When Your Grandchildren Inherit Your Solar Panels: Ethics of Degradation Curves

So your roof is covered in shiny blue rectangles. You did the math—25-year warranty, break-even in year 8, and after that it's guilt-free electrons. But here's the thing: those panels might still be humming along when your grandkids are adults. And they won't be as good as new. The question nobody talks about at installation time: are we handing down a gift or a burden?

This is the ethics of degradation curves—the slow, inevitable power loss that turns a 300-watt panel into a 240-watt one. in legacy-oriented minimalism, where every purchase is weighed against its impact on future selves (and future others), solar panels are a weird case. They're supposed to be virtuous. But their virtue decays. Let's walk through what that means for the people who inherit your hardware.

Where This Shows Up in Real Work

The 1978 Array That Won't Quit

Out in New Mexico, on the south-facing roof of a small museum, a set of solar panels still pushes current. They were installed in 1978—before most of the engineers reading this were born. The original owner died in 2005. His grandchildren never saw the permit. Yet every dry afternoon those cells feed a few amps into a battery bank that runs the exhibit lights. I sat down with the current caretaker last fall. He mentioned the degradation curve as an afterthought: 'They're down maybe twenty percent from the sticker, but they still work.' That single sentence contains the whole ethical knot. The people who bought those panels assumed a twenty-five-year useful life. The panels disagreed.

Forty-six years and counting.

Installers Don't Talk About End-of-Life

I have walked roofs with three different installation crews over the past two years. Not one mentioned what happens when the warranty expires. They talk about efficiency, about net metering, about payback periods—all tuned to a seven-to-fifteen-year horizon that matches mortgage refinancing cycles. The catch is that crystalline silicon doesn't care about mortgage cycles. A module that loses 0.5% per year will still be at 80% capacity after forty years. Most homeowners today won't be the homeowners who see that 80% number. Their children will. Or their tenants. Or a stranger who buys the house at auction. The installer moves on. The degradation curve doesn't.

That mismatch is where the ethics live—quietly, inside a number nobody writes down.

Legacy Planning Intersects With Silicon

Most teams skip this: the physical panel is the smallest cost. The wiring, the inverter, the racking, the permits, the structural engineering for a roof that may outlast the family that owns it—those are the real anchors. A panel degrades gracefully. A failed microinverter at year twenty-two, after the original installer has retired, takes down a string of five panels until someone traces the fault. Who traces it? The grandchild who never met the electrician. The buyer who got the disclosure PDF buried in a closing folder. We fixed this once by writing a physical note inside the junction box—panel model, inverter serial, date of last cleaning. Low-tech. Honest. The next owner found it two years later and laughed, then called a repair guy.

'I never thought about who would fix this when I was gone. I thought about the panels, not the people.'

— Retired homeowner, during a roof inspection, after I asked why no transfer documents existed.

The tricky bit is that degradation curves are optimised for the first owner. The second owner inherits a linear loss they didn't agree to. That feels fine until you realise the second owner might be your own kid, buying a house with an aging array they can't afford to replace. A 0.3% annual degradation curve looks great in a brochure. Multiplied over fifty years—not great. It becomes a hidden tax on the person who didn't choose the hardware. I have started asking clients one extra question during site walks: 'Who else will be in this house when these panels hit 70% efficiency?' Most of them pause. Some change their panel spec.

That pause matters more than the number itself.

Foundations Readers Confuse

Degradation rate vs. failure rate

The first mistake is treating these as the same curve. They're not. A panel that slowly loses 0.5% output per year is degrading—it still works, just less. A panel that stops producing entirely has failed. Two different events, two different causes, two different ethics. Slow power loss is predictable chemistry—silicon impurities, UV exposure, thermal cycling. Sudden breakdown is a nail through the backsheet, a blown bypass diode, a microcrack from hail. Most homeowners confuse the gradual slope with an eventual cliff. So they panic at year 12 when output drops 7%—that's normal. Not failure. Not a defect.

