One of the most common and cost-effective applications of photovoltaics is the stand-alone system, which typically employs a photovoltaic array to charge a battery. The battery furnishes power at night and when skies are cloudy; the system may include a charge controller to regulate operation of the battery and an inverter to convert the DC electricity of the battery into AC electricity, for those applications requiring it. In some systems, such as those providing power for water pumping, the battery is not necessary and the PV array may be connected to the load directly or via an electronic controller.