Panel Degradation, Warranties, and What Year 25 Really Looks Like

Solar manufacturers advertise 25 or 30 year production warranties. Buyers often read this as 'the panels stop working after that.' That is not what happens. Panels degrade gradually, and most modules installed in the last decade are on track to be producing 85% to 90% of their original output at year 30.

Degradation rates are published by NREL and are tighter than they used to be. Monocrystalline silicon panels manufactured since 2018 degrade at roughly 0.4% to 0.6% per year, with a slightly larger drop of 1% to 2% in the first year as the cells stabilize. Older polycrystalline panels and some thin-film products degrade faster.

A 20 kWh per day system in year one, degrading at 0.5% per year, is still producing about 18 kWh per day in year 25. That is meaningful production, and the panels keep producing past the warranty, just more slowly. There are panels installed in the 1980s in California that still work, at roughly 70% of their original output.

The warranty document is where the marketing claims meet the legal reality. There are two warranties on every panel: a product warranty and a performance warranty. The product warranty covers manufacturing defects and is typically 12 to 25 years. The performance warranty guarantees a minimum percent of nameplate output at year 25 or 30, typically 80% to 87%.

Read both warranties carefully. A 25 year performance warranty is worthless if the product warranty is 10 years and the manufacturer is bankrupt by year 12. The solar industry has a long history of warranty companies disappearing. Suntech, Solyndra, and Sungevity were all major players that are now gone, and their warranty obligations went with them.

Tier 1 manufacturers with strong balance sheets currently include LG (though LG exited solar in 2022, they still service existing warranties), Panasonic, REC, Q Cells, Canadian Solar, JinkoSolar, and Trina. Domestic content rules under the Inflation Reduction Act have brought some manufacturing back to the United States, and First Solar, Silfab, and Mission Solar now build panels in the US. Domestically made panels typically cost more but qualify for additional incentives in some states.

Inverters are the component most likely to fail during a system's life. Plan on one inverter replacement around year 12 to 15 for a string inverter, or a small number of microinverter swaps spread across the warranty period. Budget $1,500 to $3,000 for this expense and build it into your financial model.

Roof penetrations are the other quiet maintenance item. Good installers use flashing products like Quick Mount PV or IronRidge with proper sealing, and these last as long as the roof. Bad installers use lag bolts with sealant and pray. If you have a leak at year 8, it is almost always a roof attachment, not a panel.