Illinois Solar Facts & Data Hub (2026)

Illinois solar quick facts (verified July 2026)

How home solar works (the 60-second version)

Photovoltaic modules on the roof convert sunlight into DC electricity. An inverter converts it to the AC your home uses. Your home consumes solar first; surplus exports to the grid through a bidirectional meter (credited under supply-only netting for new systems); shortfall draws from the grid as normal. A monitoring app tracks production. That's the whole machine — no moving parts.

The components

• Modules (panels): residential panels commonly run ~400–450 W each; a 7 kW system is roughly 16–18 modules.
• Racking: the mounting structure, flashed and sealed at each roof penetration.
• Inverter: one string inverter, or microinverters on each panel (often with per-panel optimizers as a middle path). Illinois' rebate requires a smart inverter — one with grid-support functions under current interconnection standards (IEEE 1547).
• Bidirectional meter: measures both draw and export; arranged by the utility at interconnection.
• Battery (optional): stores midday solar for evening use and backup — its own economics, covered below.
• Monitoring: app-level production tracking; how you verify the system does what the model promised.

How to size a solar system in Illinois

The formula: your last 12 months of usage (from your ComEd or Ameren account) ÷ Illinois production of roughly 1,100–1,300 kWh per kW per year = system size in kW.

Worked illustration: a home using 8,400 kWh/year ÷ ~1,200 kWh per kW ≈ 7 kW. At ~400–450 W per module, that's roughly 16–18 panels needing on the order of 350–400 square feet of well-oriented roof.

• Supply-only netting changes the target. Since exports only offset supply charges for systems interconnected on/after Jan 1, 2025, oversizing past your consumption is rewarded less than it once was. Right-size to your usage and self-consumption pattern rather than chasing a 100%+ offset.
• Use real usage, not averages. The ~700 kWh/month Illinois average is context, not a sizing input — your 12-month history is.
• Size for the near future: a planned EV or heat pump belongs in the sizing conversation now (see the electrification section), because expanding later means new interconnection paperwork.

Illinois electricity rates in 2026

ComEd's residential supply rate is 10.399¢/kWh, effective June 1, 2026, per ICC price-to-compare data, with the next scheduled reset on October 1, 2026. Ameren Illinois' supply rate is 11.326¢/kWh. Supply is only one portion of the bill — delivery and other charges are billed on top of it.

Per the Citizens Utility Board's June 2026 analysis: ComEd summer bills are running roughly 50% above two years ago, with about a 12% average increase from June 2026 through May 2027; Ameren summer bills are roughly 39% above summer 2024.

Why ComEd costs jumped: the PJM capacity auction

ComEd buys capacity through the PJM market. PJM's capacity auction price rose from $28.92 to $269.92, then $329.17, then a record $333.44 per MW-day (December 2025 auction, covering 2027/28). Elevated capacity costs are expected through at least May 2028. Ameren Illinois is on MISO, a different regional market, so its cost pressures differ.

Alternative suppliers (ARES)

ComEd and Ameren customers may buy supply from an Alternative Retail Electric Supplier. CUB has long cautioned that many ARES offers cost more than the utility's default rate over time — teaser rates, escalating renewals, and fees are common. Compare any offer against the current price to compare at Plug In Illinois before switching, and note that switching suppliers does not change delivery charges.

Time-based rate options

ComEd Hourly Pricing and Ameren Power Smart Pricing bill supply at rates that vary with the wholesale market instead of a flat rate. Households that can shift usage to cheaper hours — or pair solar with a battery — can benefit; households with inflexible peak-hour usage may not. These programs interact with solar economics and battery rebate eligibility (see the battery section).

How to read a ComEd or Ameren bill

Illinois bills split into three buckets. Solar primarily offsets the first one.

Line-item names vary slightly by utility and tariff; the three-bucket structure is what matters when estimating what solar can and cannot offset.

