Solar Panel Degradation: How Much Power Will You Really Have in 25 Years?

Every solar proposal projects decades of savings — but panels don't produce the same amount forever. They degrade. Understanding the real numbers protects you from both over-optimistic sales projections AND needless worry.

## What degradation actually is

Solar panels slowly lose output as the photovoltaic material ages from UV exposure and heat cycling. It's gradual, predictable, and far slower than most people fear.

## The real numbers

- **Year 1:** panels typically drop ~1-2% (initial "light-induced degradation," then it stabilizes) - **Years 2-25:** roughly **0.4-0.55% per year** for quality Tier-1 panels - **At year 25:** a good panel still produces **86-92%** of its original rating

So a 410W panel producing 410W today produces roughly 360-377W at year 25. You lose output, but you keep the large majority of it.

## What the warranty actually promises

This is where panel brands differ and where it matters:

| Brand | 25-yr power warranty (min output at yr 25) | |---|---| | REC Alpha | 92% | | QCells Q.Peak | 86% | | Silfab | 86% | | Trina Vertex | 87% | | Generic Tier 2 | often 80% or unstated |

A "linear power warranty" guarantees the panel will produce at least X% of rated output at year 25, declining on a straight line. REC's 92% is industry-leading; the 86-87% of QCells/Silfab/Trina is standard and perfectly fine.

**Avoid panels with an 80% (or unstated) warranty** — that's a tell for lower-tier equipment.

## How it changes your savings math

Here's the honest part most proposals gloss over: their "25-year savings" number should account for degradation, but many use year-1 production for all 25 years, overstating savings.

Realistic adjustment: over 25 years, average production is roughly **93% of year-1** (because you're declining linearly from 100% to ~87%). So if a proposal claims $94,000 in lifetime savings using flat year-1 output, the degradation-adjusted figure is closer to $87,000. Still excellent — just not the inflated headline.

## What degradation does NOT mean

- **It doesn't mean panels "die" at 25 years.** They keep producing well past 25 — just below the warranty floor. Many 1990s panels are still running at 80%+ today. - **It's not sudden.** No cliff. It's a slow, linear glide. - **Inverters fail before panels do.** Your microinverters/optimizer (10-25 yr warranty) or string inverter (10-12 yr) will likely need replacement once during the system's life — budget ~$1,500-$3,000 for that, NOT panel replacement.

## The questions to ask

1. "What's the exact panel model and its 25-year power warranty percentage?" 2. "Does your savings projection account for annual degradation, or use flat year-1 output?" 3. "What's the inverter warranty, and what does replacement cost around year 12?"

## Bottom line

Quality panels lose ~0.5%/year and still produce ~87-92% at year 25 — degradation is real but mild. The bigger risks to your savings math are (a) inflated proposals using flat production, and (b) low-tier panels with weak warranties. Get the exact model + warranty %, and adjust any "lifetime savings" claim down ~7% for honest degradation.

Want me to sanity-check a proposal's production + degradation assumptions? Send it over. [reviewingsolar.com/upload](https://reviewingsolar.com/upload).