Photovoltaic panels power generation efficiency on rainy days

While solar panels are most efficient under bright, direct light, they can still produce approximately 10-25% of their maximum solar energy output on a fully overcast cloudy day. [pdf]

Solar cells that generate electricity on rainy days

Yes, solar panels work on rainy days, but with less efficiency and power. On rainy days, you can get up to 25% of its total power delivery capacity. [pdf]