Solar modules come with two different guarantees. The product guarantee covers material and manufacturing defects – the module itself breaks. The performance guarantee assures that the module will still deliver a certain minimum percentage of its initial output after many years – so it protects against aging too quickly. Both numbers are in the data sheet, and you should know both before you sign. (As of: July 2026)
Key points in brief
- Product guarantee: protection against defects, material and manufacturing flaws on the module itself.
- Performance guarantee: assurance of a minimum output after many years of operation – against degradation that is too fast.
- The performance guarantee usually runs significantly longer than the product guarantee.
- Longer and higher guarantees are a signal of quality – but only worth as much as the manufacturer behind them.
- A guarantee is not an yield promise: it assures minimum values, not a specific annual production.
Two guarantees, two different promises
Anyone reading a module data sheet comes across two guarantee specifications – and they mean fundamentally different things. Knowing this distinction is half the battle for a good module comparison.
The product guarantee concerns the module as an object: it applies if the module itself has a material or manufacturing defect – delamination, a defect in the encapsulation, a manufacturing flaw. It is the classic guarantee in the sense of «if the thing breaks».
The performance guarantee, on the other hand, concerns production over time: it assures that the module will still deliver at least a certain percentage of its original output after a certain number of years. It is the manufacturer's response to the natural aging of the modules – a promise that this aging will not exceed an assured extent.
How does the performance guarantee work?
Every solar module slowly loses power over the years – this is normal and unavoidable, but the degradation is well under one percent per year. The performance guarantee sets a lower limit: it states a starting value, an annual maximum loss, and a guaranteed residual value after many years. Market-standard today are assurances of around 87 to over 90 percent of the initial output after 25 to 30 years – this corresponds to guaranteed degradation rates of about 0.3 to 0.4 percent per year for current top modules (as of: July 2026). If a module falls below this curve, the guarantee applies.
The practical benefit is planning security: you know what minimum output you can still expect even after decades. The important reservation to this: the performance guarantee is a lower limit, not an yield promise. It says how much the module can at least still achieve – not how many kilowatt-hours your roof will produce in a specific year. That depends on weather, orientation, and shading, and is a completely different question. Anyone who confuses the two reads a promise into the guarantee that it does not give.
The difference at a glance
| Product guarantee | Performance guarantee | |
|---|---|---|
| Protects against | Material and manufacturing defects | Power aging that is too fast |
| Relates to | The module as an object | Production over time |
| Typical term | Usually 10–15 years, with premium manufacturers 25–30 | Mostly 25–30 years |
| Applies when | The module is defective | The output falls below the assured curve |
Simplified comparison with market standard guide values, as of: July 2026. The specific guarantee conditions of the manufacturer are decisive.
Both guarantees are in the data sheet, and a reputable quote details them. If one of the two specifications is missing or remains vague, it is worth asking – the guarantee is a part of what you pay for.
What should you look out for with guarantees?
Three things separate a strong guarantee promise from a nice-sounding one.
The term and the guaranteed residual value. Longer terms and higher guaranteed residual values after many years are a signal of quality: they show how much confidence the manufacturer has in its product. The more robust glass-glass construction, for example, often comes with longer performance guarantees.
The manufacturer behind it. A guarantee is only as good as the company that is supposed to redeem it in an emergency – over decades. A 30-year guarantee from a manufacturer that might not exist in ten years is worth less than a slightly shorter promise from an established provider. This assessment flows into the choice of components and provider.
The processing. In the event of a warranty claim, what counts is how uncomplicated the replacement is – and who organises it. Exactly here the value of a regional specialist company shows: it is the point of contact who handles the guarantee with the manufacturer, instead of leaving you alone with a data sheet. Seamless documentation of the system, as belongs to proper operation, shortens any guarantee discussion.
A final thought on classification: the inverter has its own, shorter guarantee and service life periods – module guarantees say nothing about it. Anyone wanting to understand the coverage of the whole system looks at the module and inverter separately.
«30 years guarantee» is on many a brochure, and the number impresses – rightly so, if you know what it means, and with caution, if not. We take the two guarantees apart in the consultation: the product guarantee is the protection in case the module itself has a defect; the performance guarantee assures that it still performs enough after many years. And then we say the sentence that grounds the euphoria: a guarantee is only as good as the manufacturer who can still redeem it in twenty years. We therefore do not choose modules according to the largest number on paper, but according to the combination of a solid promise and a manufacturer who will probably still be there when it counts. And we add that the guarantee is a lower limit, not a yield promise – how much the roof produces next summer is not in any guarantee document.
Frequently asked questions
What is the difference between product and performance warranty?
The product guarantee protects against material and manufacturing defects on the module itself – if the module breaks. The performance guarantee assures that the module will still deliver a certain minimum percentage of its initial output after many years – it protects against aging too quickly. Both are in the data sheet.
Why does the performance guarantee run longer than the product guarantee?
Because it covers different things: the product guarantee concerns defects that typically occur early, if at all; the performance guarantee accompanies the slow aging over the entire service life of the modules. Therefore it extends over significantly more years.
Is a longer warranty automatically better?
Longer and higher guarantees are a signal of quality, but only worth as much as the manufacturer behind them. A very long guarantee from an insecure provider can be worth less than a slightly shorter promise from an established one. Look for the combination of guarantee and solidity of the manufacturer.
Does the performance guarantee mean that my roof delivers a specific amount of electricity?
No – that is a common misunderstanding. The performance guarantee is a lower limit for the module output, not a promise about the annual production. How many kilowatt-hours your roof delivers depends on weather, orientation, and shading, and is a different question than the guarantee.
Who processes a warranty claim?
In practice, your specialist company: it is the point of contact who clarifies the case with the manufacturer and organises the replacement. Seamless documentation of the system helps with this. That is exactly why an accessible, regional company is worth more in a warranty claim than the cheapest provider without after-sales service.
Free initial consultation
Guarantees that keep what they promise.
We select modules according to guarantee and manufacturer solidity, show both guarantees in the quote – and are your point of contact in a warranty claim, not just a data sheet.
Prefer to talk? +41 78 830 83 35
Have a photovoltaic system installed →
Swissolar-certified specialist company · ESTI installation authorisation (Art. 14 NIV) · in Zurich since 2017 · over 150 systems completed · a personal answer from the specialist company, no call centre
Sources: Manufacturer data sheets and guarantee conditions of current module manufacturers (market standard terms and residual power values, as of: July 2026); Swissolar; empirical values from the planning and service practice of ecoEn GmbH, Zurich region.
Last updated: 9 July 2026 · Author: ecoEn editorial team