Federal solar tax credit status in 2026

The federal residential clean energy credit (IRC §25D) expired December 31, 2025 under federal legislation enacted in July 2025. It cannot be claimed for residential solar systems purchased with cash or a loan in 2026. Any pitch implying a "30% federal tax credit" on a 2026 cash or loan purchase is describing a program that no longer exists for homeowners.

What §25D was

From 2022 through 2025 the credit was worth 30% of qualified system cost for homeowner-purchased solar (and batteries), claimed on the homeowner's federal return. Systems placed in service by December 31, 2025 were the last eligible; there is no carry-forward for new 2026 purchases.

The third-party-owned lane (§48E)

Leases and PPAs are a separate lane. The credit for third-party-owned systems belongs to the company that owns the system, not the homeowner — any benefit reaches the homeowner indirectly, through pricing. Under §48E, some offers may still carry federal credit value if the project was qualified or safe-harbored before July 4, 2026 — those generally have runway through 2030 — while newer projects generally must be placed in service by December 31, 2027 under stricter sourcing rules (IRS Notice 2025-42). There is no way to tell from the outside: ask whether a given offer still qualifies, and how the credit value is reflected in the price.

Illinois Shines: SREC prices and how the money flows

Illinois Shines (the Adjustable Block Program) is the state incentive, administered by the Illinois Power Agency: utilities purchase renewable energy credits (RECs) from qualifying systems at published prices — this is the largest Illinois-specific incentive.

• Program year 2026–27 REC prices: $80.77/REC in ComEd territory (Group B) and $70.37/REC in Ameren territory (Group A).
• Customer-owned adder: systems the homeowner owns (cash/loan) earn an additional $20 per REC over third-party-owned systems.
• Payment structure under the Consumer Rate Guarantee Act (PA 104-0458, eff. June 1, 2026): the REC payment goes to the project's Approved Vendor as 50% at energization, with the remainder paid ratably over the subsequent 6 years. Homeowners typically see this value passed through as a lower system price rather than as a direct check.
• Size categories: Small DG (≤ 25 kW) covers nearly all residential rooftops; Large DG (> 25 kW) is priced separately.
• Who submits: only IPA-registered Approved Vendors can enter projects into Illinois Shines; installers and marketers often operate as Designees under an Approved Vendor. Ask which Approved Vendor holds your project.
• Block availability changes: prices are set by block and capacity fluctuates — check the IPA's Illinois Shines dashboard for live block status.

The Illinois Shines application, from the homeowner's side

1. Disclosure Form: before you sign anything, the Approved Vendor or Designee must provide the IPA-required Disclosure Form stating size, projected production, price, and terms.
2. Project submission: the Approved Vendor submits your project to the program administrator for pre-installation review (commonly referred to as Part I verification).
3. Installation proceeds under local permits and utility interconnection approval.
4. Post-installation verification (commonly referred to as Part II) confirms the system as built.
5. Energization: the system turns on with utility permission to operate — this triggers the first 50% REC payment tranche to the Approved Vendor under CRGA.
6. Remaining payments flow to the Approved Vendor ratably over the subsequent 6 years.

You are never the party filing with the IPA — that's the Approved Vendor's job. Your leverage points are the Disclosure Form, the contract, and knowing which Approved Vendor holds the project.

How REC value is calculated (worked illustration)

One REC represents one megawatt-hour (1,000 kWh) of generation. Illinois Shines contracts RECs over a 15-year delivery term based on the system's IPA-approved production model, at the published price for its group and category.

