guide10 min read

Roof Too Shaded for Solar in Illinois? The State's 2× Tree Test and the Dollar Math

Ryan Cook•October 13, 2026

Shade alone usually doesn't rule out solar in Illinois, but it can make a roof a bad deal. The state's Illinois Shines program has a simple yardstick for it. An array counts as minimally shaded when no tree or other obstruction to the south, east or west stands closer than twice the height it rises above the panels. A tree that clears your array by 25 feet needs to be at least 50 feet away. Trees north of the array don't count at all.

If your trees fail that test, the next step isn't the chainsaw. Put a dollar figure on the shade first. Then find out who owns the tree and who's allowed to touch the wire next to it. Here's how I walk homeowners through it, from Chicago bungalows under old elms to Belleville houses tucked behind pin oaks.

The key numbers

What	Figure	Source / date
Illinois Shines "minimally shaded" test	No obstruction closer than 2× the height it rises above the array; north-side obstructions ignored; trees count at mature height, and so does any utility pole within 30 ft	Illinois Shines 2026-27 Program Guidebook (Apr. 17, 2026), Glossary
How Illinois Shines estimates production	PVWatts v8 with standard 14% system losses; vendors may use a lower capacity factor	Same guidebook, Section 4 J
Share of yearly output made May–Sept (south roof, 30° tilt)	About 48% (Springfield) to 51% (Chicago)	PVWatts v8, run Oct. 11, 2026
Supply price used for the math below	ComEd 10.103¢/kWh; Ameren 10.441¢ first 800 kWh, Oct. 1, 2026–May 31, 2027	Plug In Illinois Price to Compare pages
Riskiest months to prune oaks in Illinois	April, May and June (oak wilt)	University of Illinois Extension Plant Clinic
Service wire to your house	You trim it; ComEd drops or de-energizes it at no charge; Ameren says the drop must be disconnected first	ComEd and Ameren tree pages, Oct. 2026

Run the 2× test on your own trees

Stand where you can see the roof and the tree together. Guess how far the top of the tree rises above the highest panel spot closest to it, then double it. If the tree is closer than that number, and it sits anywhere from the east around through south to the west, it'll shade the array at some point in the year.

The program's definition, from its glossary, covers more than trees. Vents, chimneys, neighboring buildings, terrain, and any utility pole within 30 feet all count. It even counts trees that haven't grown yet: a tree planted on your lot or a neighbor's is judged by its mature height.

That last part matters more than people expect. The 15-foot maple your neighbor put in three years ago is the one that'll cost you production in year twelve of a 25-year system.

What shade actually costs, in dollars

Shade cost depends on timing. In the federal PVWatts model, a south-facing Illinois array makes roughly half its yearly power from May through September, when every tree is in full leaf. November through March makes about a third. Bare branches still cast shadows in winter, and the low sun makes them long, but the big money is in summer afternoons.

The table below takes the average-size Illinois system from our how many panels guide, about 6 kW, and prices each level of shade loss at today's supply price. That's what a kilowatt-hour you send to the grid earns under net metering for systems connected since 2025. Power you use at home is worth more, because it also skips per-kWh delivery charges. Treat these as illustrations, not a quote for your roof.

Shade loss	Chicago, 6 kW (8,052 kWh/yr)	Belleville, 6 kW (8,580 kWh/yr)
5%	403 kWh ≈ $41/yr	429 kWh ≈ $45/yr
10%	805 kWh ≈ $81/yr	858 kWh ≈ $90/yr
20%	1,610 kWh ≈ $163/yr	1,716 kWh ≈ $179/yr
30%	2,416 kWh ≈ $244/yr	2,574 kWh ≈ $269/yr

Production from PVWatts v8 (south roof, 30° tilt, run Oct. 11, 2026). Dollars at ComEd's 10.103¢ and Ameren's 10.441¢ Price to Compare (Oct. 2026–May 2027), held flat. Our math.

Here's how I read it. Under 10%, I'd rarely cut a healthy shade tree; trimming one limb or moving a few panels usually wins. At 20% to 30%, you're giving up an estimated $4,000 to $6,700 over 25 years at today's prices, before any rate changes. That's real money, and it's worth a tree quote.

Ask for the shade-adjusted estimate, not the standard one

When an Approved Vendor applies to Illinois Shines, the application portal runs PVWatts Version 8 with a standard 14% loss setting. That model doesn't know about your oak. The guidebook lets vendors enter a lower capacity factor when they decide it's appropriate, or a custom capacity factor from production-modeling software or a professional engineer.

