Modern PV cells are pretty effective even in cloudy weather. Mine seem to produce more energy on overcast wintery days than on sunny wintery days because there are fewer harsh shadows that way.

This depends on the kind of clouds. Thick, low hanging clouds look gray for a reason.

Make and model please. I'll be adding more solar on my roof and the current ones (sunpro SP460-N120M10) don't perform well during cloudy days.