Solar Payback Period Calculator

Both electricity rates and panel output change every year rather than staying fixed, so a single static "annual savings" figure applied uniformly across the system's life would misrepresent the real trajectory. Projecting year by year lets rising electricity rates and slowly declining panel output offset each other realistically, giving a payback period and total savings figure that better reflects how the system will actually perform over its lifetime.

It's a sentinel value indicating that cumulative savings never caught up to the net system cost within the full 25-year projection this calculator runs — in other words, under the entered assumptions, the system doesn't pay for itself within that modeled window. It isn't a literal prediction that payback happens in year 26; it simply flags that payback wasn't reached in the timeframe modeled.

They move in opposite directions but at very different magnitudes for most systems — panel degradation typically runs well under 1% per year, while electricity rate increases are commonly assumed in the low single digits percent annually, so rate increases generally outpace degradation's drag on savings. That's why savings in later years of the projection are usually still higher than first-year savings, even though the system is producing somewhat less electricity by then.

This calculator adds up nominal dollars from every year without adjusting for the time value of money, which is a simpler, more intuitive figure for a homeowner comparing solar against their current electric bill than a full net-present-value analysis would be. The tradeoff is that these totals treat a dollar saved in year 25 as equally valuable as a dollar saved today, so they'll read somewhat higher than a properly discounted figure would.