You'll collect the most power from the sun on bright, clear days. That being said, solar panels utilize IR, UV, and visible rays from the sun that can penetrate through clouds. Although the efficiency of the solar panel will decrease in cloudy conditions, you'll still be collecting valuable power from the sun. Also, keeping your solar panel angled toward the sun can dramatically increase efficiency. Set it up and let Mother Nature do the rest. Shop Goal Zero with us for highest cash back, exclusive coupons and promotions.