Solar Answers → Your Home & Roof
How many solar panels do I need for my Illinois home?
Most Illinois houses need about 7 to 9 kW of solar, roughly 18 to 23 panels at 400 watts, to match a year of their own use. A typical single-family house uses about 933 kWh a month, and each kW of panels makes about 1,240 kWh a year in northern Illinois. Your size is your yearly kWh divided by 1,240. The calculator below does it in seconds.
Sizing comes down to two numbers: how much electricity your home uses in a year, and how much each kW of panels makes where you live. This page gives you both from public data, and shows the four system sizes that change your permits and incentives in Illinois.
Independent public sources we cite and link — The Day Company is not affiliated with or endorsed by any of them. We are an Illinois solar and battery information resource and a lead-generation business.
Solar size calculator: how many panels do you need?
Enter your average monthly kWh or your monthly bill, pick your utility and choose how much of your use solar should cover. You'll get a system size, a panel count, the roof space it needs and any Illinois size lines it would cross. It all runs in your browser.
Want this checked against your real bills and roof? The free eligibility check takes about a minute, and your numbers come with you, so you won't have to retype them.
Get my size verified →Nothing you enter is sent or stored by this page — the math runs in your browser. If you continue to the eligibility check, your size estimate comes with you. The calculator assumes south-facing, unshaded panels at 400 watts each; east- or west-facing roofs need more. Bill estimates use ComEd and Ameren prices for October 2026 to May 2027, before city taxes.
How many solar panels does the average Illinois home need?
About 17 panels, or 6.7 kW, for the average Illinois home, and about 23 panels, or 9 kW, for a typical single-family house. The difference is usage. The state's average of 693 kWh a month includes apartments, while a typical Midwest single-family house uses about 933 kWh a month.
Sizing starts from usage because usage is what solar replaces. The 693 kWh figure is the U.S. Energy Information Administration's 2024 average across all Illinois homes. The 933 kWh figure comes from the agency's household survey, where Midwest single-family detached houses averaged 11,196 kWh a year.
Swipe the table sideways to see every column →
| Home | Monthly use | Size to cover a year | Panels (400 W) |
|---|---|---|---|
| Average Illinois home, all types | 693 kWh | 6.7 kW | 17 |
| Typical single-family house, Midwest | 933 kWh | 9.0 kW | 23 |
| Median new U.S. home system, 2025 | — | 7.7 kW | 19 |
Sizes use 1,240 kWh per kW a year, the northern Illinois figure explained below. The median system size is from Berkeley Lab's U.S. Distributed Solar and Storage 2026 Data Update; most home systems installed in 2025 fell between about 5 and 12 kW.
Illinois homes use less electricity than the U.S. average, 693 kWh a month against 863 in 2024, so panel counts built on national averages tend to oversize an Illinois roof. Berkeley Lab also notes that California, about half of its sample, has relatively small systems, which pulls the national median down.
How do I find my usage on a ComEd or Ameren bill?
Look for kilowatt-hours, not dollars. Every bill lists the kWh for that billing period, usually beside a 12-month chart, and your online account keeps the history. Add up 12 months — the University of Illinois Extension suggests looking at 12 to 24 — and you have the one number sizing depends on.
One month isn't enough. A July bill in an air-conditioned home sizes you too big, and an April bill too small. If you only know your bill in dollars, the calculator above estimates kWh from current published prices, before city taxes. How a bill splits into supply, delivery and fixed charges: the average electric bill in Illinois. Every ComEd and Ameren price change since 2024: the Illinois electric rate tracker.
How much electricity does 1 kW of solar produce in Illinois?
About 1,230 to 1,350 kWh a year, depending on where you live. That's the federal PVWatts model for a south-facing, unshaded roof, after a federal study's average snow losses: about 1,230 in Chicago, 1,250 in Rockford, 1,275 in Peoria, 1,315 in Springfield and 1,350 near the Metro East.