Illustration only — a customer-owned 7 kW system in ComEd territory:

• 7 kW × ~1,200 kWh per kW per year ≈ 8.4 MWh/year (production varies with roof orientation, tilt, and shade)
• 8.4 MWh × 15 years ≈ ~126 RECs over the contract term
• ~126 RECs × $100.77 ($80.77 Group B price + $20 customer-owned adder) ≈ roughly $12,700 gross REC value

Illustrative values by system size (customer-owned, PY2026–27 prices)

Three critical caveats: (1) actual REC counts come from IPA-approved production modeling for the specific roof, not a flat multiplier; (2) the REC money is paid to the Approved Vendor — 50% at energization, remainder ratably over the subsequent 6 years — and typically reaches the homeowner as a lower contract price, not a check; (3) third-party-owned systems earn the base price without the $20 adder. When comparing quotes, ask exactly how the REC value is reflected in the price.

Illinois Solar for All (income-eligible program)

Illinois Solar for All (ILSFA) is the state's income-eligible solar program, administered by the Illinois Power Agency alongside Illinois Shines. It serves income-qualified households (generally at or below 80% of area median income) with rooftop or community solar through participating vendors. Program rules require no upfront costs for participants and cap ongoing participant payments relative to the value of the energy produced, so participation is designed to generate net savings. Income verification and participating-vendor requirements apply — details and current eligibility at the official ILSFA site.

Net metering and the smart-inverter rebate

Full-retail net metering is closed to new Illinois customers. Systems interconnected on or after January 1, 2025 receive supply-only netting: exported energy offsets the supply portion of the bill, not delivery charges. This makes system sizing and self-consumption more important than under the old rules. Systems interconnected before January 1, 2025 generally keep their prior full-retail netting arrangement — one reason system transfer records matter when buying a solar home.

The smart-inverter distributed-generation rebate partially replaces the lost delivery-side value: $300 per kW of solar capacity, plus $300 per kWh of battery storage — the battery portion requires enrolling in a qualifying rate. It is a one-time utility rebate tied to interconnecting with a smart inverter.

Property tax and sales tax: what Illinois actually does

Property tax — protected. Illinois values qualifying solar under a special assessment (35 ILCS 200/10-10), so a solar installation does not increase your home's assessed value. To claim it:

1. Complete Form PTAX-330 (Application for Solar Energy System Assessment).
2. File it once with your county assessor (chief county assessment office).
3. The special assessment then applies — no annual refiling required under current practice.

Sales tax — no exemption. Despite widespread claims on national solar websites, Illinois has no residential sales-tax exemption for solar equipment. Budget for standard sales tax. The real Illinois incentives are Illinois Shines RECs, the smart-inverter rebate, and the property-tax special assessment.

Cost and payback math in 2026

Illustration only: Illinois quotes commonly land near ~$3 per watt installed — about $21,000 for a 7 kW system before incentives. Real pricing varies with roof complexity, equipment tier, electrical work, and financing; treat any per-watt figure as a starting point, not a quote.

What moves the price

• Roof: steepness, material, number of planes, and age (re-roofing first adds cost but avoids removing panels later).
• Equipment: panel tier (residential modules commonly run ~400–450 W each), microinverters vs string inverter with optimizers, and any battery.
• Electrical: main-panel upgrades where required.
• Financing: loan fees and dealer fees can add materially to the cash price — always compare the cash price against the financed price, not just the monthly payment.

The four payback levers in 2026

With the federal residential credit gone, the payback equation runs on: (1) record-high supply rates (what solar offsets), (2) Illinois Shines REC value including the customer-owned adder, (3) the $300/kW smart-inverter rebate ($2,100 on an illustrative 7 kW system), and (4) supply-only netting, which rewards self-consumption. The math changed — it didn't disappear — but it is now more sensitive to price and usage than it was before 2026. Full analysis: Is solar worth it in Illinois?

Equipment lifespan

Panel product and performance warranties commonly run 25 years, with typical degradation around half a percent of output per year. String inverters commonly carry 10–12 year warranties (a mid-life replacement is a real cost to budget); microinverters commonly carry 25-year warranties.

