My dad installed solar panels at our house recently and I was wondering why they generate so little electricity when it's cloudy. I get that the sun is covered, but doesn't light still pass through the clouds anyway?
The reason is that although light does pass through clouds, it arrives much weaker. Clouds aren't transparent - they reflect, absorb, and scatter a good portion of solar radiation before it reaches the panel. Imagine it's like looking at the sun through a curtain: you can see it's there, but the amount of light that gets through is a fraction of what you'd get without the curtain. Solar panels need photons with enough energy, and clouds dramatically reduce that flow.
Also, a panel's efficiency depends on the intensity of direct radiation. On a clear day they receive direct light and also reflected light from the surroundings. With dense clouds, most of that radiation gets blocked, and what does arrive is scattered. Depending on the type and thickness of the clouds, panels can be producing between 10 and 50 percent of their normal capacity. It's not that they stop working completely, but that's why your dad probably noticed such a big drop when the sky gets cloudy.
The good news is that even on cloudy days the panels generate some energy, so it's never a total loss. In the long run, it adds up.
Technically yes, light does pass through clouds, but what matters is the *intensity* of that radiation. Clouds absorb and scatter a huge amount of the photons coming from the sun, so what reaches the panels is maybe 10-25% of the radiation on a very cloudy day versus a clear day. Solar panels don't work like a lamp that detects any light; they need a minimum density of photons to be efficient, and on gray days that density drops quite a bit. That's why your dad probably sees a drastic difference in production between a sunny week and a rainy one.
Do you know how much energy solar panels lose when it's completely clear versus cloudy? The thing is, panels don't need to see the sun directly, but they do need radiation at a certain intensity, and clouds block about 50-80% of that energy depending on how thick they are. What a lot of people don't realize is that even on partly cloudy days, when it seems like there's plenty of light, your dad's panels are probably working at a fraction of their capacity because diffuse radiation (the kind that scatters through the atmosphere) is way less dense than direct radiation.
It's not that the panels stop working, it's that they lose a lot of efficiency 🌧️ What most people don't know is that even on cloudy days they keep generating something, but at a fraction of their rated capacity - it depends quite a bit on the type of cloud cover and how long the sky's been covered. If your dad has a monitoring system (most come with an app), you'll see that some gray days still produce 10-20% of what they generate with direct sunlight, so it's not absolute zero, but yeah it drops a lot.
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