What should you know about solar battery parameters?

Solar battery technology is the core of the solar power revolution that is still all the rage today. As battery technology develops, and the demand for renewable energy solutions such as solar increases, the accessibility to solar batteries is only rising. Since the battery is such a critical part of the energy system, it must be chosen carefully. As such, whether you’re already operating with a solar panel system or you’re considering investing in solar, it is essential to be well-aware of your battery storage options.

In this article, we will talk about some important parameters to keep in mind while choosing the right batteries for your system.

Storage Capacity

It determines for number of hours for which the battery can be discharged at a constant current to a defined cutoff voltage. The value of this capacity depends on the ambient temperature, the age of the battery, and the discharge rate. The higher the discharge rate, the lower the capacity, although it affects each battery technology differently. Additional to the Ampere-hour unit, the storage capacity can also be defined in Watt-hours (Wh=V x Ah), where 1 Wh represents 3600 J.

Cycle life

The number of charge/discharge cycles a battery has before it is considered to have reached its ‘end of life’. Some battery manufacturers give cycle life as full cycles, while others may count even a partial cycle as one full cycle. Lithium batteries will typically have a cycle life of 4,000-10,000 cycles, while a lead battery might be as low as 1,000 cycles. For lead batteries, cycle life can be extended by designing the system to have a lower depth of discharge.

Depth of Discharge

In many types of batteries, the full energy stored in the battery cannot be withdrawn (in other words, the battery cannot be fully discharged) without causing serious, and often irreparable damage to the battery. The Depth of Discharge (DOD) of a battery determines the fraction of power that can be withdrawn from the battery. For example, if the DOD of a battery is given by the manufacturer as 25%, then only 25% of the battery capacity can be used by the load.

Nearly all batteries, particularly for renewable energy applications, are rated in terms of their capacity. However, the actual energy that can be extracted from the battery is often (particularly for lead acid batteries) significantly less than the rated capacity. This occurs since, particularly for lead acid batteries, extracting the full battery capacity from the battery dramatically reduced battery lifetime. The depth of discharge (DOD) is the fraction of battery capacity that can be used from the battery and will be specified by the manufacturer. For example, a battery 500 Ah with a DOD of 20% can only provide 500Ah x .2 = 100 Ah.

Maximum Power

The maximum amount of power that a battery can generate at a given time, for a short period (usually 3-30 seconds), in kilowatts (kW). An example of when maximum power might be required is when you switch on a blender or vacuum cleaner, both of which cause a sudden surge before leveling off. Maximum output power may be limited by the capacity of the system’s inverter.

Round-Trip Efficiency

Due to internal losses and material degradation, not all the energy supplied to the battery during charging can be recovered during discharge. The amount of energy that can be taken from the battery during the discharging process over the energy supplied determines the round-trip efficiency. This efficiency is sensitive to the charging and discharging currents. At higher currents, thermal losses increase and therefore the efficiency is reduced.

The above is the introduction for some important solar battery parameters. Knowing more about these parameters helps you choose the suitable storage battery for your solar energy system.