Solar panels lose a small percentage of their power output each year — a process called degradation. Understanding the degradation rate of your panels helps you accurately model long-term energy production, evaluate manufacturer warranties, and calculate the true 25-year financial return on a solar investment. Panel technology has improved considerably, and modern premium panels degrade significantly more slowly than older designs.
What Is Solar Panel Degradation?
Solar panel degradation is the gradual decline in a panel’s maximum power output (Pmax) over time due to physical and chemical changes in the photovoltaic cells, encapsulant, and other materials. A panel that produced 400W at installation might produce 380W five years later due to degradation — still functional, but with reduced output.
Degradation is expressed as a percentage per year or as a guarantee at a specific age. For example, a panel with a “25-year power warranty guaranteeing 80% of rated output” implies approximately 0.9%/year degradation: (100% − 80%) ÷ 25 years = 0.8%/year (or stated as a stepped guarantee).
Most panel degradation is gradual and predictable. Degradation is factored into production models used by installers — PVWatts, Aurora Solar, and Helioscope all include an annual degradation rate in their energy production calculations (default is typically 0.5–0.7%/year in most modeling software).
Degradation Rates by Panel Technology
Degradation rates vary significantly by cell technology. 2026 benchmark rates from NREL and industry performance data:
PERC monocrystalline (p-type): 0.40–0.55%/year. The most widely installed panel type 2018–2022. Subject to Light-Induced Degradation (LID) — an initial output loss of 1–3% in the first few hours of light exposure caused by boron-oxygen defects in p-type silicon. Most manufacturer warranties account for this by guaranteeing output from the “stabilized” post-LID value rather than the initial STC rating.
TOPCon monocrystalline (n-type): 0.30–0.40%/year. N-type silicon does not have the boron-oxygen defect mechanism, so TOPCon panels experience no LID. Lower ongoing degradation rate. The dominant premium residential panel technology in 2026.
HJT (Heterojunction Technology, n-type): 0.25–0.35%/year. The lowest degradation rate of commercially available monocrystalline silicon panels. The amorphous silicon layers provide additional passivation that further reduces long-term degradation. HJT panels also have better temperature coefficients, which reduces heat-related output loss in hot climates.
IBC (Interdigitated Back Contact, n-type): 0.25–0.35%/year. Similar to HJT in degradation characteristics. SunPower Maxeon cells (IBC) have some of the strongest long-term field performance data, with measured degradation rates below 0.3%/year in long-term monitoring studies.
CdTe thin-film (First Solar): 0.4–0.5%/year. Comparable to PERC monocrystalline. First Solar’s Series 7 panels carry a 30-year linear power warranty to 90.1% of rated output — notably longer than most crystalline silicon warranties.
Legacy polycrystalline: 0.5–0.7%/year. Higher than modern monocrystalline. Most polycrystalline is now 5+ years old in the field — systems installed in 2018–2020 are measurably below their initial rated output but still performing within most warranty parameters.
What Causes Solar Panel Degradation?
Light-Induced Degradation (LID): Occurs in p-type (PERC) panels in the first hours to days of light exposure. Boron-oxygen defects form in p-type silicon under illumination, reducing cell efficiency. LID is largely eliminated in n-type panels (TOPCon, HJT, IBC). Treated as an initial offset rather than ongoing annual degradation in performance models.
Light and Elevated Temperature-Induced Degradation (LeTID): A more complex degradation mechanism that occurs in PERC panels over longer periods under combined light and heat stress. LeTID can cause initial degradation followed by partial recovery, then further loss. Panel manufacturers have improved cell passivation to reduce LeTID in newer PERC generations.
UV degradation of encapsulant: The EVA (ethylene vinyl acetate) encapsulant that surrounds the solar cells yellows and becomes more absorptive over time under UV exposure. This reduces light transmission to the cells. Modern UV-stabilized EVA has significantly lower yellowing rates than early 2000s formulations.
Thermal cycling: Daily heating and cooling cycles stress solder joints, cell metallization, and module lamination. Over decades, this can cause micro-cracking in cells and delamination at edges — both of which increase series resistance and reduce power output.
Potential-Induced Degradation (PID): Affects panels in high-voltage string systems where voltage differential between cell and module frame drives ion migration through the glass and encapsulant, disrupting cell performance. Modern anti-PID treatments in cell manufacturing and coatings significantly reduce PID risk. System-level mitigations (grounding polarity, night-time voltage equalization) also reduce PID.
