Use this worksheet to determine the total energy in amp-hours per day used by all the AC and DC loads in your system.

To find average sun-hours per day in your area (line 3), check local weather data, look at the map here or find a city here that has similar weather to your location.  If you want year-round autonomy, use the lowest of the two figures.  If you want 100% autonomy only in summer, use the higher figure.  If you have a utility intertie system with net metering, use the yearly average figure.  The peak amperage of the module you will be using can be found in the module specifications.  You can also get close enough if you divide the module's rated wattage by the peak power point voltage, usually 17 to 17.5 for a 12 volt module or 35 to 35 volts for a 24 volt module.

Step 1 Total average amp-hours per day needed from the Off-Grid Loads Worksheet, line 10

 

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Step 2 Multiply line 1 by 1.2 to compensate for loss from battery charge / discharge

 

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Step 3 Average sun-hours per day in your area

 

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Step 4 Divide line 2 by line 3.  This is the total solar array amps required

 

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Step 5 Optimum or peak amps of solar module used.  See module specifications

 

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Step 6 Total number of solar modules in parallel required.  Divide line 4 by 5

 

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Step 7 Round off to the next highest whole number

 

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Step 8 Number of modules in each series string to provide DC batter voltage - See chart below

 

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Step 9 Total number of solar modules required.  Multiply line 7 by line 8. _____________

 

 

Nominal System Voltage Number of Series Connected Modules Per String
Volts 12V Module 24V Module
12 1 N/A
24 2 1
48 4 2