Solar panels perform at their best on sunny days with no cloud cover.
Come clouds or rain, power generation dips. In such conditions, solar panels produce their power from diffused solar radiation (radiation scattered by molecules in the atmosphere) as there is not much direct sunlight.
On average, it can be said that a cloud cover can reduce solar panel performance by 50%. If the sun is completely blocked by a cloud, the generation could crash by 80% of peak for that brief period of time!
Such drop in generation during rainy or cloudy days is one of solar power’s key disadvantages – renewable and economical it may be, but it is also an infirm source of power.