Illinois pays about 16.1¢ per kilowatt-hour for residential electricity and receives about 4.4 kWh per square metre per day of sunlight — 18th and 34th respectively among the 50 states and DC tracked here. Those two numbers set the ceiling on what rooftop solar returns in Illinois, and they point in opposite directions.
Where Illinois sits against the rest of the country
Illinois is 1.3¢/kWh above the median residential rate across this dataset (14.8¢/kWh) and 0.2 kWh/m²/day below the median insolation (4.6 kWh/m²/day). Under this site's standard assumptions, that combination puts Illinois 27th of 51 for modeled payback speed, at 13.5 years against a dataset median of 13.5 years.
What actually drives payback in Illinois
Illinois is rate-led: upper half of the dataset for electricity price (18th), lower half for sunlight (34th). Swap Illinois's sunlight for the dataset median and payback moves to 13.0 years (0.5 years of swing). Swap its electricity rate instead and payback moves to 14.5 years (1.0 years of swing). The rate swap is the larger of the two, so what a kilowatt-hour costs is the input deciding the outcome in Illinois.
State incentives on record
Recorded for Illinois: Illinois Shines (Adjustable Block Program) pays for SRECs at fixed contract prices; Illinois Solar for All for low-income; property tax special assessment.
No federal credit is applied above (Section 25D expired 31 December 2025), and export terms often matter more than the headline rate (net metering guide).
The modeled system, in numbers
At Illinois's sunlight level a 7 kW array produces roughly 8,769 kWh a year, worth about $1,412 in first-year bill savings at 16.1¢/kWh against an assumed $22,400 installed cost. A ten-year payback at this sunlight level would require a residential rate of about 22.9¢/kWh, which is 6.8¢ above what Illinois households pay today.
States with comparable economics
Illinois's closest analogues by modeled payback are Kansas (13.5 years), South Carolina (13.5 years), Indiana (13.6 years). They arrive there from different rate and sunlight combinations, so their incentive rows are the useful comparison.
- Kansas — modeled payback 13.5 years
- South Carolina — modeled payback 13.5 years
- Indiana — modeled payback 13.6 years