Superior Technology Integration Knowledge
Having the proper battery capacity in an electrical circuit is important in order to:
- Supply the total power required by the load in a system
- Fully recharge the battery bank from the chosen power generation source or sources on a regular interval
- Ensure there is enough energy to power the load between charges
Determining the correct battery capacity to support a load requires knowing the total daily load requirements. The next step is to consider the type of battery for the application. For the purposes of this discussion, we will focus only on the lead-acid battery, as it is still the most commonly used type.
The battery bank should be sized based on the number of days you would like to operate autonomously without having to recharge the batteries. For example, if you want to operate for two days without recharging the batteries, multiply your calculated total daily load power requirements by two:
Total Daily Load Power Requirements (Wh) ∙ 2 = Battery Capacity
Image credit: Legendary Pictures
STIKmann determined the total daily electrical requirement for his appliances is 680 Wh, or 56.8 Ah. To operate autonomously for two days, STIKmann multiplies by two to get the following result:
|680 Wh ∙ 2||= 1360 Wh|
|1360 Wh ÷ 12 V||= 113.3 Ah|
STIKmann should use a 12 V battery that is rated for about 113.3 Ah or 1360 Wh of energy storage.
The average load is the determining factor for calculating how large a battery bank must be. A battery bank should be sized so the batteries are cycled (one full discharge followed by a full recharge) about twice each day. Solar Stik recommends a maximum of 50% depth of discharge for lead-acid batteries and 80% depth of discharge for LiFePO4 batteries. Properly sizing the battery bank keeps system cost down by ensuring both that the correct number of batteries is purchased (i.e., not more batteries than necessary) and that batteries are not damaged due to overcycling.