Solar Answers → Your Home & Roof
Do solar panels work in Illinois winters and snow?
Yes. Solar panels in Illinois keep producing all winter — just less. In the federal PVWatts model, December through February delivers about one-sixth of a system's yearly output in every part of the state: 15.8% in Chicago, 17.6% in the Metro East. A 10 kW Chicago system makes about 573 kWh in December and 1,580 kWh in July. Snow costs less than most people expect: a federal lab study puts the average yearly loss at 6.1% in Chicago and 4.5% in Springfield. Cold actually helps panels turn light into power. One thing winter does expose — without a battery, panels shut off during a power outage.
Independent public sources we cite and link — The Day Company is not affiliated with or endorsed by any of them.
How much do solar panels produce in an Illinois winter?
About one-sixth of the year's power arrives in December, January and February — between 15.8% and 17.6% in the five Illinois cities we ran through PVWatts, the federal solar calculator. The best month makes 2.1 to 2.8 times what the lowest month makes. Pick the city nearest you, set a system size, and see all twelve months.
Nearest city
System size
Chicago · 9.3 kW · estimated kWh each month
December–February the rest of the year
PVWatts estimates for a south-facing, unshaded roof at a 20° pitch with standard panels and default losses, before snow. The snow figure is a long-run yearly average from the federal lab's snow study — it can't be split by month, and no single winter is average. Not a quote.
The full dataset — a 10 kW system in each city, in kWh:
Swipe the table sideways to see every city →
| Month | Rockford | Chicago | Peoria | Springfield | Belleville |
|---|---|---|---|---|---|
| January | 748 | 657 | 744 | 747 | 823 |
| February | 877 | 838 | 877 | 911 | 890 |
| March | 1,153 | 1,088 | 1,159 | 1,191 | 1,143 |
| April | 1,257 | 1,271 | 1,256 | 1,318 | 1,401 |
| May | 1,428 | 1,390 | 1,347 | 1,340 | 1,409 |
| June | 1,459 | 1,452 | 1,339 | 1,485 | 1,543 |
| July | 1,496 | 1,580 | 1,543 | 1,504 | 1,460 |
| August | 1,458 | 1,385 | 1,408 | 1,382 | 1,436 |
| September | 1,228 | 1,203 | 1,329 | 1,291 | 1,310 |
| October | 977 | 936 | 1,012 | 1,095 | 1,025 |
| November | 781 | 699 | 718 | 836 | 769 |
| December | 601 | 573 | 725 | 664 | 744 |
| Year | 13,463 | 13,072 | 13,457 | 13,764 | 13,953 |
| Dec–Feb share | 16.5% | 15.8% | 17.4% | 16.9% | 17.6% |
| PVWatts' year-to-year range | 12,608–13,986 | 12,514–13,620 | 12,566–13,707 | 12,964–14,276 | not reported |
Source: PVWatts Calculator, National Laboratory of the Rockies (formerly NREL), run September 21, 2026 — 10 kW, standard panels, fixed roof mount, 20° tilt, facing due south, 14.08% default losses, which include nothing for snow. PVWatts models a “typical year” stitched together from real months of weather, which is why Peoria's typical December comes out a little sunnier than its November. Real roofs face every direction and catch some shade, so planning figures run lower than these — the state's own production assumptions are on is solar worth it in Illinois?
This is why installers size a system on the whole year, not on December: how many solar panels you need → If a quote's production number looks generous, you can test it against PVWatts yourself: is my solar quote a good deal? →
What do most pages get wrong about solar in winter?
Both directions. Some pages say winter kills solar; others, selling it, say winter makes no difference. The federal numbers say neither. Here is what you'll often read, next to what the data shows.
You'll often read: “Solar doesn't work in an Illinois winter.”
The numbers say: December through February delivers 15.8% to 17.6% of a year's output across Illinois — about one-sixth. A 10 kW system near Springfield still makes 664 kWh in its lowest month.PVWatts, five Illinois runs, September 21, 2026
You'll often read: “Solar is just as effective in winter as in summer.”
The numbers say: no. July makes about 2.8 times December in Chicago and about 2.1 times near St. Louis. Winter output is real, but it is the low season — a system is sized on the year so that summer carries winter.PVWatts, same runs
You'll often read: “Cold weather hurts solar panels.”
