Step 6 - Select an appropriate Charge controller

The third key component you need to design and select is the battery charge controller. The Battery charge controller regulates the charging of the batteries to ensure batteries have a long life. The most important specifications to look for in a controller are Voltage and Ampere capacity and a special feature called MPPT (Maximum Peak Point Tracking).MPPT controllers are more expensive but improve efficiency of the system by helping "squeeze" more out of your PV System and charge the battery bank

Ensure that the Charge controller is rated for the Nominal DC voltage of your system. Also calculate the maximum current the charge controller needs to be capable of handling using the formula below:
Maximum Input current to Charge controller = Number of PV Panels in Parallel x PV Panel rated current at Short Circuit (Isc) * 1.25

The controller you choose should be rated and capable of both the DC system voltage as well as the maximum input current to the charge controller. A charge controller that is MPPT capable is also recommended to get the most out of your PV system. Also if you are using Lead-Acid batteries, a Charge controller with built in Equalization functionality is essential to keeping the battery array efficient. More information on Equalization can be found in the section on Charge Controllers.

The design section of this site has automated the calculations above and comes with a drop down list of all available commercial charge controllers to help choose the right charge controller required for your system. Availability and pricing can be found at my partners Charge Controllers section.

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Step 0: Determine the Solar Hours of your location
Step 1: Estimate the critical loads that need to be supported
Step 2: Determine the days of Autonomy for the system
Step 3: Select a "Nominal" DC side voltage that the design will be based on
Step 4: Select the PV Panels to be used for the system
Step 5: Select the Battery manufacturer and model to be used in System
Step 6: Select an appropriate Charge controller
Step 7: Select an appropriate Inverter
Step 8: Calculate and select BOS components