Energy storage system

An energy storage system, comprising:

• a plurality of battery racks, each battery rack including a plurality of stacked battery modules;
• and
• a container accommodating the plurality of battery racks,
• wherein the container includes:
• a bottom plate in which the plurality of battery racks are disposed;
• a fire fighting water collection chamber including a water level sensor;
• and
• a valve unit coupled to a wall of the container to drain a fire fighting water collected in a fire fighting water collection chamber out of the container,
• wherein the valve unit is configured to be opened or closed based on a signal from the water level sensor.