Solar Panel Degradation Calculator
Project how much energy your solar panels will produce in any future year as their output gradually declines with age. Use it to model long-term performance, verify warranty compliance, and forecast lifetime energy generation.
About this calculator
Solar panels lose a small but consistent fraction of their output each year due to light-induced degradation, UV exposure, thermal cycling, and gradual cell chemistry changes. The production in any given year is modeled by an exponential decay formula: Production(year n) = initialProduction × (1 − degradationRate)^n. For example, a panel degrading at 0.5% per year retains (1 − 0.005)^10 ≈ 95.1% of its original output after 10 years. Most tier-1 monocrystalline silicon panels carry a linear performance warranty guaranteeing at least 80% output at year 25, implying a maximum degradation rate of roughly 0.8% per year. Thin-film and older polycrystalline panels can degrade faster at 1.0–1.5% per year. The compound nature of the formula means losses are small early but accumulate meaningfully over a 25–30 year system lifetime, making degradation rate one of the key quality differentiators between panel brands.
How to use
A system produces 10,000 kWh in year one. The panel's annual degradation rate is 0.6% (0.006). You want to know production at year 20. Step 1 — apply the formula: Production = 10,000 × (1 − 0.006)^20. Step 2 — compute (0.994)^20: ln(0.994) ≈ −0.006018; × 20 = −0.12036; e^(−0.12036) ≈ 0.8866. Step 3 — final output: 10,000 × 0.8866 ≈ 8,866 kWh. That means at year 20 the system produces about 11.3% less than it did originally — still well above the typical 80% warranty threshold.
Frequently asked questions
What is a typical solar panel degradation rate and why does it matter?
The median degradation rate for modern monocrystalline silicon panels is approximately 0.5% per year, based on large-scale studies by NREL and other research institutions. That means a panel rated at 400W new will produce about 390W after 5 years and roughly 357W after 25 years. The rate matters because it directly determines how much energy — and therefore money — your system produces over its lifetime. A seemingly small difference between a 0.5% and a 0.8% annual degradation rate compounds to a roughly 7% gap in cumulative output over 25 years, which can represent thousands of kWh and hundreds of dollars.
How do I know if my solar panels are degrading faster than expected?
The most reliable method is to compare your system's actual annual production (from your inverter monitoring portal) to the expected output calculated using your original system specs and local irradiance data for each year. Many monitoring platforms like Enphase Enlighten or SolarEdge show production trends over time. A sudden drop — rather than the slow linear decline characteristic of normal degradation — may indicate a failed microinverter, a broken string, shading from new obstructions, or a soiled panel. If annual production is declining faster than 1% per year consistently, it is worth having a certified solar technician perform an IV curve trace or thermal imaging inspection to identify defective cells or modules.
What does a solar panel performance warranty actually guarantee?
A performance warranty (distinct from the product or workmanship warranty) guarantees that your panels will still produce at least a specified percentage of their original rated power after a set number of years — most commonly 80% at 25 years, though many premium manufacturers now offer 90% at 25 years. If your panels fall below the warranted threshold, the manufacturer is obligated to repair, replace, or compensate for the shortfall. In practice, claiming performance warranties requires documented evidence of output, a working monitoring system, and dealing with manufacturers who may have changed hands over 25 years. The warranty is most useful as a signal of manufacturer confidence in their product quality rather than as a routine claim mechanism.