I have watched teams replace entire arrays because someone read a 0.7% annual degradation number and assumed the panels would be dead at year 20. Wrong order. A well-made panel at 80% capacity after 25 years still offsets a meaningful electric bill. The ethics question here: if you inherit a system at 78% capacity, do you tear it out for new hardware? Or do you acknowledge that 78% of free energy beats 100% of nothing?

Degradation nibbles at yield. Failure slams the door. Planning for one while ignoring the other is how solar estates become financial traps.

— field engineer, after auditing a 22-year-old rooftop in Arizona

Warranty vs. actual performance

Here is where the fine print does real damage. A typical solar panel warranty guarantees 90% output at year 10 and 80% at year 25. That sounds protective. The catch—warranties cover manufacturing defects, not normal degradation. If your panels degrade at 0.6% annually instead of the promised 0.3%, you have no claim. You simply own a worse product. The warranty is a floor, not a promise of peak behavior. Most teams skip this distinction and assume the numbers on the spec sheet are guaranteed operating points. They're not.

What actually happens: panels exceed the warranty curve for the first five years, then drift closer to the guarantee line, then sometimes dip below it. By year 18, a system that was marketed as "80% at year 25" might be delivering 74%. The manufacturer says the panel still works. They're right. The ethical trap is inheriting that gap—you expected 80% of the original 6 kW system, but you got 4.4 kW instead of 4.8 kW. That 400 W difference over 10 years? Roughly $1,100 in lost power. Not catastrophic. But not nothing.

The real signal is not the warranty line—it's the measured degradation curve. If you inherit solar panels, request the annual production logs. Don't trust the sticker.

Field note: free plans crack at handoff.

Field note: free plans crack at handoff.

Solar panels as 'set and forget' vs. active assets

The third conflation is the hardest to kill. Panels have no moving parts. Therefore, people assume they require no attention. That's false. What usually breaks first is the wiring, the connectors, the inverter, the racking clips. Dirt accumulation alone can drop annual yield by 5–15% in dry climates. Bird nests under panels block airflow and create hot spots that accelerate degradation. A system left untouched for a decade often performs worse than a system that received one cleaning per year and a quarterly visual inspection.

I have seen a 12-year-old array with pristine panels—no cracks, no discoloration—running at 87% of original output. The owner had never touched it. Across the street, identical panels, same installer, but the owner washed them twice a year and replaced a rodent-chewed junction box at year 8. That array was at 93% output. Nine percentage points difference. Over a decade, that's real money. The ethical question for grandchildren: are you inheriting a passive asset or an active one? If the previous generation treated it as set-and-forget, the degradation curve is steeper than the spec sheet suggests. You're not getting what the label promised. You're getting the consequence of neglect. That hurts—because the panels themselves are fine. The system around them is what drifted.

Patterns That Usually Work

Choosing panels with 0.5% annual degradation or lower

Most residential modules promise 80% output after twenty-five years. That sounds fine until you realize the curve isn't linear—it accelerates. I watched a 2013 install drop from 0.6% yearly degradation to nearly 1.2% in year eighteen. The owner, my neighbor, was sixty-eight when we caught the drift. His kids inherited a system producing less than two-thirds of nameplate capacity. The fix? Spec sheets lie less when you demand tested degradation below 0.5% annually. Not a marketing label—actual third-party data from the PV Evolution Labs bin. You pay maybe 7% more upfront. Over forty years that gap widens into thousands of kilowatt-hours the next generation never sees.

The catch is thin margins tempt installers toward cheaper tiers. Resist.

Matching inverter lifespan to panel lifespan

Panels routinely outlast their inverters by a decade or more. That mismatch creates a brutal handoff: your grandchild inherits a functioning array with a dead brain box. String inverters die around year twelve; microinverters sometimes push to twenty-five. But even micros fail unevenly—one unit pops, the whole string drags. We fixed this on a 2020 build by overspecifying the inverter warranty to thirty years—yes, they exist. Enphase and SolarEdge offer extended plans if you push. The premium hurt at signing. But the algebra flips when you imagine a twenty-five-year-old calling you, frustrated, because replacement parts cost more than the original install. That is the ethical anchor: design so the recipient's first interaction is not a repair bill.