I tell homeowners to ask for two production estimates from anyone quoting a shaded roof. Get one with the trees as they stand and one with the trim or removal you're considering. The gap between them is the number you price. If a quote on a shaded roof shows no shade loss at all, ask why.

Panel-level electronics (microinverters, or a small converter box behind each panel) can soften shade on part of an array, because one shaded panel doesn't drag down its neighbors as much. They don't create sunlight. They're a design answer for a chimney or a single limb, not for a roof under a canopy.

Before anyone cuts: who owns the tree?

Your own tree is your call. Weigh the shade cost against the shade benefit. A big tree on the west side cuts your summer cooling load too, and that's a real offset.

A neighbor's tree is theirs. You can ask, and some neighbors will split a trim. You can't cut it.

A parkway tree in Chicago falls under the city's Bureau of Forestry. The bureau says it issues permits for any work involving trees, and asks for at least 10 working days for removal requests. Its 311 removal service covers dead or damaged parkway trees, and its removal guidelines say that when a replacement tree can't be planted, the applicant pays the tree's appraised value under City Code 10-32-200. Don't count on a healthy one coming down. Suburbs and downstate towns set their own parkway rules, so call your village before you plan around a street tree. And if you live under an HOA, read the landscaping rules too; our HOA solar guide covers what an association can and can't block.

The wire next to the tree is the other trap

The line from the pole to your house is the one you're on the hook for. ComEd says it doesn't do non-emergency trimming on that service wire. If you hire a contractor or trim it yourself, ComEd will drop or de-energize the wire and reconnect it at no charge. Your power is off until then, so book it ahead at 1-800-334-7661.

Ameren Illinois puts the service drop on the property owner as well. It says the drop has to be disconnected so the trees can be trimmed safely, and that only qualified line clearance contractors may work within 10 feet of higher-voltage lines.

For lines between poles on your property, ComEd offers clearance by its own crews with a written estimate, or a no-charge "line maintenance investigation." ComEd's own routine trimming runs on four-year cycles, so don't plan around a utility crew happening to show up.

Time the trimming for this winter

If trimming is the answer, the calendar works in your favor right now. University of Illinois Extension says deciduous trees are best pruned in late winter, around February and March, while they're dormant. It also says oak wilt spreads fastest here in April, May and June, and its plant clinic advises cautious owners to put off oak pruning until dormancy.

Sign this fall, trim in late winter, and the panels go up before the long days. That's the same logic I laid out in our fall and winter timing guide. Your array is producing for the May-through-September stretch that makes about half its year.

When the answer is "not this roof"

Some roofs just don't pencil out, and I'll say so. Three paths still work:

The yard. If there's open ground to the south, a ground mount sidesteps the roof shade entirely.
Community solar. You subscribe to a share of an off-site array and get bill credits. Our community solar guide covers how it works in ComEd and Ameren territory.
Solar for All, if you're income-eligible. One caution: the program's home repairs initiative pays for roof and electrical work, but the state's 2025-26 report says tree trimming and removal fall outside its scope. Our Solar for All repairs post has the details, and /solar-for-all/ has the program basics.

On a lease priced by what the panels produce, at a predictable rate as low as $0.10 per kWh, shade lowers what you pay along with what you make. It doesn't turn a heavily shaded roof into a good one, and an honest company will tell you so.

Want a straight answer on your roof and your trees? Start with our roof check tool, or call me at (618) 217-2001. I'll run the shade math with you and lay out lease, cash and Solar for All side by side. You can also reach us through /contact/.

Sources

Illinois Shines 2026-27 Program Guidebook — Illinois Power Agency, published Apr. 17, 2026 (Section 4 J, REC quantity calculation: PVWatts v8, 14% losses; Section 10 Glossary, "Minimal Shading Criteria")
PVWatts Calculator v8 API — National Laboratory of the Rockies, monthly AC output for Chicago, Springfield, Belleville, Peoria and Rockford, run Oct. 11, 2026
Price to Compare, ComEd and Price to Compare, Ameren Illinois — Plug In Illinois / Illinois Commerce Commission (Oct. 2026 through May 2027 prices)
ComEd Net Metering Frequently Asked Questions — ComEd, 2026 edition (supply-section credits for customers interconnected Jan. 1, 2025 or later)
Ameren Illinois Net Metering — Ameren Illinois, accessed Oct. 13, 2026
Tree Trimming Assistance and Maintenance — ComEd, accessed Oct. 13, 2026 (service wire; line clearance; four-year cycles)
Trees and Your Energy Service — Ameren, accessed Oct. 13, 2026 (service drop is the property owner's responsibility; 10-foot rule; ILVegetationManagement@ameren.com)
Forestry Permit Application, Dead or Damaged Trees and Tree Removal and Replacement Guidelines — City of Chicago Bureau of Forestry (guidelines dated Oct. 20, 2005), accessed Oct. 13, 2026
Proper Pruning of Trees — University of Illinois Extension, Feb. 4, 2021 (late-winter dormant pruning)
Plant Clinic Fact Sheet: Oak Wilt — University of Illinois Extension (ILPC-3608)
Home Repairs and Upgrades Initiative Report, PY 2025-26 — Illinois Power Agency, Aug. 18, 2026 (tree alteration outside the Initiative's scope)

