In Illinois, a 4.8-kW system for an average home costs about $12,778 after incentives in 2026, saves about $824 in the first year and pays back in 13.3 years.
| Item | Amount |
|---|---|
| Solar, 4.84 kW × $2.94/W | $14,230 |
| Federal credit (0%) | $0 |
| State incentive | −$1,452 |
| Net cost | $12,778 |
| Scenario | Net cost | Year-1 savings | Payback | 25-yr net |
|---|---|---|---|---|
| State averages (above) | $12,778 | $824 | 13.3 yr | $15,319 |
| Rates rise 5.6%/yr (2020–25 pace) | $12,778 | $824 | 11.7 yr | $26,678 |
| Rates stay flat | $12,778 | $824 | 16.1 yr | $6,636 |
| Survey price $3.6/W (LBNL) | $15,972 | $824 | 16 yr | $12,125 |
| Add 13.5-kWh battery | $29,518 | $1,107 | 20.7 yr | $8,213 |
| Size to 100% of use instead | $18,586 | $1,199 | 13.3 yr | $22,283 |
Verdict: at average Illinois numbers, solar is a marginal investment in 2026 — payback takes 13.3 years, leaving you $15,319 ahead after 25 years. The main reasons: weak sun (the 7th-lowest yield of 51); export credits below retail (exports earn ~50% of retail), so only the solar you use yourself earns full value; a state incentive worth about $1,452. Get at least three quotes: every $0.25/W you shave off the price moves payback by roughly a year or more here.
Net metering and exports in Illinois: Since 2025-01-01 new ComEd/Ameren/MidAmerican systems get supply-only net metering (credits offset supply+transmission, not delivery); pre-2025 systems grandfathered.
Battery: a 13.5-kWh battery at the Illinois average of $1,240/kWh adds $16,740 and shifts about 3,306 kWh a year from low-paid exports to your own use; payback becomes 20.7 years.
EnergySage's Illinois page lists a 12.6-year payback. Its method is not fully published; ours uses EIA's Jan–Aug 2026 price, 40% self-use and the state's export credit, 3%/yr rate growth and 0.5%/yr panel aging, with no federal credit.
The full method, material data and tips are on the main solar payback calculator page.