Here’s something nobody tells you on installation day: your solar panels will produce a little less electricity every single year for the rest of their lives. Year by year, the numbers tick down. And if you’ve been watching your production closely, that slow decline can be unsettling.
Take a breath, because here’s the reassuring part. That decline isn’t a defect. It isn’t a sign your installer cut corners. It’s physics, and it happens to every solar panel ever made, from the cheapest budget brand to the most expensive premium model. The real question isn’t whether your panels are degrading. They are. The question is how much is normal, and how much means something is actually wrong?
That’s exactly what this article will help you figure out. By the end, you’ll be able to look at your own system’s numbers and know, with confidence, whether you’re seeing healthy aging or a genuine problem worth a phone call. If you haven’t already, it pairs well with [LINK: How to Tell If Your Solar Panels Are Actually Working].
What Degradation Actually Is
Degradation is the gradual loss of a panel’s ability to convert sunlight into electricity. It happens for entirely ordinary reasons: years of ultraviolet light slowly altering the materials, the daily expansion and contraction as panels heat up in the sun and cool at night (called thermal cycling), and long-term exposure to humidity and weather.
None of that is a malfunction. It’s the natural wear of a device that sits outside, exposed to the elements, every day for decades. A panel that’s degrading at a normal rate is a healthy panel. It’s doing exactly what it was designed to do.
The Numbers That Matter
This is where you get to replace worry with facts. Here’s what the research actually shows.
- The industry standard is about 0.5% per year. This figure comes from long-term work by the National Renewable Energy Laboratory (NREL), the federal government’s renewable energy research arm.
- The real-world median is closer to 1.09% per year, according to data from kWh Analytics reported by pv-magazine. Real rooftops in real weather tend to age slightly faster than lab estimates.
- Premium panels (think LG, Panasonic, and SunPower) often degrade more slowly, around 0.3% to 0.4% per year.
- Budget panels can run higher, sometimes 1.5% to 2% per year.
- Most manufacturer warranties guarantee that your panels won’t degrade faster than about 0.7% to 0.8% per year. Hold onto that number, because it’s your benchmark.
So if you’ve been seeing your output slip by roughly half a percent to one percent a year, congratulations: that’s textbook normal. Nothing to fix.
What This Looks Like in Practice
Numbers on a page are one thing. Let’s make it concrete with a worked example.
Say you have an 8kW system degrading at a steady 1% per year, which is right around the real-world average. Here’s how your output holds up over time:
- Year 1: 100% output (your starting baseline)
- Year 5: roughly 95% output
- Year 10: roughly 90% output
- Year 25: roughly 78% output
Look at the shape of that. After a full decade, you’re still producing around 90% of what you did on day one. Even at the 25-year mark, near the end of the panels’ design life, you’re still pulling close to 80%. This is a slow, gentle, predictable slide, not a collapse. A system that follows this curve is aging gracefully, and there’s nothing here that should alarm you.
How to Check YOUR System’s Degradation
General averages are helpful, but you probably want to know about your roof. Here’s how to check.
Compare your first year of production to your most recent year, using the same months. This last part is critical. Solar production swings dramatically with the seasons. June will always crush December. So comparing this past December to your very first June will give you a wildly misleading answer. Match like with like: this year’s spring against your first spring, or better yet, a full 12 months against a full 12 months.
Use your monitoring app’s lifetime graphs. Both Enphase and SolarEdge keep long-term production history. Most apps let you pull up yearly totals or lifetime graphs. (If you’re not sure how to navigate yours, [LINK: How to Read Your Enphase/SolarEdge App] walks through it step by step.)
Do the math and compare to the benchmark. Take your annual decline and ask where it falls. 0.5% to 1.1% per year is normal. If you’re seeing 3% or more per year, that’s no longer ordinary degradation. Something is wrong, and it’s worth investigating.
The most reliable way to track your system’s production year over year independently, outside of your installer’s app, is a home energy monitor like the Emporia Vue 3. It reads your production directly and keeps its own records, which is handy if you ever want a second opinion on what your installer’s software is telling you.
What’s NOT Normal Degradation
Some production losses have nothing to do with aging. These are the patterns that signal a real problem rather than healthy wear:
- A sudden 20% or more drop in production. Real degradation is gradual, measured over years. A sharp cliff, especially overnight, points to something like an inverter or wiring fault, not aging panels. (See [LINK: Why Are My Solar Panels Producing Less Than Expected?].)
- One panel producing far less than its neighbors. On a clear day, all your panels should perform similarly. If one is lagging well behind the others, you may be looking at a failed microinverter or unexpected shading rather than degradation.
- Visible physical damage. Cracks, delamination (the layers of the panel separating or bubbling), or discoloration such as yellowish or brownish tinting are signs of a damaged panel, not a normally aging one.
- A production drop on a panel that’s under 5 years old. New panels shouldn’t be losing meaningful output yet. If a young panel is underperforming, that’s a flag worth raising with your installer.
If you spot a sudden single-panel issue like this, it’s often an equipment fault rather than the panel itself. Our guide [LINK: Is My Solar Inverter Failing?] covers how to tell the difference.
Snail Trails and Hot Spots
Two specific panel defects come up often enough to deserve a mention, and the good news is you can usually spot both from the ground with a pair of binoculars.
Snail trails are thin, dark, wandering lines that appear on the surface of a panel, a bit like the trail a snail leaves behind, which is how they got the name. They’re caused by tiny microcracks in the cells reacting with moisture and the panel’s materials over time. A faint snail trail isn’t always an immediate problem, but it can signal underlying cracks that may worsen, so it’s worth noting and mentioning to your installer.
Hot spots are areas of a panel that run abnormally hot because a damaged or shaded cell is being forced to dissipate energy instead of producing it. You generally can’t see a hot spot with the naked eye (it shows up on thermal cameras), but its effects can: localized discoloration, scorch-like marks, or a panel that consistently underperforms. Hot spots can shorten a panel’s life and, in rare cases, pose a fire risk, so a panel you suspect of running hot deserves a professional look.
A word of caution: spotting these is a binoculars-from-the-driveway job, not a climb-on-the-roof job. Leave the up-close inspection and any repairs to a licensed solar professional.
What Your Warranty Promises
Most solar panels come with a 25-year performance warranty. The standard promise is that your panels will still produce at least 80% of their original output at the 25-year mark. Look back at our worked example: a panel degrading at 1% per year lands right around 78% at year 25, which is why warranties are written around that 80% line.
If your panels are degrading faster than the warranty allows, and you can document it, you may have a valid claim. To check, dig out your original warranty paperwork (or look it up on the manufacturer’s website using your panel model). Note the maximum annual degradation rate it guarantees, then compare it to what your system is actually doing. If your real-world decline clearly exceeds the warranty terms, contact your installer or the manufacturer to start a claim.
The Bottom Line
Let’s make this easy to remember.
If your system is 10 years old and producing 8% to 10% less than it did in year one, that’s almost certainly normal. Your panels are aging exactly the way they’re supposed to. Stop worrying.
But if your system is only 3 years old and already producing 15% less, that’s not normal. Pick up the phone and call your installer.
Most of the time, the homeowners who fret about degradation are watching a perfectly healthy system do exactly what physics says it should. Now you have the numbers to know the difference for certain, which means you can stop guessing and get back to enjoying the power your roof is quietly making every single day.
Last reviewed: June 2026 | solarschoice.com is independent — not affiliated with any solar installer.