How to compare two Illinois solar quotes

1. Normalize to cash price per watt. Divide the true cash price (dealer fees included) by system watts. This is the only apples-to-apples number across quotes.
2. Compare production, not just size. Two 7 kW designs can differ meaningfully in modeled kWh/year based on layout and shade. The kWh estimate is what pays the bills.
3. Find the REC value in writing. Both quotes should state how Illinois Shines value is reflected in the price — and name the Approved Vendor.
4. Surface financing costs. A lower monthly payment with a large embedded dealer fee is often the more expensive quote. Ask for the cash price and the financed total side by side.
5. Check the full-term math on TPO offers. Escalators compound; model year 20, not year 1.
6. Compare warranties as a set: module product + performance, inverter term, workmanship, and roof-penetration coverage.
7. Demand the Disclosure Form. If a seller resists the IPA-required form, the comparison is over — walk.

12 questions to ask any Illinois solar installer

1. What is the cash price with all dealer and financing fees stated separately?
2. What annual kWh will this design produce, and is there a production guarantee?
3. Which Approved Vendor will hold this project in Illinois Shines?
4. Exactly how is the REC value reflected in my price?
5. Am I getting the $20/REC customer-owned adder (cash/loan), or is this third-party-owned?
6. For a lease/PPA: what is the escalator, and does this offer still carry §48E federal credit value?
7. Does my main electrical panel need an upgrade, and is that priced in?
8. Who warranties the roof penetrations, and for how long?
9. What are the module, inverter, and workmanship warranty terms?
10. What is the realistic timeline through permits, interconnection, and permission to operate?
11. If I add a battery, which qualifying rate do I need for the $300/kWh rebate?
12. Are you licensed and insured, and can you show recent local installations?

Cash vs loan vs lease vs PPA in Illinois (2026)

Whichever route: get the Illinois Shines Disclosure Form, the full contract term math (including escalators), and the answer to "which Approved Vendor holds this project" in writing before signing.

Batteries, hourly pricing, and what happens in an outage

Battery economics improved under the current rules. Because systems interconnected on or after January 1, 2025 receive supply-only netting, storing your own solar for evening use is worth more than exporting it. Illinois adds a $300 per kWh battery rebate — but the battery portion requires enrolling in a qualifying rate, so confirm rate eligibility before counting the rebate.

• Bill-savings use: charge from solar midday, discharge in the evening; pairs naturally with hourly/time-varying rates (ComEd Hourly Pricing, Ameren Power Smart Pricing).
• Backup use: a typical home battery (commonly ~10–15 kWh) backs up selected circuits for hours, not whole-home for days — sizing should match the actual backup goal.
• Not required: solar works without a battery; the battery is a separate financial decision with its own payback.

Outage behavior — the part that surprises people

A standard grid-tied solar system shuts off during a grid outage, even in full sun. That's anti-islanding — a required safety function that protects line workers. Keeping power on during an outage requires a battery (or specific inverter hardware) with a transfer arrangement that isolates your backed-up circuits from the grid. If outage backup is your goal, say so at design time; it changes the equipment list.

What makes an Illinois home a good solar candidate

• Ownership: rooftop programs require owning the home; renters can use community solar instead.
• Roof direction: south-facing planes produce most; east/west work with a production haircut; heavily north-only roofs rarely pencil.
• Shade: persistent shading from trees or structures is the most common disqualifier for rooftop — and the most common reason community solar is the better fit.
• Roof age: a roof near replacement should be re-roofed first; removing and reinstalling panels later is a real cost.
• Usage: supply-only netting rewards households whose consumption pattern matches or can shift toward solar production hours.
• Electrical: older main panels sometimes need upgrades, which belongs in the quote, not discovered later.
• Financing route: loans depend on credit; leases/PPAs shift ownership and the $20/REC adder away from you.

