guide9 min read

How Many Solar Panels Do I Need in Illinois? About 15, Town by Town

Ryan Cook•October 11, 2026

The average Illinois home needs about 15 solar panels, assuming 400-watt panels on a south-facing roof. That's a system of roughly 6 kW. The U.S. Energy Information Administration puts the average Illinois household at 693 kWh a month (2024 data), and the federal PVWatts calculator says a south-facing, 30-degree array here makes 1,342 to 1,430 kWh a year per kilowatt, from Chicago down to Belleville.

The part that surprised me when I ran the numbers: it barely matters where in Illinois you live. Rockford, Peoria, Springfield and Carbondale all land within about one panel of each other. What moves the count is how much power your house uses and which way your roof faces.

The key numbers

What	Figure	Source / date
Average Illinois home usage	693 kWh/month (about 8,316 kWh/year)	EIA Table 5.A, 2024 data
Yearly output per kW, south roof, 30° tilt	1,342 (Chicago) to 1,430 (Belleville) kWh	PVWatts v8, run Oct. 11, 2026
Panels for the average home (400 W)	about 14.5 to 15.5	Our math from the two rows above
East- or west-facing roof	about 20% less output (Chicago 1,067 to 1,080 kWh per kW)	PVWatts v8, run Oct. 11, 2026
Credit for power you export (connected 2025 or later)	Supply section of the bill only; credits don't expire	ComEd Net Metering FAQ; Ameren Illinois net metering page
Supply price, Oct. 2026 through May 2027	ComEd 10.103¢/kWh; Ameren 10.441¢ first 800 kWh, 8.262¢ above	Plug In Illinois Price to Compare pages, checked Oct. 11, 2026

Town by town: it's about one panel, north to south

I ran PVWatts for ten Illinois towns with the same setup: 1 kW of panels, facing due south, tilted 30 degrees, standard 14% system losses. Then I divided the average Illinois home's 8,316 kWh by each town's output.

Town	kWh per kW per year	kWh per 400 W panel	System for the average home	Panels (400 W)
Rockford	1,383	553	6.0 kW	15.0
Chicago	1,342	537	6.2 kW	15.5
Naperville	1,343	537	6.2 kW	15.5
Peoria	1,384	554	6.0 kW	15.0
Bloomington	1,395	558	6.0 kW	14.9
Champaign	1,405	562	5.9 kW	14.8
Springfield	1,394	558	6.0 kW	14.9
Quincy	1,421	568	5.9 kW	14.6
Belleville	1,430	572	5.8 kW	14.5
Carbondale	1,420	568	5.9 kW	14.6

Belleville makes about 6.6% more per panel than Chicago. On a 15-panel system, that's one panel.

Rockford beat Chicago in the same model, which tells you latitude isn't the whole story.

I'm using 400-watt panels because that's a common residential size. If yours are bigger, say 430 watts, you'll need a panel or so fewer for the same output.

Your bill moves the count far more than your town

The average home in that table doesn't exist. Some of the homes I see use 500 kWh a month; others with electric heat use several times that in January. Here's how the panel count shifts with usage, south-facing roof, 400-watt panels, rounded to the nearest panel:

Household	kWh per year	Chicago	Rockford	Springfield	Belleville
Light user, 500 kWh/month	6,000	11	11	11	10
Illinois average, 693 kWh/month	8,316	15	15	15	15
Average home plus an EV (about 3,600 kWh/yr)	11,916	22	22	21	21
Average home plus a heat pump (about 6,000 kWh/yr)	14,316	27	26	26	25
Big user, 1,500 kWh/month	18,000	34	33	32	31

The EV figure comes from a car driven 12,000 miles a year, which I worked through in the cost to charge an EV at home in Illinois. The heat pump figure is the middle of the 5,600 to 6,700 kWh range from my heat pump vs. gas furnace breakdown. If either one is in your plans for the next couple of years, size for it now. Adding panels later can mean another permit and another interconnection application with the utility.

Roof direction is the second-biggest factor

A south-facing roof is the benchmark. PVWatts puts an east-facing array in Chicago at 1,067 kWh per kW and a west-facing one at 1,080, against 1,342 facing south. That's about 20% less. Belleville shows the same drop: 1,154 east and 1,155 west, against 1,430 south.