How Degradation Affects 25-Year Production
A 400W panel’s output at year 25 depends on its annual degradation rate. Starting from 400W (year 1):
At 0.3%/year degradation (HJT/IBC): Year 25 output = 400W × (1 − 0.003)^24 = 400W × 0.931 = 372W (93.1% of initial)
At 0.5%/year degradation (PERC): Year 25 output = 400W × (1 − 0.005)^24 = 400W × 0.887 = 355W (88.7% of initial)
At 0.7%/year degradation (older polycrystalline): Year 25 output = 400W × (1 − 0.007)^24 = 400W × 0.844 = 338W (84.4% of initial)
Integrated over 25 years, the cumulative production difference between a 0.3%/year panel and a 0.7%/year panel on the same 10 kW system: approximately 5–8% more lifetime energy from the lower-degradation panel — a meaningful difference when total production represents $30,000+ in electricity value.
Reading Panel Power Warranties
Performance warranties specify the minimum power output at specific points in the panel’s life. Common formats:
Linear power warranty: Guarantees a maximum annual degradation rate (e.g., “no more than 0.4%/year after year 1 stabilization, to no less than 86% at year 30”). This is the most consumer-protective format. Premium panel manufacturers (SunPower, Panasonic, REC Group, LONGi) offer linear warranties.
Step warranty: Guarantees output at specific intervals (e.g., “90% at year 10, 80% at year 25”). Implies potentially steeper degradation within intervals — less favorable than linear warranties that guarantee the annual rate.
What warranties don’t guarantee: Power warranties don’t guarantee against physical failure of the panel (glass breakage, junction box failure, connector failure) — those are covered by the product/materials warranty (typically 10–15 years). A panel can fail completely within its power warranty period without the power warranty covering replacement.
Frequently Asked Questions
What is the typical solar panel degradation rate?
The industry average for modern monocrystalline panels is approximately 0.4–0.5%/year. NREL (National Renewable Energy Laboratory) has tracked real-world solar panel performance and found median degradation rates of approximately 0.5%/year across a large sample of installed systems. Premium n-type panels (TOPCon, HJT, IBC) achieve 0.25–0.40%/year. Standard PERC monocrystalline and older polycrystalline panels typically degrade at 0.45–0.7%/year. Significant outliers (panels degrading 2–5%/year) exist due to manufacturing defects, installation damage, or harsh environmental conditions.
How much do solar panels degrade after 25 years?
Most modern panel warranties guarantee at least 80–87% of rated output at year 25. Actual measured degradation is often better than warranty minimums — NREL field data suggests well-installed panels from reputable manufacturers frequently retain 85–92% of initial output at 25 years. Premium HJT and IBC panels with 0.25–0.30%/year degradation retain 93–94% of initial output by year 25. This means a 400W panel installed in 2026 will likely produce 360–380W (premium) to 340–360W (standard) by 2051 under typical conditions.
What is LID in solar panels?
LID (Light-Induced Degradation) is an initial output loss that occurs in p-type silicon solar panels (standard monocrystalline PERC) during the first hours to days of light exposure. When light hits p-type silicon, boron-oxygen complexes form that act as electron traps, reducing cell efficiency by 1–3%. LID is largely irreversible under normal conditions (though light soaking techniques can mitigate it). Panel manufacturers account for LID in their warranties by measuring performance from the post-LID “stabilized” value. N-type panels (TOPCon, HJT, IBC) do not experience LID because they don’t contain the boron-oxygen defect mechanism.
Do solar panels lose efficiency over time?
Yes — all solar panels lose some efficiency over time, but at a slow and predictable rate. The average annual efficiency loss for modern residential panels is 0.4–0.5%. This means a panel producing 400W in year 1 produces approximately 380–392W by year 10, and 340–370W by year 25. This gradual decline is factored into installer production models and warranty structures. The efficiency loss is not uniform — it’s steepest in the first year (LID for p-type panels) and then levels off to a more consistent annual rate. High-quality installations in favorable climates with regular panel cleaning maintain the lower end of degradation rates.
How do I know the degradation rate of my solar panels?
Check the panel’s datasheet or warranty documentation. The performance warranty section specifies either the guaranteed annual degradation rate (linear warranty format) or the guaranteed output percentages at specific years. If the datasheet states “80% at 25 years,” the implied degradation rate is approximately 0.83%/year — use a linear warranty or one specifying a per-year rate for better clarity. Your installer’s production model should also document the degradation rate assumed in the energy production estimate — standard modeling software uses 0.5%/year as a conservative default; request to see this assumption if it’s not shown in your proposal.
Summing Up
Solar panel degradation rates typically range from 0.25%/year (premium HJT and IBC n-type panels) to 0.55%/year (PERC monocrystalline) to 0.70%/year (older polycrystalline). Over 25 years, a well-specified modern panel retains 85–93% of its initial output — within manufacturer warranty parameters and sufficient to provide meaningful electricity production through the warranty period and beyond. The key factors in degradation are panel technology (n-type LID-free panels degrade more slowly), encapsulant quality, and installation conditions. When comparing panels, look for the linear power warranty format that specifies the maximum annual degradation rate, rather than step warranties that only guarantee output at specific intervals.
Updated