Swipe the table sideways to see every column →
| Area | PVWatts, before snow | Average yearly snow loss | After snow |
|---|---|---|---|
| Rockford | 1,346 kWh | 7.2% | 1,249 kWh |
| Chicago | 1,307 kWh | 6.1% | 1,227 kWh |
| Peoria | 1,346 kWh | 5.3% | 1,274 kWh |
| Springfield | 1,376 kWh | 4.5% | 1,314 kWh |
| Metro East (Belleville) | 1,395 kWh | 3.2%* | 1,351 kWh |
PVWatts runs by the National Laboratory of the Rockies' calculator (formerly NREL), done September 21, 2026 and published in our winter guide: standard panels, fixed roof mount, 20° tilt, due south, 14.08% default losses, divided by 10 from a 10 kW run. Snow losses are from NREL Technical Report NREL/TP-6A20-68705 (2017), Table A-1, at a 20° tilt. *St. Louis is the study's nearest site to the Metro East.
A simpler check comes from the University of Illinois Extension: 4 to 4.5 peak sun hours a day, times 365 days, times 0.80, gives 1,170 to 1,310 kWh per kW. Its 0.80 factor also allows for panels slowly losing output over their life. This page plans with 1,240 kWh per kW a year in ComEd's northern Illinois territory and 1,300 in Ameren's central and southern territory.
Real roofs face other directions and catch some shade, so a design for your roof can come in lower. For your exact address, run the free PVWatts Calculator. Month by month, and why winter matters less than it looks: how solar does in an Illinois winter.
How do I calculate my own system size?
Multiply your yearly kWh by the share you want solar to cover, then divide by what 1 kW makes where you live. A northern Illinois house using 11,196 kWh a year needs about 11,196 ÷ 1,240 = 9.0 kW, or 23 panels at 400 watts. The University of Illinois Extension suggests starting with a goal of 50 to 75 percent.
(use 1,300 in central and southern Illinois)
System size in kW × 1,000 ÷ panel watts = panel count
Worked example. Twelve bills add up to 12,000 kWh. To cover all of it, 12,000 ÷ 1,240 = 9.7 kW, or 24 panels at 400 watts. To cover 75 percent, 9,000 ÷ 1,240 = 7.3 kW, or 18 panels. Planning on an electric car adds about 3,600 kWh to the yearly total.
Swipe the table sideways to see every column →
| Monthly use | Yearly use | Size, ComEd area | Panels | Size, Ameren area | Panels |
|---|---|---|---|---|---|
| 500 kWh | 6,000 kWh | 4.8 kW | 12 | 4.6 kW | 12 |
| 693 kWh, Illinois average | 8,316 kWh | 6.7 kW | 17 | 6.4 kW | 16 |
| 750 kWh | 9,000 kWh | 7.3 kW | 18 | 6.9 kW | 17 |
| 933 kWh, typical house | 11,196 kWh | 9.0 kW | 23 | 8.6 kW | 22 |
| 1,000 kWh | 12,000 kWh | 9.7 kW | 24 | 9.2 kW | 23 |
| 1,250 kWh | 15,000 kWh | 12.1 kW | 30 | 11.5 kW | 29 |
| 1,500 kWh | 18,000 kWh | 14.5 kW | 36 | 13.8 kW | 35 |
ComEd area at 1,240 kWh per kW a year; Ameren area at 1,300. Panel counts assume 400-watt panels, rounded to the nearest panel — arithmetic, not a product spec. A real design starts from your own 12 months of usage and your actual roof.
This page answers how big, not how much. What a system costs: solar panel cost in Illinois. Whether it pays for your home: is solar worth it in Illinois?
How many solar panels does a 2,000 sq ft house need?
About 22 panels, or 8.7 kW, if the house uses what the average 2,000 to 2,499 square foot Midwest home does: about 10,700 kWh a year in the Energy Information Administration's household survey. Square footage is a rough guide at best, and your own bills always beat it.