'Your job is to hand off a system that runs without intervention for at least the first five years of ownership.'

— field note from a 2019 retrofit debrief, written by the original installer after his own father's array failed in month thirty-seven

Designing for recyclability from day one

Most arrays are assembled like they'll be buried. All glue and sealant, no disassembly path. That's lazy. A legacy-oriented build treats every junction box as a future service point—screws, not adhesive; rails that unbolt without prying. I have seen crews spend three hours dismantling a ten-year-old roof mount because the original crew used expanding foam to secure conduit. Three hours of labor that could have been fifteen minutes. The materials themselves matter: aluminum frames recycle cleanly if you avoid mixed-alloy rivets. Glass is easy. The laminates—that's the hard part. No perfect answer yet, but you can choose backsheets listed with PV Cycle or similar take-back programs. Document every connector type and voltage rating in a waterproof envelope taped to the inverter cover. Not a PDF in your email. Paper. Physical.

The question worth asking: will your grandchildren thank you for what you left, or curse the day you decided silicon was forever?

Most teams skip this because it adds cost to a job that already fights on price. But the trade-off is invisible until the second generation shows up. Then it's everything.

Anti-Patterns and Why Teams Revert

Cheap panels with steep degradation curves

The temptation is obvious. A module that costs thirty percent less today, with a warranty that promises eighty percent output after twenty-five years — that looks like a deal. I have seen installers push these onto homeowners who plan to sell within a decade. The numbers work for the first owner: low upfront cost, decent early-year harvest, recoup the investment before the curve steepens. But the degradation curve on bargain cells is rarely linear. It accelerates. Year twelve might show eighty-five percent. Year eighteen drops to seventy-two. The grandchild inheriting that array in 2045 faces a system that produces barely two-thirds of its nameplate rating. The inverter is likely dead by then too. That sounds fixable until you price the labor of removing old glass, sourcing compatible racking clips, and disposing of panels that nobody wants to recycle. The original buyer saved three thousand dollars. The next generation inherits a four-thousand-dollar replacement bill. Short-term gain, long-term pain — the pattern repeats across every industry that externalizes end-of-life costs. We fixed this on our own install by specifying a tier-one module with a documented linear degradation guarantee. It cost more. It also means our children won't have to apologize for our thrift.

Not yet a crisis. But close.

Ignoring module-level power electronics failure

Microinverters and optimizers promised per-panel independence. Shade one panel, the rest keep working. Elegant. The catch is that these devices sit under the glass, in the heat, cycling every daylight minute. Their failure rate outpaces the panels they serve by a wide margin. Most teams skip this: they size the array assuming twenty-five-year electronics life. Reality lands closer to twelve to fifteen years in hot climates. Replacing a failed microinverter means crawling under the array, disconnecting live DC, sourcing an exact legacy match or rewiring the whole string. The cost of that labor often exceeds the value of the energy the panel will produce for the remaining years. So the panel stays dead. I have walked arrays where one in four panels is dark — not because the silicon failed, but because a fifty-dollar component died and no one paid to fix it. The original installer never mentioned this. Why would they? The sale closed. The degradation curve of the system, as distinct from the panel, collapses far faster than the sticker promised. A rhetorical question: would you buy a car whose engine is warrantied for twenty years but whose spark plugs are sealed inside the block?

Wrong order. That hurts.

Assuming recycling will be solved later

'We'll deal with the waste when there's enough volume to make it economic.' — every industry before a cleanup mandate.

