How much power do solar panels produce on a cloudy day?
A solar panel produces about 10 to 25 percent of its clear-sky output under a thick, dark overcast, and roughly 25 to 50 percent under a bright gray or thin, broken cloud cover. The single variable that matters most is how much light the clouds let through: a light haze barely dents production, while a black storm cloud can drop it below 10 percent for a while. There is no fixed number because no two cloudy skies are the same.
Two details surprise people. First, a passing cloud can briefly push output above a clear-sky reading. When the sun sits just at the edge of a cloud, the panel gets full direct sun plus extra light bouncing off the bright cloud edge, a real effect called cloud enhancement. Second, cloudy days are usually cooler, and panels are slightly more efficient when cool, so a little of the light loss is clawed back. Neither changes the headline: expect a fraction of a sunny day, not nothing.
You never plan a system around a single gray afternoon anyway. Production is figured across a whole year, and the estimate in the solar panel calculator already blends sunny, cloudy, and rainy days into one annual number.
Why do solar panels still work when it is cloudy?
Solar panels keep working under clouds because they use diffuse light, not just direct sunbeams. Sunlight reaching the ground comes in two forms: direct light straight from the sun, and diffuse light scattered by the atmosphere, clouds, and haze. On a clear day most of it is direct; under an overcast sky nearly all of it is diffuse. A photovoltaic cell converts both, so as long as it is bright enough outside to see without a flashlight, the panel is generating.
The proof is on your own skin. You can still get sunburned on a cloudy day because plenty of the sun's energy, including the ultraviolet and visible light panels feed on, passes right through the cloud layer. Clouds scatter and weaken that light, they do not absorb all of it. That is the whole reason a panel behaves like a dimmer switch in bad weather rather than an on-off switch.
Does solar still make sense in a cloudy climate?
Yes. Cloudy regions get less sun than the desert Southwest, but solar still pencils out in most of them, and the proof is that Germany, one of the cloudiest developed countries, has long been among the world leaders in installed solar. Closer to home, the Pacific Northwest around Seattle and Portland has a healthy solar market despite its reputation for gray winters. Fewer sunny hours means a longer payback, not a dead deal.
What matters is the yearly total, captured by your peak sun hours, the daily average of full-strength sun your location gets after all the clouds and short days are averaged in. A cloudier area simply has a lower peak-sun-hour number, so you may size a slightly larger array to hit the same output. See what peak sun hours are for how that average is built, and how much energy a solar panel produces for the daily and yearly math.
Run your own address through the solar panel calculator rather than trusting a gut feel about your weather. The regional sun-hour data already accounts for your local cloud cover, so the estimate you get is a realistic full-year figure, not a best-case sunny-day dream.
Cloudy days vs shade vs night: what is the difference?
Clouds, shade, and night hurt solar output in three different ways. Clouds dim every panel evenly, so the whole array drops together to some fraction of full power. Hard shade from a tree limb, chimney, or vent is worse per square foot, because one shaded panel wired in a string can drag down the healthy panels around it. Night is the only true zero: with no light at all, panels make no power.
That difference is why shade, not clouds, is the case where equipment choice matters. Microinverters or power optimizers let each panel work independently, so shade on one does not sink the rest, and they do far more for a partly shaded roof than for a cloudy sky, which affects all panels the same. If trees or a neighbor's roofline shade your array, read what a solar microinverter is and what a power optimizer does.
For the after-dark gap, clouds have nothing to do with it. Power you use at night comes from the grid through net metering or from a battery that banked the day's surplus, covered in do solar panels work at night. Cloudy winters combine short days and gray skies, which is why do solar panels work in winter is worth a look if you live somewhere with long overcast stretches.
How cloudy days affect solar batteries and off-grid systems
On a grid-tied home, cloudy days barely register. When your panels underproduce, the house quietly pulls the difference from the grid, and net metering smooths the whole month out, so a run of gray days just means you draw a bit more from the utility and bank fewer credits. You do not notice it day to day.
On an off-grid system, cloudy stretches are the hard design problem. A battery only holds what the panels put in, so several dim days in a row can leave you short. Off-grid builders handle this two ways: sizing the battery for two to three days of autonomy so it rides through bad weather, and oversizing the array so even a cloudy day tops the bank up partway. A backup generator often covers the rare long overcast spell rather than paying for a battery big enough to never need one.
Either way, treat a cloudy day as a partial charge, not a full one, and plan around clear-day production. To weigh storage for backup or off-grid use, see best solar battery backup for home.
Do you need special panels for cloudy days?
No. There is no special cloudy-day solar panel worth paying extra for, and any pitch built around one is marketing. Every silicon panel responds to low light in roughly the same proportional way, so the honest move is to buy the most efficient panel you can afford, because a higher-wattage panel simply makes more power in any light, sunny or gray.
You may hear that thin-film panels handle diffuse light better. There is a grain of truth in the lab, but modern high-efficiency monocrystalline panels still produce more total energy per square foot across a real year, cloudy days included, so they win for almost any rooftop. The low-light edge, if any, is small and swamped by the efficiency gap. See solar panel efficiency explained for what the rating actually buys you.
So the smart response to a cloudy climate is not a magic panel. It is a slightly larger array of ordinary high-efficiency panels, sized from your local sun hours, which the solar panel calculator works out for you.
Frequently asked questions
How much electricity do solar panels produce on a cloudy day?
About 10 to 25 percent of their clear-sky output under a thick, dark overcast, and roughly 25 to 50 percent under bright or broken cloud. The driver is cloud thickness: light haze barely lowers production, while a heavy storm cloud can push it below 10 percent. A brief spike above normal can even happen when the sun peeks past a cloud edge, an effect called cloud enhancement.
Do solar panels work in the shade?
Partly, but shade hurts more than clouds do. A cloud dims every panel evenly, while hard shade from a tree or chimney can drag down a whole string of panels wired together. This is why microinverters or power optimizers help a shaded roof: they let each panel work on its own so one shaded module does not sink the rest. For a sky-wide overcast, though, that equipment makes little difference since all panels dim together.
Do solar panels work in the rain?
Yes, at reduced output, the same as any cloudy day, since rain comes with clouds that cut the light to roughly 10 to 25 percent of clear-sky levels. Panels are fully weatherproof, so rain causes no harm, and there is a small upside: rain rinses off dust and pollen, which can slightly improve output once the sun returns.
Are there special solar panels for cloudy days?
No. There is no cloudy-day panel worth a premium; all silicon panels lose output proportionally in low light. The best choice for a gray climate is simply the most efficient panel you can afford, since a higher-wattage panel makes more power in any light. Thin-film panels are sometimes marketed for low light, but modern high-efficiency monocrystalline panels still produce more total energy across a real year.
Do solar panels work with moonlight or at night?
No, not in any useful way. Moonlight is roughly one four-hundred-thousandth as strong as sunlight, so panels make essentially zero power from it, and none at all in full dark. Any electricity you use at night comes from the grid through net metering or from a battery that stored the day's surplus, not from the panels themselves.