Solar Energy Batteries / The 2 Types of Batteries
Batteries serve important roles in solar energy systems. They are used as back-up resources in grid-connected systems while they are the main component in stand-alone systems. Because of their importance it is crucial to have the right type of battery.
Generally, there are two types of batteries. These are NiCad (Nickel-Cadmium) and L-A (Lead-Acid) batteries. L-A batteries are often those that are readily available and affordable. However, typical L-A batteries are composed of cells that are not sealed and are thus prone to leaks. To counter that problem, gel and AGM batteries have been developed. These are types of L-A batteries that are sealed and maintenance-free.
Solar Energy Batteries / Deep vs Shallow
Apart from choosing battery types, you have to take into consideration the depth of charging cycles as there are both shallow and deep cycle batteries and only the latter is suitable for use with solar energy systems.
Shallow cycle batteries are not capable of withstanding repeated deep discharging. They generate high currents only for a short period of time and less than 20% of the stored energy can be discharged. Shallow cycle batteries are not suitable for use in solar energy systems but are particularly useful to power cars that need current only to start.
On the other hand, deep cycle batteries are ideal for solar energy systems because stored energy can repeatedly be discharged by up to 80%. Nevertheless, it is recommended for these types of batteries to be discharged only at a maximum of 50% to ensure long battery life.
Solar Energy Batteries / Capacity and Size
When choosing batteries for a solar energy system, it is also important to take battery capacity and size into consideration. The battery capacity is determined by how much electrical energy (measured in Ampere hours) a battery can supply throughout a specific period of time.
A battery that delivers 1 ampere of current for 20 hours would then have a rating of 20Ah. On the other hand, the size of the battery is determined by the required storage capacity. To compute for this, one needs to know the solar energy system’s voltage, the number of days the battery should serve as back up, and the amount of energy required per day.
The required discharge load (in watt-hours) should then be multiplied by the required storage days and the product should be divided by the system voltage while taking losses into account. For example, a 5-day back up for a 12-volt solar energy system that discharges at the rate of 1.44kW per day would require a total of 7200 watt hours over 5 days (1440 watt hours x 5 days). The required storage capacity at 12 volts would then be 750Ah (7200 watt hours / 12 * 0.8). The system would then need 4 200Ah batteries (750Ah / 200Ah).
There is no standard battery requirement for all energy systems and it can only be determined by taking into consideration the required battery cycle depth, battery capacity, and battery size.
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