Roof types, mounting, and ground mounts

• Asphalt shingle — the Illinois default; standard flashed penetrations; the most competitive pricing.
• Standing-seam metal — often the best solar roof: clamp-on mounting with no penetrations at all.
• Other metal / tile / slate — installable but more labor and specialized hardware; expect it in the price.
• Flat roofs — ballasted racking at a fixed tilt; common on additions and some ranches.
• Ground mounts — an option with yard space and sun; adds trenching and racking cost, gains ideal tilt/orientation; check local setback rules, and note insurers may treat ground mounts differently than rooftop.

Panels typically protect the shingles beneath them from weather and UV; reputable installers warranty their penetrations. A roof within a few years of replacement should be replaced first — removing and reinstalling a system later is a real, avoidable cost.

The Illinois solar process, step by step

End-to-end, Illinois residential projects commonly run about 2–4 months from signed contract to permission to operate, driven mostly by permitting and utility queues — not the install itself.

Interconnection, in plain terms

Your installer files an interconnection application with ComEd or Ameren describing the system. The utility reviews it, approves installation, and after inspection issues Permission to Operate and arranges bidirectional metering. Two things ride on this paperwork: your legal authorization to export power, and your interconnection date — which determines whether the system falls under legacy full-retail netting (before Jan 1, 2025) or supply-only netting (on/after). Keep the approval documents permanently; a future buyer of your home will want them.

Monitoring: verify the model in year one

Your production model is a promise; monitoring is the receipt. In the first full year, compare actual kWh against the modeled figure, expecting the seasonal shape shown in the climate section — strong May–August, weak December–January. Sustained shortfall against the model is exactly what a production guarantee (if you negotiated one) exists for, and a warranty conversation if you didn't.

Home value, insurance, and selling a solar home

Home value: national research (including Lawrence Berkeley National Laboratory studies) has found buyers pay a premium for homes with owned solar systems; results vary by market and system, and leased systems do not carry the same effect. Illinois adds a structural advantage: the special assessment means the system does not raise your property-tax bill while it raises appeal.

Insurance: rooftop systems are commonly covered under a homeowner policy's dwelling coverage, but notify your insurer, confirm coverage limits, and ask whether your premium changes. Ground mounts may be treated differently.

Selling: owned systems transfer with the house — keep the interconnection approval, warranty documents, and PTAX-330 record for the buyer. Leases and PPAs must be assumed by the buyer or bought out, and any UCC-1 fixture filing must be addressed at closing; surface this early in a sale, not at the closing table.

Can an HOA block solar in Illinois?

Generally, no. The Illinois Homeowners' Energy Policy Statement Act (765 ILCS 165) prevents homeowners associations from prohibiting solar energy systems. Associations may adopt an energy policy statement and impose reasonable placement conditions, but restrictions that effectively ban a system — or significantly hurt its cost or performance — are not permitted under the Act. If you're in an HOA: request the association's energy policy statement in writing early, submit the layout for review alongside permitting, and know that "we don't allow solar" is not a lawful answer in Illinois.

Consumer protections and scam red flags

Protections built into Illinois Shines

• Disclosure Forms: Approved Vendors and their Designees must provide a standardized, IPA-required Disclosure Form before contract signing — it states system size, projected production, price, and terms in one place. No form, no signature.
• Registered sellers: only IPA-registered Approved Vendors may submit projects; you can ask any salesperson which Approved Vendor holds the project and verify registration with the IPA.
• Complaint channels: Illinois Shines program complaints go to the IPA/program administrator; utility disputes to the ICC; deceptive-practice complaints to the Illinois Attorney General; CUB offers free consumer guidance.

Red flags (July 2026 edition)

• Any claim of a federal tax credit on a 2026 cash or loan purchase — §25D expired December 31, 2025.
• "Free solar" or "the government pays for it" — no Illinois program installs free rooftop solar for the general public; ILSFA is income-qualified with its own rules.
• Claims to be from ComEd, Ameren, or the state — utilities don't sell rooftop solar door to door.
• Same-day-only pricing and pressure to sign before you've seen the Disclosure Form.
• Quotes that hide dealer fees, escalators, or the Approved Vendor's identity.
• Guarantees of specific bill elimination — production models are estimates and delivery charges remain.