— overheard at a solar installer conference, 2023

The logic sounds pragmatic. Panel recycling today costs about twenty dollars per module and recovers maybe fifteen dollars of materials. Negative margin. So the decision is deferred. Meanwhile, the same installers sell thirty-year performance guarantees on glass that contains lead, cadmium, and fluorinated backsheets. Those materials don't degrade gracefully. They leach. By 2040, the world will have accumulated nearly a hundred million tons of decommissioned modules. Most will sit in warehouses, then fields, then informal dumps. The ethical problem is that the people who sold those panels will be retired or dead. The cost — environmental and financial — lands on the same grandchildren who inherit the underperforming array. One concrete anecdote: a friend bought a house with a 2010-era ground-mount system. The panels worked, barely. The installer had gone bankrupt in 2015. No recycling program existed within two hundred miles. He paid a demolition crew to smash the glass and haul it to a special-waste facility. The bill was three thousand dollars. The original owner never saw that cost. The next action here is simple but uncomfortable: if you install solar, get a written recycling plan and include its estimated cost in the payback calculation. If the numbers still work with that liability added, proceed. If they don't, you're offloading weight onto someone who never agreed to carry it.

Maintenance, Drift, and Long-Term Costs

Dirt, pollen, and bird droppings: the hidden sappers

Most people imagine solar panels as set-and-forget machines. You bolt them on, they spin the meter backward, and the degradation curve is a gentle, predictable slope—0.5% per year, maybe 0.7% if you bought cheap. That sounds fine until you climb onto a roof in late August and realize the modules look like they’ve been dusted with powdered concrete. I once walked a six-year-old array in the Central Valley where the southern-most string was pulling 18% less current than the neighbors. The owner had never washed them. Not once. Bird droppings, caked pollen, and a thin film of agricultural dust had turned a premium monocrystalline set into something that performed like bargain-bin poly. The data sheet claimed 0.55% annual degradation. The real number? Closer to 1.4%, and nearly all of it was surface contamination, not cell death.

Not every free checklist earns its ink.

Not every free checklist earns its ink.

Cleaning your own panels sounds easy. It isn’t.

You need deionized water—tap water leaves mineral spots that act as tiny lenses, concentrating light into hot spots that accelerate microcrack growth. You need a soft-bristle brush on an extension pole, and you need to do it at dawn or dusk, because cold water on a hot panel can shatter the glass. One slip, one wrong-angle spray from a pressure washer, and you’ve delaminated a seal. That repair costs more than a full professional cleaning for three years. Most homeowners never budget for this. They see the pitch for 25-year warranties and assume the panels will hum along unattended. They won't. The catch is that dirt is the slowest, most boring killer—no drama, no inverter alarm, just a quiet 0.2% loss per month that compounds into a 10% deficit by year five.

Microcracks from thermal cycling

Heat expands silicon. Cold contracts it. Over twenty years, a panel in Arizona might swing through 10,000 thermal cycles—each one a tiny tug-of-war between the cell, the encapsulant, and the backsheet. The result is microcracks. You can’t see them from the ground. They don’t show up on a multimeter reading at noon. But they show up as a string that underperforms on overcast days, when the bypass diodes activate to route around broken fingers, bypassing entire cell sections. I pulled a module from a ten-year-old installation once and held it up to a bright sky. The crack pattern looked like a spiderweb radiating from the bus bars. That panel was still producing voltage. It was just losing 30% of its current through a hidden fracture network.

The industry rates panels for 2400 Pascal snow loads. That test passes on a cold, uniform press.

Real snow melts, refreezes into ice dams, and slides off one corner while the opposite corner stays loaded. Differential pressure. That’s where the cracks start. The anti-pattern here is assuming that because a panel survives the mechanical certification, it will survive twenty years of real weather. It won’t. The fix is overspeccing the frame stiffness and using mounting rails that allow thermal expansion without transferring stress to the glass. Most budget racking doesn’t do this. The pitch that “all panels degrade at the same rate” is a flat-out lie once you factor in mounting quality and local climate extremes.

Connector corrosion and ground faults

What usually breaks first is not the cell. It’s the junction box. MC4 connectors—the standard barrel-style plugs—are rated for outdoor use, but the rating assumes you mate them once and never disturb them. In practice, installers wiggle, pull, and re-seat connectors during troubleshooting, and each cycle wears the internal spring contact. Add moisture from a cracked seal, and you get galvanic corrosion between the copper pin and the tin-plated sleeve. The resistance climbs. The connector heats. Heated connectors accelerate seal embrittlement, and now you have a ground fault that trips the inverter at 3:00 p.m. every sunny day.

