Solar panels usually keep generating for 25 to 30 years, and often longer, losing only about half a percent of their output each year. They do not stop dead at some expiry date; they fade slowly, and a panel fitted today will very likely still be producing most of its power when it is old enough to vote twice over. The part you are more likely to replace along the way is the inverter, not the panels. This guide sets out what actually wears out, how much output you lose to age, and whether any of it changes the case for fitting solar at all.
The short answer. Expect the panels themselves to last 25 to 30 years or more, degrading by roughly 0.3% to 0.5% a year, so after 25 years they still make around 85% to 90% of what they made when new. The inverter typically lasts 10 to 15 years and will probably need replacing once over the panels' life, at something like £800 to £1,500. None of this dents the payback much, because most systems pay for themselves in well under half their working life.
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Lifespan and what the warranty really promises
Solar panels come with two separate warranties, and it pays to know which is which. The product warranty covers the panel against manufacturing faults and physical failure, and runs anywhere from 10 to 25 years depending on the maker. The performance warranty is the interesting one: it guarantees the panel will still produce at least a stated share of its original output after a set time, commonly around 85% to 87% at year 25, with some premium panels promising 90% or more.
Read that carefully, because it tells you the maker expects the panel to still be working hard after a quarter of a century. Panels have no moving parts, which is the root of their long life. There is nothing to wear against anything else, no bearings, no pump, nothing that spins. They just sit on the roof turning light into electricity, and the main thing that happens to them over the years is a slow, gentle fade.
Degradation: how much output you actually lose
That fade is called degradation, and for a decent modern panel it runs at about 0.5% a year, with the better ones closer to 0.3%. The first year sometimes sees a slightly larger drop as the cells settle, then it flattens into that steady annual decline. It is small enough that you would never notice it year to year, but it does add up over decades.
| Age | Output at 0.5%/yr | Output at 0.3%/yr |
|---|---|---|
| Year 1 | 100% | 100% |
| Year 10 | ~96% | ~97% |
| Year 20 | ~91% | ~94% |
| Year 25 | ~88% | ~93% |
Put that in kilowatt hours. Take an example 4kWp system that generates around 3,600 kWh in its first year on a typical British roof. At 0.5% a year, by year 25 it is still making roughly 3,170 kWh, about 88% of where it started. Across the whole 25 years it would produce somewhere near 85,000 kWh in total, only a few percent below what a panel that never aged would have made. You can model output for your own roof with the solar output calculator, and turn it into a payback estimate with the payback calculator.
Percentages are illustrative and rounded, based on steady annual degradation of 0.5% and 0.3%. Real figures vary by panel and by year-to-year weather.
The inverter is the part that wears out first
If anything on a solar system needs replacing during its life, it is almost always the inverter, the box that converts the panels' direct current into the alternating current your home uses. Inverters work hard, run warm and contain electronics that age faster than glass and silicon do. A string inverter typically lasts 10 to 15 years, so over a 25 to 30 year panel life you should budget for replacing it once, at somewhere around £800 to £1,500 fitted depending on size.
There are two other layouts. Microinverters or power optimisers sit under each panel rather than in one central box, and often carry longer warranties of 20 to 25 years, though replacing one means getting up on the roof. A hybrid inverter, the type used when you add a home battery, handles both the panels and the battery and follows similar lifespans. Whichever you have, treat one inverter replacement as a normal, expected cost of owning solar rather than a nasty surprise.
What actually fails, and what rarely does
In practice the panels are the reliable part. What causes most solar callouts is everything around them. The inverter, as above, is the usual culprit. After that come the small things: a failed isolator switch, a corroded or loose connector, water getting into a junction box, or bird muck and nests building up under the array and shading cells. Physical damage from a falling branch or a stray football can crack a panel, though the glass is toughened and this is uncommon.
Roof problems can masquerade as solar problems too. If the mounting was done poorly, a leak around the fixings shows up years later as a damp patch, which is a roofing fault rather than a fault with the panels. Choosing a certified installer and keeping the roof itself in good order heads off most of that. The panels themselves failing outright, within their warranty and through no external damage, is genuinely rare.
Does the lifespan change the payback sums?
This is what most people are really asking. A domestic solar system in the UK typically pays back its upfront cost in around 8 to 12 years, depending on the system size, what you paid, how much you use during daylight and your export rate, as set out in is solar worth it. Set that against a panel life of 25 to 30 years and the picture is straightforward: after the system has paid for itself, you get well over a decade of near-free generation on top.
Slow degradation does not wreck that, because losing a few percent of output over 25 years is a small dent next to a payback that arrives at the one-third mark. Even factoring in one inverter replacement, the maths comfortably survives. Winter output is lower than summer, of course, which is a seasonal pattern rather than ageing, and it is covered in do solar panels work in winter. The one thing that changes the sums more than age is what you do with the power: using it yourself or storing it beats exporting it, as the Smart Export Guarantee guide explains.
Keeping them going for the long haul
Solar needs very little looking after, which is part of the appeal. Rain does most of the cleaning, and on a pitched roof panels rarely need more, though flatter arrays or panels under trees can collect grime and dropped leaves that cut output, covered in solar panel cleaning and maintenance. The habit that matters most is watching the numbers: check the inverter display or its app now and then, and if generation drops off a cliff rather than fading gently, something has failed and is worth investigating. Keep your paperwork, register the warranties, and note when the inverter was fitted so you are not caught out when its time comes.
When it is worth thinking about replacement
Three situations bring replacement into view. The first is a genuine fault, where output falls sharply rather than slowly, which usually points at the inverter and often means replacing that one part rather than the whole array. The second is a re-roof: if the roof needs stripping, it can make sense to take the panels down and put newer, more powerful ones back up while the scaffolding is there. The third is simply wanting more capacity, in which case modern panels pack more watts into the same space, so you may fit fewer of them for the same or greater output. Barring those, a working solar array is best left alone to quietly earn its keep for decades. For the wider picture, start with solar panels: the basics.