A new thermodynamic model for Heat Pump Energy Storage (HPES) is derived. HPES is a large scale electric energy storage technology that stores energy as thermal energy. This model utilizes the partition of energy into exergy and anergy to account for the quality of energy conversion or transfer processes. The model is used to identify and categorize the exergy losses of HPES systems. The exergy losses lead to the degree of utilization. For demonstration the model is applied to the HPES system described in [1] which works with a gaseous working fluid and stores the thermal energy in two regenerators.
