Solar Degradation Calculator

Most crystalline silicon solar cells undergo light-induced degradation (LID) during their first meaningful exposure to sunlight, a one-time structural settling in the cell material that causes a larger initial output drop than what happens in any subsequent year. After that first year, the cell has stabilized and the ongoing annual decline reflects slower, more gradual wear mechanisms, which is why manufacturers and this calculator both treat year one differently from every year that follows.

Compounding applies each year's degradation percentage to the previous year's already-reduced output rather than to the original rated output, which better reflects how real panel degradation actually behaves — a panel that's already lost some output loses a proportional amount of what remains, not a fixed slice of its original day-one capacity. Over a 25-year system life, this produces a meaningfully different (and generally more accurate) total than a simple year-by-year linear subtraction would.

It's the cumulative dollar value of the energy your system won't produce over its lifetime purely because of normal panel aging, calculated by comparing your actual projected output each year against what the system would have produced every year if it stayed at its original, undegraded output level. It isolates degradation specifically — it doesn't include losses from other real-world factors like shading, soiling, or equipment downtime, which are separate issues this calculator doesn't model.

Because the rate compounds year over year, even a modest difference — say 0.3% versus 0.7% annual degradation — produces a noticeably different final output percentage after 25 years, since the gap widens with every additional year of compounding. This is why panel warranties and spec sheets typically guarantee a specific degradation rate ceiling, since it materially affects how much energy (and revenue) a system will realistically produce over its full lifespan.