Solar PV system needs light to generate electricity. If Sunlight is low, as on a cloudy day, the solar system still generates electricity but the generation is lower. This reduced generation, however, may not create any disruptions for you. If you have a grid-connected Solar PV system, electricity will be automatically sourced from the grid in case Solar PV generates less. In case of an off-grid system with battery backup, energy will be sourced from the storage battery.