"Peak-load shifting" aka "peak shaving" or "peak smoothing." The energy storage system (ESS) is charged (a) while the cost of electric usage is low, such as at night during off peak hours and (b) while the solar system is generating power.
It is then discharged to provide additional power during periods of increased loading, while costs for using electricity are increased - peak time period.
Peak shaving describes when a facility uses a local energy storage system to compensate for the facility's large energy consumption during peak hours of the day.
Most facilities do not operate 24 hr/day. In fact, most facilities do not even operate most of the day. In this scenario, the energy demand, typically measured in kW, remains relatively low most of the day and rises only during operational hours.
By charging an energy storage system during the off hours of the day and discharging it during the operational hours, the peak demand charge from the utility can be reduced.