For the average home in Chicago, an east-facing roof means about 19 or 20 panels instead of 15 or 16. That's about four extra panels, against a one-panel gap between Chicago and Belleville.

Tilt matters much less. Dropping from 30 degrees to 20 in Chicago cost under 3% in the same model. Shade from a big oak is the one that can really wreck a design, and you can't see that in a statewide table. Our roof check tool looks at your actual roof.

Do the math with your own bill

You can get within a panel or two in five minutes:

Add up twelve months of kWh. Both utilities show your usage history in your online account. Ameren Illinois points customers to their billing statements and usage data for sizing. Don't size from one month; an Illinois August and an Illinois March look nothing alike. The average Illinois electric bill post shows where a typical home lands.
Divide by your town's output per kW. Use the table above, or about 1,340 for the Chicago area and 1,430 for southern Illinois if your town isn't listed. That gives you system size in kW.
Divide the kW by the panel size. For 400-watt panels, divide by 0.4.

A Springfield home using 10,000 kWh a year: 10,000 ÷ 1,394 = 7.2 kW. 7.2 ÷ 0.4 = 18 panels.

Why I size to 100%, not 130%

Older guides told you to overbuild and bank the extra. In Illinois, that changed on January 1, 2025.

For anyone connected since then, ComEd and Ameren credit the power you send to the grid against the supply section of your bill only. A kilowatt-hour you use in your own house still offsets supply and delivery. A kilowatt-hour you export earns a supply credit worth about the utility's price to compare: 10.103¢ on ComEd this winter, 10.441¢ on Ameren for the first 800 kWh. I explained the full change in the Illinois net metering changes post.

The good news: for new customers, those credits don't expire. Both utilities say so. That matters because Illinois production swings hard with the seasons. In PVWatts, a Chicago system sized for the average home makes roughly 410 kWh in December and roughly 950 in July, against 693 a month of use. The summer surplus carries into winter. That's why sizing to 100% of your yearly usage works, and why going past it mostly buys you the lower-value kind of kilowatt-hour. How solar output falls in fall and winter has the month-by-month curve, and the credit-expiration post covers the older accounts where credits do still reset.

ComEd's own guidance says the system "should be sized to meet some or all of your current or future energy needs." That's the rule I follow.

What this means on a lease

The leases I offer bill the power the panels produce at a predictable rate as low as $0.10 per kWh, with $0 down and a 25-year term. That makes right-sizing even more important. Every panel past your usage makes power you pay the lease rate for, and it earns back roughly the supply price, about ten cents this winter. You'd be paying the lease rate to earn back about the same, or less.

A system sized to your twelve-month usage puts nearly every kilowatt-hour to work on the expensive side of the bill. I walked through monthly lease cost in how much a solar lease costs per month in Illinois. If you'd rather own the system, the sizing logic is the same; only the payback math changes.

Why the old answer was 24 panels

Some of the Illinois pages still ranking for this question were written around 250-watt panels and full retail net metering. At 250 watts, the average home needs about 24 panels. At 400 watts, the same power takes about 15. Those pages also predate the 2025 credit change, so they'll still tell you overbuilding pays. Check the date on whatever you're reading, this page included.

Get your real number

Send me twelve months of your Ameren or ComEd bills and your address, and I'll tell you how many panels your roof can hold and how many your usage actually justifies. Start with the savings calculator, or call me at (618) 217-2001.

Sources

EIA Table 5.A, 2024 Average Monthly Bill, Residential — U.S. Energy Information Administration, Form EIA-861 data for 2024 (Illinois: 693 kWh per month, 15.87¢/kWh, $109.99)
PVWatts v8 calculator — National Laboratory of the Rockies (U.S. DOE); 1 kW DC, 30° tilt, 14% losses, fixed roof mount, south (180°), east (90°) and west (270°) runs for Rockford, Chicago, Naperville, Peoria, Bloomington, Champaign, Springfield, Quincy, Belleville and Carbondale, run Oct. 11, 2026 (NSRDB PSM V3 TMY weather data)
ComEd Net Metering Frequently Asked Questions — ComEd, 2026 edition (supply-section credits from Jan. 1, 2025; credits don't expire for customers interconnected Jan. 1, 2025 or later; "sized to meet some or all of your current or future energy needs")
Ameren Illinois Net Metering — Ameren Illinois, accessed Oct. 11, 2026 (excess generation credited to the Supply section for applications after Jan. 1, 2025; credits "will not expire")
Price to Compare, ComEd and Price to Compare, Ameren Illinois — Plug In Illinois / Illinois Commerce Commission (Oct. 2026 through May 2027 prices)

Interactive Tool

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Enter your monthly electric bill for an instant lease-vs-utility estimate built on your numbers — not a national average.

