#Residential Solar: Cost, Payback and Panel Lifespan

Residential solar is where most of the decisions on this site get made, and it is also where the arithmetic is least forgiving. A system that looks like a fifteen-year payback on one set of assumptions can land at nine years on another, without anybody lying about the inputs.

Four numbers do most of the work. Installed cost per watt sets the denominator. Local electricity price sets what each generated kilowatt-hour is worth. The export tariff decides what happens to production the house cannot use at the moment it is made. And degradation, typically 0.4 to 0.55% per year on current monocrystalline modules (NREL), decides how much of year one you still have in year twenty.

The fourth one is the one homeowners underweight. A 25-year performance warranty is not a promise that output holds flat; it is a floor, usually around 85 to 87% of nameplate at year 25. Panels themselves rarely fail outright. Field data puts module failure rates well under 1% over a decade, while inverters, the component nobody photographs, are the part most likely to need replacing once inside a system's life.

Incentives change the picture but not the structure. The US federal ITC steps down after 2032, and any payback figure quoted today carries an implicit assumption about whether the buyer catches that window. European schemes vary by country and shift faster than most published calculators track.

The articles collected here work through each of those inputs separately: real installed prices, what a panel is doing at night, how much of a roof's output a household can actually self-consume, and what twenty-year ownership looks like once inverter replacement is priced in rather than assumed away.