It’s January in Louisville, and the sky has been gray for a week. If you have been thinking about solar, it’s natural to wonder whether panels would do anything at all on days like this.
Here is the short answer. Yes, solar panels work on cloudy days. They make less power than in full sun, often about 10% to 25% of their normal output under heavy clouds, but they don’t stop. And what really matters is how much sunlight your roof gets over a whole year, not how one gray day goes.
How Solar Panels Make Power When It’s Cloudy
Solar panels run on light, not heat. Even when you can’t see the sun, daylight is still reaching your roof.
Clouds don’t block all sunlight. They scatter it, bouncing it around so it comes from the whole sky instead of one bright spot. This scattered light is called diffuse light, and your panels can still turn it into electricity.
Think of it like getting a sunburn on an overcast day at the pool. You can’t see the sun, but its light is clearly getting through.
How Much Do Clouds Lower Solar Output?
It depends on how thick the clouds are. Here is a rough guide based on figures that line up across several independent solar sources:
| Sky condition | Rough output compared to full sun |
| Clear and sunny | Close to full output |
| Thin or broken clouds | About 30% to 80% |
| Heavy, dark overcast | About 10% to 25% |
| Steady rain | Around 10% to 20% |
| Night | None |
For example, a system that makes 30 kWh on a bright spring day might make somewhere around 3 to 7 kWh on a dark, overcast one. (A kWh, or kilowatt-hour, is the unit your electric bill uses.)
Partly cloudy days can be better than you’d expect. When the sun breaks through between clouds, panels can briefly jump back up to strong output.
Do Solar Panels Work in Rain, Snow and Winter?
Rain
Output drops during rain because of the thick clouds, not the water itself. A steady rain also rinses dust and pollen off the panels, which can help them work a little better afterward.
Winter
Solar panels in winter make less power, mostly because days are shorter and the sun sits lower in the sky. But cold itself is not a problem. Panels actually work more efficiently when they are cool, because heat makes the electrical parts inside them less effective. A crisp, clear winter day can be a surprisingly good solar day.
Snow
A light layer of snow often slides off on its own, because panels are smooth, tilted and warm up a little in daylight. Heavy snow will block the panels until it melts or slides away.
- Don’t climb on the roof to clear snow. It’s dangerous, and you can scratch or crack the panels.
- If you want to clear snow, use only a soft roof rake from the ground, and only if the panels are within easy reach.
Snow, dirt and leaves are all part of normal solar maintenance, and most of the time nature does the cleaning for you.
Shade
Shade from trees or chimneys can lower output more than clouds do, because it can block a panel completely. On some systems, panels are wired together in a row, so shade on one panel can drag down others in the same row. Many newer systems use small devices on each panel, called microinverters or optimizers, so each panel works on its own and shade on one doesn’t pull down the rest.
Do Solar Panels Work at Night?
No. Solar panels need light to make electricity, and moonlight is far too weak to produce useful power.
That doesn’t mean your lights go out at night. Homes with solar usually get evening power in one of two ways:
- From the grid. You use utility power at night, just as you do now.
- From a battery. A home battery stores extra power made during the day so you can use it after dark. Adding a solar battery can also keep some power on during outages.
Is Solar Worth It in Louisville’s Climate?
Louisville gets less sun than Arizona or Florida, but it still gets a fair amount. Solar planners measure sunlight in peak sun hours. One peak sun hour is one hour of full, strong sunlight. A gray day might add up to only one or two peak sun hours, while a clear June day can add up to six or more.
Based on National Renewable Energy Laboratory (NREL) data, Louisville averages roughly 4.4 to 4.8 peak sun hours a day over a full year. That is a little below the U.S. average. The seasons make a big difference:
- Summer: long, bright days. June gets more than twice the usable sunlight of December.
- Winter: short days and more cloud cover, so output is lowest.
- Spring and fall: steady, in-between production.
This is why a good solar design is based on a full year of sunlight, not a single cloudy week. Sunny months make up for gray ones.
How your utility handles extra power matters too. Kentucky law requires electric utilities to offer net metering. With net metering, power your panels send to the grid earns a credit on your bill, and extra credit carries over to your next bill. The credit rate is set by the Kentucky Public Service Commission and can be lower than what you pay for power, so it is worth asking your utility for its current rate.
Whether solar is worth it for your home comes down to your roof, your electric use and your goals, not just the weather.
How to Get More From Solar on Cloudy Days
You can’t control the clouds, but you can set up your system to make the most of the light you do get:
- Use the best side of your roof. In Louisville, south-facing roofs usually get the most sun, with east and west as good second choices. The best roof for solar is also one in good shape, so panels don’t have to come off for repairs soon after install.
- Trim trees that shade the roof. This often helps more than anything else, especially in winter when the sun is low.
- Choose panels carefully. Some panels handle low light better than others. Comparing specs is part of choosing solar panels that fit your home.
- Consider a battery if you want power during outages or after dark.
Solar and Cloudy Weather FAQs
What is the biggest drawback of solar panels?
Their output depends on the weather and daylight. They make the most power on long, clear days and less on cloudy days, in winter and not at all at night. A system sized for your full year of sunlight handles this best.
Do solar panels work with moonlight?
Technically, moonlight is reflected sunlight, but it is far too dim to make any useful power. For practical purposes, panels produce nothing at night.
Do solar panels work in the shade?
Yes, but less well. Light shade lowers output, while heavy shade can nearly stop a panel. Trimming trees and using panel-level electronics can reduce the effect.
Should you clear snow off solar panels?
Usually not. Most snow slides off within a day or two of sun. If you do clear it, stay on the ground and use a soft roof rake. Never climb onto a snowy roof.
Find Out How Much Sun Your Roof Really Gets
Cloudy days lower solar output, but they don’t make solar a bad fit for Louisville. What matters is how much sunlight your specific roof gets over a full year, which depends on its direction, angle and shade.
GoRoofGuys is a licensed and insured roofing and solar company serving Louisville and Cincinnati. We can look at your roof, check for shade and give you an honest estimate of what solar installation could produce for your home. Reach out to schedule your free solar consultation.