How the solar payback calculator works
The payback arithmetic
Net cost (after the 30% federal credit and any state/utility incentives) ÷ annual savings (production × your rate, growing with inflation) = years to payback. After that, the system's output is pure savings for its remaining ~15–20 years. The calculator runs the compounding year by year rather than pretending rates stand still.
The three inputs that dominate
Your electricity rate (high-rate markets pay back in 6–9 years; cheap-power states can stretch past 15), the quote's price per watt (shop at $2.50–3.50/W installed pre-incentive), and actual production (south-facing, unshaded, right tilt). Two of the three you control by shopping; the third by design.
What the lifetime number is worth
A 25-year net gain of $25–60k is typical for a well-bought system in a mid-rate market — but only if the roof outlives the panels and the home is kept through payback. Solar improves sale value (studies show a premium roughly matching net system value) yet financing structure matters: owned systems transfer cleanly; leases complicate sales.