Solar Panel Degradation Calculator

How to use this calculator

Enter seven values and the calculator returns current output, output at year 25, 25-year cumulative kWh, and the lifetime kWh and revenue you’ll lose to natural decay:

1. System size (kW) — total nameplate. A 6 kW system is 6 kW; a 25-panel 400 W array is 10 kW.
2. Peak sun hours per day — local average. Continental US ranges 3.5 (Seattle) to 6.5 (Phoenix). NREL’s PVWatts gives the value for any ZIP code.
3. System efficiency (%) — the derate factor. 78% is NREL PVWatts v6 default for residential rooftop.
4. Panel age today (years) — 0 for a brand-new install; 8 for an 8-year-old system.
5. First-year LID drop (%) — 1.5–2.5% for typical p-type mono-PERC panels, 0.3–0.5% for n-type (SunPower Maxeon, LG NeON R).
6. Annual degradation (%/yr) — 0.5% NREL median, 0.3–0.4% for Tier-1, 0.7–1.0% for cheap modules or thin-film.
7. Electricity rate ($/kWh) — your current utility rate, used to value the kWh lost to decay.

How solar panel degradation works

Every solar panel loses output over time. The decay has three distinct phases:

Phase 1 — LID (light-induced degradation). In p-type crystalline silicon (the dominant residential technology), the first 30–100 hours of sun exposure trigger boron-oxygen defects that drop output by 1–3%. The reaction completes within two weeks and never reverses. Some Tier-1 manufacturers compensate by binning panels at +1.5% over rated power, so the panel you buy stabilises right at nameplate. N-type silicon, gallium-doped p-type (used in modern Trina and Jinko panels), and HJT cells are essentially LID-free.

Phase 2 — linear degradation, years 1–25. After LID stabilises, the panel decays at a steady 0.3–0.7% per year. Causes include slow EVA (encapsulant) yellowing, microcracks from thermal cycling, soldering fatigue, and PID where high-voltage stress drives sodium ions into the cell. NREL’s Jordan & Kurtz 2016 review of 11,000 systems puts the median at exactly 0.5%/yr for crystalline silicon and 0.7%/yr for thin-film.

Phase 3 — accelerated failure, post-warranty. Beyond the 25-year warranty endpoint, failures accelerate: junction box delamination, glass fracture, severe backsheet cracking. Most modern panels keep producing usable power past 30 years, but at 70–75% of nameplate. The Solar Energy Research Institute of Singapore has data on panels from 1986 still producing 75% of original output after 35 years.

The degradation math

For year n of system life, output relative to STC nameplate is:

year_factor(n) = (1 - LID) × (1 - degradation_rate)^(n - 1)

For year 0 (before any sun exposure), the factor is 1.0. For year 1 the LID drop applies. From year 2 onward, the annual degradation compounds.

A worked example for a 6 kW system, 2% LID, 0.5% annual degradation:

• Year 1: 6 kW × (1 − 0.02) × (1 − 0.005)^0 = 5.88 kW effective = 98.0% of STC
• Year 5: 5.88 × (1 − 0.005)^4 = 5.762 kW = 96.0% of STC
• Year 10: 5.88 × (1 − 0.005)^9 = 5.620 kW = 93.7% of STC
• Year 15: 5.88 × (1 − 0.005)^14 = 5.481 kW = 91.4% of STC
• Year 20: 5.88 × (1 − 0.005)^19 = 5.346 kW = 89.1% of STC
• Year 25: 5.88 × (1 − 0.005)^24 = 5.214 kW = 86.9% of STC

That matches what almost every Tier-1 manufacturer guarantees — 85–87% at year 25 for standard mono-PERC, 90–92% for premium panels.

Degradation rates by panel type

NREL’s median rates by technology, from peer-reviewed reliability data:

Cheap import panels (typically Tier-3 Chinese brands you’ve never heard of) often show 0.8–1.2% annual degradation in NREL’s field studies — translating to 60–65% output at year 25. The savings on day one rarely justify the lifetime kWh loss.

What accelerates degradation

Temperature

Hot panels degrade faster. Every 10°C rise in operating temperature roughly doubles the EVA yellowing rate (Arrhenius kinetics). A black-roof installation in Phoenix routinely runs cells at 60–70°C in summer — that pushes annual degradation toward 0.7–0.8%/yr versus 0.4–0.5% for the same panel in San Francisco. Roof clearance of 4 inches or more for airflow buys back 5–10°C and meaningfully extends panel life.

Mechanical stress

Microcracks from snow loads, hail, or installer foot traffic propagate over years and cause stepped output losses. EL (electroluminescence) imaging during commissioning catches existing microcracks. Installers who insist on never walking on panels — and use rail spans that limit deflection under snow — see noticeably better long-term data.

PID (potential-induced degradation)

In transformerless inverter systems, panels at the negative end of a string can develop a high voltage potential relative to ground. Sodium ions migrate from the glass into the cell and create short paths. PID-affected panels lose 5–30% within a few years. Modern panels are PID-resistant (look for “PID-free” or “PID-resistant” on the datasheet), and grounding the negative terminal eliminates the problem.

Salt and ammonia

Coastal installations face salt-mist corrosion of cell ribbons and junction boxes. Farm installations near intensive livestock operations face ammonia attack on the backsheet. Both are covered by IEC 61701 (salt mist) and IEC 62716 (ammonia) — confirm the panel datasheet lists these certifications if you’re in an exposed environment.

Reading your warranty

Two warranties cover panel output:

• Product warranty — 10–25 years, covers manufacturing defects (cell cracks, junction box failure, hot spots). SunPower, REC, and Maxeon offer 25-year product warranties.
• Performance warranty — 25–30 years, guarantees a minimum output curve. Linear is friendlier than stepped.

If your panel falls below the warranty curve, the manufacturer typically refunds the prorated cost of underperforming wattage or supplies replacement panels. Warranties almost universally require the original installer’s commissioning report, periodic IV-curve data, and electroluminescence imaging at the failure year. Keep these records.

Common mistakes

• Confusing nameplate with year-1 output. Most p-type panels lose 1–2% within the first 100 hours. A 400 W panel is really a 392–396 W panel after stabilisation.
• Forgetting tariff escalation when valuing lost kWh. A kWh lost in year 25 is worth roughly 2× as much as a kWh lost in year 1 at 3% annual rate increases. Lifetime revenue loss is meaningfully higher than naive nominal-rate math suggests.
• Treating Tier-1 and Tier-3 as equal. A $0.10/W discount on a Tier-3 panel costs you 4–6× that in lifetime kWh. Pay for Tier-1.
• Ignoring degradation in payback calculations. Without degradation, payback for a typical US system is 7–9 years; with degradation, 7.5–10 years. The solar panel payback calculator handles this correctly.

Sources

• NREL — Photovoltaic Degradation Rates: An Analytical Review (Jordan & Kurtz, 11,000-system meta-analysis)
• NREL PVWatts v6 — production modeling with default 0.5%/yr degradation
• DOE — Solar Module Reliability Workshop annual proceedings — current research on PID, LID, and field failures
• EnergySage — 2026 Panel Brand Reliability Report — actual residential degradation data by manufacturer
• SEIA — Module Quality Field Survey