Batteries for Solar Systems

There are several different types of battery chemistry including liquid lead-acid, nickel-iron (NiFe), nickel-cadmium (NiCad), alkaline, and gel-cell. Batteries are either sealed or vented. Simply, there are only two principal types of batteries: starting and deep-cycle.

Starting Batteries

Starting batteries are designed for high cranking power, but not for deep cycling. Used as energy storage, they will not last long in a deep cycle application. Starting batteries use lots of thin plates to maximize the surface area of the battery. This allows very high starting current but lets the plates warp when the battery is cycled. This type of battery is not recommended for the storage of energy in hybrid system. However, they are recommended as starting battery for the back-up generator.

Deep Cycle Batteries

Deep cycle batteries are the type of battery best suited for use with inverters. The physical dimension of the plates is thicker and the active material that holds the charge is denser to increase cycle life. The deep cycle type of battery is designed to have the majority of their capacity used before being recharged. They are available in many sizes and in either non-sealed or sealed types.

Usual battery inverters are optimized for use with lead acid batteries that have a nominal voltage of 2.0 volts per cell. NiCad/NiFe batteries (also called alkaline batteries) have a nominal cell voltage of 1.2 volts per cell. The nominal voltage of a NiCad / NiFe battery bank can be made the same as a lead acid bank just by juggling the number of cells (10 cells for 12 volts, 20 cells for 24 volts and 40 cells for 48 volt systems). However, the NiCad/NiFe battery bank must be charged to a higher voltage to fully recharge and will drop to a lower voltage during discharging compared to a similarly sized lead acid type battery.