Solar Panel Degradation Rate: What 0.5% Per Year Actually Means

Average Solar Panel Degradation Rates by Panel Type

The industry benchmark for solar panel degradation is 0.5% per year, derived from long-term field studies published by NREL. But that number masks significant variation between panel types and manufacturer quality tiers.

Premium monocrystalline panels from top-tier brands — the kind that carry a 0.25–0.30% annual degradation guarantee in their product warranty — will retain around 92% of their rated output after 25 years. A standard monocrystalline panel degrading at 0.5% annually will deliver roughly 88% of original output at year 25. Older polycrystalline panels, once the industry standard, typically degraded at 0.7–0.8% per year and are now largely phased out of new residential installations. For more on this topic, see our guide to Solar Panel IRR.

Where you live also influences observed degradation. Panels in Hawaii and Florida — high UV, high humidity environments — tend to show faster encapsulant breakdown than panels installed in dry climates like Nevada. A 2022 NREL field study of over 50,000 residential systems found that climate zone accounted for as much as 0.15 percentage points of difference in annual degradation rate, which sounds small but adds up to nearly 4% of lifetime output over 25 years.

When comparing quotes, look beyond the efficiency rating printed on the spec sheet and go straight to the product warranty’s “year 25 guaranteed output” figure. The Solar Energy Industries Association (SEIA) recommends treating anything below 80% at year 25 as a red flag. Premium manufacturers now commonly guarantee 87–92% at year 25, which reflects genuine advances in cell technology over the past five years. That guaranteed floor is the single most useful number for comparing panels across different brands and price points.

Reading the Solar Panel Performance Warranty

Solar panel warranties come in two parts, and most homeowners conflate them. The product warranty (also called the materials warranty) covers manufacturing defects — typically 10–15 years. The performance warranty is the degradation guarantee — it specifies what minimum output percentage the panel must maintain after a set number of years, usually 25.

Performance warranties are not all created equal. A warranty that guarantees “80% at year 25” with only an endpoint guarantee is very different from one that guarantees “97% in year one, then no more than 0.5% decline per year thereafter.” The first structure protects you only at the endpoint — a panel could drop to 83% by year two and still technically meet the warranty if it recovers to 80% by year 25. The second, linear structure defines the permissible decline for every single year and is far more homeowner-friendly.

NREL and SEIA both recommend looking for linear performance warranties from manufacturers with a proven track record of honoring claims. Warranty claims require the manufacturer to still be in business, which is one reason buying from an established brand matters beyond product quality alone. Several manufacturers that entered the US market aggressively in the 2010s have since ceased US operations, leaving their warranties effectively void.

Also check who backs the warranty. Some manufacturers assign warranty obligations to a separately capitalized subsidiary rather than the parent company. If that subsidiary dissolves, your warranty goes with it. Ask your installer for documentation showing the warranty is backed directly by the parent manufacturer or a third-party insurer — not a shell entity.

One more term to understand: “first-year degradation.” Many panels lose 1–2% in the first year — called initial light-induced degradation — before settling into their long-term annual rate. A warranty that advertises 0.5% annual degradation may actually allow a 2% drop in year one and 0.5% thereafter, resulting in meaningfully lower lifetime output than the headline number suggests. Premium manufacturers now offer warranties with no first-year cliff, guaranteeing no more than 0.25% decline from day one. Before signing a contract, use a solar savings calculator to model the real 25-year output using the exact degradation rate stated in the warranty document itself.