Degradation and warranties at 5, 10 and 20 years

The question always turns up in the after-dinner stage of the decision, once you've seen numbers and liked them: "but how long does this last?". It's THE right question, because it determines whether panels are an expense or an investment.

The short answer is reassuring: a long time, and predictably so. The complete answer (what ages, by how much, and who signs which document) is this article, because you'll need it both to buy well and to claim well.

A solar panel has no moving parts. It doesn't wear out like an engine or run down like a phone battery. What it does is lose efficiency very slowly: each year it generates a fraction of a percentage point less than the one before.

That process is called degradation, it's normal, it's been studied and, this is the important part, it's guaranteed in writing: manufacturers commit to the panel still delivering a minimum percentage of its original output at 25 or 30 years, with intermediate values year by year. The exact figure is on your panel's datasheet. It's one of the few products you buy with the ageing curve signed.

In practice: at 20 years your system will still be generating the great majority of what it generated when new. It doesn't die of old age at 10. It reaches 25 a little weaker, and will probably keep going after that.

Here's the knowledge that prevents 90% of the confusion in a claim. Different warranties coexist in your installation, from different parties, with different durations:

The panels' performance warranty. The degradation one, just described. It's the longest: 25 to 30 years depending on manufacturer. It covers the panel generating what's promised for its age. It does not cover breakage.

The panels' product warranty. Covers manufacturing defects: premature failure, delamination, internal problems. It's shorter than the performance warranty, typically on the order of 10 to 15 years depending on manufacturer, and it's the one invoked if a panel fails, not if it ages.

The inverter's warranty. And here's a truth we'd rather tell you before you discover it: the inverter is the component you'll probably replace during the system's life. It works hard every day, it's power electronics, and its expected life is shorter than the panels'. Its warranty is usually on the order of 5 to 10 years, sometimes extendable for a fee. A replacement in year 10 or 12 isn't a failure of the project: it's part of the long-term plan, and it's worth bearing in mind.

And the fourth, which isn't from the factory: the installation warranty. The work (fixings, cabling, roof watertightness, distribution board) is warranted by your installer, for the term agreed in writing. A leak from a badly sealed anchor isn't the panel manufacturer's problem: it's the problem of whoever mounted it.

Have batteries? They add their own warranty, measured differently (by years or by energy cycled, whichever comes first) and deserving of a separate article.

At 5 years: the system generates practically as when new; accumulated degradation is only a few points. Everything under warranty. If something failed before this point, it was a defect or the installation, not ageing, and the warranties cover it.

At 10 years: generation is still excellent. Attention shifts to the inverter: depending on brand and luck, it may be reaching the end of its warranty or its life. If it has to be replaced, it's a real but contained expense against what's already been saved. And the inverters of that time will be better than the one they replace.

At 20 years: the system is a productive veteran. It generates the great majority of its original capacity, the panels are still within their performance warranty, and the project paid for itself years ago. Everything it generates from here on is profit with the wind behind it.

• Ask for the warranty sheets for panel and inverter: real years and conditions, not the verbal summary
• Ask who honours it in Argentina: is there local representation or does the claim travel alone?
• The installation warranty in writing, with scope and years
• The serial numbers documented on handover: without them, the warranties are theoretical
• Mentally budget for a new inverter at some point in the first-to-second decade

And a final reassurance, which is the honest summary of the topic: in this industry, ageing is the most predictable part of the project. It's measured, it's guaranteed by contract, and it's slow. Of everything you weighed up in deciding, how long the panels last is, paradoxically, the least uncertain of all.