What is a typical annual degradation rate?

Most monocrystalline and polycrystalline panels degrade at 0.5%/year or less. Premium panels (e.g. Panasonic HIT, SunPower) are closer to 0.25–0.3%/year. Thin-film panels can be 0.7–1%/year. Check the manufacturer's linear power warranty for the official figure.

What does the 80% warranty threshold mean?

Most panel warranties guarantee at least 80% of rated output at year 25. A 400 W panel rated at 0.5%/year degradation produces about 348 W at year 25 — 87% of original — comfortably inside the 80% warranty floor.

What are peak sun hours?

Peak sun hours (PSH) is the number of equivalent hours per day at 1,000 W/m² irradiance. Annual kWh/kWp = PSH/day × 365. A site with 5 PSH/day gives 1,825 kWh/kWp/year, which is the default here. Adjust for your location using NREL's PVWatts or SolarGIS.

Does this account for inverter or wiring losses?

No. The calculation is panel-level only. Real system output is typically 15–25% lower after inverter efficiency (~96%), temperature derating, shading, soiling, and wiring losses. Multiply the kWh figures by 0.75–0.85 to approximate AC output at the meter.

Can I use this for a whole array?

Yes. Enter the total rated wattage of the array (e.g. 10,000 W for a 25-panel × 400 W system). The degradation rate applies uniformly across all panels.

Solar Panel Degradation Calculator

Name: Solar Panel Degradation Calculator
Availability: InStock
Author: Nham Vu

Enter panel wattage, annual degradation rate, and system lifetime to see year-by-year output and total energy yield.

Panel Parameters

Initial Panel/Array Wattage (W)

Nameplate DC wattage at STC (e.g. 400 W per panel)

Annual Degradation Rate (%)

Typical: 0.5%/yr standard, 0.25%/yr premium

System Lifetime (years)

1–40 years; 25 is the standard warranty horizon

Annual Peak Sun Hours (kWh/kWp)

PSH/day × 365; default 1825 ≈ 5 h/day moderate climate

Year-by-Year Output

Year	Output (W)	% of Original	Annual kWh

Enter panel parameters above and click Calculate.

Summary

Enter panel wattage, annual degradation rate, and system lifetime to see year-by-year output and total energy yield.

How it works

Enter the initial panel (or array) wattage in watts — for example, 400 W for a single panel.
Set the annual degradation rate. Most manufacturers rate panels at 0.5%/year; higher-quality panels are closer to 0.25%.
Choose the system lifetime in years (default 25, which is the standard warranty horizon).
Optionally adjust peak sun hours per year to see energy yield in kWh (default 1825 kWh/kWp, typical for moderate climates).
The calculator applies P_n = P_initial × (1 − rate)^n each year and sums annual energy output.

Use cases

Estimate remaining output at year 25 against a manufacturer's power warranty threshold (typically 80%).
Compare two panels with different degradation rates over a 30-year horizon.
Project total lifetime kWh yield for a financial return-on-investment model.
Check whether an aging system still meets a load requirement after 10 or 15 years.

Frequently Asked Questions

Last updated: 2026-07-04 · Reviewed by Nham Vu