Scenario: a $125/month electric bill. Assumes 3%/yr rate increases, 0.5%/yr panel degradation and no federal tax credit (the 30% §25D credit ended for systems installed after Dec 31, 2025). How we calculate
Data approachEIA rates · NREL sun hours · 2026 federal policy · methodology
A $125/month electricity bill in Illinois represents roughly 650 kWh per month at the state average rate of 19.22¢/kWh (EIA, Jan–Jul 2026 year-to-date). With 4.4 peak sun hours per day, offsetting that usage takes about a 5.9 kW solar system — roughly 15 panels at 400W — costing about $17,800 installed. Because the 30% federal tax credit ended for systems installed after 2025 and Illinois has net billing / reduced export credit, simple payback is about 16.9 years, with an estimated $18,000 net over 25 years.
How Many Solar Panels for a $125 Electric Bill in Illinois?
Illinois electricity rates and sun hours change the math versus the US average. The sizing formula:
System size (kW) = Annual kWh ÷ (Peak sun hours × 365 × 0.82)
For a $125/month bill in Illinois:
Annual usage: ~7,804 kWh/year
Peak sun hours: 4.4 h/day (Illinois)
System size:5.9 kW DC (~15 × 400W panels)
Metric
Illinois
US average
Rate
19.22¢/kWh
18.19¢/kWh
Sun hours
4.4 h/day
4.5 h/day
System size
5.9 kW
6.1 kW
Panels (400W)
15
16
Illinois requires a similar system than the national average for the same dollar bill because higher rates reduce required kWh. Use our solar system size calculator with your ZIP code for a roof-specific result.
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💰 System Cost
What Does Solar Cost for a $125/Month Bill in Illinois in 2026?
At about $3.00/W installed (a blended 2026 US price; marketplace quotes often run lower), a 5.9 kW system in Illinois costs about $17,800.
The 30% federal Residential Clean Energy Credit (IRC §25D) ended for systems installed after December 31, 2025, so a solar system you buy and install in 2026 gets no federal tax credit. Leases and PPAs are different: the installer that owns the system can still claim the commercial §48E credit for systems placed in service by the end of 2027 and may pass part of that value on through a lower monthly price.
Cost line
Amount
Installed cost (5.9 kW)
$17,800
Federal credit (25D) for 2026 installs
$0
Your cost before state/local incentives
$17,800
Getting three or more quotes matters more than ever without the federal credit: installed prices for the same system often differ by 20–30%.
📈 Payback Period
How Long Is Solar Payback on a $125 Bill in Illinois?
Simple payback divides installed cost by first-year bill savings. Since 2025, new Illinois ComEd and Ameren customers receive a supply-only credit for exports rather than full retail. We therefore assume solar offsets about 70% of a $125/month bill in Illinois — roughly $1,050/year — for a simple payback of about 16.9 years.
Over 25 years, with 3% annual rate increases and 0.5%/year panel degradation, cumulative bill savings minus the installed cost come to about $18,000. Shifting usage (EV charging, laundry, pool pumps) into daylight hours raises the value of each kWh you produce. Model your own numbers in our solar payback calculator.
Solar vs utility company · 25-year comparison
25-year totals for a $125/month electric bill: 3%/yr rate increases, 0.5%/yr degradation, no federal credit. Methodology
Illinois Solar Incentives for a $125/Month Electric Bill
State and local incentives: Illinois Shines pays Renewable Energy Credit (REC) incentives for 15 years of production, usually passed to the homeowner as an upfront discount by the installer.
Net metering: Since 2025, new Illinois ComEd and Ameren customers receive a supply-only credit for exports rather than full retail.
Check DSIRE and our Illinois solar page for current rebates, net metering rules, and utility-specific programs before signing an install contract.
⚡ System Size
Illinois vs US Average: $125/Month Bill Comparison
Illinois
US average
Monthly bill
$125
$125
System size
5.9 kW
6.1 kW
Installed cost
$17,800
$18,400
Bill offset assumed
70%
75% (blended)
Simple payback
16.9 yrs
16.3 yrs
25-year net savings
$18,000
$20,000
Bottom line: A $125/month bill in Illinois is a marginal solar candidate with about 16.9-year payback in 2026. Calculate your Illinois savings or compare all states on the $125 bill hub.
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At Illinois's average rate of 19.22¢/kWh and 4.4 peak sun hours, a $125/month bill (~7,804 kWh/year) typically requires a 5.9 kW system — about 15 panels at 400W each. Use our solar system size calculator with your ZIP for a roof-specific estimate.
A 5.9 kW system in Illinois costs roughly $17,800 installed at about $3.00 per watt. The 30% federal tax credit (25D) ended for systems installed after December 31, 2025, so there is no federal credit for a system you buy in 2026. Illinois Shines pays Renewable Energy Credit (REC) incentives for 15 years of production, usually passed to the homeowner as an upfront discount by the installer.
At $17,800 installed and ~$1,050/year in bill savings, simple payback in Illinois is about 16.9 years. Since 2025, new Illinois ComEd and Ameren customers receive a supply-only credit for exports rather than full retail.
With about 16.9-year payback and roughly $18,000 in estimated 25-year net savings, a $125/month bill in Illinois is a marginal case for buying solar in 2026. See the [Illinois solar page](/states/il/) for net metering and incentive details.
The US average needs a 6.1 kW system at 16.3-year payback. Illinois needs 5.9 kW with 16.9-year payback — driven by Illinois's 19.22¢/kWh rate and 4.4 daily sun hours.
19.22¢/kWh — Illinois average residential price. Source: EIA Electric Power Monthly, Table 5.6.B (year-to-date through July 2026), residential average retail price (July 2026) (EIA)
Solar production
4.4 peak sun hours/day × 0.82 system derate. Approximate state-average daily solar resource (peak sun hours) based on NREL solar resource data (NSRDB); not location-specific — use NREL PVWatts for an address-level estimate. (NREL PVWatts)
Installed price
$3.00 per watt before incentives. Blended 2026 US residential installed price used by this site; EnergySage marketplace reported about $2.60/W (mid-2026); full-market medians are higher.
Federal tax credit
$0 for homeowner-owned systems installed in 2026 — the 30% §25D credit ended Dec 31, 2025 (IRS)
Net metering
Net billing / reduced export credit — solar assumed to offset 70% of the bill. Since 2025, new Illinois ComEd and Ameren customers receive a supply-only credit for exports rather than full retail.
Estimates only — not tax, legal or financial advice. Get at least three installer quotes and confirm incentives with your utility and a tax professional.