Solar · Illinois
How many solar panels do I need in Illinois?
For the average Illinois home, which uses 693 kWh a month (EIA, 2024), about 15 × 400 W solar panels (5.83 kW) facing south at the best tilt. One kW of panels in Illinois makes about 1,427 kWh a year, 4.8 kWh a day in July and 2.4 in December, the 37th sunniest of 51.
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Solar output by month in Illinois
Output falls to 50% of the July level in December. Grid-tied homes are sized on the year; anything off-grid has to be sized for December.
| Month | kWh per kW | Per day | 200 W panel, Wh/day into a battery |
|---|---|---|---|
| January | 85 | 2.73 | 464 |
| February | 102 | 3.64 | 618 |
| March | 127 | 4.09 | 695 |
| April | 132 | 4.41 | 750 |
| May | 140 | 4.52 | 768 |
| June | 142 | 4.74 | 806 |
| July | 148 | 4.77 | 811 |
| August | 143 | 4.62 | 785 |
| September | 134 | 4.47 | 759 |
| October | 112 | 3.62 | 616 |
| November | 88 | 2.94 | 499 |
| December | 74 | 2.37 | 403 |
Charging a power station in Illinois
A 200 W panel propped up facing south refills a 1,000 Wh power station in about 1.2 days in July and 2.5 days in December. To refill it in one day you’d need about 250 W of panels in July and 500 W in December. Check your station and panel →
A balcony or plug-in panel in Illinois
A 400 W panel hanging upright on a south-facing railing makes about 384 kWh a year, worth about $74.10 at Illinois’ average rate (19.32¢/kWh, August 2026), if you use the power as it’s made. Shade and the rules where you live matter more than anything here. Try your kit →
The rules in Illinois: We found no state law on plug-in solar in Illinois as of November 5, 2026; ask your utility. Every state we track →
Across Illinois
Illinois’s figure is the population-weighted average of Chicago, Aurora and Naperville, its three largest cities; across them, a kW makes 1,408 to 1,429 kWh a year.
| City | Population (2024) | kWh per kW a year |
|---|---|---|
| Chicago | 2,721,308 | 1,429 |
| Aurora | 180,710 | 1,413 |
| Naperville | 153,124 | 1,408 |
Cross-check: an estimate from NASA POWER sunshine came out at 1,249 kWh per kW, 14% below the Global Solar Atlas figure. That’s more than our 12% review threshold, so we checked it by hand: both sources agree on the sunshine itself; the gap comes from the cross-check’s simpler tilt model and its fixed losses, which understate output in cool climates. We use the Global Solar Atlas figure.
Electricity rates and appliance costs in Illinois →
FAQ
How many solar panels do I need in Illinois?
For the average Illinois home, which uses 693 kWh a month (EIA, 2024), about 15 × 400 W solar panels (5.83 kW) facing south at the best tilt. One kW of panels in Illinois makes about 1,427 kWh a year, 4.8 kWh a day in July and 2.4 in December, the 37th sunniest of 51.
How much does a solar panel produce in Illinois?
A 400 W panel facing south at the best tilt makes about 571 kWh a year in Illinois: about 59 kWh in July and 29 kWh in December (Global Solar Atlas).
How long does a 200 W solar panel take to charge a 1,000 Wh power station in Illinois?
About 1.2 days in July and 2.5 days in December, propped up facing south, at 85% charging efficiency. Lying flat, about 4.4 days in December.
How many solar panels for the U.S. average home in Illinois?
The U.S. average home uses 863 kWh a month (EIA, 2024). In Illinois that takes about 7.26 kW: 19 × 400 W panels.
Is there still a federal solar tax credit?
Not under the residential credit for systems installed after 2025: the IRS says the section 25D credit will not be allowed for any expenditures made after December 31, 2025, and an expenditure counts as made when installation is completed.
Sources and assumptions
- Solar output (kWh per kW of panels, by month): Global Solar Atlas 2.0, long-term averages to 2025 (data version 2.2.68, updated 2026-04-01), for crystalline-silicon panels facing south at the best fixed tilt, after typical system losses. Data obtained from the “Global Solar Atlas 2.0, a free, web-based application is developed and operated by the company Solargis s.r.o. on behalf of the World Bank Group, utilizing Solargis data, with funding provided by the Energy Sector Management Assistance Program (ESMAP). For additional information: https://globalsolaratlas.info” Licensed CC BY 4.0; we rounded and combined it as described here. Not affiliated with or endorsed by Solargis or the World Bank Group.
- State figure: population-weighted average of the state’s three largest cities (U.S. Census Bureau Vintage 2024 population estimates; coordinates from the 2020 Census Gazetteer). Hawaii and DC use one city.
- Cross-check: NASA POWER sunshine climatology (2001–2025), tilted with a standard isotropic-sky model × 0.80. States more than 12% apart were reviewed by hand; the gaps are explained on our methodology page.
- Home use: EIA Table 5A, 2024 average monthly residential kWh by state. Rates: EIA Electric Power Monthly, August 2026.
- Tax credit: IRS FAQ on the One, Big, Beautiful Bill (FS-2025-05, Aug. 21, 2025).
- Assumptions: 85% charging efficiency into a battery, 85% from battery to appliance, panel counts rounded up, off-grid sizing for the worst month.