# Off grid Solar Array Sizing

Date: 11/19/2014

### FAQS Summary:

Determine how much current the solar array must produce to identify the total number of solar modules required for the system.

### FAQS Content:

# WORKSHEET OFF-GRID SOLAR ARRAY SIZING

**Worksheet:** Off-Grid Solar Array Sizing

Determine how much current the solar array must produce to identify the total number of solar modules required for the system.

________ Step 1: List the total average amp-hours per day needed. Obtain this number from the Off-Grid Loads Worksheet.

________ Step 2: Multiply the amp-hours per day needed by 1.2 to compensate for battery charge/discharge losses.

________ Step 3: List the average sun-hours per day in the system’s area.

Check local weather data, look at the map below, or find a city on the Solar Insolation Table in the Reference Section that has similar latitude and weather to your location. If you want year-round autonomy, use the lower of the two figures. If you wnat 100% autonomy only in summer, use the higher figure. If you have a utility grid-tie system with net metering, use the yearly average figure.

________ Step 4: Divide the result of Step 2 by the average sun-hours per day from Step 3 to get the total solar array amps required.

**Sizing Solar Arrays with PWM Charge Controllers**

*If you are planning a small low-cost system with a PWM charge controller, continue to Step 5 below. If you are planning a larger system with an MPPT charge controller, go to Step 5 in “Sizing Solar Arrays with MPPT Charge Controllers.” Information on the different types of PV charge controllers can be found in the Charge Controller section.*

________ Step 5: Find the peak amperage of the module you will be using form its specifications or Data Sheet. We provide the peak power current of our most popular modules in the Solar Module Section.

________ Step 6: Divide the total solar array amps required from Step 4 to get the total number of parallel strings of modules required. Round up to the nearest whole number.

________ Step 7: Use the table below to determine the number of modules in each series string needed to provide DC battery voltage.

Note: Due to the industry shift to larger PV cells, 24 VDC solar modules may not be available from NET-ENERGY.US.

________ Step 8: Multiply the number of strings from Step 6 by the number of modules per string from Step 7 to get the total number of solar modules required.

Sizing Solar Arrays with MPPT Charge Controllers

________ Step 5: Note the total solar array amps required. Obtain this number from Step 4 of the Off-Grid Solar Array Sizing worksheet.

________ Step 6: Enter the average charging voltage. Use 13.5 VDC for 12 VDC systems; 27 VDC for 24 VDC systems; or 54 VDC for 48 VDC systems.

________ Step 7: Multiply the total solar array amps required from Step 5 by the average charging voltage from Step 6 to determine to total PV array wattage required.

________ Step 8: Enter the nameplate power (in watts) of the PV module you plan to use.

________ Step 9: Divide the total PV array wattage required from Step 7 by the module nameplate power from Step 8 to determine the total number or modules needed. Round up to the nearest whole number. (NOTE: This number may need to be adjusted in Step 11).

________ Step 10: Use the table below to determine the number of modules in each series string.

________ Step 11: Divide the total number of modules from Step 9 by the number of modules per series string from Step 10.

* This is the total number of array series strings.* If this is not a whole number, increase or decrease the number of modules to obtain a whole number of series strings.

* CAUTION*: Decreasing the total number of modules may result in insufficient power production.

________ Step 12: Multiply the module nameplate power from Step 8 by the number of modules per string from Step 10 to determine the total wattage per string.

________ Step 13: Find the total number of chosen controllers needed.

Divide the appropriate wattage figure from the chart below by the wattage per series string from Step 12 to determine the total number of module strings per controller. Round down to the nearest whole number. If you have more series strings (from Step 11) than can be handled by the chosen controller, either use a larger controller or use multiple controllers in parallel.

________ Step 14: Divide total number of strings from Step 11 by the number of strings per controller from Step 13. Round up to the nearest whole number.