Battery generally converts electrical energy stored into chemical energy for storing purpose. Batteries are charged and discharged. Basically it is a storage device which stores the excess power generated and uses it to supply the load in addition to the generators when power demand exists. Both solar PV and wind energy systems are integrated together with battery bank connected to a common DC bus of constant voltage. Power transfer from the battery bank to the load takes place via this constant voltage DC bus.
There are various types of batteries in the market like Lithium Ion, Lead-Acid, Nickel Cadmium, and Nickel Metal Hydride. High discharge rates are achieved by Lead-Acid batteries; these batteries offer a better solution for applications of energy storage. Nickel Cadmium (NiCd) batteries are better in all qualities and have low maintenance requirements than the Lead-Acid batteries. Storage capacity of the battery is measured by Ah (Ampere –hour). Battery Capacity is expressed in KWh (Kilowatt-hour).
The amount of energy or charge in the battery is represented in percentage of energy available in electrical fully charged battery as State of charge of battery represented as SOC of battery