In solar lights, the energy output from solar photovoltaic systems is generally stored in a rechargeable battery or in an array of rechargeable battery cells (battery bank). During the day, solar panels convert solar energy into electrical energy using the photovoltaic effect of a p-n junction. The generated electrical energy is stored as chemical energy in the battery. During the hours of darkness, the chemical energy stored in the battery of an off-grid system is discharged in a controlled state to drive an external electrical load (i.e. an LED luminaire). In the case of grid connected system, rechargeable batteries are used as a backup system or an auxiliary power supply to deliver emergency lighting or to provide voltage and current stabilization.