For those solar panels that you install on your rooftops, do they generate electricity when it's cloudy? And if yes, how much electricity does it generate compared to sunny days? For example...like only 25% electricity generated compared to sunny days?
No, silicon photovoltaics reacts to a very specific frequency of infrared light which matches the bandgap energy of it's outer electron shell. This frequency is reflected by clouds. However, thermal solar collectors such as evacuated tube collectors can function under cloudy skies albeit at a lower rate and there is at least one hybrid photovoltaic and thermal panel designed to take advantage of this.
Yes. If there is any light, even on a cloudy day, a solar panel can generate power. But the amount of power generated is much less when the solar panel is not in direct sunlight (about 90% less). On a cloudy day, typical solar panels can produce 0-25% of their rated capacity. The exact amount will vary depending on the density of the clouds, and may also vary by the type of solar panel; some kinds of panels are better at receiving diffuse light. SunPower solar cells, for example, have been designed to capture a broader range of the solar spectrum. By capturing more red and blue wavelengths, their solar panels can generate more electricity even when it’s overcast. Ultraviolet light also reaches the earth’s surface in abundance during cloudy days (if you’ve ever been at the beach when it’s cloudy and gotten a sunburn, you’ve experienced this firsthand). Some solar cells are in development that can capture UV rays, although these are not out on the market yet. Even with a standard solar panel on a cloudy day, though, you will be able to generate some power when it’s daylight. The same thing is true in foggy weather. If you live in a city with frequent fog, like San Francisco, you’ll still be able to generate electricity when the fog rolls in. :)
From my understanding they generate electricity when the suns out and when its out and there aren't too many clouds around covering up. They store some electricity for the winter and cloudier times but I'm not really an expert!
