To Calculate Solar Battery Bank Sizing

Choose the battery you want to use. (See our Battery Info sheet and Catalog of batteries) The first decision you have to make is how much storage you would like your battery bank to provide. Often this is expressed as "days of autonomy" because it is based on the number of days you expect your system to provide power without receiving an input charge from the solar panels. In addition to the days of autonomy, you should also consider your usage pattern and the critical nature of your application. If you are installing a system for a weekend home, you might want to consider a larger battery bank because your system will have all week to charge and store energy. Alternatively, if you are adding a solar panel array as a supplement to a generator based system, your battery bank can be slightly undersized since the generator can be operated in needed for recharging. Once you have determined your storage capacity, you are ready to consider the following key parameters.

Battery Sizing Sheet
1. Enter daily Amp hours ( line 5 of the DC Electrical Load Sizing Sheet)
2. Enter number of days of storage capacity ( typically 5 days no input )
3. Multiply line 1 by line 2 to get the amount of Amp hour storage needed.
4. Enter the discharge limit for the batteries ( between 0.2 - 0.8 ) Deep-cycle lead acid batteries should never be completely discharged, an acceptable discharge average is 50% or a discharge limit of 0.5
5. Divide line 3 by line 4.
6. Select the closest multiplier below for the average ambient winter temperature your batteries will experience. Enter the multiplier here.
Temperature F 80 F 70 F 60 F 50 F 40 F 30 F 20 F	Temperature C 26.7 C 21.2 C 15.6 C 10.0 C 4.4 C -1.1 C - 6.7 C	Multiplier 1.00 1.04 1.11 1.19 1.30 1.40 1.59
7. Multiply line 5 by line 6. This enables the battery capacity to endure cold temperatures. This is the total battery capacity needed.
8. Enter the Amp hour rating for your batteries.
9. Divide line 7 by line 8. Round off to the next highest number. This is the number of batteries wired in parallel needed.
10. Divide system voltage ( typically 12, 24 or 48 ) by battery voltage. This is the number of batteries wired in series needed.
11. Multiply line 9 by line 10. This is the total number of batteries needed.

Your next step is to calculate your solar module requirements.

Advance to solar module sizing work sheet.