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The off-Grid system relies heavily on better-abled storage systems. 

Battery: Stores energy by chemical reactions. Most stand-alone PV systems use lead-acid batteries.

Flooded lead-acid battery: A battery that has a liquid electrolyte (fluid) and uses chemical reactions between lead and acid to store energy.

Sealed valve regulated flooded lead-acid battery: This type of battery is often known to be maintenance-free,  since you cannot add fluids to a sealed battery. There are valves present, used for releasing gasses, so the battery does not explode.

Charge controller: These are an important part of off-grid systems. Controllers help regulate the charging of batteries, so they are not overcharged or undercharged. Controllers can be for stand-alone systems or grid-tied battery backup systems. The highest voltage for a charge controller is for the equalization charge, which is only used on flooded lead-acid batteries that fluid can be added to. The equalization charge is simply meant for battery maintenance.

Battery inverter: An inverter that makes voltage from a battery and produces current and power, as it is needed. A battery inverter is hooked up to a battery and not the PV module.

Battery inverter input circuit: The conductors between the battery and the battery inverter, which are sized according to the power of the inverter and the lowest battery voltage. A lower voltage requires more current for the same power since power = voltage × current.

Maximum Power Point Tracking (MPPT) charge controllers: MPPT is used only for devices that are connected to PV and will optimize production. MPPT controls the IV parameters and will cause the inverter or charge controller to work on the point of maximum power on the IV curve. It is important to note that, an off-grid inverter connected to a battery, does not have MPPT.

Most of the basic system components for a PV system have been covered here.