Illinois solar calculator
Estimate system size, panels, roof space, gross cost, savings, and payback using Illinois starter assumptions.
No email required
Enter monthly kWh or electric bill. The calculator uses state-level assumptions and shows the math behind the result.
Your estimate
Example resultEstimated system size: 10.0 kW. This is an estimate, not an installer quote.
Confidence
Medium
Planning estimate only — not an installer quote, engineering design, or tax advice.
Payback uses gross system cost before verified incentives, financing fees, batteries, and roof work.
Annual usage: 10,800 kWh
Annual production target: 10,800 kWh
State rate: 19.89 cents/kWh
Export assumption: Partial export credit
Direct solar use: 5,940 kWh
Modeled exports: 4,860 kWh
Panel count view
24-28 panels
Estimate shape
Privacy note: the printable report link stores estimate inputs in the URL, including ZIP and usage or bill values. Keep it private if those details are sensitive.
Local scenarios
Compare a few assumptions without creating an account.
Saved scenarios stay in this browser only and may include ZIP, bill, and usage inputs. SolarCalcNow does not sync them or send those values to analytics.
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Confidence drivers
Expected production: 10,800 kWh
System loss: 14%
Export value: Partial export credit
Direct solar use: 5,940 kWh
Modeled exports: 4,860 kWh
State production default: 1,250 kWh/kW/year
EIA Electric Power Monthly, Table 5.6.A — June 2026 - 2026-09-04
SolarCalcNow author-created production assumption - 2026-09-04
EnergySage marketplace + SolarCalcNow cost scenario - 2026-09-04
Production evidence: California has a saved full PVWatts response; eight states have successful API yields recorded to two decimals. Colorado, Illinois and Pennsylvania retain explicit author assumptions. The download distinguishes these evidence levels.
$0.1989/kWh
19.89 ¢/kWh
EIA Table 5.6.A, June 2026 residential column; published August 26, 2026. Divide the published cents/kWh by 100. This preliminary statewide average is a fallback, not your utility tariff. Use your bill's energy-only rate; fixed charges remain payable.
1,250.0 kWh/kW/year
kWh/kW/year
Author-created pre-loss planning input, not a retrieved PVWatts result or a measured state average. This state could not be verified within the provider quota. The model applies 14% system loss once. Verify production before using cost or payback.
$2.38–$3.58/W
$2.98/W × 0.8…1.2
EnergySage's state marketplace average, table updated August 28, 2026. We calculate an author-selected range of average × 0.8 to average × 1.2, rounded to cents/W. This ±20% scenario is not an observed price distribution or confidence interval. Cash solar only, before incentives; compare like-for-like local quotes.
SolarCalcNow provides planning estimates only. Results are not installer quotes, engineering designs, tax advice, financing recommendations, or utility interconnection approval.
Optional next step
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Installer quote matching is not active yet. You can still calculate, save, and print your estimate before contacting installers directly.
State-specific review
These planning notes interpret the same source-linked inputs used by the calculator. They do not add an incentive, utility tariff, or site-specific claim to the estimate.
Illinois planning in 2026 should start from the gross contract price. SolarCalcNow's reviewed IRS record treats the homeowner Section 25D credit as unavailable for expenditures after the 2025 cutoff, so older examples that subtract a federal percentage can understate the cash price and shorten payback on paper. Keep state, utility, local, or certificate-related claims separate until the current program source, status, amount, timing, ownership rule, and household eligibility are verified. This calculator does not subtract those claims automatically. Its result is deliberately a pre-incentive baseline that can be compared with a written proposal without assuming a tax outcome or future payment that may not apply.
Sources: IRS Section 25D update (reviewed 2026-09-04); EnergySage marketplace + SolarCalcNow cost scenario (reviewed 2026-09-04)
A single high cooling month or low shoulder-season bill can distort an Illinois system-size estimate. Average twelve months of kWh where possible and separate any planned EV, heat pump, or other new electric load from the historical baseline. The state production input annualizes output, so it does not promise that monthly production will follow monthly demand. Ask an installer to show the seasonal production profile, snow and shade losses, roof-plane assumptions, and the DC-to-AC relationship behind its annual number. The useful comparison is not whether two models match exactly, but whether every difference has a visible input and a reasonable physical explanation.
Sources: SolarCalcNow author-created production assumption (reviewed 2026-09-04)
The displayed electricity rate is a consistent statewide reference from EIA, not a ComEd, Ameren, municipal, or cooperative tariff. It excludes the detailed account structure that can determine actual avoided cost, including fixed charges, supply and delivery components, settlement periods, and time-varying prices. Compare it with the energy portion of recent bills before trusting annual savings. If a proposal applies the highest bill component to every solar kWh or assumes repeated rate increases, ask for the exact source and calculation. SolarCalcNow does not publish city-level precision from state-level data and does not create a utility claim without a reviewed tariff record.
