Degradation Calculator: 25-Year Output

How fast do solar panels degrade?

Solar panel degradation — year-by-year output tables for a 4kW system (3,800 kWh year 1): AT 0.25%/yr (SunPower, REC): Year 5: 3,752 kWh. Year 10: 3,705. Year 15: 3,659. Year 20: 3,613. Year 25: 3,568 (93.9%). 25yr total: 91,900 kWh. AT 0.4%/yr (LONGi, JA Solar): Year 5: 3,724. Year 10: 3,650. Year 15: 3,577. Year 20: 3,506. Year 25: 3,436 (90.4%). 25yr total: 89,500 kWh. AT 0.7%/yr (budget brands): Year 5: 3,668. Year 10: 3,541. Year 15: 3,418. Year 20: 3,299. Year 25: 3,185 (83.8%). 25yr total: 85,700 kWh. FINANCIAL IMPACT (at 24.5p/kWh, 40% self-consumption): 0.25% vs 0.7%: 6,200 kWh difference = £610 more savings over 25yr. Plus higher SEG income on remaining export. TOTAL FINANCIAL DIFFERENCE: £800-£1,200 lifetime. Premium panels (0.25% degradation) cost £1,000-£2,000 more but save £800-£1,200 in extra generation. Net: approximately break-even — choose based on warranty length and brand confidence. Sources: Manufacturer warranty datasheets, NREL PV degradation studies (Jordan & Kurtz), IEA PVPS.