Ultimately it is solar radiation that produces the energy and the light energy is given off from the sun. As you can appreciate different areas receive different amounts of solar radiation. European Commissioned software has estimated the differences in energy production from PV Panels in the south and in the north of the UK and has found that a roof with the same angle and aspect in the north of Scotland produces considerably less energy when compared to the south of England.
The sun gives off light energy every day, even though it might be cloudy. So regardless of the weather this energy technique can still produce results. This energy is collected by the cells in the panels and turned into electricity. This electricity flows into the inverter which changes the energy into AC Electricity which is fed through a meter and can be used as a power source for your home. Your house will then run off of this generated electricity until the demand of your home outgrows the supply of you system or the sun goes down, only then will it start to draw from the national grid again/your energy provider.