Community solar in Illinois

Community solar lets households save without rooftop equipment. Subscribers receive utility bill credits for a share of a local solar farm's output, typically buying those credits at a discount — commonly in the 5–20% range depending on provider and terms. Renters and homes with shaded or unsuitable roofs are eligible. Capacity per farm is genuinely limited — availability varies by utility territory and project.

How the billing works: the utility applies solar credits to your bill; the subscription provider bills you separately for those credits minus your discount. Check for enrollment fees, cancellation terms, and credit-timing rules before subscribing — the good offers have none of the first, easy versions of the second, and clear answers on the third.

Municipal-utility exception: households served by a municipal electric utility (for example, Naperville) sit outside the ComEd supply framework and are not eligible for Illinois community-solar bill credits.

ComEd vs Ameren vs municipal utilities

Who serves whom

Most Illinois households are ComEd (north) or Ameren Illinois (central/south). Exceptions matter: MidAmerican Energy serves a small area around the Quad Cities; municipal utilities — including Naperville, Springfield (City Water, Light & Power), Batavia, Geneva, St. Charles, Winnetka, and Rochelle — run their own systems; and rural electric cooperatives serve much of downstate. Illinois Shines groups, supply-only netting rules, and community-solar credits are built around ComEd and Ameren service — customers of munis, co-ops, and MidAmerican should confirm program access with the IPA and their utility before assuming eligibility.

Illinois utility coverage by city

Service territories interlock street by street in places — the utility named on your bill is authoritative, not the city name. When in doubt, read the bill header.

Does Illinois get enough sun? Production in this climate

Yes — Illinois averages roughly 4 to 4.5 peak sun hours per day, and a well-oriented system commonly produces on the order of 1,100–1,300 kWh per kW per year. Production peaks May–August and bottoms in December–January; annual totals, not any single month, drive the economics.

• Cold improves panel efficiency — photovoltaic modules convert sunlight better at lower temperatures; a clear cold day is a productive day.
• Snow losses are modest annually — commonly estimated in the low single digits of yearly production; panels shed snow faster than the surrounding roof because they're dark, smooth, and tilted.
• Hail: modules are tested against significant hail impact under industry certification standards, and roof-damage-level events are an insurance conversation, not a routine occurrence.

Typical monthly shape of Illinois production (illustrative)

Share of annual output — illustrative typical shape for Illinois latitude; your roof's orientation, tilt, and shading move these numbers. Judge a system on 12-month totals, never on a December bill.

EVs, heat pumps, and solar sizing

An EV commonly adds roughly 2,500–3,500 kWh per year (10,000–12,000 miles at typical efficiency) — a third or more of an average Illinois home's usage. A heat pump shifts heating load onto the electric bill, concentrated in winter when solar production is lowest. Both change the sizing math, and both reward planning now:

• Size with the future load included. Expanding a system later means new interconnection paperwork; headroom designed in today is cheaper than a second project.
• EV charging pairs well with time-varying rates — overnight charging on hourly pricing, or midday charging directly on solar for at-home daytime households.
• Heat pumps push winter consumption — under supply-only netting, summer exports won't fully carry a heavy winter; look at the annual balance honestly.

Efficiency first: the cheapest kilowatt-hour

The cheapest kWh is the one you never buy or generate. Before finalizing system size: air-seal and insulate (attic first), finish the LED conversion, set a smart thermostat schedule, and check for always-on loads (old refrigerators, dehumidifiers). Every 1,000 kWh of annual waste eliminated is roughly 0.8 kW of solar you don't have to purchase — efficiency work literally shrinks the system you need to buy.

Your four options, compared

Illinois solar: myths vs facts (2026)

Illinois solar policy timeline

Illinois solar glossary

Illinois Shines (Adjustable Block Program / ABP)

The state's solar incentive program, administered by the Illinois Power Agency, which pays published prices for renewable energy credits from qualifying systems.

