Calculating the configuration of your array based on your charge controller and calculating the number of controllers needed is not rocket science—just gather the necessary info, then use simple formulas to come up with the results.

**1. Find the maximum Voc per module based at a record low temperature of -29°C (-20°F). (Find your site’s record low temp at www.weather.com.)**

Voc per module at STC (25°C) = 33.2 V

Temperature difference between STC & record low = 25°C - (-29°C) = 54°C

Use the module’s temperature coefficient specification to find the Voc increase at record low temperature = 54°C x 0.12 V/°C = 6.48 V

Voc/module at record low temperature = 33.2 V + 6.48 V = 39.68 V

**2. Find the maximum number of modules that can be used in series based on the example controller’s 150 V maximum Voc.**

Two series modules: Voc = 39.68 V x 2 = 79.36 V = OK

Three series modules: Voc = 39.68 V x 3 = 119.04 V = OK

Four series modules: Voc = 39.68 V x 4 = 158.72 V = Too high!

Three modules in series is the maximum.

**3. Find the number of controllers required and the number of module series strings per controller.**

4,920 W (array peak size) ÷ 46 V (min. battery voltage anticipated) = 107 A

107 A (total max. output current required from MPPT controllers) ÷ 60 A (output per controller) = 1.8 controllers. Two 60 A controllers are needed.

For our total of eight series strings (24 modules at 3 modules per series string = 8 strings), put four strings on each of two 60 A charge controllers. Each charge controller will be wired to 12 modules (4 strings x 3 modules per string).