Swipe the table sideways to see every column →
| Home size | Average yearly use | Per month | Size to cover it | Panels (400 W) |
|---|---|---|---|---|
| Under 1,000 sq ft | 6,156 kWh | 513 kWh | 5.0 kW | 12 |
| 1,000 to 1,499 sq ft | 8,168 kWh | 681 kWh | 6.6 kW | 16 |
| 1,500 to 1,999 sq ft | 9,788 kWh | 816 kWh | 7.9 kW | 20 |
| 2,000 to 2,499 sq ft | 10,735 kWh | 895 kWh | 8.7 kW | 22 |
| 2,500 to 2,999 sq ft | 10,886 kWh | 907 kWh | 8.8 kW | 22 |
| 3,000 sq ft or more | 13,876 kWh | 1,156 kWh | 11.2 kW | 28 |
Usage: U.S. Energy Information Administration, 2020 Residential Energy Consumption Survey, Table CE2.3, Midwest homes of all types. The survey's square footage counts basements and conditioned attic and garage space. Sizes use 1,240 kWh per kW a year.
Why square footage misleads: in the same survey, Midwest homes heated with electricity used about 12,900 kWh a year, against about 8,700 for homes heated with natural gas. That's about as big a jump as going from 1,500 square feet to more than 3,000. One-person homes averaged about 6,700 kWh a year, and four-person homes about 12,100.
Which system sizes change the rules in Illinois?
Four sizes, all measured at the inverter in AC: about 7.7 kW, what a standard 200-amp panel accepts without changes; 10 kW, where the Illinois Shines credit price steps down; 13.44 kW, Chicago's express-permit limit; and 25 kW, the top of the program's small-system category and of the utilities' fast-track review.
- 7.7 kW — standard 200-amp panel limit
- 10 kW — Illinois Shines price step
- 13.44 kW — Chicago express-permit limit
- 25 kW — small-system and Level 1 limit
Swipe the table sideways to see every column →
| Size line (AC) | What changes | Who it matters to |
|---|---|---|
| About 7.7 kW | The electrical code's 120% rule allows a 40-amp solar breaker on a 200-amp panel with a 200-amp main, about a 7.7 kW inverter. Bigger systems need a panel upgrade, a smaller main breaker or a connection ahead of the panel. | Most homes with 200-amp service. The panel check |
| 10 kW | Illinois Shines pays $80.77 per credit (ComEd area) or $70.37 (Ameren area) up to 10 kW AC for 2026–27. Just over it, the whole system gets $79.21 or $60.92: about 2% less in the ComEd area and 13% less in the Ameren area. | Larger homes, especially in Ameren territory. How Illinois Shines works |
| 13.44 kW | Chicago's Express Permit Program covers inverter output up to 13.44 kW. Bigger systems go through standard plan review. | Chicago homes. Chicago solar permits |
| 25 kW | The top of Illinois Shines' Small DG category, and of Level 1, the utilities' fast-track interconnection review, unless export is limited. | Very large homes and small farms. |
Sources: NEC 705.12, with the arithmetic in our house-fit guide; Illinois Shines Final 2026-27 REC Prices and Small Distributed Generation pages; City of Chicago Express Permit Program; 83 Ill. Adm. Code 466.80.
Quotes usually lead with the DC size, the panels added together. The inverter is rated in AC and is usually smaller: Berkeley Lab's median ratio for home systems was 1.22, so a 12 kW DC array often runs on about a 10 kW AC inverter. Rules written in AC follow the inverter. A typical 9 kW house system lands around 7.5 kW AC, just under the 200-amp panel line.
The utility solar rebate is paid per kW, so it grows with system size: the ComEd solar rebate. How the Illinois Shines credits are paid, to your installer and typically passed along in the price: Illinois Shines, explained. Every incentive in one place: Illinois solar incentives 2026.
Want your size checked against your real bills and roof?
Free, about a minute, no obligation. If solar isn't right for your roof or your usage, it tells you so instead of booking a sales call.
Get my size verified →How many panels is that, and will they fit on my roof?
Divide the size in watts by the panel's watts: 9 kW is 23 panels at 400 watts, or 21 at 430. Plan on very roughly 50 to 65 square feet of open, sunny roof per kW, about 450 to 580 square feet for 9 kW. Compare quotes on kW and yearly kWh, not on panel counts.
