How long do solar panels last in Illinois?

Most panels last 25 years. The U.S. Department of Energy says the average working life rose from about 20 years in 2007 to 25 to 35 years in 2025. It cites a Berkeley Lab survey of industry professionals. The Environmental Protection Agency says silicon panels are expected to last 25 years or longer.

There is no day when a panel stops. It loses a small share of its output each year, and the loss is slow. Researchers often count a 20% loss as the end of "useful life." There is no agreed rule, and a system at 80% still makes power. Whether it is worth keeping is a money question, and the tool below helps you answer it.

Type your quote's numbers. The tool shows output in years 25 and 30, the year the power has paid for the system, and what an inverter replacement does to that. The starting numbers are an example for a 9.3 kW roof near Chicago.

This is an estimate, not a quote or a promise of savings. It assumes the panels and the roof last that long. The first-year power per kW of 1,300 matches the Chicago runs on our winter guide.

The best evidence is not a sales page. It is a handful of long government studies of panels on real roofs and fields.

Three things to know about these numbers:

• They are medians. Half of systems did better and half did worse. In the 2022 fleet study, 1 in 10 lost more than 1.9% a year.
• Newer is not always better. The 2023 study found newer designs fade at about the same rate as older ones, and some may miss their warranty rate.
• Cooler places lose less. The fleet study found the coolest zone lost 0.48% a year and the hottest 0.88%. It did not publish an Illinois-only number, so plan on 0.5% to 0.75%.

Illinois hail and snow are separate questions. Read how panels handle hail and how they do in winter.

The inverter turns the panels' power into the power your home uses. It has electronics and a fan, so it wears out sooner than glass and silicon.

NREL researchers who reviewed the field record found inverters made up 43% to 70% of service requests at solar plants. That number is from large plants, not homes. It points the same way as the one home-size array NREL watched for 20 years, which needed 4 inverter replacements. The makers' paper agrees. One major maker's standard string inverter warranty is 12 years. A microinverter, which sits under each panel, carries 25 years from another.

Inverter replacement costs, cleaning and who to call are covered in our solar maintenance guide. Here the point is timing: add the inverter bill to your payback math, as the tool does.

There are three warranties, and each has its own length and its own company behind it.

1. 1
   The equipment warranty

   covers a defective part. It comes from the maker.

2. 2
   The performance warranty

   promises a floor for output, such as 92% in year 25.

3. 3
   The workmanship warranty

   covers the installer's work, such as leaks at the mounts. It comes from the installer and its length varies.

We list these only as examples of the paper. They are not a ranking or an endorsement, and your panels may be a different model.

For companies in the state programs, Illinois sets a floor for the paper. The Illinois Power Agency's handbook, in force since June 1, 2026, says a home solar contract for a purchase, lease or PPA must state:

• the size of the system and the type of panels;
• the estimated first-year production and the estimated yearly degradation;
• the warranty term, who gives it, what it covers, any dollar limit and how to file a claim;
• who maintains the system and who files the utility paperwork.

Illinois Solar for All goes further. Its offers must include a written warranty or guarantee of at least 15 years at no extra cost. It must cover parts and labor and keep the system running to industry standards. It must also promise no more than 15% loss of output in the first 15 years. A lease or PPA must also let you choose, at the end of the term, removal at no cost, buying, or renewing. The program says participants get 15 years of routine maintenance at no cost.

Most owners never replace panels, only an inverter. Replace when a part fails or when the output falls under what the warranty promises, not at a certain age.

1. 1
   Watch the monitoring.

   Compare a clear day this year with a clear day last year. A slow drift is normal. A sudden drop is a fault.

2. 2
   Compare with the warranty floor.

   For example, a panel promised at least 92% in year 25 should not read 85%.

3. 3
   Get a written diagnosis.

   A single bad panel, a failed inverter and a loose wire look the same on your bill.

4. 4
   Ask who pays the labor.

   The paper above shows warranties often cover the part but not the visit.

5. 5
   Think twice about swapping at year 25.

   If the system still makes real money, as the tool shows, the cheaper move is often to keep it and replace only the inverter.

The panels may outlive the shingles under them. Taking panels off and putting them back for a new roof is real work. That is why CUB says Illinois Solar for All homes need a roof at least 15 years from replacement, and why a tired roof should be redone first. Our roof requirements guide covers roof age, the re-roof job and who covers the mounts. A heavily shaded roof is a separate problem. See solar on a shaded roof.

At the end of life, panels are not simple trash. The EPA says some panels count as hazardous waste and some do not, even within one model. As of its September 30, 2026 update, panels are not yet listed as universal waste. The Department of Energy says recycling still costs more than landfilling for silicon panels in the U.S. We found no Illinois rule for homeowners. Ask your installer in writing who removes and recycles panels at the end, and what it costs.

This is the table most pages skip. It uses the tool's starting numbers. The roof is 9.3 kW near Chicago. You pay $16,000 after rebates. Power is worth 10 cents a kWh, and output falls 0.75% a year. The cost is inside the range shown in our Illinois solar cost guide.

Two changes move that picture. A $3,000 inverter in year 13 pushes payback from year 14 to year 17. Power prices that rise 3% a year pull it in to year 12. Your roof, your bill and your quote decide the real numbers, which is why the first step is to check the roof itself. Our Is solar worth it guide has the full calculator.