guide10 min read

How Long Do Solar Panels Last in Illinois? 25 to 35 Years, Still Making About 89% at Year 25

Ryan Cook•October 15, 2026

Most solar panels going on Illinois roofs today should keep working for 25 to 35 years. That's the U.S. Department of Energy's current estimate, up from about 20 years in 2007. They don't die at the end of that stretch; they fade. At the 0.5% a year that the Illinois Shines program writes into every contract, a panel still makes about 89% of its first-year power in year 25 and about 86.5% in year 30.

The bigger point for Illinois homeowners is that slow aging rarely ends a system early. A part that breaks and doesn't get fixed does. The numbers below show why, and what to ask before you sign.

The key numbers

What	Figure	Source / date
Typical solar panel lifespan	25 to 35 years (about 20 years in 2007)	U.S. Department of Energy, End-of-Life Management for Solar Photovoltaics, accessed Oct. 15, 2026
Median aging rate, nearly 2,000 field measurements	0.5% a year (average 0.8%)	National Renewable Energy Laboratory review, June 2012
Median performance loss, about 2,200 U.S. non-residential sites	About 0.75% a year; slower in cooler climates	U.S. Department of Energy success story, June 27, 2023
Aging rate Illinois Shines assumes	0.5% a year; "Alternative degradation rates will not be accepted"	Illinois Shines 2026-27 Program Guidebook (Apr. 17, 2026), Section 4 J
Illinois Shines contract for home systems	15 years; expected deliveries drop 0.5% a year	Same guidebook, Section 7 C
Company collateral on each contract	5% of contract value; drawn only once a shortfall reaches $5,000	Same guidebook, Section 7 C
Supply price used below	ComEd 10.103¢/kWh; Ameren 10.441¢ for the first 800 kWh, Oct. 1, 2026–May 31, 2027	Plug In Illinois Price to Compare pages

What year 25 actually looks like

Here's how much of its first-year output a panel keeps at three aging rates. The 0.5% column is the Illinois Shines assumption. The 0.75% column is the median from the federal fleet study, and 1% is a pessimistic case.

Year	0.5% a year	0.75% a year	1% a year
1	100%	100%	100%
10	95.6%	93.4%	91.4%
15	93.2%	90.0%	86.9%
20	90.9%	86.7%	82.6%
25	88.7%	83.5%	78.6%
30	86.5%	80.4%	74.7%

Our math: first-year output × (1 − rate) for each year after the first.

To put dollars on it, take the average-size Illinois system from our how many panels guide, about 6 kW. In Chicago it makes an estimated 8,052 kWh in its first year, worth about $813 at ComEd's 10.103-cent Price to Compare. At 0.5% a year, year 25 makes about 7,139 kWh, or roughly $721 at today's price.

Added up over 25 years, aging costs that Chicago system an estimated 11,600 kWh, about $1,175 at today's price. At the federal median of 0.75% it's about 17,100 kWh, or $1,730. A 6 kW system in Belleville makes more, an estimated 8,580 kWh a year, so it gives up a bit more: an estimated $1,294 to $1,904 at Ameren's 10.441 cents.

That's real money, but it's spread over a quarter century, and an honest estimate already includes it. If a quote shows the same production in year 20 as in year 1, ask why.

Illinois weather isn't the enemy people think it is

The 2023 federal study found panels age more slowly in cooler climates. Illinois summers get hot, but our climate is a lot closer to the cool end of that range than Phoenix is.

Winter does show up in the research. The National Renewable Energy Laboratory's review noted higher aging rates at some alpine sites with heavy snow and wind loads. It also cited two other cold sites, one in the Canadian Arctic and one high in the Alps, where rates were very low, though those panels were mounted on walls and carried no snow load. Snow mostly costs winter production, not panel life, and our snow guide explains why I tell people to leave it alone.

Hail is the Illinois weather risk that matters, and it's damage, not aging. Read how your policy treats panels in our homeowners insurance post before you sign anything.

The Illinois twist: a 15-year production promise

This part almost never shows up in national lifespan articles. When an Illinois Shines system is energized, the program sets a 15-year schedule of renewable energy credits (one credit per 1,000 kWh) that the system is expected to deliver. That schedule drops 0.5% every year, the same aging the program assumes.

