Do I need to replace solar panels after 25 years?

Almost never. At typical degradation a 25-year-old panel still produces 85-90% of its original output and keeps working. You replace panels when they are physically damaged, when you want more capacity in the same area, or when the roof work makes it convenient — not because a warranty period ended.

How often do solar panels need cleaning?

In most climates, rain handles it and cleaning gains are small. It matters where there is heavy dust, pollen, bird activity or long dry spells, in which case soiling can cost several percent. Clean from the ground with a soft brush and water; never use pressure washers or abrasives, and never climb onto a wet or snow-covered roof to do it.

What is the most common reason a solar system underperforms?

Shading and soiling first, then wiring and connector faults, then inverter problems. Panel degradation is slow and predictable, so a sudden drop in output is never ageing — check for new shade, dirty modules, a tripped breaker or an inverter fault before suspecting the panels.

How Long Do Solar Panels Actually Last? Degradation Explained

Panels do not fail at 25 years — they fade at about 0.5% a year and keep working. What actually ends a system is usually the inverter, the roof or the wiring.

The 25-year warranty on a solar panel is not an expiry date. Panels rarely stop working; they slowly produce less, at a rate of roughly 0.4-0.5% a year, and a well-made panel is typically still delivering 85-90% of its original output after a quarter of a century. What fails first is almost always something else in the system.

What the two warranties actually promise

Warranty	Typical term	What it covers
Product warranty	10-25 years	Manufacturing defects — delamination, frame failure, junction box faults
Performance warranty	25-30 years	That output stays above a stated percentage, commonly 85-90% at year 25

The performance warranty is the one describing degradation, and it is a floor rather than a prediction. Most panels comfortably beat it.

The degradation curve

Two phases. There is an initial drop in the first year — light-induced degradation, typically 1-3% — and then a slow linear decline of about 0.4-0.5% annually.

Year	At 0.4%/yr	At 0.7%/yr
1	98%	97%
10	94%	91%
20	90%	84%
25	88%	81%
30	86%	77%

A 400W panel at year 25 is still producing about 350W. That is a meaningful decline and nowhere near a failure — which is why plenty of 1990s installations are still generating today.

What actually ends a solar system

The inverter. String inverters typically last 10-15 years and are the component you should budget to replace once during the panels' life. Microinverters generally carry 25-year warranties and last longer.
The roof. If the roof needs replacing at year 15, the array comes off and goes back on — a real cost, and the reason to re-roof before installing.
Connectors and wiring. MC4 connectors degrade under UV and thermal cycling, and a poor crimp becomes a hot spot years later. This is a common cause of mysterious output loss.
Physical damage. Hail, falling branches and someone walking on a module. Micro-cracks from mishandling during installation are the insidious version — invisible at first, showing up as degraded output years later.
The mounting. Corroded hardware or a failed roof penetration, which is a leak long before it is an electrical problem.

None of those is the panel. Budgeting for one inverter replacement is realistic financial planning; budgeting for panel replacement generally is not.

What accelerates degradation

Sustained high temperature — the single biggest factor, and an argument for mounting with airflow underneath
Thermal cycling in climates with large daily temperature swings
Humidity and salt air, which attack seals and frames — coastal installations should use panels rated for it
Micro-cracks from installation handling, hail or foot traffic
Persistent partial shading, which can cause hot spots on the shaded cells

What this means for the payback numbers

Degradation makes payback marginally longer than a flat calculation suggests, while historic electricity price inflation pulls in the other direction and usually wins. For a first-pass estimate the two roughly cancel, which is why our payback guide leaves both out and says so.

The more useful framing: a system paying back in six years and degrading at 0.5% a year still delivers around nineteen more years of nearly-free electricity. The decline is real and it is not what determines whether solar was worth it.