Solar Panel Degradation Loss Calculator

Apply a simple degradation curve to see how much production your solar array is losing each year. Provide the first-year kWh output and years in service; optionally adjust the annual degradation rate to mirror your module warranty.

Expected or metered kWh output in the first full year of operation.
How many years the array has been operating.
Defaults to 0.5% per year if blank. Use your module's warranted degradation rate.

Simplified degradation model. Actual production varies with weather, shading, maintenance, and inverter efficiency.

Examples

  • 12,000 kWh year-1 output, 8 years in service, 0.6% degradation ⇒ Current output at year 8.00: 11,444 kWh/year • Cumulative loss versus year 1: 556 kWh/year • Nameplate output retained: 95.37%.
  • 9,500 kWh year-1 output, 5 years, rate blank (defaults to 0.5%) ⇒ Current output at year 5.00: 9,267 kWh/year • Cumulative loss versus year 1: 233 kWh/year • Nameplate output retained: 97.54%.

FAQ

Does this include inverter replacements?

No. It models module degradation only. If inverter downtime reduced production, lower the first-year baseline accordingly.

Can I model a step change after cleaning?

Run the calculator twice—before and after the cleaning—to see how much soiling recovery offsets long-term degradation.

What rate should I use for bifacial modules?

Use the rate specified in the warranty or performance ratio tests for your module type; 0.3–0.8% per year is typical.

Additional Information

  • The calculator compounds a constant annual degradation rate to approximate long-term production decline.
  • Outputs are expressed per year; multiply current output by your utility rate to estimate revenue impact.
  • Retained percentage shows how close the system remains to its nameplate output for warranty claims and energy forecasts.

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