The 2026 guide · verified July 2026
Five programs decide the economics of commercial solar in Illinois right now: one of them disappears on December 31, 2027. Here is every current number, what changed, and how they stack, in plain English. All figures verified July 2026 against the official program sources linked at the bottom.
1 · The federal clock
The federal investment tax credit pays back 30% of a commercial solar project's cost on your next tax return. Congress ended the program: a new project (construction starting after July 4, 2026) must be placed in service, energized and running, by December 31, 2027 to claim it. There is no phase-down; on January 1, 2028 it is zero.
Systems under 1 MW AC are exempt from prevailing-wage and apprenticeship requirements: the full 30% applies automatically. Larger projects qualify too, with certified prevailing-wage crews.
Projects meeting the domestic-content threshold (50% for 2026 construction starts) earn an extra 10 percentage points: 40% total. An energy-community location adds another possible 10.
For construction starting in 2026+, equipment containing restricted foreign-entity content can disqualify the entire credit. Sourcing must be documented: this is now a design decision, not an afterthought.
2 · The write-off
A business can write off the full depreciable basis of a solar system in year one (basis = cost minus half the ITC, i.e. 85% of cost with the 30% credit). For a profitable company at combined federal + Illinois rates, that's worth roughly another quarter of the system cost, realized the first year. Unlike the ITC, this one isn't expiring, but it only has value against taxable income.
3 · The state program
Illinois Shines (the Adjustable Block Program) awards a 15-year contract that pays for each renewable energy credit (REC) your system produces: one REC per megawatt-hour. The 2026–27 program year opened June 2026 with blocks available. Under the current contract, most of the cash arrives early: 15% at energization and the remainder over roughly six years for systems over 25 kW.
| Group A = ComEd territory (Chicagoland). Group B = Ameren territory (downstate). Source: Illinois Power Agency final price sheet, June 2026. | ||
| System size (AC) | Group A: ComEd | Group B: Ameren |
|---|---|---|
| 0–10 kW | $70.37 | $80.77 |
| >10–25 kW | $60.92 | $79.21 |
| >25–100 kW | $59.53 | $69.65 |
| >100–200 kW | $55.63 | $65.09 |
| >200–500 kW | $45.64 | $53.40 |
| >500–2,000 kW | $42.37 | $49.57 |
| >2,000–5,000 kW | $31.96 | $37.39 |
Customer-owned systems up to 25 kW that don't claim an investment tax credit earn an extra $20 per REC: the state's answer to the expired federal residential credit. Rule of thumb in ComEd territory: a commercial rooftop earns roughly $1.05–1.15 per watt in nominal REC value over the contract.
4 · The utility rebate
ComEd's distributed-generation rebate pays commercial customers $250/kW (DC) after interconnection approval: cash, not a credit. Batteries earn their own $250/kWh on top (residential rates are $300). Requirements: a smart inverter, a system under 5 MW, and generation that primarily offsets your own load. See our full ComEd solar rebate breakdown for a 100 kW worked example and the claim process.
5 · What changed in 2025
Full retail net metering closed to new Illinois systems on January 1, 2025. Exported electricity now earns only the supply portion of the rate: roughly half of retail. The design consequence: systems are sized to on-site consumption first, because a kilowatt-hour you use is worth about twice one you export. The DG rebate above is the legislature's compensation for the change, and batteries increasingly make sense for the right load profile.
6 · The fear that isn't real
Illinois law (35 ILCS 200/10-5 et seq.) assesses an on-site solar system at no more than the value of an equivalent conventional energy system: the array doesn't inflate your building's assessment. A filing with the county assessor makes it official; a competent installer handles it as part of the project.
7 · Put together
For most owner-occupied Chicagoland commercial buildings, the 30% federal credit, year-one depreciation, Illinois Shines RECs, and ComEd's rebate together can cover 90% or more of project cost, on top of the electricity the building stops buying. See the worked examples for a 100 kW rooftop and a 1.4 MW warehouse with real line items, or start with a free assessment that models your actual building and answers the only question that matters now: can your roof be placed in service before December 31, 2027?
Sources, official program documents, all verified July 2026: Illinois Shines / Illinois Power Agency (PY2026–27 REC price sheet and program guidebook) · IRS Notice 2025-42 (beginning-of-construction rules for §48E) · ComEd distributed-generation rebate · 35 ILCS 200/10-5 (property tax treatment). Not tax advice: confirm your position with your CPA.
The next step
Free assessment: load analysis from your bills, roof condition report, and an incentive model for your address.
