Rack for an energy storage system

An embodiment of the present invention provides an energy storage system, which can suppress trays from vibrating in a rack. In one embodiment, the energy storage system includes a rack including side frames; a guide plate formed between the side frames; at least one tray fixing unit inwardly protruding from the guide plate; a tray supporting unit inserted into a portion between the side frames along the guide plate and having one end positioned between the guide plate and the tray fixing unit.