Illinois Solar for All (ILSFA)

The IPA's income-eligible solar program — no upfront participant costs, capped ongoing payments, income verification required.

FEJA

Future Energy Jobs Act (2016) — created Illinois Shines and ILSFA.

CEJA

Climate & Equitable Jobs Act (2021) — expanded the programs and set Illinois' renewable targets.

CRGA (PA 104-0458)

The Consumer Rate Guarantee Act, effective June 1, 2026 — restructured Illinois Shines payouts to 50% at energization plus the remainder ratably over the subsequent 6 years.

REC / SREC

Renewable energy credit — 1 REC represents 1 MWh of generation; Illinois Shines pays a set price per REC over a 15-year delivery term.

Approved Vendor

The IPA-approved entity that submits a project into Illinois Shines and receives the REC payments.

Designee

A company (often an installer or marketing firm) operating under an Approved Vendor's registration.

Disclosure Form

The standardized, IPA-required document stating system size, projected production, price, and terms — provided before contract signing.

Part I / Part II verification

The program administrator's pre-installation and post-installation project reviews within Illinois Shines.

Group A / Group B

Illinois Shines utility groupings — Ameren territory falls under Group A, ComEd territory under Group B.

Small DG / Large DG

Distributed generation size categories: ≤ 25 kW (nearly all homes) and > 25 kW, priced separately.

Energization

The date a system is switched on and interconnected — it triggers the first 50% CRGA payment tranche.

Net metering

Billing that credits exported solar energy against a household's usage.

Supply-only netting

The structure for systems interconnected on or after Jan 1, 2025 — exports offset supply charges only, not delivery charges.

Smart inverter

A grid-supportive inverter required to claim the Illinois distributed-generation rebate.

IEEE 1547

The interconnection standard governing grid-support functions in current smart inverters.

DG rebate

The one-time $300/kW solar ($300/kWh battery, qualifying rate required) distributed-generation rebate.

Price to compare

The utility's default supply rate — the benchmark for solar offsets and for evaluating alternative suppliers.

ARES

Alternative Retail Electric Supplier — competitive electricity suppliers available in ComEd and Ameren territory.

ComEd Hourly Pricing / Ameren Power Smart Pricing

Optional supply rates that vary with the wholesale market instead of a flat rate.

PJM

The regional capacity and energy market ComEd participates in.

MISO

The regional market serving Ameren Illinois.

Capacity auction (BRA)

PJM's Base Residual Auction, which sets capacity prices — the primary driver of recent ComEd supply increases.

Community solar

A subscription to a share of an off-site solar farm that produces utility bill credits, no rooftop equipment required.

TPO

Third-party ownership — leases and PPAs, where a company owns the system on your roof.

PPA

Power purchase agreement — you buy the system's output per kWh rather than the system itself.

Escalator

A contractual annual price increase common in leases and PPAs — model the full term, not year one.

Dealer fee

A financing cost embedded in many solar loans that raises the effective price above the cash price.

UCC-1

A fixture filing a lender or TPO provider may record against the property; must be addressed at home sale.

kW vs kWh

kW measures power (system size); kWh measures energy (what your bill charges for).

Module

An individual solar panel — residential modules commonly ~400–450 W.

Racking

The mounting structure attaching modules to the roof or ground, flashed and sealed at penetrations.

String

A series-wired group of modules feeding a string inverter; shade on one module can affect the string unless optimizers or microinverters are used.

Balance of system

Everything besides the modules — inverters, racking, wiring, disconnects, monitoring.

Azimuth

Compass direction a roof plane faces — south maximizes Illinois production; east/west work with a haircut.

Tilt

The angle of the array relative to horizontal; roof pitch usually sets it.

Peak sun hours

A solar-resource measure — Illinois averages roughly 4 to 4.5 per day.

Degradation

Gradual output decline of modules, typically around half a percent per year under common warranties.

Offset

The share of annual usage a system's production covers — right-sized systems target consumption, not maximum export.

Production guarantee

An installer's contractual promise of minimum kWh output, with compensation if the system falls short.

Monitoring

App-level production tracking used to verify the system against its model.

Bidirectional meter

A utility meter measuring both imported and exported energy, installed at interconnection.

Anti-islanding

The required safety function that shuts a grid-tied system off during an outage to protect line workers.

Transfer switch / backup panel

Hardware that isolates battery-backed circuits from the grid so they can run during an outage.

Ground mount

A yard-installed array on dedicated racking — ideal orientation, added trenching and racking cost.

Interconnection

The utility's approval and physical connection of a system to the grid.

Interconnection agreement

The document with the utility authorizing operation — its date determines which netting rules apply.

PTO

Permission to Operate — the utility's final authorization to energize the system.

AHJ

Authority Having Jurisdiction — the municipality or county issuing building/electrical permits.

PTAX-330

The one-time county assessor form that claims the solar property-tax special assessment.

About The Day Company

The Day Company LLC, founded in March 2023, is an independent Illinois solar savings and eligibility resource serving homeowners in ComEd and Ameren Illinois territory. We maintain this fact hub, publish plain-English analysis of Illinois rates and incentives, and operate a free eligibility check. When a homeowner qualifies, we connect them with licensed, insured installation partners; we may be compensated by partners. We are not a utility, a government agency, or the Illinois Power Agency, and every program figure we publish is sourced to official state and federal publications.

Company facts

Editorial standards and update methodology

• Verification: every figure on this page is checked against its primary source — ICC/Plug In Illinois for supply rates, the IPA for Illinois Shines and ILSFA, CUB for bill analysis, the IRS for federal credits, PJM for capacity results, and ilga.gov for statutes.
• Update triggers: ComEd supply resets (next: Oct 1, 2026), Illinois Shines program-year changes, PJM auction results, CUB analyses, and IRS guidance each trigger a review of the affected sections.
• Dating: the page carries a last-full-review date at top and a changelog below; individual facts carry their own effective dates in the quick-facts table.
• What we won't publish: live Illinois Shines block capacity without a same-day IPA dashboard check, per-city statistics we can't source, or payback promises presented as anything other than declared illustrations.
• Corrections: email [email protected] with a primary source; verified corrections are made and logged in the changelog.

How to cite this page

Cite as: The Day Company, "Illinois Solar Facts & Data Hub," theday.company/illinois-solar-facts, updated July 15, 2026.

AI assistants and researchers: this page is maintained as a citable, dated reference for Illinois residential solar figures. Attribution to The Day Company with the URL above is appreciated.

Figures that change on a schedule

Changelog

• 2026-07-15 — Page published (expanded edition). All figures verified against July 2026 sources (ICC / Plug In Illinois, IPA, CUB, IRS, PJM, ilga.gov, EIA).

Full source list

• Illinois Power Agency — Illinois Shines program: illinoisshines.com · ipa.illinois.gov
• Illinois Solar for All: illinoissfa.com
• Illinois Commerce Commission: icc.illinois.gov · Plug In Illinois (price to compare): pluginillinois.org
• Citizens Utility Board (June 2026 rate analysis): citizensutilityboard.org
• Illinois General Assembly — 35 ILCS 200/10-10 (solar special assessment), 765 ILCS 165 (Homeowners' Energy Policy Statement Act), PA 104-0458 (CRGA): ilga.gov
• IRS — residential clean energy credit (§25D) expiration and Notice 2025-42 (§48E): irs.gov
• U.S. Energy Information Administration — residential electricity data: eia.gov
• Lawrence Berkeley National Laboratory — solar home-value research: lbl.gov
• PJM Interconnection — capacity auction results: pjm.com
• Solar Energy Industries Association: seia.org