Frequently Asked Questions

There's no single percentage, because it depends on when the shade lands, how much of the array it covers and how the panels are wired. Midday summer shade costs the most, since May through September makes roughly half of a south-facing Illinois array's yearly output in the federal PVWatts model (about 48% to 51% from Springfield to Chicago). Morning or late-afternoon shade costs far less. The Illinois Shines program gives a useful yardstick: it calls an array minimally shaded when no tree or other obstruction to the south, east or west stands closer than twice the height it rises above the panels. To put dollars on it, a 6 kW Chicago system loses about 805 kWh a year at 10% shade. Valued at ComEd's 10.103-cent Price to Compare, that's roughly $81 a year, or about $2,000 over 25 years at today's price. Ask for a shade-adjusted production estimate for your roof.

Sometimes, but price the shade first. Ask for two production estimates, one with the tree as it stands and one with it trimmed or removed. Then value the difference at your supply price. In Chicago, 20% shade on a 6 kW system costs an estimated 1,610 kWh a year, or about $163 at ComEd's 10.103-cent Price to Compare. In Belleville it's about 1,716 kWh, or $179 at Ameren's 10.441 cents. That's roughly $4,000 to $4,500 over 25 years at today's prices, before rate changes. Compare that with a written quote for the tree work and with what the tree does for your summer cooling and your yard. A tree on the north side doesn't shade a south-facing array at all, so it can stay. Check ownership before anyone cuts. In Chicago, parkway trees fall under the city's Bureau of Forestry, and other Illinois towns have their own rules.

Late winter, around February and March, while the trees are dormant. University of Illinois Extension calls that the best time to prune deciduous trees, partly because it helps avoid diseases like oak wilt. Its plant clinic says oak wilt spreads fastest in Illinois during April, May and June, when sap-feeding beetles are drawn to fresh pruning cuts, and recommends avoiding oak pruning in spring and early summer. Dormant-season work also lets you see the branch structure clearly, and it lines up well with an installation calendar. A homeowner who signs this fall can have trimming done in late winter and panels on the roof before the long spring and summer days. Those months, May through September, make roughly half of a south-facing array's yearly output in Illinois. If a limb comes down in a storm, deal with the hazard right away. If the work is near the wire to your house, call ComEd or Ameren first. Neither one does routine trimming on that line for you.

Not on your own. In Chicago, parkway trees fall under the city's Bureau of Forestry. The bureau says it issues permits for any work involving trees and asks for at least 10 working days for removal requests. Its removal service, requested through 311, covers parkway trees that are dead or damaged. Its removal guidelines also say that when a replacement tree can't be planted, the applicant pays the tree's appraised value under City Code 10-32-200. Don't plan on a healthy parkway tree coming down; plan around it. If your house faces north, the parkway tree sits north of a south-facing back roof, and the Illinois Shines shading definition ignores obstructions north of the whole array. Suburbs and downstate towns set their own parkway rules, so call your village or city forester before anyone touches a street tree. Contact the Bureau of Forestry at 312-746-5254.

You do, for the wire that runs to your house. ComEd says it does not do non-emergency tree trimming on the service wire. If you hire a contractor or trim it yourself, ComEd will drop or de-energize the wire and reconnect it afterward at no charge. Your home is without power until it's reconnected, so schedule it. Call 1-800-EDISON-1 (1-800-334-7661). Ameren Illinois says trees along the service drop are the property owner's responsibility. It says the drop has to be disconnected so the trees can be trimmed safely, and that only qualified line clearance contractors may work within 10 feet of higher-voltage lines. For lines between poles, ComEd offers line clearance by its own crews with a written estimate, plus a no-charge line maintenance investigation. Ameren lists ILVegetationManagement@ameren.com for Illinois questions. Never climb or cut near a line yourself.