Buyers guide

Check out the latest developments in charge controllers.

by Justine Sanchez & Brad Burritt

Charge controllers are vital components in battery-based PV systems, keeping the PV array from overcharging the batteries and optimizing charge current. These smart little boxes are placed between the PV array and the battery bank, and allow maximum energy in when the batteries are at a low state of charge (SOC) and reduce incoming energy from the array as the batteries approach full. When the battery reaches 100% SOC, the charge controller reduces the energy flow to a small maintenance (float) charge. Without a charge controller, a battery can be overcharged, resulting in excessive battery gassing and, in chronic cases, damage to the battery, shortening its life span.

Matching the appropriate charge controller to a particular PV system is important for proper system function and for maximizing the amount of solar energy harvested. This guide lists charge controllers 40 amps or above commonly used for whole-house PV systems.

OutBack's FlexMax charge controller.

Array & MPPT Charge Controller Sizing Example

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

Example Array & Charge Controller Specs

PV Modules Spec


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