Each fall, the program administrator compares a three-year average of what each system delivered against its schedule. The math runs across all of the selling company's systems under that contract, so one system's surplus can cover another's shortfall. The utility draws on the company's collateral only when the shortfall reaches $5,000. That collateral starts at 5% of the contract's value, and later top-ups are figured on the remaining value, which drops by one-fifteenth each contract year.

Here's the math I find most useful. Say a 6 kW Chicago system ages at 0.75% a year instead of the program's 0.5%. By year 15 it's about 3.5% behind schedule. That's about 0.26 credits a year, or roughly $21 at the $80.77 price for ComEd-area systems up to 10 kW. Over all 15 years the gap comes to about 2 credits, roughly $162.

Compare that with one dead inverter. If the inverter quits in May and nobody notices until August, that same system misses roughly 2,480 kWh. That's about 2.5 credits and about $251 of power at ComEd's current price, lost in one summer. (PVWatts puts about 51% of a Chicago array's yearly output in May through September; we split that evenly by month.)

Three dead summer months cost more credits than 15 years of faster-than-average aging. The things that eat into a system's life in Illinois are a failed part and a company that doesn't answer the phone. Our repairs post covers who pays for what. Our fall and winter production curve shows how to tell a normal winter dip from a real problem.

The selling company, the Approved Vendor, posts the collateral, but your contract decides whether a shortfall ever gets passed back to you. Ask that question in writing. Our Illinois Shines page covers how the credits work.

What wears out before the panels do

The inverter. It converts the panels' power for your house, and the Department of Energy expects inverters to need replacing at least once in an array's 25-year life. If you own the system, ask for the replacement cost and the inverter warranty term in writing. Microinverters, which mount behind each panel, carry their own warranty terms; check the written term on any quote.

The roof. If your shingles have less life left than the panels, the array has to come off and go back on when you reroof. Our roof-age guide walks through when to replace first.

The fine print. A panel's performance warranty is a written minimum output at a set year. The laboratory's review cited a 2008 reliability model finding that panels need to age less than 0.5% a year to satisfy long-term warranties. Get the warranty number in writing and compare it with the table above.

Own or lease: who carries the aging

If you buy with cash or a loan, you keep every kilowatt-hour for the full 25 to 35 years, long after the system is paid off. You also own the inverter replacement, the repairs, and whatever your Shines contract says about shortfalls.

On a 25-year lease, the leasing company owns the equipment, so monitoring, repairs and inverter swaps are its job and its cost. You pay for the power at a predictable rate, as low as $0.10 per kWh, and the equipment risk stays with the owner. What happens at the end of the term is spelled out in the contract, so read that page before you sign. Our lease vs. buy breakdown lays the two side by side.

I lead with a lease for a lot of Illinois families for this reason. Panels are boring, reliable hardware, and the things that go wrong in years 10 through 25 shouldn't be the homeowner's problem.

What happens when they're finally done

Very few panels have reached that point yet. The Department of Energy says few systems are entering the waste stream right now, more will over the next few decades, and recycling still generally costs more than a landfill.

Illinois has started working on it. Public Act 102-1025 created a state task force to investigate recycling and other end-of-life options for renewable energy equipment, solar panels included, and energy storage devices, and to identify preferred methods. Its final report was due by July 1, 2025, and the act was set to repeal on December 31, 2025.

My take: a 30-year-old panel making 85% of its original output isn't trash. Most owners will keep running it as long as the inverter and roof cooperate.

Get your own numbers

Want to see what your roof makes in year 1 and year 25? Run your bill through our savings calculator, or call me at (618) 217-2001. I'll lay out lease, cash and Solar for All side by side, aging included. You can also reach us through /contact/.

All production and dollar figures are estimates based on federal models and current prices. Your roof, equipment and contract terms will move the numbers.

