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WattCurious

Do Solar Panels Work on Cloudy and Rainy Days?

Updated 8 October 20267 min readSolar Energy

Yes. A solar panel converts whatever light reaches its surface, not only direct sunbeams, so it keeps producing under cloud and rain. Heavy overcast typically leaves a tenth to a quarter of clear-sky output; bright cloud leaves far more. What the weather takes away is irradiance, not the panel's ability to work.

Key takeaways

  • Cells respond to photons, not to warmth or to direct beam. Under cloud nearly all the light arriving is diffuse, and diffuse light frees electrons exactly as direct light does.
  • Current tracks irradiance almost proportionally, so output falls roughly in step with how much light the cloud lets through — not off a cliff.
  • Rain costs little by itself, and often pays for itself by washing off the soiling that had been quietly costing output for weeks.
  • Broken cloud is not overcast: bright cloud edges can briefly push output above the clear-sky value before the next shadow arrives.
  • A weather dip follows the sky and recovers with it. A fault does not. That difference is the fastest diagnostic available.
On this page
  1. What cloud actually blocks
  2. How much output you lose under different skies
  3. Why cells respond to diffuse light at all
  4. What rain adds, and what it takes away
  5. The shape of a cloudy day
  6. Telling weather apart from a fault

What cloud actually blocks

Sunlight arrives at a panel by two routes. Direct beam travels in a straight line from the sun's disc. Diffuse light has been scattered by air molecules, water droplets and dust, and arrives from the whole sky dome at once. Add them together — plus whatever bounces up off the ground — and you have the irradiance the panel actually sees.

Cloud does not switch light off. It converts it. A droplet-laden cloud scatters the beam so thoroughly that the sun stops being a disc and becomes a bright patch, and eventually a uniform grey ceiling. Some of that scattered light continues downward and reaches the panel; some is reflected back to space. On a clear day the beam does most of the work. Under heavy overcast the beam is effectively gone and the panel runs entirely on diffuse light.

A rooftop solar panel under a partly clouded sky. Direct beam reaches the panel where the sky is clear, while a cloud scatters sunlight into diffuse light that arrives at the panel from many directions across the sky dome, plus a smaller component reflected from the ground.A rooftop solar panel under a partly clouded sky. Direct beam reaches the panel where the sky is clear, while a cloud scatters sunlight into diffuse light that arrives at the panel from many directions across the sky dome, plus a smaller component reflected from the ground.
Cloud does not switch sunlight off — it scatters it. Some of the scattered light still reaches the panel, arriving from all over the sky instead of from one direction.

That is the whole reason panels keep working in bad weather: a cell has no way of knowing which direction a photon came from.

Diagram showing global irradiance on a panel as the sum of three components: direct beam from the sun's disc scaled by the angle of incidence, diffuse light arriving from across the sky dome, and light reflected from the ground.Diagram showing global irradiance on a panel as the sum of three components: direct beam from the sun's disc scaled by the angle of incidence, diffuse light arriving from across the sky dome, and light reflected from the ground.
What the panel receives is the sum of three components. Cloud shifts the balance from the first to the second; it does not remove all three.

How much output you lose under different skies

Short-circuit current in a silicon cell rises and falls almost in proportion to irradiance. That makes the arithmetic refreshingly simple: let a quarter of the light through and you get roughly a quarter of the current, and therefore roughly a quarter of the power.

What different skies typically leave you
SkyWhat reaches the panelShare of clear-sky output
Clear, sun highMostly direct beam, with a modest diffuse component100% (reference)
Thin or high cloud, sun visible as a discBeam attenuated, diffuse risingroughly 60–80%
Bright overcastAlmost entirely diffuseroughly 20–40%
Heavy storm cloudDiffuse only, strongly attenuatedroughly 5–15%
FogDiffuse, scattered in all directions including upwardroughly 5–20%, highly site-dependent

Illustrative ranges for a fixed array with the sun reasonably high. Cloud thickness, cloud type, sun elevation and how much sky the array can see all move these figures, so treat measured data from your own site as the authority.

Bar chart comparing typical plane-of-array irradiance for clear sky, thin cloud, bright overcast, heavy storm cloud and fog, with clear sky near one thousand watts per square metre and heavy cloud a small fraction of it.Bar chart comparing typical plane-of-array irradiance for clear sky, thin cloud, bright overcast, heavy storm cloud and fog, with clear sky near one thousand watts per square metre and heavy cloud a small fraction of it.
Illustrative, not measured: the point is the shape, not the exact bars. Output falls steeply under thick cloud but never reaches zero in daylight.

Notice what is missing from that table: temperature. Panels are rated at a cell temperature of 25 °C (77 °F), and a cool overcast day keeps them much closer to that than a hot clear one does. Some of the loss to cloud is quietly returned as a voltage gain, which is why the relationship between sunshine and output is never quite linear. That trade is the subject of why panels lose efficiency in hot weather.

Why cells respond to diffuse light at all

A photon frees an electron if it carries more energy than the semiconductor's band gap — about 1.12 eV for silicon. Energy depends on wavelength, not on direction of travel. A blue photon scattered twice inside a cloud carries exactly the energy it started with, so when it finally arrives at the cell it does the same job it would have done on a clear day.

Direction still matters, but only for how much light gets *in*. Light striking the glass at a shallow angle reflects more readily than light arriving head-on. Modules fight this with an anti-reflective coating and a textured cell surface, both of which work across a wide range of incidence angles — a design choice that pays off precisely when light is arriving from everywhere at once.

