Solar Panel Degradation: How Much Power Do Panels Lose Over Time?

Modules: about 0.5% a year. The national laboratory (formerly NREL) compiled more than 11,000 degradation rates from about 200 studies in 40 countries. For crystalline silicon the median is about 0.5% a year and the mean 0.8–0.9%; the average sits higher because a minority of cases degrade much faster. The data associate hotter climates and hotter-running modules with faster degradation (Compendium of PV Degradation Rates; analytical review).

Whole systems: about 0.75% a year. The laboratory’s PV Fleet study measured performance loss on 4,915 inverters across US fleets and found a median of 0.75% a year, which it describes as an updated system value rather than 0.5% (PV Fleet final report, 2025). The same program puts typical annual soiling losses at 2–3%, and up to 15% at dirtier sites.

Home rooftops: about 1.3% a year of energy yield. A study of 503 systems, 387 of them residential, found a median residential energy-yield decline of 1.3% a year, and 2.1% where shade was medium or heavy. That is a whole-system number — growing trees, dirt and inverter losses included — and its authors caution against reading it as panel decline (Deceglie et al.).

Two things stand out. The warranty floors sit above the measured system and rooftop rates, because a warranty covers the panel’s own power, measured under standard test conditions, while your meter also sees dirt, shade, heat and the inverter. And none of the lines hits zero: a panel at year 30 still makes most of its original power, which is why systems are planned around 25–35-year lives.

The performance guarantee is the one about degradation: if the panel’s tested power falls below the schedule, it is a claim. The product warranty covers defects that make the panel fail. Several of the longest terms depend on registration or on a certified installer, so ask which terms apply to your install, in writing. How these fit with the inverter, workmanship and battery warranties is in solar warranties explained, and the full panel comparison in the best solar panels for California.

Many panels sold in 2026 use newer TOPCon cells, which typically carry 30-year warranties at 0.4% a year after a 1% first year. Their field record is still short. In a July 2026 presentation the national laboratory reported a first-year loss of 1.3–1.8% on TOPCon modules from two makers at its test sites — within warranty expectations — and, across the TOPCon data it analyzed, a median of 1.1% a year, close to the 1% it measured on bifacial PERC modules. It flagged high uncertainty (short records, partly residential data) and a measurement effect that can make TOPCon modules test lower after sitting in the dark, and concluded that new module types can bring new degradation mechanisms and need more monitoring. The same study found the TOPCon modules ran 1.7°C cooler than PERC side by side, with a 2.2% higher performance ratio (NLR, 2026).

The data come largely from bifacial test modules, not the typical home panel, so they don’t settle the question — but they are a reason to weigh the warranty and the company behind it, not only the headline degradation rate.

Seven years of decline at each measured rate would explain: 3.4% at the module median, 5.1% at the US fleet median, 8.8% at the home-rooftop median, and 13.8% on rooftops with medium or heavy shade. The warranty schedules allow even less decline for the panels alone — 1.8–2.8% over the same years on the three above. So a 12% drop is more than typical aging. Work through the usual causes before blaming the panels:

1. Weather. Compare the same months across several years; one cloudy spring can move a year’s total.
2. Dirt. Soiling commonly costs 2–3% a year and much more at dusty sites, and a wash recovers it — see solar panel cleaning in California.
3. New shade. Trees grow; the rooftop study’s shaded homes lost 2.1% a year. See solar and shade.
4. Equipment. A failed microinverter or optimizer shows up as one panel at zero in your monitoring app, a failed string inverter as the whole system — see solar not producing.
5. Then the panels. A performance-warranty claim rests on the panel’s tested power against its schedule, so ask your installer to test suspect modules before filing.

Cali Energy (CSLB #1032379) designs and installs solar across Los Angeles and the San Fernando Valley. We can recommend panels whose warranty terms hold up on your roof, or look at your monitoring data to tell normal decline from a fixable problem.

Figures on this page come from the primary sources below and, where noted, from Cali Energy calculations using the stated assumptions. Rates, incentives, and program terms change; each was verified September 28, 2026.

1. Compendium of Photovoltaic Degradation Rates (Jordan, Kurtz, VanSant, Newmiller)
2. Photovoltaic Degradation Rates — An Analytical Review (Jordan & Kurtz), via OSTI
3. PV Fleet Performance Data Initiative — Final Technical Report (NREL/TP-5K00-92444, 2025)
4. Deceglie et al. — Fleet-Scale Energy-Yield Degradation Analysis of Residential and Nonresidential PV Systems
5. NLR — PV Durability at Scale: Assessing Bifacial and TOPCon Field Performance (NLR/PR-5K00-101394, 2026)
6. NLR — PV reliability and system performance research
7. Maxeon — Limited Warranty for PV Modules (document 545700, Rev G, effective May 1, 2026)
8. Silfab Solar — Limited Product and Linear Performance Warranty (SIL-CS-WRTY-010, Rev Q)
9. Canadian Solar — TOPHiKu6 datasheet and warranty terms
10. REC — Alpha Pure-RX series
11. Qcells — Q.TRON BLK M-G2+