess off-peak power. This study proposes a dimensionless analysis method to evaluate the quantity, quality, and comprehensive energy quality of stored energy in electric heat/cold storage. The findings show that cold storage can achieve higher energy quality by sacrificing quantity, while direct heat storage has lower energy quality.