The numbers say: the opposite. In PVWatts' Illinois results, each unit of January sunlight yields 15% to 18% more electricity than the same sunlight in July. Panels run on light, and they convert it better when they're cold. Winter is low because days are short and the sun is low — not because it's cold.Our arithmetic on PVWatts' monthly sunlight and output figures
You'll often read: “Snow wipes out your production.”
The study says: modeled over 30 years of weather, snow cost a 20°-tilt system an average of 7.2% of its yearly output in Rockford, 6.1% in Chicago, 5.3% in Peoria and 4.5% in Springfield. Single digits — though a heavy winter runs above the average and a mild one below.NREL Technical Report NREL/TP-6A20-68705 (2017), Appendix A
You'll often read: “Get up there and clear the panels after every storm.”
The Department of Energy says: a dusting barely matters, and once heavier snow starts to slide, even a partly exposed panel is generating again. The few covered days are already inside the averages above — they are not worth a fall from an icy roof.U.S. Department of Energy, “Let it Snow”
You'll often read: “With solar, your lights stay on when a winter storm knocks out the grid.”
How it works: a standard grid-tied system shuts itself off when the grid goes down, so it can't feed power into lines that crews are repairing. The Department of Energy notes it takes a solar-plus-battery system with an inverter designed for it to run without the grid.U.S. Department of Energy, Solar Integration: Inverters and Grid Services Basics
What does snow actually do to solar panels?
It blocks light while it sits there, and then it leaves — usually faster than it leaves the rest of your roof. The Department of Energy's summary of its cold-climate test sites: a dusting has little effect because wind clears it and light scatters through a thin layer; heavy snow stops generation; and generation restarts as soon as sliding snow uncovers even part of a panel.
How much that costs over a year has been modeled city by city. The federal lab now called the National Laboratory of the Rockies ran 30 years of weather data for 239 U.S. locations through its snow model. These are its Illinois-area results:
Swipe the table sideways to see every column →
| Location | Average yearly loss, 20° tilt | Steeper tilt (equal to latitude, about 40°) | Year-to-year spread |
|---|---|---|---|
| Rockford | 7.2% | 6.0% | ±3.3 points |
| Chicago | 6.1% | 5.2% | ±2.6 points |
| Moline (Quad Cities) | 5.8% | 4.8% | ±2.6 points |
| Peoria | 5.3% | 4.3% | ±2.6 points |
| Springfield | 4.5% | 3.8% | ±2.0 points |
| St. Louis, MO (nearest site to the Metro East) | 3.2% | 2.5% | ±1.6 points |
Source: Ryberg and Freeman, Integration, Validation, and Application of a PV Snow Coverage Model in SAM, NREL/TP-6A20-68705, August 2017, Table A-1 — weather years 1961–1990. The authors say the results should inform yearly estimates only, not single months, and may not represent any particular year. The spread shown is one standard deviation.
Two things stand out. Steeper roofs shed snow sooner, so they lose less. And the farther south you live in Illinois, the less snow matters at all.
On a snow day, do
- Let it slide. Panels are smooth, dark and tilted; they usually clear before the shingles around them.
- Keep the ground under the array clear. Snow leaves panels in sheets — mind doorways, walkways and parked cars.
- Check your monitoring app, not the roof. Output returning is how you know the panels are clear.
- Read your panel warranty's line on snow removal before you touch anything.
Don't
- Climb onto a snowy or icy roof. No day of production is worth the fall.
- Use metal shovels, ice scrapers, salt or hot water on the glass.
- Judge your system by one buried week. The yearly averages already include it.
Do solar panels work in the cold and on cloudy days?
Yes to both. Panels make electricity from light, not heat — ComEd's own solar team puts it plainly: panels convert sunlight into electricity regardless of how cold or hot it is. Cold is in fact the better condition. In the PVWatts results above, a unit of January sunlight produces 15% to 18% more electricity than a unit of July sunlight, because panels lose efficiency as they heat up.
Clouds cut output rather than stopping it, and you don't have to guess by how much: PVWatts builds its estimates from real weather records, so Illinois' gray days are already inside every monthly figure on this page. In Chicago, the sunlight reaching a 20° south-facing surface averages 2.17 kWh per square meter a day in December and 6.77 in July. Across the five cities the yearly average runs from 4.51 to 4.98.
How does the winter dip show up on your electric bill?