Sources: EIA Electric Power Monthly, Table 5.6.A — June 2026 (reviewed 2026-09-04)
Export compensation and incentive value answer different questions. Export value affects what an excess kWh is worth in the annual savings model; an incentive or certificate program can affect project economics through separate eligibility, timing, and ownership rules. Combining the two makes it hard to see why payback changed. SolarCalcNow models direct use and exported energy separately, then leaves unverified incentives outside net cost. Run several export scenarios first, identify how much production is expected to leave the home, and only then review the current program documents. A proposal should identify whether the homeowner or another party owns any certificate or payment it includes.
Sources: EIA Electric Power Monthly, Table 5.6.A — June 2026 (reviewed 2026-09-04); SolarCalcNow author-created production assumption (reviewed 2026-09-04)
Use the state cost-per-watt range against the solar-only gross price, not the financed total and not a payment advertised after assumed incentives. List batteries, roof work, electrical upgrades, dealer fees, interest, monitoring, and optional service as separate lines. A price outside the benchmark can be justified by scope, but the scope should be written. Ask for model and quantity of panels, inverter architecture, DC and AC capacity, workmanship coverage, equipment warranties, production assumption, and exclusions. This creates a comparison that remains useful even if loan terms, program values, or utility rules change after the initial sales conversation.
Sources: EnergySage marketplace + SolarCalcNow cost scenario (reviewed 2026-09-04)
Treat the state calculator as the middle layer between raw bills and a site proposal. Bills are the evidence for household demand. The calculator translates that demand through visible state rate, production, cost, loss, and export assumptions. The installer should then replace state-level uncertainty with roof measurements, shade analysis, equipment, electrical work, interconnection requirements, and a written schedule. Do not let local wording imply local data that has not passed the utility source gate. When a bidder changes the annual kWh, production, price, or export value, record the change explicitly so the resulting panel count and payback can be reproduced rather than accepted as a sales estimate.
Sources: EIA Electric Power Monthly, Table 5.6.A — June 2026 (reviewed 2026-09-04); SolarCalcNow author-created production assumption (reviewed 2026-09-04); EnergySage marketplace + SolarCalcNow cost scenario (reviewed 2026-09-04)
Production evidence: California has a saved full PVWatts response; eight states have successful API yields recorded to two decimals. Colorado, Illinois and Pennsylvania retain explicit author assumptions. The download distinguishes these evidence levels.
$0.1989/kWh
19.89 ¢/kWh
EIA Table 5.6.A, June 2026 residential column; published August 26, 2026. Divide the published cents/kWh by 100. This preliminary statewide average is a fallback, not your utility tariff. Use your bill's energy-only rate; fixed charges remain payable.
1,250.0 kWh/kW/year
kWh/kW/year
Author-created pre-loss planning input, not a retrieved PVWatts result or a measured state average. This state could not be verified within the provider quota. The model applies 14% system loss once. Verify production before using cost or payback.
$2.38–$3.58/W
$2.98/W × 0.8…1.2
EnergySage's state marketplace average, table updated August 28, 2026. We calculate an author-selected range of average × 0.8 to average × 1.2, rounded to cents/W. This ±20% scenario is not an observed price distribution or confidence interval. Cash solar only, before incentives; compare like-for-like local quotes.
Source coverage: ComEd
For new residential interconnections from January 1, 2025, ComEd credits offset supply charges, not the entire delivered retail bill. Verify supplier terms and interconnection date. REC payments are separate.
Read the primary source — ComEd Net Metering — 2025 onwardSource checked: · Next review due: 2026-10-04
Source coverage: Illinois Shines
Illinois Shines buys RECs through approved vendors. Check category, current block, vendor contract, REC ownership and the amount passed to the homeowner. A vendor's REC contract is not automatically your rebate.
Read the primary source — Illinois Shines Program Year 2026–27Source checked: · Next review due: 2026-10-04
Program documented; eligibility required · Not subtracted from calculator cost
Planning example
This example uses the same calculator engine as the interactive form: 400W panels, low shade, 100% target offset, and no ZIP-level PVWatts override.
System size
10.0 kW
Panel range
24-28 panels
Roof area
628 sq ft
Gross cost
$23,911-$35,967
Annual savings
$1,520
Simple payback
15.7 years-23.7 years
For a home using 900 kWh per month in Illinois, the default planning estimate is a 10.0 kW system with 24-28 panels at 400 W each, producing about 10,800 kWh per year and needing roughly 628 sq ft of roof. Estimated gross cost is $23,911-$35,967 before incentives, with simple payback of 15.7 years-23.7 years. The estimate uses EIA Electric Power Monthly, Table 5.6.A — June 2026 (updated 2026-09-04) and SolarCalcNow author-created production assumption (updated 2026-09-04).
Usage sensitivity
These rows keep every input fixed except monthly usage. If your home is closer to 600 or 1,200 kWh/month, this gives a faster sanity check than reading one generic state paragraph.
| Usage | System | Panels | Gross cost | Payback |
|---|---|---|---|---|
| 600 kWh/mo | 6.7 kW | 15-19 | $15,940-$23,978 | 15.7 years-23.7 years |
| 900 kWh/mo | 10.0 kW | 24-28 | $23,911-$35,967 | 15.7 years-23.7 years |
| 1,200 kWh/mo | 13.4 kW | 32-36 | $31,881-$47,955 | 15.7 years-23.7 years |
Local context
Savings depend on utility rules and available state/local programs.