That roof-space range is our estimate for 350- to 400-watt panels, the same one used in is my house good for solar? Berkeley Lab found that home systems installed in 2025 typically covered 16 to 39 percent of the total roof area. Vents, skylights and dormers eat into the usable part.
The roof can cap the size before your bill does. East- or west-facing panels make less per kW, so the same use needs more of them. Midday shade cuts output the most, and a roof near the end of its life should be replaced first. Each one in detail: solar roof requirements in Illinois and is your roof too shaded for solar?
Does the 2025 net-billing change mean I should go smaller?
It means don't go much bigger than you need. For systems connected since January 1, 2025, power you send back is credited at the supply rate rather than the full retail price, and Illinois Shines says unused credits expire at the end of your annual period. A kWh you use yourself is worth more than one you export.
The details differ by utility. ComEd credits the supply portion of the price, and Ameren also credits transmission: ComEd net metering and Ameren net metering. Credits do roll forward month to month, so summer surplus carries into winter, which is why systems are sized on the whole year. The big exception is ComEd's Hourly Pricing, covered below.
Should I size up for an electric car or a battery?
For a car you own or are sure you're buying, yes. One electric car adds roughly 3,600 kWh a year, which takes about 2.9 kW more solar, or 7 panels, in northern Illinois. A battery doesn't change your size. It stores what the panels already make and shifts when you use it.
That estimate is about 1,000 miles a month at about 30 kWh per 100 miles. Your car's EPA label at fueleconomy.gov lists its own kWh per 100 miles. For reference, the average U.S. light-duty vehicle went 10,787 miles in 2024, according to the Federal Highway Administration. For a car you're only considering, size for today: adding panels later is its own project, but it can be done.
Batteries are their own decision, with their own rebate and commitments: is a home battery worth it in Illinois? and the ComEd battery storage rebate.
Can solar zero out my electric bill?
On standard rates, no. Fixed charges stay — $19.07 a month with ComEd and $14.51 with Ameren — and you pay delivery on every kWh you draw from the grid at night and in winter. The exception is ComEd's Hourly Pricing, where solar credits are dollar values applied to the whole bill, so a system sized past your use can bring it to zero.
So sizing for a $0 bill only makes sense on Hourly Pricing. On fixed-price supply, extra panels mostly make credits that expire. How the hourly credits work: the Hourly Pricing exception and ComEd Hourly Pricing with solar. What a standard-rate bill looks like afterward: your electric bill after solar.
How do I check an installer's proposed size?
Ask for four numbers in writing: the yearly kWh they used for your home, the system's DC and AC size, the yearly production estimate, and the share of your use it covers. A production estimate well above PVWatts for your address, or a system sized far past your use, deserves a question before you sign.
With a lease or PPA, the provider designs the system, but the same four numbers apply. The full checklist, including the documents to ask for: how to vet a solar quote in Illinois. Owning versus leasing: solar lease vs PPA vs buying.
Illinois solar sizing FAQ
How many solar panels do I need for my Illinois home?
Most Illinois houses need about 7 to 9 kW of solar, or roughly 18 to 23 panels at 400 watts, to match a year of their own use. A typical single-family house uses about 933 kWh a month and needs about 9 kW. The average Illinois home, apartments included, uses 693 kWh and needs about 6.7 kW, or 17 panels.
How many kWh does the average Illinois home use?
693 kWh a month in 2024, about 8,316 kWh a year, according to the U.S. Energy Information Administration. That average includes apartments. A typical single-family house in the Midwest uses about 933 kWh a month, and the U.S. average across all homes in 2024 was 863 kWh.
How much electricity does 1 kW of solar produce in Illinois?
About 1,230 to 1,350 kWh a year for a south-facing, unshaded roof after average snow losses: roughly 1,230 in Chicago and 1,350 near the Metro East, using the federal PVWatts model and a federal snow study. The University of Illinois Extension method gives 1,170 to 1,310. This page plans with 1,240 in ComEd territory and 1,300 in Ameren territory.
What is the formula to size a solar system?
