Solar Panel Degradation & Performance Loss Calculator
Estimate how much power your solar panels lose over time due to natural degradation, and calculate remaining output and cumulative energy production over the system lifetime.
Nameplate wattage of one panel (STC rating)
Total panels in your system
Typical range: 0.3%–0.8%/year; industry standard ~0.5%
Many panels degrade more in year 1 (LID effect); 0 if not applicable
How many years the system has been operating
Typically 25–30 years for warranty analysis
Average daily peak sun hours for your location
Accounts for inverter, wiring, shading losses; typically 75%–85%
Your local utility rate for savings estimation
Formulas Used
Year-1 Power Factor (LID effect):
P(1) = P₀ × (1 − L₁)
where L₁ = first-year degradation rate (fraction)
Power Output at Year t (t ≥ 2):
P(t) = P₀ × (1 − L₁) × (1 − d)^(t−1)
where d = annual degradation rate (fraction), t = year number
Annual AC Energy Output at Year t:
E(t) = P(t) × PSH × 365 × PR
where PSH = peak sun hours/day, PR = performance ratio (system efficiency)
Cumulative Lifetime Energy:
E_total = Σ E(t) for t = 1 to N
Performance Ratio (PR): Accounts for inverter efficiency, wiring losses, temperature derating, and shading.
Assumptions & References
- Degradation follows a linear annual model after the first-year LID (Light-Induced Degradation) loss.
- Industry standard annual degradation rate is 0.5%/year per NREL (Jordan & Kurtz, 2013, Progress in Photovoltaics).
- First-year LID loss is typically 1%–3% for standard crystalline silicon panels; PERC and LeTID-resistant panels may show less.
- Most manufacturer warranties guarantee ≥80% output at 25 years, implying ~0.7%/year max degradation.
- Performance Ratio (PR) of 75%–85% is typical for well-maintained grid-tied systems (IEA PVPS Task 13).
- Peak Sun Hours vary by location: ~3–4 h/day (northern Europe), ~5–6 h/day (US average), ~6–7 h/day (desert regions).
- Energy calculations assume constant peak sun hours and performance ratio over the system lifetime.
- Temperature, soiling, and inverter replacement cycles are not individually modeled but are captured in the PR factor.
- Reference: NREL PVWatts methodology; IEC 61724 performance monitoring standards.