Cross-section of a silicon photovoltaic cell showing photons arriving from several directions through the anti-reflective coating, each one freeing an electron-hole pair at the junction, with the junction field sweeping electrons toward the front contact.Cross-section of a silicon photovoltaic cell showing photons arriving from several directions through the anti-reflective coating, each one freeing an electron-hole pair at the junction, with the junction field sweeping electrons toward the front contact.
A cell cannot tell which direction a photon came from. What matters is whether the photon carries more energy than the band gap, and whether it gets through the glass.

What rain adds, and what it takes away

Rain arrives attached to thick cloud, so production drops during a shower — but blame the cloud, not the water. A film of water on glass reflects a little more light than dry glass and costs a few percent at most.

The compensation is soiling. Dust, pollen, salt and bird droppings build up continuously and reduce output by blocking light before it reaches the cell. In a dry spell this loss grows week by week, invisibly, because there is no sudden change to notice. A decent rain shower resets much of it in an afternoon.

Chart of daily output over several weeks showing a slow decline as dust accumulates during a dry spell, followed by a step back up to the clean baseline after rainfall, then another slow decline.Chart of daily output over several weeks showing a slow decline as dust accumulates during a dry spell, followed by a step back up to the clean baseline after rainfall, then another slow decline.
Illustrative: soiling accumulates slowly and invisibly, then rain resets most of it. The rainy day itself produces less; the following week produces more.

Where rain does not help is when the deposit is greasy, cemented by long-dry mineral dust, or concentrated along the lower frame edge where water drains and evaporates. A residue line along the bottom of the glass is the classic sign that rain alone is no longer doing the job, and that a careful manual clean is.

The shape of a cloudy day

A clear day produces a smooth arc: output rises with the sun, peaks near solar noon, falls away symmetrically. Overcast produces the same arc at a fraction of the height. Broken cloud produces neither — it produces a spiky mess, and one feature of that mess surprises people.

When the sun clears the edge of a bright cumulus cloud, the panel briefly receives the full direct beam plus unusually strong diffuse light reflected off the white cloud face. For a few seconds the irradiance can exceed what a clear sky would deliver at that moment, and output can spike above its clear-sky value. It is real, it is called cloud enhancement, and a good inverter simply clips or rides through it.

Line chart of array power through a day, comparing a smooth clear-sky arc, a low flat overcast curve, and a broken-cloud curve that swings rapidly between the two with short spikes above the clear-sky line at cloud edges.Line chart of array power through a day, comparing a smooth clear-sky arc, a low flat overcast curve, and a broken-cloud curve that swings rapidly between the two with short spikes above the clear-sky line at cloud edges.
Illustrative day curves. Broken cloud swings between the two extremes within seconds, and the brief spikes above the clear-sky arc at cloud edges are genuine.

Very low light has one more consequence. An inverter needs a minimum input voltage before it can start, so under deep overcast a small array may sit below the threshold and the inverter stays asleep. It will start late, may drop out during the darkest part of the day, and restart as the light improves. That behaviour is designed in.

Telling weather apart from a fault

The useful question is not "is it cloudy?" but "is the output consistent with the sky?" Four checks separate the two, and none of them need a meter:

  1. Does the loss track the weather? Weather losses vary day to day and recover when the sky clears. A fault holds the output down on a bright day too.
  2. Does the shape match? Cloud produces a ragged or uniformly lowered curve. A notch at the same time each day, drifting slowly with the season, is a shadow — see how partial shade affects solar panels.
  3. Do the strings agree? Two strings with the same orientation should fall and rise together under cloud. One string down while the other is fine is not weather.
  4. Is the drop proportional? Heavy overcast cutting output to a fifth is normal. A bright day at a fifth is not, and belongs in the systematic hunt described in why a system produces less power than expected.

The deeper point is that cloudy climates are not unsuitable for solar; they are simply lower-yield. What they change is not whether an array works but how much energy it delivers over a year — and, if the array is paired with storage in an off-grid or hybrid system, how much capacity is needed to ride through a dull week. That sizing question turns on the battery's chemistry as much as the weather, which is where the differences between LFP, NMC and lead-acid start to matter.

Frequently asked questions

Do solar panels work in the rain?

They do, at reduced output. The rain itself blocks very little light; the thick cloud that comes with it blocks a great deal. A wet panel also runs cool, which slightly raises its voltage, and rain washes away dust that was reducing output before the shower.

Do solar panels work in fog?

Yes, but poorly. Fog scatters light in every direction, including back upward, so only a small fraction of it reaches the panel. Fog that burns off by late morning usually costs less over the day than a full overcast that lasts until dusk.

Is a cloudy day the same as shade?

No, and the difference matters. Cloud dims the whole array evenly, so every cell produces a little less. Shade darkens part of the array while the rest stays lit, which forces mismatched cells into bypass and costs far more than the shaded area suggests.

Do panels produce any power at night?

No. Moonlight is roughly a millionth of the intensity of sunlight, which is far below the level at which a cell can drive a useful current, and an inverter will not start on it. Any output recorded overnight is a metering artefact, not generation.

Will the inverter shut down on a very dark day?

It may. Inverters have a minimum input voltage and power at which they start, published on the datasheet, and under deep overcast a small array can sit below it. The inverter waking late and sleeping early on a dark day is normal behaviour, not a fault.

Sources

Named organisations whose published material underpins this article. Where no link is given, the source is named rather than linked.

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Last reviewed 8 October 2026. How we research and review