Multiply your yearly kWh by the share you want solar to cover, then divide by what 1 kW of panels makes where you live: about 1,240 kWh a year in northern Illinois or 1,300 in central and southern Illinois. Multiply the result by 1,000 and divide by the panel's watts to get a panel count.
How many solar panels does a 2,000 sq ft house need?
About 22 panels, or 8.7 kW, if it uses what the average 2,000 to 2,499 square foot Midwest home does: about 10,700 kWh a year in the Energy Information Administration's household survey. Square footage is only a rough guide. Electric heat and household size change usage as much as home size does, so your own bills are better.
Should I size my solar system to cover 100 percent of my usage?
Not necessarily. The University of Illinois Extension suggests starting with a goal of 50 to 75 percent. Systems connected since January 1, 2025 earn supply-rate credits for power they send back, and Illinois Shines says unused credits expire at the end of each annual period, so sizing well past your own use usually pays less.
What changes when a solar system goes over 10 kW in Illinois?
The Illinois Shines credit price. For 2026–27, systems up to 10 kW AC earn $80.77 per credit in the ComEd area and $70.37 in the Ameren area. Just over 10 kW AC, the whole system gets $79.21 or $60.92. The line is measured at the inverter, in AC, not by the panels.
What size solar system can a 200-amp panel handle?
About 7.7 kW of inverter output, if the panel has a 200-amp main breaker. The National Electrical Code's 120 percent rule allows a 40-amp solar breaker on that panel. Larger systems are common, but they usually need a panel upgrade, a smaller main breaker or a connection ahead of the panel.
How much more solar do I need for an electric car?
About 3,600 kWh a year per car, which takes roughly 2.9 kW more solar, or 7 panels at 400 watts, in northern Illinois. That assumes about 1,000 miles a month at about 30 kWh per 100 miles. Your car's EPA label lists its own efficiency, and the average U.S. light-duty vehicle went 10,787 miles in 2024.
Will solar zero out my electric bill?
Not on standard rates. Fixed charges of $19.07 a month with ComEd and $14.51 with Ameren stay, and you pay delivery on the power you draw from the grid. The exception is ComEd's Hourly Pricing, where solar credits are dollar values applied to the whole bill, so a system sized past your use can bring the bill to zero.
Do homes in southern Illinois need fewer solar panels?
A few. In the federal PVWatts model, after average snow losses, 1 kW of south-facing panels makes about 1,350 kWh a year near the Metro East and about 1,230 in Chicago. A home with the same usage near St. Louis needs roughly 9 percent fewer panels than one in Chicago.
How many solar panels is a 10 kW system?
About 25 panels at 400 watts, or 23 at 430 watts. Panel wattage varies by product, so the count changes while the system size stays the same. That's why quotes are best compared on kW and yearly kWh, not on how many panels they show.
What is the difference between kW DC and kW AC on a solar quote?
kW DC is the panels' combined rating, and kW AC is what the inverter puts out. Inverters are usually smaller than the array, and Berkeley Lab's median ratio for home systems was 1.22, so a 12 kW DC system often has about a 10 kW AC inverter. Several Illinois limits, including the Illinois Shines price tiers, are written in AC.
Does this sizing method work for Ameren Illinois customers?
Yes. The method is the same: a year of your own kWh divided by what 1 kW makes where you live. Ameren's territory in central and southern Illinois gets a little more sun, so use about 1,300 kWh per kW a year instead of the 1,240 used for ComEd's northern Illinois territory.
Related answers
More answers: is a home battery worth it? · Chicago solar permits · Illinois Shines, explained · ComEd net metering · the ComEd solar guide · Illinois solar facts · every Illinois solar answer.
Get your size checked against your real bills and roof.
Free, about a minute, no obligation. If rooftop solar isn't the right fit for your roof or your usage, it says so instead of handing you to a salesperson.
Free eligibility check · ComEd & Ameren · No obligationThe Day Company is an Illinois solar and battery information resource and a lead-generation business. Information you submit may be used by our review team and one authorized partner to contact you about your request. Checking eligibility creates no obligation, and nothing on this site is a quote or a guarantee. How we’re funded and how we source figures: our editorial standards.
