Step 5 - Select the Battery manufacturer and model to be used in System

The second key component you need to design and select are the batteries. The Batteries store energy during the day when the PV array is producing energy and release energy when the PV Array is not producing energy. The most commonly used batteries in PV systems are Lead Acid Batteries and Alkaline Batteries. More information on batteries can be found in the section "Batteries". Most batteries are specified in AmpHours based on discharge rates and Voltage. When choosing the battery bank for your PV system, keep in mind that the best choice for the battery bank is to have a voltage rated at the nominal voltage of the PV Array system designed above. Battery banks can have a voltage rating below the nominal PV array voltage, in which case you must use a MPPT Capable Charge controller to improve efficiency, but the battery bank voltage must never be designed at a higher voltage than the PV Array system. Also the following parameters affect the size of the battery bank needed for the system: Depth of Discharge, State of Charge, temperature Effects on the battery and inverter efficiency.

The following calculations need to be done to design and select the battery bank:

Amp Hour Capacity of Battery Bank =	Amp Hours per Day x Days of Autonomy
	Losses to be taken into account

Where Losses =

Battery Max Depth of Discharge x Nominal State of Charge x (1-losses due to temperature effects) x (1-losses due to Inverter Inefficiency)

Allowable voltage drop =

DC system voltage x 2%

Number of Batteries in Parallel =	Amp Hour Capacity of Battery Bank
	Battery rated Amp Hours

Number of Batteries in Series =	DC System Voltage
	Battery Rated Voltage

Total number of batteries in the bank = Number of batteries in Series x Number of batteries in Parallel

The design section of this site has automated the calculations above and comes with a drop down list of all available commercial batteries to help calculate the number of batteries required for your system. In addition to calculating the size of the battery bank for your system you will also have an estimate of the price, the warranty and other characteristics of the batteries.

Next-->

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