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An 8 kW array loses 19,982 kWh to degradation over 25 years — $3,397 at $0.17/kWh. That is the exact budget for paying extra for 0.25%/yr panels.
Every solar quote shows year-one production; almost none show year twenty-five. Panels degrade: a 1–3% hit in year one (light-induced degradation), then 0.25–0.7% every year after, compounding. An 8 kW system producing 11,200 kWh in year one still produces 9,781 kWh in year 25 — but the cumulative loss is 19,982 kWh, worth $3,397 at $0.17/kWh. That number converts a vague warranty spec into a price: if a premium panel line degrades at 0.25%/yr instead of 0.55%/yr, it recovers roughly half that loss — so a $1,400 premium pays for itself while a $4,000 premium does not. Run your quoted production and the warranty degradation rate here before choosing between panel tiers.
Solar shoppers use it before picking a panel tier: an 8 kW array loses 19,982 kWh ($3,397) to degradation over 25 years — so a $1,400 premium for 0.25%/yr panels pays for itself, a $4,000 one does not.
The one printed in the warranty — that is the manufacturer putting money behind a number. Premium lines (Maxeon/SunPower, some Panasonic and REC models) warrant 0.25–0.4% per year with an 88–92% year-25 floor. Standard tier warrants ~0.55% with an 84–85% floor. Budget panels warrant 0.7% and an 80% floor. First-year degradation (light-induced degradation, or LID) is separate: 1–3% in year one before the annual rate starts. NREL field studies of real arrays cluster around 0.5–0.8%/yr median for older fleets, but modern mono PERC panels test better. Use the warranty number for the decision, not the lab number — the warranty is the part you can collect on.
Do the arithmetic this calculator sets up: total degradation loss at your rate, then compare tiers. At the defaults, going from 0.55%/yr to 0.25%/yr recovers about 8,000 kWh over 25 years — roughly $1,400 at $0.17/kWh, more in high-rate states like California or the Northeast where the same kWh are worth $0.25–0.35. So the premium is worth it up to about that recovered value, minus a discount for the fact that year-20 dollars are worth less than year-one dollars. Where the premium math breaks: if you will sell the house before year 12, you capture little of the tail production — degrade the premium by your expected ownership years. Where it clearly wins: high electricity rates, long ownership, and net-billing regimes where exported kWh still pay retail.
Two big line items. First, the inverter: string inverters typically last 12–15 years, so budget one replacement ($1,500–3,000 installed) inside any 25-year horizon; microinverters often carry 25-year warranties but failure rates are not zero. Second, real-world shading change — trees grow, neighbors build second stories — which can cost more than panel degradation and is never in the quote. Also separate: soiling (dust, pollen) is recoverable with cleaning and is usually already inside the production derate, and catastrophic events (hail, fire) are insurance questions, not degradation. The honest way to use this tool: it prices the panel-line decision cleanly; then carry a one-time inverter replacement as a separate lump in your payback math.