Less than the production chart suggests, because net metering carries credits across the seasons. Illinois Shines, the state's solar program, explains it this way: surplus credits from the sunny months don't vanish when the month ends. They roll forward and cover later usage until your annual period closes — you pick an April or an October year-end — and whatever is left at that point expires.
Your first winter can look different. Illinois Shines notes that a system installed in fall or winter hasn't had a high-production season to bank credits yet, so the first winter's bill may not drop by much. That isn't the system underperforming — it's the calendar.
What a credit is worth depends on when the system was connected. Illinois Shines' consumer guidance says systems interconnected after December 31, 2024 are credited at the electricity supply rate rather than the full retail rate. How that works on each utility's bill is on our ComEd net metering guide and our Ameren net metering guide, and a month-by-month walk-through is on what your electric bill looks like after solar.
Winter bills are also when Illinois rates bite hardest. Why they've climbed: ComEd bills · Ameren bills.
Will solar keep the lights on in a winter storm?
Not by itself. A standard grid-tied system switches off the moment the grid goes down, so it can't push power into lines that crews are working on. It comes back on when the grid does. The Department of Energy notes that running a home without the grid takes solar paired with battery storage and an inverter designed for that job.
If riding through ice storms is part of why you're looking at solar, that's a battery decision, and it has its own math: is a home battery worth it in Illinois? In ComEd territory a solar-paired battery can also earn $300 per kWh, with conditions attached: the ComEd battery storage rebate. Ameren customers start with Illinois battery incentives, explained.
Is winter a bad time to go solar in Illinois?
No — the calendar argues the other way. A solar project runs through paperwork, permits, installation and utility approval before it produces anything. Start in winter and the system is positioned to be running for the high-production months, banking the credits that carry you through the next winter. Start in late spring and part of that first summer is gone before you're switched on.
- Winter: compare quotes and sign. Make sure the installer is an Illinois Shines Approved Vendor (five minutes, here's how) and check the quote's production estimate against the PVWatts numbers on this page. What else to check →
- ComEd rebate value locks for 24 months
Interconnection agreement signed. ComEd customers can apply for the $300-per-kW solar rebate that same day, which holds the rebate value while the project is built. How the ComEd solar rebate works → - Permit and install. Your town issues the permits — we cover Chicago and Aurora in detail. Ice and heavy snow can push a roof day, so winter schedules flex.
- Utility approval. The utility grants permission to operate and your net metering starts. The clock for that step is on our ComEd and Ameren guides.
- April–September: over 60% of the year's output
The high season. In PVWatts' Illinois runs, April through September delivers 60% to 63% of the year's production. A system that is live for all of it banks the most credits before its first full winter.
Incentive timing is the other half. Illinois Shines sets its renewable energy credit prices by program year: Illinois Shines, explained. What a system costs before any of it: solar panel cost in Illinois. The whole stack in one place: Illinois solar incentives 2026.
Want your roof's twelve months, not a typical one's?
The free check looks at your roof's direction, pitch and shade along with your usage and your utility — and tells you plainly if solar isn't a fit.
Solar in an Illinois Winter: FAQ
Do solar panels work in winter in Illinois?
Yes. In the federal PVWatts model, December through February delivers about one-sixth of a system's yearly output everywhere in Illinois — 15.8% in Chicago, 16.5% in Rockford, 17.4% in Peoria, 16.9% in Springfield and 17.6% in the Metro East. Output is lower than in summer because days are short and the sun is low, not because panels stop working.
How much less do solar panels produce in winter in Illinois?
The best month makes roughly 2.1 to 2.8 times the lowest. A 10 kW south-facing system in Chicago is modeled at 573 kWh in December and 1,580 kWh in July; near Springfield, 664 kWh and 1,504 kWh. June through August delivers about a third of the year, December through February about a sixth.
Do solar panels work when they're covered in snow?
A dusting has little effect — the Department of Energy notes wind clears it and light scatters through a thin layer. Heavy snow stops generation until it starts to slide, and generation restarts once even part of the panel is exposed. Because panels are smooth, dark and tilted, they usually clear sooner than the roof around them.
How much production does snow cost over a year in Illinois?
A federal lab study that modeled 30 years of weather found average yearly losses, for a 20°-tilt system, of 7.2% in Rockford, 6.1% in Chicago, 5.8% in Moline, 5.3% in Peoria and 4.5% in Springfield; St. Louis, the nearest site to the Metro East, was 3.2%. Steeper roofs lost less. Any single winter can land above or below those averages.
