Battery Bank – Solar Battery Storage

Working off from your power requirements, we will need to work out how many batteries you require and what type of batteries that would suitable. In finding out the capacity of your solar battery storage, there are numerous parameters we would need to obtain from you in order to properly size up the batteries.

We will require:

• Your energy consumption in kWh per day
• The voltage of your battery bank (usually around 12, 24 or 48 volts)
• The number of days in a row in which you expect there will be no sun
• Your preferred depth of discharge. This is almost always 50%
• The multiplier for a specific temperature for where the batteries will be stored. Below is a table which will help you understand which multiplier to use.

It is important to note that colder temperatures will have an effect on the capacity of the batteries. You can only take into account this multiplier if the room temperature is less than 26°C.

For example, a family’s energy usage is 10kWh per day and the voltage of their selected battery bank is 24V. Firstly, the initial capacity is calculated by dividing your energy usage in kWh by the voltage of the battery bank (10/24 = 0.4 AHr). Then the days of autonomy are taken into account, by multiplying those days by the capacity. The days of autonomy are normally around 2-3 days (0.4 * 3 = 1.2 AHr). Then the depth of discharge is considered next. For a DoD which is normally around 50%, this will mean that the current capacity of 1.2 AHr will be doubled to 2.4 AHr. Then, if your solar battery storage is in a room with cold temperature of less than 26°C, then a temperature multiplier will have to be taken into account. This number will be multiplied by the capacity to calculate the final amount. You can view this table below:

Ambient Temperature Multiplier
80ºF 26.7ºC 1.00
70ºF 21.2ºC 1.04
60ºF 15.6ºC 1.11
50ºF 10.0ºC 1.19
40ºF 4.4ºC 1.30
30ºF -1.1ºC 1.40
20ºF -6.7ºC 1.59

So now what are the type of batteries that you would be after? Selecting the battery you want will depend on the capacity and voltage of both the entire bank and of the individual battery. Two highly reputable battery brands are known as Trojan and Surrette.