Installing solar panels is a significant investment, so naturally homeowners want reassurance that they’ll provide power for many years. But how much do solar panels degrade each year? What is the annual performance decline percentage and factors that impact solar panel lifespan?
In this guide, we’ll dig into the real-world solar panel degradation data and what causes power to dwindle over decades of operation. Let’s shine some light on quantifying solar panel aging.
Why Do Solar Panels Degrade Over Time?
Before looking at degradation rates, it’s important to understand what causes solar panels to lose power-generating capacity as they age. There are several factors at play:
Solar Cell Decay
Prolonged exposure to sunlight causes the silicon solar cell materials to slowly break down, reducing current flow. Ultraviolet wavelengths deteriorate materials the fastest.
Thermal cycling and moisture can cause electrical connectors and internal wiring to corrode or break over years of operation. This increases resistance.
Transparent Cover Yellowing
The polymer encapsulation protecting solar cells tends to yellow with UV exposure, reducing light transmission to the cells.
Expansion/contraction from temperature swings plus wind and impact stresses can cause solar cell cracking over time. Cracks lower conductivity.
Humidity ingress can delaminate waterproof backing or cause cells to separate, allowing corrosion and shorts.
Dirt, dust, bird droppings, pollen, and other debris accumulating on panels block sunlight, reducing power. This is reversible with cleaning.
Now let’s look at real-world degradation rates from solar panel studies…
Measuring Degradation from Field Data
Lab testing provides accelerated lifetime estimates, but real-world solar panel degradation is best measured through longitudinal field studies. Researchers compare initial power to ongoing output over years of operation.
NREL Solar Panel Degradation Study
A 2020 field study from the National Renewable Energy Lab tracked degradation on over 250,000 PV systems. They found the following:
- Year 1: 2.6% median degradation
- Year 2: 0.5% median degradation
- Years 3-30: 0.4% median degradation
This equates to around 0.5% annual degradation after the first year. Total around 20% over 30 years.
Jordan and Kurtz Degradation Study
A 2012 study by Dirk Jordan and Sarah Kurtz analyzed over 1,000 PV systems. Key findings:
- 0.2 – 0.5% annual degradation for crystalline silicon panels
- 0.7 – 1% annual degradation for thin-film panels
Silicon showed around 0.3% annual loss on average.
Oozeki et al Panel Degradation Analysis
A 2016 paper by Oozeki et al studied commercial rooftop solar panel degradation by measuring multiple installation sites over 15 years.
Their degradation rate findings:
- Monocrystalline silicon: 0.16% annual loss
- Polycrystalline silicon: 0.27% annual loss
- Amorphous silicon thin-film: 0.47% annual loss
Factors That Influence Degradation Rates
While around 0.5% annual degradation is typical, specific conditions influence actual loss rates:
Thin-film amorphous silicon degrades faster than crystalline silicon on average according to field data.
More stringent manufacturing and material controls result in slower degradation over decades of field use.
Roof-mount vs. tracker systems see different structural stress, humidity, and light exposure conditions affecting longevity.
More UV exposure, larger temperature swings, coastal humidity/salt exposure, and wind/hail events accelerate degradation.
Proper operations/maintenance like cleaning and vegetation control reduce soiling and physical damage that worsen degradation.
More hours of operation with sustained high voltages and currents speed breakdown of panel components.
Estimating Lifetime Panel Degradation
Based on large-scale solar panel degradation datasets, we can estimate the typical annual and lifetime power loss:
- Year 1: 2-3% decrease due to initial light stabilization
- Years 2-20: ~0.5% decline per year
- Years 20-30: ~0.7% annual decrease as aging accelerates
- Total lifetime degradation: ~80% original power at 30 years
So you can expect around a 0.5% yearly drop in solar panel output on average, equating to around 20% loss over the entire 30-year lifetime.
Maintaining Solar Panels to Slow Degradation
While solar panel degradation is inevitable, proper maintenance and care can reduce the rate of age-related power loss:
- Perform regular cleanings to reduce shading from soiling buildup.
- Inspect panels and cables yearly for any damage or corrosion.
- Reseal any water ingress around panel edges or mounts.
- Prune any encroaching tree branches or vegetation.
- Keep roof mounts clear of debris and snow buildup.
- Avoid putting unnecessary stress on panels when cleaning.
- Track power output changes monthly to catch big drops early.
- Follow manufacturer and installer O&M recommendations.
With close monitoring and care, solar panel lifetimes can extend past 30 years in many cases.
When to Consider Panel Replacement
Even with maintenance, expect solar panels to slowly generate less power each year. At some point, upgrading the panels will provide better returns than stretching more years from the original ones. When is replacement warranted?
Industry experts suggest considering new solar panels when degradation causes power output to drop:
- Below 80% original rating after 25 years of use
- Below 70% original rating after 30+ years
- After visible degradation from storm, fire, or accident damage
Upgrade earlier if efficiency incentives make replacement financially favorable.
Key Takeaways on Solar Panel Aging
When evaluating solar power systems, anticipate around a 0.5% decline in performance annually from solar panel degradation. Less in early years, accelerating later in life. This typical degradation rate allows for the productive operation of most panels for 25-30 years with proper maintenance. Being aware of factors influencing degradation can help maximize the investment return achieved from solar installations over their full lifetime.