Two Warranties On One Solar Panel: What Each Covers

Why one panel carries two separate promises

A solar panel is unusual among household products in that it is both a physical object and a generator. Most things you buy are judged on whether they still work. A panel is judged on whether it still works *and* on how much it still produces — and those two questions have genuinely different failure modes.

Hardware faults tend to be discrete events: a delaminating laminate, a cracked frame, a failed junction box, water ingress where there should be none. They either happen or they do not, and they usually happen early if they are going to happen at all. Output, by contrast, declines gradually and predictably. Silicon cells lose a small fraction of their performance each year for perfectly ordinary physical reasons, and a well-made panel does this slowly and consistently across decades.

Because those are two different risks, manufacturers cover them with two different guarantees. The product warranty handles the event. The performance warranty handles the drift. Putting both under one number would mean either under-promising on output or over-promising on hardware, so the industry splits them — and the shorter of the two is almost always the product cover.

What the product warranty actually covers

The product warranty — sometimes called the materials and workmanship warranty — is the one that ends first. As RoboMo puts it in the episode, it is the cover on the panel as a thing: glass, frame, junction box, the bonded layers, the internal connections, the manufacturing quality.

In practice, it is the warranty you would lean on if a panel physically failed: moisture getting into the laminate, a junction box or bypass diode failing, backsheet or frame defects, or a manufacturing fault that stops the panel functioning as a panel. It is not a weather-damage policy and it is not an all-risks insurance — impact damage, storm damage and anything caused by poor installation or later alterations usually sit elsewhere, either with your installer's workmanship guarantee or your home insurance. That distinction matters, because people often assume one document covers everything on the roof. It rarely does.

The exact length of a product warranty varies by manufacturer and by panel model, and it has generally been getting longer as module construction has improved. The only reliable source is the datasheet and warranty terms for the specific product on your roof — not a sales brochure, and not a figure someone quoted you once.

Out of product warranty, still covered: what that means day to day

situation the episode is built around, and it is a real one on thousands of British roofs. The shorter bar has finished. The longer bar is still running. The panel is simultaneously "out of warranty" in one sense and "covered" in another.

What that means practically is this. If the panel physically fails after the product warranty has expired — a dead junction box, say — you are generally looking at a replacement at your own cost, or at whatever remedy your installer or supplier offers. But if the panel is still intact and functioning while producing measurably less than the guaranteed minimum for its age, the performance warranty may still apply.

It is also why the phrase "is it still under warranty?" is the wrong question to ask about a solar array. The better question is "which warranty, and for what?" One expired promise does not cancel the other, and a panel quietly outperforming its floor line for decades is the normal, boring, successful outcome — which is rather the point of a well-chosen module.

What British weather does to the output curve

There is a useful piece of engineering reality buried in all of this: solar panels generate more efficiently in cold weather than in hot weather. Panel efficiency falls as cell temperature rises, which is why a crisp, bright February afternoon can be a surprisingly flattering day for a UK array, while a still, sweltering July noon is working against its own efficiency curve.

That has two consequences for warranty thinking. First, the UK's temperate climate is comparatively gentle on modules — less brutal thermal cycling than hot, arid regions, which is one reason long performance terms tend to hold up well here. Second, it means a single day's reading tells you almost nothing about whether your panels are meeting their guaranteed minimum. Output on any given day depends on irradiance, temperature, soiling, shading and time of year. UK homes still produce useful power on overcast days, but comparing a damp November morning against a datasheet's lab-condition rating is not a measurement, it is a mood.

A genuine performance claim is assessed against standard test conditions, usually by testing a sample panel or by a properly instrumented comparison — not by squinting at your app in the rain.

Follow-up questions people ask

If my panel is out of product warranty, is it "at risk"? Not inherently. The expiry of a term is a contractual date, not a prediction about that specific panel. A module that has performed normally for years has already survived the period in which manufacturing faults usually show up.

Does the performance warranty cover a panel that has stopped completely? Generally, no — a total failure is a hardware matter, which is the product warranty's territory. The performance guarantee is about the level of output from a working panel.

Who actually pays for labour and access? This is one of the most important things to read in the terms. Manufacturer cover is frequently about the module itself; removal, access equipment, re-installation and testing may be treated separately. Clarify it at quotation stage rather than year fifteen. Does the inverter share these timelines? No. Inverters, optimisers and batteries each carry their own warranties on their own terms, and they are usually shorter than a panel's performance warranty. Treat each component's paperwork on its own merits. Does normal decline mean my savings collapse? No — the decline rates in modern performance warranties are deliberately gradual, which is why they can be guaranteed over such long horizons. The system you install is expected to be a long-lived asset that quietly fades, not a device that stops. Can I claim just because output looks low? Only against the warranty's own measurement basis. Low output is far more often explained by shading, soiling, a faulty inverter, a tripped string or seasonal weather than by panel degradation — so diagnosis comes before claims.

Video transcript

Mo: A panel has one warranty... doesn't it? RoboMo: Two. One on the hardware, a longer one on output.

Mo: So what actually ends first? RoboMo: The product cover — glass, frame, junction box. The output promise runs on.

Mo: So it can be out of warranty and still covered? RoboMo: Correct. Same panel. Two promises. One is still running. Mo: A panel has one warranty... doesn't it? RoboMo: Two. One on the hardware, a longer one on output. / Mo: So what actually ends first? RoboMo: The product cover — glass, frame, junction box. The output promise runs on. / Mo: So it can be out of warranty and still covered? RoboMo: Correct. Same panel. Two promises. One is still running.

Wrapping up

Two bars, one panel. The upper one covers the object and finishes earlier; the lower one covers the output and keeps running, with a declining curve that is meant to stay above a guaranteed floor for decades. Understanding that split changes how you read a quote, because it turns "how long is the warranty?" into two much better questions: how long is the hardware covered, and what output is guaranteed in which year? It also changes how you look after the system, because the longer promise is only worth as much as the paperwork and the performance history you can put behind it. Knowledge beats marketing here, as usual — the warranty terms are the engineering talking, and they are freely available on every reputable datasheet. Read them before you sign, file them once, and the panel on your roof can comfortably outlive the first of its two promises while the second carries on doing its job.