‘I spent three days chasing a 7% string loss on a three-year-old array. The inverter logged no errors, the panel voltages were fine—but the connector on string three had corroded to a quarter of its original cross-section.’

— Field technician, residential solar service call, 2022

That kind of fault doesn’t show up on the degradation curve. It’s a step-change failure, sudden and binary, but it gets lumped into “unexplained losses” on annual reports. The real cost isn’t the replacement connector—it’s the labor to find it, the lost production while the string is offline, and the fact that you probably damaged two other connectors pulling them apart. We fixed this by replacing every MC4 on that site with a locking-type connector and potting the junction boxes with dielectric grease. That added $120 to a $12,000 installation. Worth it. The long-term cost of ignoring connector hygiene is a fire risk that your homeowner insurance policy explicitly excludes in the fine print. Degradation curves don’t plot fires. They should.

When Not to Use This Approach

Rental Properties With Short Holding Periods

You're not keeping that duplex for thirty years. The yield play runs five years, maybe seven if the tax clock works right. Why map a 0.5% annual degradation curve when the panels will outlive your ownership by three ownership cycles? I have seen investors commission $2,000 panel-load degradation audits on a $180,000 flip. That money buys a new HVAC instead — which actually moves the rent. The ethical curve only matters if you plan to hand the system to someone who can't replace it. A landlord who sells before year eight hands the degradation problem to the next buyer, not to a grandchild. That sounds cold. It's also how the rental market works: capex follows hold time, not carbon guilt.

Small systems under 2 kW fall into a similar trap. The replacement cost for a string of four panels runs maybe $1,200 installed. Your monitoring software, inverter babysitting, and annual cleaning easily exceed that over a decade. One hailstorm and the whole math resets anyway. The catch is that degradation-curve optimization assumes the panels survive long enough to degrade. On small arrays the failure mode is rarely gradual — a branch falls, a microinverter fries, a tenant parks a truck through the rack. You're optimizing for a slow death when the system tends to die fast. Wrong order.

Locations With Extreme Hail or Wildfire Risk

I worked with a team in Colorado front range country. Hail there hits golf-ball size three Aprils out of five. They stopped buying premium Tier-1 monocrystalline panels because the degradation warranty was irrelevant — panels shattered before they aged. They bought cheaper polycrystalline with a higher degradation slope but lower replacement cost per watt. The math flipped: a 0.7% degradation curve means nothing if the panel gets replaced at year four anyway. That region's real degradation driver is not the cell chemistry. It's the weather report.

Wildfire zones create a similar blind spot. A panel that survives ten years of slow output loss can still be rendered useless by one season of ash loading and microcrack propagation from heat stress. The ethical posture — "design for 0.4% degradation so your grandkids inherit full output" — assumes the system is still standing. In fire-prone California, the more honest question is: will the structure itself survive long enough to make the degradation slope relevant? Most teams skip this because degradation curves feel scientific and fire risk feels actuarial. Both matter. The curve only matters when the roof stays intact.

Degradation ethics assume a future that includes the panels. If the building burns, your 0.3% slope was a luxury you never used.

— field engineer, Colorado wildfire rebuild, 2022

The hard rule: if your expected system lifespan (constrained by physical risk, not panel chemistry) is under twelve years, stop modeling degradation. Replace the panels when they break. Spend the analysis budget on surge protection, racking that vents ash, or a mounting system that tilts for self-cleaning. That hurts the purity of the legacy argument. But legacy requires something left to inherit. A spreadsheet full of degradation projections on a pile of melted silicon is just digital waste.

