Energy storage
There are many different types of batteries on the market. This is the case because there is no single type of battery that is superior in all applications. Each type of battery has uses different combinations of materials that have different advantages and disadvantages. All battery designs have to balance the following characteristics:
- Cycle life (life span)
- Cost
- Specific energy (energy capacity relative to size)
- Specific power (power capacity relative to size)
- Safety
- Performance under variable conditions
- Maintenance
A battery may have a long life span and be able to handle large loads, but it will have large and heavy or cost too much. A battery may be able to supply lots of power and be realtively small in size, but it wil not have a long lifespan. A battery must therefore be chosen based upon the particular application. A radio needs a different batter than a PV system. Small-scale PV systems with batteries typically rely upon lead acid batteries. Lead acid batteries are a good compromise between all of these different factors.
Contents
Characteristics of batteries
Voltage
Batteries are rated with a nominal voltage (Vn). This voltage is called a nominal voltage as the voltage of batteries constantly varies depending on if they are being charged/discharged, their State of charge and the Temperature.
Storage capacity
The energy storage capacity of a battery will be rated in Amp-hours (Ah). or Watt-hours (Wh). Amp-hours is the standard for lead acid batteries, but it is becoming more common to rate batteries in Watt-hours because to design an energy storage system it is necessary to convert from Amp-hours to Watt-hours to understand the capacity of the system relative to the loads. This calculation is simple:
Storage capacity = Ah × Vn
- Example 1: You have a 12V 120Ah battery. What is the capacity of the battery?
- Storage capacity = 12V × 120Ah
- Storage capacity = 1440Wh
- Example 2: You have two batteries connected together that are each 12V and 60Ah. What is the capacity of the battery bank?
- Storage capacity = 12V × 60Ah × 2 batteries
- Storage cpacity = 1440Wh
Different sizes and voltage of batteries can be conneted together to achieve the same amount of storage capacity.
Cycle life
Cycle life is the number of charge and discharge cycles that an energy storage device can provide before performance decreases to an extent that it cannot perform as required. The cycle life, or longevity, of all batteries depends upon the following factors:
