I Got a Solar Quote. Now What? 10 Numbers Illinois Homeowners Should Check Before Signing

Updated: September 11, 2026 · Estimated read time: 11 minutes

You got the solar quote.

It has a picture of your house covered in panels, a monthly payment, a savings chart stretching 20 or 25 years into the future, and enough numbers to make the average homeowner wonder:

Which of these numbers actually matter?

The answer is: not all of them matter equally.

A solar proposal can look attractive because of one low monthly payment or one big projected savings number while leaving much more important questions unanswered.

Before you sign, there are 10 numbers every Illinois homeowner should understand.

If the company can't clearly explain them, the proposal probably isn't ready for your signature.

Quick Answer

Before signing an Illinois solar proposal, check these 10 things:

1. Your actual annual electricity usage — kWh

2. Solar system size — kW

3. Projected annual solar production — kWh

4. Solar offset — %

5. Price per watt — $/W

6. Total installed project price — $

7. Financing or PPA terms — APR, term, starting rate, escalator

8. Incentives — $ and who receives them

9. Battery capacity and power — if included

10. Total long-term cost and the assumptions behind projected savings

Then ask one more question:

Are these calculations using the correct rules for my actual utility?

Ameren Illinois, ComEd, and CWLP do not treat residential solar identically.

A proposal isn't complete until the numbers match the homeowner and the utility.

Table of Contents

1. Start with your electric bill

2. Number 1: Annual electricity usage

3. Number 2: Solar system size

4. Number 3: Annual solar production

5. Number 4: Solar offset

6. Number 5: Price per watt

7. Number 6: Total project price

8. Number 7: Financing or PPA terms

9. Number 8: Incentives

10. Number 9: Battery size and power

11. Number 10: Total long-term cost

12. The number people forget: utility assumptions

13. How to compare two solar proposals

14. What the Illinois Shines Disclosure Form adds

15. Questions to ask before signing

16. Frequently asked questions

First: Start With Your Electric Bill, Not the Solar Quote

Before looking at the proposed system, look at the problem the system is supposed to solve.

Your electricity consumption.

A solar company can produce an impressive proposal using sophisticated software, satellite imagery, charts, and financial projections.

But if the underlying electricity-usage number is wrong, many of the numbers after it can also become misleading.

Whenever possible, start with approximately 12 months of actual electricity usage.

Why?

Because Illinois homes don't use the same amount of electricity every month.

July air conditioning can look very different from October.

A single electric bill might represent:

700 kWh

while another month is:

1,600 kWh.

Designing an entire solar system from one month can distort the picture.

If you're still at the beginning of the process, read LuNova's 7 things Illinois homeowners should check before going solar.

Number 1: Your Annual Electricity Usage

Look for:

Annual Usage: ____ kWh

Kilowatt-hours, or kWh, measure electricity consumption.

Imagine your last 12 months total:

12,000 kWh

That becomes one of the most important numbers in the entire proposal.

Now ask:

Where did the company get that number?

Your actual utility history?

A utility bill?

An estimate?

One month's usage multiplied by 12?

Did they include future electricity needs?

Maybe you're planning to:

• Buy an EV

• Add a second EV

• Install a heat pump

• Electrify your water heater

• Install a pool

• Add a hot tub

• Finish a basement

• Add another occupant

Illinois solar rules recognize reasonable future electrical requirements, so legitimate expected increases can be considered when designing the system.

But “future usage” shouldn't become an excuse to sell unnecessary equipment.

The estimate should have a reason behind it.

Number 2: Your Solar System Size

Look for something like:

System Size: 9.84 kW DC

This describes how large the solar array is.

For example, approximately:

24 × 410-watt panels

would equal:

9.84 kW DC

before considering other system-design factors.

But system size alone doesn't tell you how much electricity those panels will actually produce.

Two 9.84 kW arrays can produce differently because of:

• Roof direction

• Roof pitch

• Shade

• Tree coverage

• Geographic location

• Equipment

• System losses

So don't stop at:

“I'm getting 24 panels.”

Ask what those panels are expected to produce.

Number 3: Projected Annual Solar Production

Look for:

First-Year Production: ____ kWh

This may be more important than the panel count.

Suppose:

System A: 9.5 kW

Projected production:

12,000 kWh/year

Another home might have the same 9.5 kW system but produce:

10,700 kWh/year

because of different roof conditions or shading.

That's why:

kW = system size

while:

kWh = energy produced over time

Those are different measurements.

Ask what production model was used and whether the estimate accounts for:

• Shading

• Orientation

• Roof pitch

• Weather assumptions

• Inverter losses

• System losses

• Equipment performance

A large system with poor production isn't automatically a good system.

Number 4: Solar Offset

Now compare annual production with annual usage.

The basic calculation is:

Projected solar production ÷ annual electricity consumption × 100

Suppose your home uses:

12,000 kWh

and the proposed system generates:

12,000 kWh.

Estimated annual offset:

100%

If production is:

13,200 kWh

the projected offset becomes:

110%

But here's the important part:

110% is not automatically better than 100%.

And 90% isn't automatically bad.

The right offset depends on:

• Future electricity use

• Roof conditions

• System price

• Utility

• Export-credit value

• Net-metering rules

• Battery plans

Our complete 100% vs. 110% Solar Offset guide explains why the percentage should be the result of good system design, not a sales target.

CHECK MY HOME

Already have a proposal and want to understand whether the system size actually makes sense?

CHECK MY HOME

Start with your address, electricity usage, utility, and roof—not simply the panel count shown on somebody else's proposal.

Solar production, incentives, savings, and system-sizing estimates vary by household, property, utility, equipment, weather, financing, and other factors.

Number 5: Price Per Watt

Now we get into the money.

Look for or calculate:

Price Per Watt: $____ / W

The basic calculation is:

Solar-system price ÷ system watts

Imagine an illustrative system:

10 kW = 10,000 watts

and the solar-only project price is:

$30,000

Then:

$30,000 ÷ 10,000 watts = $3.00/W

This makes it easier to compare systems of different sizes.

For example:

Quote A

8 kW system
$24,000

= $3.00/W

Quote B

10 kW system
$35,000

= $3.50/W

The larger system costs more overall, which isn't surprising.

But price per watt shows that it also costs more relative to its size.

Still, don't turn $/W into the only metric.

A proposal can include:

• Battery storage

• Electrical upgrades

• Roof work

• Trenching

• Premium equipment

• Other project adders

Those can distort a simple solar-only price-per-watt comparison.

Compare like with like.

Number 6: Total Installed Project Price

This seems obvious.

Yet homeowners can sometimes go through an entire solar presentation without focusing on:

What is the actual total price?

A salesperson may emphasize:

$189/month

instead of:

$42,750 total financed price.

Those aren't interchangeable pieces of information.

Ask for:

Solar-only price

Battery price, if applicable

Project adders

Financing-related costs

Total installed price

Price before incentives

Price after incentives

And ask whether the number you're seeing is:

Cash price

or:

Financed price.

A lower interest rate doesn't automatically mean cheaper financing if the financed project price itself is materially higher.

The total price deserves its own line in your comparison sheet.

Number 7: Financing Terms—or PPA Terms

This number depends on how you're paying for solar.

If It's a Solar Loan

Check:

APR

Loan term

Monthly payment

Total financed amount

Prepayment terms

and:

Total payments if held to maturity

A 25-year loan with a low-looking monthly payment can cost very differently from a shorter loan.

The monthly payment tells you what happens:

this month.

The full financing terms tell you what happens:

over the agreement.

For more, see LuNova's Illinois solar financing guide.

If It's a Solar PPA

Check:

Starting PPA rate

For example:

$0.165/kWh

Annual escalator

For example:

2.99%

Contract length

For example:

25 years

That escalator matters.

A rate that starts at:

16.5¢/kWh

with a 2.99% annual increase doesn't remain at 16.5¢.

The homeowner should understand how the rate changes over the agreement.

Also ask:

• Who owns the equipment?

• Who handles maintenance?

• What happens if you sell?

• What are the buyout terms?

• Can the agreement transfer?

Read LuNova's Illinois homeowner's guide to Solar PPAs before judging a PPA solely by its first monthly estimate.

Number 8: Incentives

A proposal might have a section labeled:

INCENTIVES: $____

Don't stop there.

Ask:

What specific incentive is this?

Illinois Shines REC value?

Utility solar rebate?

Battery-storage rebate?

Something else?

Then:

Who receives it?

The homeowner?

Approved Vendor?

Third-party system owner?

Financing provider?

When is it received?

Immediately?

After energization?

Over time?

Is the value guaranteed?

Or estimated?

Is it already included in the advertised project price?

You don't want an incentive counted twice in a savings presentation.

Illinois continues to have meaningful state and utility-level solar programs, but the incentive structure changed significantly in 2026.

Read LuNova's Illinois Solar Incentives 2026 guide for the current overview.

Number 9: Battery Capacity and Power

If your quote includes a battery, don't accept:

“One battery.”

as the specification.

Ask for:

Battery energy capacity — kWh

and:

Battery power output — kW

Capacity tells you approximately how much energy can be stored.

Power output helps determine how much electrical demand can be supported at one time.

Those are not the same thing.

A battery may have plenty of stored energy but still be unable to operate every large appliance simultaneously.

Ask:

• What exactly is backed up?

• Can it operate central air conditioning?

• Can solar recharge it during an outage?

• What's the usable capacity?

• What's the warranty?

• What storage rebate is being assumed?

• What utility-program obligations come with that rebate?

Our Illinois Solar Battery guide explains why a battery should solve an actual homeowner need—not simply make the proposal look more impressive.

Number 10: The Total Long-Term Cost

This might be the most overlooked number in the entire proposal.

Ask:

“What am I expected to pay over the full agreement?”

Not:

What do I pay next month?

Over:

20 years?

25 years?

What happens?

For a loan, consider the full financing schedule.

For a PPA, consider the cumulative effect of the rate and escalator.

Then compare that against the utility-cost projection.

And this is where another important number appears:

Assumed future utility-rate increase.

If the proposal predicts:

$80,000 in future savings

ask what electricity escalation assumption produced that number.

Was the model assuming utility prices increase:

2% annually?

4%?

6%?

Something else?

Nobody can guarantee exactly what electricity will cost 18 or 24 years from now.

Long-term modeling can still be useful.

But assumptions need to be visible.

A projection should never be presented as a guarantee.

The Number Behind All the Numbers: Your Utility

Here's something that deserves attention even though it isn't technically one of the 10 proposal numbers.

Which utility assumptions are being used?

This can change the entire model.

New Ameren Illinois and ComEd residential solar customers generally operate under newer supply-only net-metering rules.

CWLP in Springfield currently operates under its own municipal net-metering structure.

That can affect:

• Export value

• Delivery charges

• Credit rollover

• Credit expiration

• Solar rebates

• Battery economics

• Ideal system size

If someone designs a Springfield CWLP proposal using Ameren assumptions, the math can be wrong even if every spreadsheet formula is working perfectly.

Read our Ameren vs. ComEd vs. CWLP Solar guide and Illinois Net Metering guide before accepting generic statewide assumptions.

Let's Compare Two Hypothetical Solar Quotes

Suppose your home uses:

12,000 kWh per year

Now you receive two proposals.

Quote A

System size: 8.5 kW

Projected production: 10,800 kWh

Offset: 90%

Project price: $25,500

Price per watt: $3.00/W

Quote B

System size: 10.0 kW

Projected production: 13,200 kWh

Offset: 110%

Project price: $34,000

Price per watt: $3.40/W

Which one is better?

You still don't know.

Now ask:

Why does Quote B cost $8,500 more?

Where are the additional panels?

How much of the extra 2,400 kWh is likely to be exported?

What does your utility credit for those exports?

Are you buying an EV next year?

Is Quote A intentionally undersized?

Is Quote B unnecessarily oversized?

Is the equipment different?

Are financing costs included differently?

Do both production models use the same assumptions?

Now you're actually comparing solar.

Not just monthly payments.

What Should the Illinois Shines Disclosure Form Tell You?

For participating Illinois Shines distributed-generation projects, homeowners receive a standardized Disclosure Form.

Illinois Shines requires the customer to sign the completed Disclosure Form before signing the distributed-generation contract.

There are different versions for:

• Purchase

• Lease

• PPA

The Disclosure Form contains standardized project information intended to help consumers understand and compare important parts of the solar offer.

That doesn't mean you should ignore the installation agreement.

The Disclosure Form and contract serve different purposes.

But they should not tell contradictory stories about the project.

Compare the information carefully.

If:

The proposal

says one thing,

the Disclosure Form

says another,

and:

the contract

says something else,

stop.

Ask questions before signing.

Our Solar Sales Red Flags in Illinois guide explains other situations that should make homeowners slow down.

Before Signing: Put These 10 Numbers on One Page

You shouldn't need to flip through a 40-page presentation to remember the essential economics.

Create a simple comparison sheet:

1. Annual usage

____ kWh

2. System size

____ kW

3. Annual production

____ kWh

4. Solar offset

____ %

5. Price per watt

$____ /W

6. Total system price

$____

7. Financing/PPA terms

8. Incentives

$____

9. Battery

____ kWh / ____ kW

10. Total long-term cost

$____

Then add:

Utility

Net-metering treatment

Now put Quote A beside Quote B.

Suddenly the decision becomes far easier to understand.

12 Questions to Ask Before You Sign

1. Is my annual electricity usage based on actual bills?

2. Why was this system size selected?

3. What annual production are you projecting?

4. What creates the stated solar offset?

5. What's the solar-only price per watt?

6. What's the full cash-equivalent project price?

7. What financing costs or PPA escalators apply?

8. Which incentives are included and who receives them?

9. What utility and net-metering assumptions are being used?

10. Why is a battery included—or excluded?

11. What am I projected to pay over the entire agreement?

12. What happens if I sell my home?

That last question is worth asking now—not ten years from now.

See LuNova's Selling a House With Solar in Illinois guide for the ownership and transfer implications.

Frequently Asked Questions

What is the most important number on a solar proposal?

There isn't one single number. Annual electricity usage, system production, offset, total project price, financing terms, utility rules, and long-term cost work together. Focusing on only the monthly payment can hide important differences between proposals.

What does kW mean on a solar quote?

Kilowatts, or kW, generally describe the solar system's rated capacity. It is different from kWh, which measures energy produced or consumed over time.

What does annual production mean?

Annual production is the estimated amount of electricity the solar system will generate during a year, generally measured in kilowatt-hours.

What is a good solar offset?

There is no universal perfect percentage. A system below, at, or above 100% can make sense depending on utility rules, future energy needs, roof conditions, economics, and other factors.

Should I compare solar quotes by price per watt?

Price per watt is useful when comparing similar solar-only systems, but equipment differences, batteries, roof work, electrical upgrades, financing, and other adders need to be considered.

Should I choose the quote with the lowest monthly payment?

Not automatically. The lower payment may come from a longer term, different financing cost, smaller system, different production, or different ownership arrangement.

Is the Illinois Shines Disclosure Form the same thing as my solar contract?

No. Illinois Shines describes the Disclosure Form as a standardized document containing key project information. Your actual installation contract, lease, or PPA remains a separate legal agreement.

Can 100% solar offset eliminate my utility bill?

Not necessarily. Fixed charges, delivery-related charges, taxes, grid purchases, and utility-specific billing rules can remain.

Does the federal 30% residential solar credit still apply to new 2026 installations?

Under current federal guidance, the former Residential Clean Energy Credit is not available for residential clean-energy property placed in service after December 31, 2025. Illinois state and utility programs are separate.

Should I get more than one solar quote?

Comparing multiple properly structured offers can help you understand whether system sizing, production assumptions, equipment, pricing, financing, and savings claims are reasonable.

A Solar Proposal Should Become Easier to Understand the Longer You Look at It

A good proposal shouldn't rely on:

A giant savings number.

One low monthly payment.

or:

“Trust me, this is the best option.”

The important numbers should connect logically.

Your annual electricity usage should help explain your system size.

Your system size and roof should help explain projected production.

Production and usage should explain solar offset.

The system and equipment should explain the price.

The financing structure should explain the payment.

Your utility rules should explain how exported electricity is treated.

And those pieces together should support the long-term comparison.

If they don't:

Keep asking questions.

Already Have a Solar Quote?

At LuNova Solar, we believe homeowners should understand the proposal before deciding whether the proposal is good.

Start with:

Your electricity usage.

Your home.

Your utility.

Your roof.

Your future energy needs.

Then evaluate the system being proposed.

SEE IF YOUR HOME QUALIFIES

No pressure.

Just a clearer look at the numbers before you make a long-term decision.

Related Illinois Solar Guides

10 Solar Sales Red Flags Illinois Homeowners Should Know

100% vs. 110% Solar Offset: How Much Solar Does an Illinois Home Actually Need?

Ameren vs. ComEd vs. CWLP Solar: Why Your Utility Changes Everything

Illinois Net Metering Changed: What Homeowners Need to Know

Illinois Solar Incentives in 2026

Solar Battery or No Battery? What Illinois Homeowners Actually Need

What Is a Solar PPA? The Illinois Homeowner's Guide

Selling a House With Solar in Illinois

Before You Go Solar in Illinois: 7 Things Every Homeowner Should Check

Illinois Solar Financing Options

Illinois Solar Questions & Answers

Sources & References

Illinois Shines — Disclosure Forms Deep Dive
Current Illinois Shines information explaining the standardized Purchase, Lease, and PPA Disclosure Forms and the requirement that participating distributed-generation customers sign the completed Disclosure Form before the DG contract.

Illinois Shines — Consumer FAQs
Current homeowner information explaining Disclosure Forms, project structures, incentives, net metering, and consumer protections.

Illinois Shines — 2026–27 Program Documents
Current Disclosure Form templates, Program Guidebook, Consumer Protection Handbook, and other Illinois Shines program materials.

LuNova Solar provides general educational information and does not provide tax, legal, engineering, lending, or financial advice. Solar pricing, financing, production estimates, utility tariffs, incentives, net-metering treatment, equipment performance, and savings vary. Review your actual proposal, Disclosure Form, contract, utility information, and financing documents before making a decision.

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