Short answer: yes, but less. In the northern US, a balcony panel makes about a quarter to a half of its summer output in December, and on heavily overcast days only 5 to 15% of a sunny day. Cold doesn't hurt (panels are more efficient when cold); short days, low sun, clouds and snow do. Annual savings estimates, including ours, already include winter.
Month by month
Approximate share of a year's output from a south-facing panel in a northern US city such as Boston or Chicago. These are our rounded estimates; exact figures for your address are free on NREL's PVWatts.
| Month | Tilted 35° | Vertical on a railing |
|---|---|---|
| December–January | ~4–5% each | ~6–8% each |
| February–March | ~7–9% each | ~8–10% each |
| April–August | ~10–11% each | ~7–9% each |
| September–October | ~8–9% each | ~9–10% each |
| November | ~5% | ~7% |
Two patterns stand out. Tilted panels have a strong summer peak. Vertical panels are much flatter across the year, because a low winter sun hits a vertical surface almost head-on. That's why a vertical railing kit loses about 30% over a whole year but much less in winter. In the South, winter output drops far less. Check your own months on PVWatts.
Clouds
Panels use diffuse light as well as direct sun, so they never go to zero in daylight. Rough rules:
- Thin, bright clouds: 50 to 80% of sunny output.
- Overcast: 20 to 40%.
- Dark, rainy days: 5 to 15%.
At 800 W, even a gray day can cover your fridge and router for a few hours. Microinverters with a low start-up voltage squeeze a bit more from dim light.
Cold is good, snow is not
Solar cells lose efficiency as they heat up, roughly 0.3 to 0.4% per degree Celsius above 25°C (77°F). On a crisp, sunny winter day a panel can briefly exceed its rated output per hour of sun. Snow is the real problem: a covered panel makes nothing.
- Mount vertically or steeply in snowy areas so snow slides off.
- Brush gently with a soft brush or foam rake if you can reach safely. Never use metal scrapers or hot water.
- Keep clear of roof slides: snow sliding off a roof above can bend a railing mount.
- Check clamps after storms, especially on exposed balconies.
Does winter make a kit not worth it?
Not by itself. Annual figures already include dark months. What matters is sun times price: Maine and Massachusetts get less sun than Arizona but pay twice as much per kWh, so a kit there can save more. Compare by state in how much balcony solar saves, or run your numbers in the calculator. For placement tips, see the best angle and direction.
Frequently asked questions
Do balcony solar panels work in winter?
Yes. They make less because days are shorter and the sun is lower, typically a quarter to a half of their summer output in the northern US. Cold itself helps: solar panels are more efficient at low temperatures.
Do solar panels work on cloudy days?
Yes, but much less. Under bright overcast a panel may make 20 to 40% of its sunny output; under heavy cloud or rain, 5 to 15%. Your annual estimate already includes cloudy days.
What happens to balcony solar in snow?
Snow on the panel stops production until it slides or melts off. Vertical railing panels shed snow almost at once, which is why they do well in snowy states. Don't scrape panels with hard tools.
Is balcony solar worth it in a cloudy state?
It depends mostly on your power price. Cloudy New England has high prices, so kits there save as much as in sunnier, cheaper states. Use the calculator with your state's sun and price.
Update log
- Guide published.
Sources and official texts