The ornamental design for an energystoragesystem, as shown and described.
FIG. 1 is a front elevation view of an energy storage system of our design;
FIG. 2 is a rear elevation view thereof;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a perspective view thereof.
This energy storage system is used for storing wind power, photovoltaic and other clean energy or power peak clipping and valley filling, etc., and is applied to UPS (i.e. Uninterruptible Power System) power supply, telecommunication base station energy-storage power supply, etc.