Before using this as a purchase decision, compare a no-battery and battery quote, verify your utility export rate, and check current incentives from state or utility sources.
For a home using 900 kWh per month, the Illinois starter model estimates about 10.0 kW, 24-28 panels, roughly 628 sq ft of roof area, and a gross installed-cost range of $23,911-$35,967. Simple payback is shown as 15.7 years-23.7 years before verified incentives, financing, batteries, roof work, or utility-specific export rules.
Illinois estimates use 19.89 cents/kWh as the residential rate assumption. Higher retail rates can improve the value of self-consumed solar, while lower rates usually make system size, export credit, and installed cost more important to the payback result.
Illinois estimates should separate energy export value from incentive/REC treatment before modeling net cost. SolarCalcNow's default advanced setting models exported kWh below retail value until utility-specific rules are verified. This keeps the planning estimate conservative when a home exports more power than it uses immediately.
The current production assumption is 1,250 kWh per kW per year. This is a state-level starter value, not a roof-specific PVWatts result. Actual output can change with azimuth, tilt, shade, snow, weather, usable roof planes, setbacks, inverter choice, and module degradation.
The gross cost range uses a starter benchmark of $2.38-$3.58/W. SolarCalcNow does not subtract incentives from this estimate unless each incentive has an official or reviewable source, updated date, eligibility note, active status, and explicit permission to be included in net-cost math. Use the quote checker to compare installer price per watt against the same gross-cost baseline.
Data status
Electricity rate
EIA Electric Power Monthly, Table 5.6.A — June 2026
Updated 2026-09-04 - Confidence: official
Solar production
SolarCalcNow author-created production assumption
Updated 2026-09-04 - Confidence: starter-assumption
Installed cost
EnergySage marketplace + SolarCalcNow cost scenario
Updated 2026-09-04 - Confidence: market-benchmark
FAQ
Start with a full-year average of monthly electricity use, then choose how much of that use the system should offset. The Illinois calculator converts annual kWh into a system-size estimate using the visible state production assumption, shade setting, and system-loss factor. It then divides system watts by the selected panel wattage and shows a range rather than pretending the roof layout is known. Higher-wattage modules can reduce the count for the same system size, while setbacks, vents, separate roof planes, and shade can change the installable layout. Treat the result as a planning range and compare it with a site-specific design before signing a proposal.
The calculation uses 19.89 cents/kWh from EIA Electric Power Monthly, Table 5.6.A — June 2026, reviewed 2026-09-04. The figure is a statewide residential average, not a promise about a particular utility account. It helps value solar energy used directly in the home, while exported energy is valued separately under the selected export assumption. A real bill can include fixed charges, seasonal pricing, time-of-use periods, minimum bills, taxes, and other terms that the statewide rate does not reproduce. Use the source-linked average for early comparison, then verify the exact tariff and recent usage history on the account before treating savings or payback as project-specific.
No incentive is subtracted from the default gross-cost estimate. SolarCalcNow requires an official or otherwise reviewable source, a review date, active status, eligibility rules, ownership conditions, and an explicit inclusion decision before a program can enter net-cost math. This prevents an expired, conditional, or third-party-only benefit from making a planning result look cheaper than the written project price. Review the state incentive page and the primary program source separately, confirm personal eligibility with qualified professionals, and keep each claimed credit or rebate on its own line when comparing proposals. Gross price, financing charges, battery cost, roof work, and incentives should not be collapsed into one unexplained number.
Illinois estimates should separate energy export value from incentive/REC treatment before modeling net cost. Solar used immediately in the home is valued at the residential rate assumption, while exported energy is valued under the selected export scenario. If the export credit is below retail, a system designed for full annual usage offset can save less than a simple one-for-one net-metering model suggests, especially when much of its production leaves the home. The calculator therefore separates direct solar use from export and keeps the assumption editable. Confirm the serving utility, tariff, settlement period, fixed charges, rollover rules, and time-of-use treatment before relying on the modeled annual savings or simple payback.
The model combines user inputs with Illinois statewide rate, production, and cost assumptions, but it cannot inspect the property. It does not measure roof orientation, tilt, shade patterns, structural condition, usable roof planes, setbacks, electrical-service capacity, or interconnection constraints. It also cannot know the final equipment package, installer scope, financing fees, insurance requirements, utility tariff, or verified incentive eligibility. Those details can change panel count, production, gross cost, and payback. Use the result to understand scale and compare assumptions, then ask installers to document their site survey, production model, equipment, exclusions, and written price so differences can be traced rather than accepted as unexplained precision.
The current calculator does not geocode ZIP codes. It uses an author-selected reference point in the selected state, including when the optional live PVWatts provider responds. Entering a ZIP does not establish property-level accuracy. The model does not know the exact roof plane, azimuth, tilt, shade, setbacks or module layout. Check which production basis appears in the result, then compare it with the installer model and the physical roof survey before relying on annual output.