Sources
Sources · 20 documents behind this page
- University of Illinois Extension — Estimate System Size and Cost — the sizing formula, 4 to 4.5 peak sun hours, the 0.80 factor, 12 to 24 months of bills and the 50 to 75% starting goal
- U.S. Energy Information Administration — Table 5A, average monthly residential use, 2024 (PDF) — 693 kWh for Illinois homes and 863 kWh for the U.S.
- U.S. Energy Information Administration — 2020 Residential Energy Consumption Survey, Table CE2.3, Midwest (PDF) — usage by home size, heating fuel, household size and housing type, including 11,196 kWh a year for single-family houses
- PVWatts Calculator — National Laboratory of the Rockies (formerly NREL) — the federal production model behind the per-kW figures
- Our PVWatts runs for five Illinois cities, September 21, 2026 — inputs and month-by-month results, on our winter guide
- Ryberg and Freeman, Integration, Validation, and Application of a PV Snow Coverage Model in SAM, NREL/TP-6A20-68705 (PDF) — Table A-1, average yearly snow losses by city
- Lawrence Berkeley National Laboratory — U.S. Distributed Solar and Storage, 2026 Data Update (PDF) — the 7.7 kW median home system in 2025, the 5 to 12 kW range and roof coverage
- Lawrence Berkeley National Laboratory — Tracking the Sun, 2023 Edition, executive summary (PDF) — the 1.22 median ratio between panel and inverter ratings for home systems
- Illinois Shines — Final 2026-27 REC Prices (PDF) — credit prices by group and size, including the 10 kW AC line
- Illinois Shines — Small Distributed Generation — the category up to and including 25 kW
- Illinois Shines — Changes to Illinois net metering bill credits — supply-rate credits for systems interconnected after December 31, 2024
- Illinois Shines — Does my system produce electricity in winter months? — credits rolling forward through the annual period, then expiring
- Illinois Administrative Code — 83 Ill. Adm. Code 466.80, Determining the Review Level — the 25 kW limit for Level 1 interconnection review
- City of Chicago — Express Permit Program: Small-Scale Solar Photovoltaic System — the 13.44 kW inverter-output limit
- Citizens Utility Board — 2026 rate guide — fixed charges, delivery charges and state tax for both utilities
- Citizens Utility Board — ComEd's price from October 1, 2026 — 10.103¢ per kWh, used to estimate kWh from a bill
- Citizens Utility Board — Ameren's price from October 1, 2026 — 10.441¢ on the first 800 kWh and 8.262¢ after, used to estimate kWh from a bill
- Federal Highway Administration — Highway Statistics 2024, Table VM-1 — 10,787 average miles per light-duty vehicle
- U.S. Department of Energy and EPA — fueleconomy.gov, electric vehicles — where each car's kWh per 100 miles is listed
- National Fire Protection Association — National Electrical Code, Section 705.12 (the 120% rule) — the 200-amp panel line, with the arithmetic on our house-fit guide
How to cite this page: The Day Company, "How many solar panels do I need for my Illinois home?", theday.company/answers/what-size-solar-system-illinois, last reviewed October 4, 2026.
Update triggers: this page is revised when the U.S. Energy Information Administration publishes newer usage figures, when Illinois Shines sets new credit prices (next expected June 1, 2027), when ComEd or Ameren change prices or net metering rules, and when the electrical code's solar rules change.
Changelog · last updated October 4, 2026 · 2 updates
- October 4, 2026 — Rebuilt. Added a sizing calculator (monthly kWh or bill, utility, coverage, electric cars), the typical single-family house next to the all-homes average, per-kW output for five Illinois areas from PVWatts after snow losses, a home-size table from the Energy Information Administration's household survey, the four size lines that change Illinois permits and incentives, the DC-versus-AC difference, a roof-space estimate matching our house-fit guide, Berkeley Lab's 2025 system-size data and ComEd's Hourly Pricing exception to the zero-bill rule. Corrected the 2024 U.S. average to 863 kWh a month, the final figure in the Energy Information Administration's Table 5A.
- July 30, 2026 — Published.