How panels age
Panels degrade by roughly 0.4% to 0.5% of output a year, and manufacturers warranty the curve: a typical performance warranty guarantees around 85% of original output at year 25. Product warranties on the panels themselves commonly run 12 to 25 years depending on the maker.
In the UK's rainy climate, panels at a reasonable pitch are largely self-cleaning, and for most roofs professional cleaning is an occasional cosmetic choice rather than a maintenance requirement. The exceptions are shallow pitches, heavy tree pollen or bird traffic, and coastal salt spray, where an occasional clean genuinely recovers output.
The inverter: the one real mid-life cost
The inverter converts the panels' DC into household AC, works hard all day, and is the component that wears. String inverters typically last 10 to 15 years against the panels' 25 or more, so most systems buy one replacement inverter in their life; several hundred pounds to around £1,000 fitted is the usual range. Inverter warranties run about 10 to 12 years as standard, and some makers sell extensions that are worth pricing at installation.
Batteries, where fitted, age like the inverter rather than the panels: ten to fifteen years of useful life, warrantied by cycles or throughput as well as years. The maths of whether one belongs in your system at all is covered in is a solar battery worth it.
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Watch the generation figures, because the app is your early-warning system: a sudden drop, or one string underperforming its twin, is how faults announce themselves. Once a year, glance at the visible kit: panels for debris or damage, the roof line for slipped fixings, the inverter for warning lights, and the isolators for anything scorched or weathered.
Keep the paperwork together: the MCS certificate, warranties and commissioning records, because export payments and warranty claims both lean on them. A professional electrical inspection every four to five years is cheap insurance. None of this changes the headline: over 25 years, a well-installed system mostly just works, which is why the installation quality you buy up front, from MCS-certified installers you have compared properly, matters more than anything you will do afterwards.
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