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How We Calculate Your Savings

This calculator uses your custom utility rate (default $0.16/kWh for Illinois) with a 4.5% annual escalator compared to our lease rate as low as $0.10/kWh (est.) plus battery backup for 25 years, with the full rate schedule set in your contract. After the 25-year lease, you can keep the system for a low fair-market buyout — then your electricity cost drops to near-zero for the remaining life of the panels. Your actual savings may vary based on your specific usage patterns and system size.

Frequently Asked Questions

About 15 panels for the average Illinois home, if they're 400-watt panels on a south-facing roof. The U.S. Energy Information Administration puts the average Illinois household at 693 kWh a month in 2024, or about 8,316 kWh a year. The federal PVWatts calculator estimates a south-facing, 30-degree array in Illinois makes 1,342 to 1,430 kWh a year per kilowatt, from Chicago to Belleville. Divide the usage by that output and you get a system of roughly 5.8 to 6.2 kW, which is 14.5 to 15.5 panels at 400 watts each. Your number depends mostly on two things: how much electricity your house uses, and which way your roof faces. A home that also charges an EV lands near 21 to 22 panels, and an east- or west-facing roof needs about a quarter more panels. Pull twelve months of kWh off your bill before trusting anyone's estimate.

A little, but less than most people expect. PVWatts estimates a south-facing, 30-degree array makes about 1,342 kWh a year per kilowatt in Chicago and about 1,430 in Belleville. That's roughly 6.6% more in the Metro East, which works out to about one panel on a system sized for the average Illinois home. Rockford, at 1,383, actually came out ahead of Chicago in the same model. The real north-south difference shows up in winter. In Chicago, December output is less than half of June's, while Belleville keeps a bit more of its summer pace. Across a full year, though, the gap is small. Your usage and roof direction move the panel count far more. An east-facing roof cuts output by about 20% in both cities, which is three times the north-south difference. Start from your own twelve months of usage before comparing any quotes.

Roughly 21 to 23 panels at 400 watts each, depending on where you live and assuming a south-facing roof. A home using 1,000 kWh a month uses about 12,000 kWh a year. PVWatts estimates a south-facing, 30-degree array makes about 1,342 kWh per kilowatt per year in Chicago, 1,383 in Rockford, 1,394 in Springfield and 1,430 in Belleville. That works out to a system of about 8.9 kW in Chicago (around 22 panels) and about 8.4 kW in Belleville (about 21 panels). If your best roof faces east or west, plan on roughly 20% less output per panel, which pushes a Chicago home closer to 28 panels. Check whether your 1,000 kWh is a steady average or a summer spike. In Illinois, the twelve-month total is the number to size from, not one hot August bill.

Usually not. Since January 1, 2025, new solar customers in Illinois have their excess power credited against the supply section of the bill only. ComEd and Ameren both say so in their net metering materials. Power you use in your own home offsets supply and delivery charges, while power you send to the grid earns the smaller supply credit. Panels beyond your yearly usage mostly make the lower-value kind of kilowatt-hour. The credits don't expire for new customers, so a summer surplus can carry into winter, which is why sizing close to 100% of annual use works well. On a lease priced per kWh the panels produce, extra panels mean paying for power that earns roughly the supply price back. Size for 100% of your twelve-month usage plus any planned EV or heat pump, and skip the extra panels.

Square footage doesn't size a solar system; your kilowatt-hours do. Two 2,000-square-foot homes in the same Illinois town can need 11 panels or 27, depending on whether they heat with gas or electricity, run central air hard, or charge an electric car. The Illinois average is 693 kWh a month, according to the U.S. Energy Information Administration's 2024 data. A home at that level needs about 15 panels at 400 watts on a south-facing roof, using PVWatts production estimates of 1,342 to 1,430 kWh per kilowatt per year. A home that swapped a gas furnace for a heat pump adds an estimated 5,600 to 6,700 kWh a year and lands around 24 to 28 panels. The fastest way to know is to add up the last twelve months of kWh on your Ameren or ComEd bill and divide by your town's production per panel.