Product warranty
This covers defects in the physical product or manufacture, subject to the manufacturer's terms and exclusions.
Think of this as: “Is the panel itself defective?”
Solar lifespan and warranties explained
How long do solar panels actually last?
Twenty-five years? Thirty years? Forty?
The confusing part is that warranty length, expected service life and the point at which a panel becomes uneconomic are three completely different things.
The short answer
A good solar panel should be thought of as a decades-long asset.
Solar photovoltaic modules have no engine, gearbox, pump or other rotating machinery.
That is one reason they can remain operational for a very long time.
They do, however, age.
Electrical output normally declines slowly as decades of sunlight, temperature changes, moisture, wind and weather affect the materials.
Ageing normally means “slightly less electricity each year” — not “working today, dead tomorrow”.
That distinction is crucial when discussing the real useful life of a solar array.
Tom Solar visual guide
Warranty milestones are not the same thing as panel death.
The biggest misunderstanding
“25-year warranty” does not mean “25-year lifespan”.
A warranty is a contractual promise.
A lifespan is how long the physical equipment remains safe and useful.
They are related, but they are not the same thing.
A panel can be outside warranty and still be producing useful electricity every day.
Equally, equipment can sometimes fail during a warranty period.
That is why both product quality and the strength of the warranty provider matter.
Two different warranties
Product warranty and performance warranty protect different things.
Performance warranty
This promises that the panel will retain at least a specified proportion of its original rated output at defined points in time.
Think of this as: “How much power should it still be capable of producing?”
A 30-year performance warranty is not automatically better than every 25-year warranty.
Compare the actual retained-output guarantee, exclusions, claim process, labour coverage, manufacturer backing and who is responsible for replacing a failed module.
Degradation
Solar panels slowly lose some of their ability to convert light into electricity.
This gradual loss is known as degradation.
A large NREL review of published field data found a median degradation rate around 0.5% per year across the technologies and systems studied.
More recent NREL field work has shown that some modern module types can perform materially better than that, while others can degrade faster.
There is no honest universal degradation number for every panel.
The correct figure for a proposed system should come from the specific module's warranted degradation curve and technical data.
What degradation looks like
A 10kWp array does not suddenly become a 5kWp array because it gets old.
Imagine a system beginning life with a particular rated capacity.
Over time, each module may become slightly less capable of producing its original maximum power under the same test conditions.
After decades, the system may still retain a substantial majority of its original output.
Degradation is normally a slope, not a cliff.
That is why an older solar array can remain economically useful even though it is no longer performing exactly as it did when new.
What physically ages?
A module spends decades outdoors in one of the harshest places on the property.
Thermal cycling
Panels repeatedly heat in sunlight and cool overnight, expanding and contracting materials thousands of times.
UV exposure
Decades of ultraviolet radiation can gradually affect polymers, encapsulants and other materials.
Moisture
Failed seals or material deterioration can allow moisture to contribute to corrosion and electrical problems.
Mechanical stress
Wind, snow, transport, installation and roof movement can place repeated mechanical stress on modules.
Cell and interconnection faults
Microcracks, damaged interconnections and hot spots can reduce module performance or create localised problems.
Junction-box and wiring issues
Connections, connectors, cables and junction boxes are also exposed to years of outdoor operation.
What normally needs replacing first?
Often the inverter — not the panels.
The inverter contains far more active electronics than a photovoltaic module.
It continuously converts power, monitors the grid and manages the array.
Energy Saving Trust currently advises homeowners that solar inverters typically need replacement roughly every 10–15 years.
A 30-year solar ownership plan should therefore allow for inverter replacement.
That does not mean every inverter fails at year 10, or survives until year 15. It is a sensible lifecycle cost to recognise.
What about the battery?
Battery life should not be confused with panel life either.
A lithium home battery is an electrochemical storage device.
Its ageing process is completely different from a solar panel.
Battery warranties may be expressed using:
years;
cycles;
energy throughput;
retained usable capacity;
or a combination of these.
Do not advertise the life of the solar panels as if every other component automatically lasts just as long.
Panel, inverter and battery warranties should all be considered separately.
Does year 30 mean replace the roof?
Not if the system is safe, productive and economically useful.
An ageing system should be assessed rather than condemned by calendar.
Useful questions include:
Is generation broadly consistent with what its age and weather would suggest?
Are the modules physically intact?
Are mounting equipment and roof fixings still sound?
Are cables and connectors in good condition?
Is the inverter operating reliably?
Are replacement components still available?
If the answer is yes, continuing to generate may make far more sense than replacing equipment simply because a warranty date passed.
The existing equipment has already been manufactured, transported and installed. Keeping functioning assets productive can have real value.
When replacement can make sense
Age alone is a weak reason. A combination of problems is much stronger.
Repowering an older system may become attractive when several factors come together:
significant unexplained degradation;
repeated module or electrical faults;
obsolete inverter technology;
difficulty obtaining compatible replacement parts;
roof work already requires the array to be removed;
or modern modules could substantially increase useful capacity on
limited roof space.
Replacement should solve a real problem.
“Your panels are old” by itself is not a particularly sophisticated engineering argument.
Monitoring
Your generation history becomes extremely valuable as the system gets older.
Solar output changes naturally from year to year because weather changes.
