Energy Storage System (ESS) is a set of device that converts electrical energy from solar energy or power systems into a form that can be stored for converting back to electrical energy when needed. ESS is structured in two main parts: the inverter or power conversion system (PCS) and the battery storage. The inveter or PCS handles AC/DC and DC/AC conversion, with energy flowing into the batteries to charge them or being converted from the battery storage into AC power and fed into the grid.