Generally, the batteries are provided are of 2V cells connected in series to reach the system voltage. Battery shall be suitable for charging from SPV system as well as from the grid in case of grid interactive system and with SPV system alone in case of stand alone system.
Normally in a solar PV system with battery, battery is first charged from solar system through Charge Controller. A charge controller monitors the battery’s state-of-charge to insure that when the battery needs charge current it gets it, and also insures the battery isn’t over-charged. Connecting a solar panel to a battery without a regulator seriously risks damaging the battery and potentially causing a safety concern.
Charge controllers (or often called charge regulator) are rated based on the amount of amperage they can process from a solar array. If a controller is rated at 20 amps it means that you can connect up to 20 amps of solar panel output current to this one controller. The most advanced charge controllers utilize a charging principal referred to as Pulse-Width-Modulation (PWM) – which insures the most efficient battery charging and extends the life of the battery. Even more advanced controllers also include Maximum Power Point Tracking (MPPT) which maximizes the amount of current going into the battery from the solar array by lowering the panel’s output voltage, which increases the charging amps to the battery – because if a panel can produce 60 watts with 17.2 volts and 3.5 amps, then if the voltage is lowered to say 14 volts then the amperage increases to 4.28 (14v X 4.28 amps = 60 watts) resulting in a 19% increase in charging amps for this example.
Many charge controllers also offer Low Voltage Disconnect (LVD) and Battery Temperature Compensation (BTC) as an optional feature. The LVD feature permits connecting loads to the LVD terminals which are then voltage sensitive. If the battery voltage drops too far the loads are disconnected – preventing potential damage to both the battery and the loads. BTC adjusts the charge rate based on the temperature of the battery since batteries are sensitive to temperature variations above and below about 75 F degrees.