But long-term monitoring can still reveal unusual performance loss.
Useful comparisons include:
annual generation against previous years;
similar months against one another;
individual MPPT or string behaviour where monitoring allows;
inverter warnings and fault history;
and unexpected changes not explained by shading or weather.
A sudden 20% loss is not “normal half-a-percent ageing”. Investigate it.
Installation quality matters
A 30-year panel deserves a 30-year-quality installation around it.
Long module warranties are less impressive if the surrounding installation fails prematurely.
The system also relies on:
roof hooks and mounting rails;
correctly torqued electrical connections;
weather-resistant cable management;
compatible DC connectors;
appropriate ventilation around electronics;
sound roof waterproofing;
and accessible documentation.
Longevity is a system-design issue, not merely a panel-brand issue.
A superb module cannot compensate for poor workmanship everywhere else.
What should you compare?
A long warranty headline is only the beginning.
| Question | Why it matters |
|---|---|
| How long is the product warranty? | This relates to defects in the physical module. |
| How long is the performance warranty? | This tells you how long the output guarantee runs. |
| What output is actually guaranteed? | Two 30-year warranties can promise different retained performance. |
| Is labour included? | A replacement module is less useful if removal and refitting costs fall entirely on the homeowner. |
| Who stands behind the warranty? | The warranty only has practical value if the responsible manufacturer or provider remains able to honour it. |
| Are there servicing or registration conditions? | Missing required paperwork or maintenance may affect a future claim. |
Buying a house with older solar
Ten-year-old panels are not automatically a liability.
When buying a property with an existing array, establish:
installation date;
original MCS documentation;
panel make and model;
inverter make, model and age;
remaining warranties;
historic generation where available;
ownership arrangements;
and whether any export or legacy tariff rights transfer.
A specialist inspection can then assess whether the system remains safe and productive.
An older paid-for solar system producing useful electricity can be an asset, not a problem.
Manufacturer strength
A 30-year promise is only as useful as the organisation standing behind it.
Solar warranties extend over unusually long periods.
That makes manufacturer durability relevant.
When comparing products, it is reasonable to consider:
manufacturer history;
financial resilience;
UK warranty support;
claims process;
insurance or third-party backing where applicable;
and availability of replacement equipment.
A spectacular warranty printed on a brochure has little value if nobody is there to honour it.
Warranty quality is about backing and terms as well as the number of years printed in large type.
Frequently asked questions
Solar-panel lifespan answered simply.
How long do solar panels actually last?
There is no fixed expiry date. Well-made modules are designed for service measured in decades and can remain useful after 25 or 30 years, although output gradually declines.
Do panels stop working after 25 years?
No. Twenty-five years is commonly a warranty milestone, not an automatic failure date.
What is a performance warranty?
It promises a minimum retained electrical-output level over a specified period, subject to the manufacturer's terms.
What is a product warranty?
It covers eligible faults or defects in the physical module for a defined period.
How quickly do solar panels degrade?
It varies. Historical field research has found central values around 0.5% per year, while some modern module technologies show lower degradation. Use the specific panel's warranted figures when assessing a proposal.
Does a 30-year warranty mean replacement in year 31?
No. The module may continue producing useful electricity for years after its performance-warranty period ends.
What usually needs replacement first?
Often the inverter. Energy Saving Trust currently gives roughly 10–15 years as a typical replacement interval for domestic solar inverters.
Should old panels automatically be replaced?
No. Condition, safety and actual performance should determine the decision rather than age alone.
What damages panels over time?
Potential issues include moisture, thermal cycling, UV exposure, corrosion, cell cracking, delamination, electrical faults and severe physical damage.
Can I tell if my system is degrading too quickly?
Long-term monitoring can reveal unexplained changes in output, although normal weather variation must be considered.
Can an old system still save money?
Yes. As long as it is generating useful energy safely, it can continue reducing grid imports or earning export income.
Should I buy whichever panel has the longest warranty?
Not automatically. Compare the actual terms, degradation promise, product quality, manufacturer backing and installation quality too.
Evidence checked
Solar-panel life is measured in decades — but there is no magic universal expiry date.
This homeowner guide was reviewed against current information including:
- Energy Saving Trust — Buying a House with Solar Panels, May 2026.
- Energy Saving Trust — Solar Panel Cleaning and Maintenance, 2026.
- National Renewable Energy Laboratory — Photovoltaic Degradation research.
- NREL — PV Lifetime Project field-performance research.
- US Department of Energy — PV system lifespan, maintenance and end-of-performance guidance.
Degradation and warranty conditions vary substantially between products. Manufacturer datasheets, warranty documents and property-specific inspection findings take precedence over the general examples in this guide.
Related Tom Solar guides
Understand the equipment around the panels too.
Tom Solar view
Buy a system that deserves to be on the roof for decades.
Solar is unusual because today's buying decision may still be affecting the property in the 2050s.
That makes chasing the cheapest panel on quotation day a very narrow way to make the decision.
Look at:
module quality;
degradation guarantee;
product warranty;
manufacturer backing;
installation workmanship;
inverter replacement expectations;
and the quality of the overall system design.
The goal is not to own a panel with an impressive warranty certificate.
The goal is to own a well-designed solar system that is still producing useful electricity many years after the installation invoice has been forgotten.