Electricity generated from solar plants is typically stored in batteries to provide steady, continuous power for a duration of time. Therefore deep discharge (also known as deep cycle batteries) are used. This is a type of lead acid battery that can repeatedly discharge itself by more than 50% of its full charge, without being damaged. These batteries are different from automotive batteries, which are designed to primarily drive starter motors – heavy discharge for short durations of time.
Solar PV systems are usually combined with VRLA (Valve Regulated Lead Acid) batteries. These are a type of sealed battery that requires little maintenance. These batteries are similar to those used in large applications like telephone exchanges, etc.
Lithium-ion batteries are an emerging storage solution being explored for solar power, but they are yet to see widespread adoption for storing solar power.
When considering batteries for a solar PV plant, it is important to remember that some energy is lost both when charging and discharging the battery. As much as 25% of may be lost totally when using lead acid batteries. This factor should also be included in cost calculations.