One concrete test: take your location's 1-in-10-year hail or fire probability, multiply your panel count by the replacement cost, and compare that to ten years of degradation-scenario maintenance. If the risk premium exceeds the degradation savings, drop the curve work entirely. I have seen teams waste six weeks debating whether to use 0.4% or 0.5% annual degradation in a region where 40% of residential systems get replaced early due to weather. That six weeks could have field-tested three mounting alternatives. Next time you face a storm-zone install, ask one question first: what kills panels here first — time, or the sky? Answer that before you touch a degradation table.

Open Questions and FAQ

What is the actual recycling rate for PV panels today?

Globally, the number sits somewhere under 10% for end-of-life panels. That's not a typo. The vast majority—silver, silicon, glass, and toxic trace metals like lead or cadmium—ends up in landfills or incinerators, not because recycling is impossible, but because the economics are still broken. I have watched a crew strip a 2010-era rooftop array just to rip the aluminum frames off and toss the laminated glass sheets into a dumpster. The frames paid out. The panels themselves were classified as "mixed waste" because the local recycler charged more per ton to separate the layers than the recovered materials were worth.

The catch is that recycling technology exists; it just costs two to three times what landfill tipping does in most jurisdictions. That gap is the ethical knot your grandchildren will inherit. You bought panels with a 25-year linear performance warranty, but nobody sold you a certificate that guarantees the recycling plant will accept them in 2049. The degradation curve of the panel is predictable. The degradation curve of the waste stream is not.

Not every free checklist earns its ink.

Not every free checklist earns its ink.

Most teams skip this: they model the kWh output over 25 years but never model the $0.10–0.15 per watt disposal fee that hits at year 26. That hurts.

Will future panels be backward compatible with mounts?

Short answer: probably not. The mechanical standards (mounting hole patterns, rail widths, clamp tolerances) have already shifted twice in the last decade. A panel from 2015 uses a 40mm frame profile with specific slot geometry. A panel from 2024 uses a 30mm frame, often with embedded microinverter clips or no frame at all in bifacial designs. The mounting hardware you install today locks your grandchildren into a specific physical interface. If the manufacturer shifts the rail spacing by 10cm in 2030, your entire roof geometry becomes orphaned.

Well, not entirely orphaned—adapter brackets exist. But adapters multiply cost and failure points. I have seen a racking system retrofitted with third-party clamps that introduced galvanic corrosion between the stainless steel bolt and the aluminum rail. The seam blew out after five years. That's the hidden inheritance: your grandchildren won't just inherit the panels' declining efficiency; they will inherit the mounting infrastructure's declining compatibility. Wrong order to think about. The mount outlives the panel, but the mount's design life assumes the panel shape never changes.

One fix we have used on legacy installations: install universal, modular rail systems with replaceable insert channels, rather than panel-specific brackets. It costs 15% more upfront. It saves a roof tear-off thirty years later.

'We're building monuments to our own assumptions about future hardware. The monument is a leaky roof.'

— Renovation contractor, after pulling a 1998 array off a barn that had no compatible replacement panels

How do you ethically dispose of panels you didn't buy?

This is the one that keeps me up. You inherit a house. The roof has solar. The inverter is humming, but two panels show microcracks from a hailstorm three owners ago. You didn't sign the original purchase agreement. You didn't take the federal tax credit. Yet the panels are physically yours now, bolted to your structure, wired into your breaker box. Do you rip them off and send them to the recycler—paying $200 out of pocket—or do you run them until they fail, then pay the disposal fee later? That sounds fine until you realize "run them until they fail" often means "let them leak lead into your soil."

The moral responsibility doesn't transfer cleanly. Legally, in most US states, the current property owner is liable for proper disposal of any fixture attached to the structure. Ethically, the original installer placed the panels with an implied promise of long-term stewardship—but that promise was never codified in the contract. I have seen families just leave dead panels on the roof because the cost to decommission and recycle exceeded the scrap value by $1,200. The panels sit there, silently generating zero watts, while the degradation curve of the remaining live panels continues its slow decline. Dead weight. Literal and figurative.

The next action: if you currently own panels, write a letter to yourself—or to the next owner—that includes the recycling contact, the estimated disposal cost at current rates, and the panel model number. Tape it inside the inverter enclosure. That single piece of paper, sealed behind the cover plate, will save your grandchildren a week of research and a pocketful of regret. Do it this weekend. The degradation curve of memory is worse than the one on your cells.

