Solar panels can still generate electricity even on dark and cloudy days. During the day, the photovoltaic effect activates solar cells, demonstrating the high efficiency of solar panels in generating. . Solar panels use sunlight to generate electricity, but they can do it around the clock, even when the sun isn't shining. We can tap the sun's power using. . Rising electricity bills, power outages and a growing interest in reducing one's carbon footprint, have all been reasons more homeowners are installing solar panels to generate their own renewable electricity. Even though this is a big drop, it doesn't mean that cloudy days are useless for solar cells. Clouds might reduce efficiency, but they won't stop solar panels completely. People often wonder about its effectiveness when the sky is overcast.