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Do Solar Panels Work on Cloudy Days and in Winter?
Yes, solar panels work on cloudy days and in winter, but they make less power. Clouds block the direct beam of sunlight, yet the scattered (diffuse) light that gets through still reaches the panels. Winter cuts output mainly because days are shorter and the sun is lower, not because of the cold. In fact, the U.S. Department of Energy notes that solar cells generally work best at low temperatures.
How clouds affect solar output
The DOE explains that sunlight reaches the ground two ways: as a direct beam and as diffuse light scattered by air, clouds, and dust. Together they make up global solar radiation. Atmospheric conditions can cut the direct beam by about 10% on clear, dry days and by 100% on days with thick clouds. Even then, the diffuse part remains, so panels keep producing at a reduced rate.
Rain is not all bad, either. The Solar Energy Industries Association points out that rain helps keep panels working well by washing away dust and dirt.
Cloudy climates still make plenty of solar power
Seattle is famous for gray skies. In NREL PVWatts runs (1 kW of south-facing panels at a 20 degree tilt), it still makes about 1,095 kWh a year. That is less than sunny cities, but far from nothing:
| City | Yearly kWh per 1 kW | Best month | December |
|---|---|---|---|
| Phoenix, AZ | 1,767 | May: 180.9 kWh | 117.3 kWh |
| Denver, CO | 1,600 | June: 160.3 kWh | 96.1 kWh |
| Chicago, IL | 1,308 | July: 158.6 kWh | 57.1 kWh |
| Seattle, WA | 1,095 | July: 144.8 kWh | 32.8 kWh |
Source: NREL PVWatts version 8, fixed open-rack array, 14% system losses, typical-year weather data. Run your own address for your local numbers.
Do solar panels work in winter?
Yes. Two things happen in winter:
- Less sunlight. The DOE notes that Denver gets nearly three times more solar energy in June than in December. Seattle's December output above is less than a quarter of its July output.
- Better efficiency in the cold. Panels lose power as they heat up, and gain a little as they cool. The rate is the "temperature coefficient" on the spec sheet.
| Panel | Temperature coefficient of Pmax | Effect at a 32°F (0°C) cell temperature |
|---|---|---|
| Rich Solar MEGA 100 | -0.35% per °C | About 8.75% more power than rated |
| Rich Solar MEGA 410 | -0.34% per °C | About 8.5% more power than rated |
| Jackery SolarSaga 200W | -(0.33 ± 0.02)% per °C | About 8% more power than rated |
Sources: Rich Solar datasheets and Jackery's product page. The effect column is our calculation versus the 25°C test temperature panels are rated at. Real gains depend on sunlight and how warm the cells actually run.
What about snow?
Snow covering the panels stops production until it slides off or melts. Sandia National Laboratories says published estimates of snow losses range from 1 to 12% a year, with monthly losses as high as 100%. Systems that shed snow quickly make more energy.
- Tilt helps in winter. In the Chicago PVWatts runs, panels at 60 degrees made 11.4% more energy from December to February than panels at 30 degrees, though about 11% less over the full year. See Best Angle for Solar Panels.
- Check load ratings. The MEGA 100 and MEGA 410 are rated for 5400 Pa snow and 2400 Pa wind loads.
- Stay off the roof. For roof snow in general, OSHA advises working from the ground with snow rakes or drag lines. Ground mounts make panels easy to reach and clear.
Batteries need care in the cold
Panels like the cold. LiFePO4 batteries do not like to be charged below freezing. Rich Solar's standard LiFePO4 batteries cut off charging at 32°F, while its ALPHA 1 has a built-in heater that turns on below 41°F. Keep batteries in a heated space if you can. More in LiFePO4 vs Lithium Ion.
Gear for year-round solar
- Rich Solar MEGA 410: 410 W, rated 5400 Pa snow load. 8 panels $2,799.99
- Rich Solar MEGA 100: 100 W, 12V. $119.99
- Rich Solar ground mount for MEGA 335/410: tilt adjusts from 18 to 45 degrees. $699.99
- Rich Solar ALPHA 1 12V 100Ah LiFePO4: self-heating below 41°F. $499.99
Browse all solar panels.
Need help sizing for winter? Call 1-888-855-7286. Tell us your location and what you need to run in December, and we will size the panels and battery for your worst month.
Cloudy day and winter solar FAQ
Do solar panels work on cloudy days? Yes, at reduced output. Thick clouds can block the direct beam completely, but diffuse light still reaches the panels.
Do solar panels work in winter? Yes. Output drops because days are shorter, but cold temperatures actually help efficiency.
How much less do solar panels make in winter? It depends on location. In PVWatts runs, Chicago's December output is about 36% of its July output, and Phoenix's is about 65% of its May peak.
Do solar panels work in the rain? Yes, at reduced output, and rain helps wash dirt off the panels.
Do solar panels work in snow? Not while they are covered. Once snow slides off, they work well, and cold panels are more efficient.