Should I clear snow off my solar panels?
Usually not. The covered days are already counted in the yearly averages, panels tend to clear themselves, and a fall from an icy roof costs far more than a few days of winter output. Never use metal tools, salt or hot water on the glass, and check your panel warranty's terms on snow removal before using anything at all.
Do solar panels work better in cold weather?
Per unit of sunlight, yes. In PVWatts' Illinois results, January sunlight yields 15% to 18% more electricity than the same amount of July sunlight, because panels lose efficiency as they heat up. Winter totals are still lower — there is simply much less sunlight to work with.
Do solar panels work on cloudy days in Illinois?
Yes, at reduced output. PVWatts builds its estimates from real weather records, so Illinois' cloudy days are already included in every monthly figure on this page — including the winter ones.
Will my solar panels work during a winter power outage?
Not without a battery. A standard grid-tied system shuts off when the grid goes down so it can't energize lines that crews are repairing, and it restarts when power returns. The Department of Energy notes that operating without the grid takes solar paired with battery storage and an inverter designed for it.
Will my electric bill still go down in winter with solar?
Usually, because credits carry across seasons. Illinois Shines explains that surplus credits from the sunny months roll forward until your annual period closes — an April or October year-end, your choice — and then expire. One caution from the same guidance: a system installed in fall or winter hasn't banked summer credits yet, so its first winter bill may not drop much.
Is winter a bad time to install solar in Illinois?
No. A project has to clear design, permits, installation and utility approval before it produces anything, so starting in winter positions the system to be running for April through September — over 60% of the year's output — and to bank credits before its first full winter. Ice and heavy snow can delay a roof day, so schedules flex.
Do I need a steeper tilt or a tracker for Illinois winters?
No. Home panels sit flush to the roof at whatever pitch it has, and systems are sized on yearly output. Steeper roofs do shed snow sooner — the federal snow study shows Chicago losing 6.1% a year at a 20° tilt and 5.2% at a tilt near 42° — but that is a small difference, and trackers are built for ground-mounted solar farms, not rooftops.
How much sun does Illinois get in winter?
On a south-facing surface tilted 20°, PVWatts puts Chicago at 2.17 kWh of sunlight per square meter a day in December and 6.77 in July. Springfield runs 2.50 and 6.55; the Metro East 2.91 and 6.46. Averaged over the year, the five Illinois cities on this page range from 4.51 to 4.98.
Related answers
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Sources
- PVWatts Calculator — National Laboratory of the Rockies (website version 8.7.4, API version 8.5; five runs on September 21, 2026 for Rockford, Chicago, Peoria, Springfield and Belleville — 10 kW, standard panels, fixed roof mount, 20° tilt, 180° azimuth, 14.08% default losses)
- Ryberg and Freeman, Integration, Validation, and Application of a PV Snow Coverage Model in SAM (PDF) (NREL Technical Report NREL/TP-6A20-68705, August 2017 — Table A-1, average yearly snow losses by city)
- U.S. Department of Energy — Let it Snow: How Solar Panels Can Thrive in Winter Weather (how light and heavy snow affect panels)
- U.S. Department of Energy — Solar Integration: Inverters and Grid Services Basics (what it takes for a solar-plus-battery system to run without the grid)
- Illinois Shines — Does my system produce electricity in winter months? (credits carrying forward, the April or October annual period, and the first-winter caution)
- Illinois Shines — Changes to Illinois Net Metering Bill Credits, consumer FAQ (supply-rate credits for systems interconnected after December 31, 2024)
- ComEd — Solar Panels in the Chill (January 19, 2024: panels convert light regardless of temperature)
- U.S. Department of Energy — Energy Department Renames NREL “National Lab of the Rockies” (December 1, 2025 — why PVWatts and older NREL reports now carry a new name)
Changelog: July 4, 2026 — first published on our blog. September 21, 2026 — rebuilt as a Solar Answers guide: added month-by-month PVWatts figures for five Illinois cities, the federal snow-loss study's Illinois results, a production tool, six myth corrections and a winter-install timeline; replaced every figure we couldn't tie to a government, utility or state-program source.
How to cite: The Day Company Editorial Team, "Do solar panels work in Illinois winters and snow?," The Day Company, updated September 21, 2026. https://theday.company/answers/solar-panels-winter-illinois