Sources

End-of-Life Management for Solar Photovoltaics — U.S. Department of Energy, Solar Energy Technologies Office, accessed Oct. 15, 2026 (lifespan 25–35 years; recycling cost vs. landfill)
Success Story — A Clearer Picture of U.S. Solar Power Performance — U.S. Department of Energy, June 27, 2023 (median performance loss about 0.75% a year; slower in cooler climates)
Solar Photovoltaic System Design Basics — U.S. Department of Energy, accessed Oct. 15, 2026 (inverters expected to need replacing at least once in a 25-year array life)
Photovoltaic Degradation Rates — An Analytical Review — D. Jordan and S. Kurtz, National Renewable Energy Laboratory, NREL/JA-5200-51664, June 2012 (median 0.5% a year, mean 0.8%)
Illinois Shines 2026-27 Program Guidebook — Illinois Power Agency, Apr. 17, 2026 (Section 1 REC prices; Section 4 J, 0.5% degradation; Section 7 C, collateral and REC delivery performance evaluation)
PVWatts Calculator v8 API — National Laboratory of the Rockies, annual AC output for Chicago and Belleville, 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)
Public Act 102-1025, Renewable Energy Component Recycling Task Force Act — Illinois General Assembly, 102nd General Assembly (final report due July 1, 2025; repealed Dec. 31, 2025)

Frequently Asked Questions

Most panels going on Illinois roofs today should keep working for 25 to 35 years. That's the U.S. Department of Energy's current estimate, up from about 20 years for panels in 2007. Panels don't switch off at the end of that window; they fade slowly. The Illinois Shines program assumes every system loses 0.5% of its output a year, which leaves a panel making about 89% of its first-year power in year 25 and about 86.5% in year 30. A 2023 federal study of about 2,200 non-residential U.S. sites found a median loss closer to 0.75% a year, which still means about 84% at year 25. The parts that usually quit first are the inverter, which converts the panels' power for your house, and sometimes the roof under the array. Plan for those, keep an eye on your monitoring app, and the panels themselves are rarely what ends a system's life.

About half a percent a year is the typical figure. A National Renewable Energy Laboratory review of nearly 2,000 field measurements found a median loss of 0.5% a year and an average of 0.8%. A newer federal study of about 2,200 commercial and utility sites put the median at around 0.75% a year and found that panels age more slowly in cooler climates. Illinois Shines writes 0.5% a year into every system's 15-year production schedule and won't accept a different rate. In dollars, a 6 kW Chicago system that makes 8,052 kWh in its first year makes about 7,139 kWh in year 25 at 0.5% a year. Over 25 years that aging adds up to an estimated 11,600 kWh, or roughly $1,175 at ComEd's current 10.103-cent Price to Compare, with prices held flat. A Belleville system on Ameren loses an estimated $1,294 over the same stretch.

Not in any way the data shows clearly. The 2023 federal fleet study found panels age more slowly in cooler climates, and Illinois runs cooler than the desert Southwest. The National Renewable Energy Laboratory's review did note higher aging rates at some alpine sites with heavy snow and wind loads. Two other cold sites, one in the Canadian Arctic and one high in the European Alps, showed very low rates, but those panels were wall-mounted and carried no snow load. Snow mostly costs production in winter, not panel life, and it usually slides off on its own. Hail is a real risk in Illinois, but it's a damage event, not slow aging. It's an insurance and roof question, so check how your homeowners policy treats panels before you sign. If a hailstorm cracks a panel, report it and get it fixed quickly, because a damaged string can drag down output for months before anyone notices.

Normal aging is already priced in. When a system is energized, Illinois Shines sets a 15-year schedule of expected renewable energy credits that drops 0.5% every year. Each fall the program compares a three-year average of what your system delivered against that schedule. Shortfalls and surpluses are pooled across the company's whole portfolio. The utility only draws on the company's collateral, which starts at 5% of the contract's value, once the shortfall reaches $5,000. In our example, a 6 kW Chicago system that ages at 0.75% a year instead of 0.5% falls about 2 credits behind over 15 years, roughly $162 at the $80.77 ComEd-area price. An inverter that sits dead for three summer months costs about 2.5 credits in a single season. Ask your company in writing whether its contract passes any shortfall back to you.

Probably the inverter, and possibly the roof. The U.S. Department of Energy expects inverters to need replacing at least once during a solar array's 25-year life, long before the panels give out, and that bill is yours if you own the system. Microinverters, small units mounted behind each panel, carry their own warranty terms, so check the written term on whatever you're quoted. The roof is the other piece. If your shingles have less life left than the panels, the array has to come off and go back on when you reroof, so it's usually cheaper to replace an aging roof first. Wiring, connectors and the monitoring hardware can need occasional attention too. On a lease, the leasing company owns the equipment, so monitoring, repairs and inverter swaps are its job and its cost. If you own the system, set money aside for the inverter and check your monitoring app monthly.