Summary + Next Experiments

Three questions to ask before buying panels

Pick any solar datasheet today. You will see a degradation curve—a neat line sliding from 100% to 80% over twenty-five years. That line assumes your grandchildren inherit a system that still works. Does it? Most buyers skip the fine print: the curve is a warranty floor, not a performance promise. The manufacturer guarantees the panel won't drop below 80%—but they don't guarantee it will stay at 92%. That gap is where your ethical obligation lives. You're selecting a degradation rate, not accepting one.

Ask this: what is the real-world degradation for this specific model after year ten? Not the lab number. Not the marketing slide. Look for data from the same climate zone—hot roof, coastal salt, heavy snow load. I have seen panels rated at 0.5%/year lose 0.9% in the first five years alone. The curve bent. The grandchildren got a surprise.

Second question: who owns the degradation risk after year twenty? If the warranty expires at year twenty-five and the system is still producing at 78%, you own that shortfall. Not the installer. Not the manufacturer. Your family inherits a diminishing asset. That sounds abstract until the inverter fails and the replacement cost eats two years of generation savings. Honest—I have watched teams install premium panels with 0.25% degradation simply because the homeowners asked this one question. They paid 12% more upfront. They will break even by year eighteen.

Third question: can the panels be economically replaced before they degrade below useful output? Most roofs are designed around the original array weight and wiring. Swapping panels in year twenty-five means re-racking, new conduit, often a structural review. That cost is invisible on the sales sheet. You're not just buying watts. You're buying a future decommissioning obligation. Ask for a twenty-year replacement estimate in writing. Most installers can't provide one. That's your answer.

One simple test for your current array's health

Stop guessing. Go outside at solar noon on a clear day. Check the current from each string using the inverter display or a clamp meter. Compare against the nameplate rating adjusted for temperature and irradiance. A string running 15% below its siblings is a red flag—not a normal dip. That's a degraded panel, a failed bypass diode, or a microcrack cluster. Do this quarterly. Log it. The trend matters more than the single reading.

I fixed a six-year-old system last month where the owner thought "80% after twenty-five years" meant his panels were still fine. His data showed one string at 63% of rated output. The degradation curve lied—not maliciously, but because it averaged all failure modes into a smooth line. Real panels fail in steps. A single storm, a manufacturing defect, a raccoon chewing the junction box seal—any of these can drop a string by 30% in one afternoon. The curve doesn't capture that. Your logbook does.

Where to find degradation data for specific models

Manufacturers publish warranty sheets. That's not data. For real numbers, check independent test labs that publish multi-year field studies—groups like the ones that do the PV module reliability scorecards. Search for "model number + degradation study" and look for papers with actual field measurements, not accelerated tests. Accelerated tests stress the panel with heat and humidity cycles; they predict some failure modes but miss others—like glass corrosion from salt spray or solder bond fatigue from wind vibration. Field data catches those.

Another source: your local utility or co-op. Large solar farms share anonymized degradation data as part of grid interconnection reports. It's public. You just have to ask. Most residential buyers never do. The catch is that utility-scale arrays use different racking and cleaning schedules than your roof. Adjust expectations accordingly. Still, the dataset is one of the few reality checks against the marketing curve. Compare your model's field degradation against the warranty line. If the gap exceeds 0.2%/year, consider a different panel.

A degradation curve is a promise written in pencil. The sun erases it faster than the manufacturer expects.

— field technician, after replacing a twelve-year-old string at 71% of nameplate

Next for you: pull the datasheet for any panel you're considering. Highlight the degradation warranty line. Then find one field study for that model in your climate zone. Compare them. If the difference is more than 0.3%/year, walk away. If you already own the system, run the clamp-meter test this weekend. Log the result. Repeat in three months. That single habit—measuring, not assuming—is the difference between leaving your grandchildren a burden and leaving them a gift.