Most solar websites run their savings math on a made-up ‘average home.’ We used a real one: a single-family home in Homer Glen, Illinois, whose owner shared a full year of ComEd usage with us. No name, no address — just the real numbers, with every assumption out in the open.
The Bill, Taken Apart
The month we used (July 7 – August 5, 2026): 900 kWh, $177.83. Here’s where that money actually goes. Supply is 10.4¢ per kWh — ComEd prints that as its official ‘price to compare.’ Delivery adds 6.5¢ per kWh, plus a fixed $19.37 a month in customer and metering charges that no solar system can erase. Taxes and state program riders add about 0.9¢. All-in, that’s about 19.8¢ per kWh — but the part a solar panel can actually avoid is roughly 17.6¢. Over the trailing twelve months this home used 6,260 kWh and paid about $1,335 (roughly $111 a month on average, with summer peaks like the $177.83 above). Sanity check: our rate model rebuilt this home’s July bill to within a dollar of what they actually paid.
The System That Fits
A 5 kW rooftop system. In the Chicago area, each installed kilowatt produces roughly 1,200 kWh a year, so 5 kW ≈ 6,000 kWh — about 96% of this home’s usage. That slight undersizing is deliberate: under Illinois net billing, power you export earns only the supply rate, so a system matched to real usage beats an oversized one.
What It Costs, Honestly (2026)
| Item | Cost |
|---|---|
| Installation | $13,000–$17,000 (at $2.60–$3.40 per watt) |
| ComEd Distributed Generation rebate | −$1,500 ($300 per kW) |
| Illinois Shines SRECs | −$6,300 to −$7,650 (this system earns about 90 solar credits over its 15-year contract; recent values run $70–$85 each — it varies by program block, and your installer handles the paperwork) |
| Federal tax credit | $0 — it ended for homeowner-owned systems placed in service after 2025, so any 2026 quote that still shows it is a red flag |
| Net cost | roughly $3,900–$9,200, with a midpoint around $6,750 |
The Savings, Split the Way Installers Don’t
Of the 6,000 kWh the system makes each year, assume 70% is used inside the home as it’s produced. That power avoids the full ~17.6¢ rate: about $739 a year. The other 30% is exported to the grid and credited at the 10.4¢ supply rate under net billing: about $187 a year. Total savings ≈ $925 a year, and the ComEd bill falls from about $1,335 to about $410 a year (the fixed charges stay). Payback at the midpoint: roughly 7 years (4–10 across the cost ranges). After that, it’s about $925 a year for the rest of the panels’ 25-year life — roughly $23,000 in gross savings, before any rate increases. And rates are increasing: this home’s own bill carries ComEd’s notice that PJM supply prices rose again in June 2026, which shortens the real payback.
The Honest Caveats
First: this is a modest-usage home. 6,260 kWh a year is below the Illinois typical, and lower usage means a longer payback — bigger households, and anyone adding an EV, will see faster math. Second: SREC prices move with program blocks, and the 70/30 self-use split depends on when your home actually uses power. A battery changes both the split and the cost. The right move is three quotes — and make every installer show you this same split, in writing.
Want this math run on your own bill? Get quotes from vetted Illinois installers — one short form, no obligation.