Solar Panel Degradation Rate Explained

What is solar panel degradation?

Solar panels lose a little output every year. That slow, permanent decline in how much power a panel can produce is called degradation, and it's normal, predictable and built into every manufacturer's specifications. A panel rated at 400 watts when new will produce slightly less each year, not because anything has broken, but because the materials inside age under sunlight, heat and weather.

The key number is the annual degradation rate — the percentage of output a panel loses per year. It is small, but it compounds over decades, so it matters for any honest estimate of lifetime production. This guide explains typical rates, what your warranty actually guarantees, what causes the decline, and how to tell genuine degradation apart from temporary problems like dirt or shade.

Typical degradation rates

Degradation isn't uniform across a panel's life. It happens in two phases:

• First year (LID): Panels lose more in year one — usually 1–2% — due to light-induced degradation (LID), a one-time settling that happens when silicon is first exposed to sunlight.
• Every year after: From year two onward the rate is far lower and steady, typically 0.4–0.7% per year for standard panels.
• Premium panels: High-quality modules (often with better cell technology and warranties) degrade more slowly, around 0.25–0.3% per year.

Put together, a standard panel might sit at roughly 85–88% of its original output after 25 years, while a premium panel can still deliver 90–92% or more. The decline is gradual and quiet — you won't notice it month to month, only across many years.

What the performance warranty guarantees

Almost every panel comes with two separate warranties. The product warranty (typically 10–25 years) covers defects. The performance warranty (usually 25 years, sometimes 30) is the one that addresses degradation: it guarantees the panel will still produce at least a stated percentage of its nameplate rating at a given year.

A common guarantee is something like at least 85–92% of nameplate output at year 25. Premium manufacturers often promise the higher end and a gentler annual curve. If your panels fall below the guaranteed line and it's genuine degradation (not damage or soiling), you have a warranty claim. This is closely tied to how long panels last — but lifespan is about when you replace the panel, while degradation is about the gradual output decline along the way.

What causes degradation

Several mechanisms slowly age a panel:

• UV exposure and LID: Sunlight triggers the initial first-year drop and continues to slowly affect the cells and materials over time.
• Thermal cycling: Daily heating and cooling expands and contracts the panel, stressing solder joints and connections.
• Microcracks: Tiny fractures in the silicon cells — from manufacturing, transport, installation or hail — can grow and reduce output.
• PID (potential-induced degradation): Voltage stress between the cells and the frame can leak current and sap performance, especially in poorly designed or grounded systems.
• Encapsulant ageing and delamination: The polymer layers that seal the cells can yellow or separate, letting in moisture and reducing light transmission.

Better manufacturing, robust cell technology and good installation all slow these processes down, which is why premium panels degrade less.

How to slow degradation

You can't stop ageing, but you can avoid accelerating it:

• Buy quality: A panel with a low published degradation rate and a strong performance warranty is the single biggest lever.
• Insist on good installation: Proper handling avoids microcracks; correct grounding and quality inverters reduce PID risk.
• Keep panels cool and ventilated: Adequate air gap behind roof-mounted panels limits heat stress.
• Address damage promptly: A cracked or shaded panel can drag down a whole string, so fix faults early.

Degradation vs soiling and faults

This is where many homeowners get confused. If your production drops noticeably and suddenly, it is almost certainly not degradation — real degradation is a fraction of a percent per year, invisible over short periods. A sudden or seasonal drop usually means something else:

• Soiling: Dust, pollen, bird droppings or snow on the glass. This is temporary and reversible — a clean or some rain restores output.
• Shading: A growing tree, a new structure or seasonal sun angles cutting across the array.
• Faults: A failing inverter, a tripped breaker, a disconnected string or a damaged panel.

The way to tell them apart is production monitoring: true degradation shows up only as a slow, year-over-year trend after you've accounted for weather, while soiling and faults appear as abrupt or recoverable dips. If output falls off a cliff, look for dirt, shade or a fault first — not degradation.

FAQ

What is a normal solar panel degradation rate? About 0.4–0.7% per year for standard panels after a 1–2% first-year drop, and around 0.25–0.3% per year for premium panels.

How much output will I lose after 25 years? A standard panel typically retains 85–88% of its original output; a premium panel often holds 90–92% or more.

Does the warranty cover degradation? The performance warranty does — it guarantees a minimum output (often 85–92% of nameplate) at year 25. Damage and soiling are not degradation.

Why did my production suddenly drop? Sudden drops are not degradation. Check for dirt, snow, shading or an inverter or wiring fault.

Bottom line

Solar panel degradation is real but small and predictable: a 1–2% dip in year one, then roughly half a percent a year, leaving most panels above 85% of their original output after 25 years. Premium modules do even better. Buy quality, install it well, monitor production, and you'll know that any sharp drop is a fault or soiling — not ageing. For the bigger picture, see how long panels last and the difference between panel types.

Last updated June 2026. Informational only — degradation rates and warranty terms vary by manufacturer and model; check your panel's datasheet and warranty document.