Any time there's light in the sky, solar PV operates to some level. Solar panels use the light from the sky either directly from the sun or scattered radiation from clouds, so even when its cloudy, solar works. It's possible to sometimes gain more energy with high or light cloud than with direct sun.
On some days when the sun is rising from the east, and there's little direct sunshine, say because of shading or because the panels face west, even if it's cloudy, the scattered radiation will start up the solar system early and produce more energy for a few hours than if it were a bright blue sky. Of course if its heavy cloud and raining - less energy is produced - but particularly in the case of solar PV it carries on working even at low light levels.
Generally, most people produce more in the summer and less in the winter and more is exported to the grid in the summer, building up a small cash reserve with Guernsey Electricity to offset your bill further. Alternatively, if you have a battery you can store energy for later when there is no sun. At certain times of year, depending on your array size and battery storage capacity, some can achieve 24 hour sun!
