Solar, Energy & Batteries · Engineering calculator

Solar Savings Calculator

Enter system size, sun hours, rates and cost per watt to get annual savings, simple payback and the 25-year figure — with the honest caveats listed.

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Engineering calculatorSolar Savings Calculator

Last updated: 2026-09-15

How the calculation works

Annual production comes from size × sun × derate — the same model as the panel output calculator.
Self-consumed energy displaces retail purchases (the valuable part); exports earn the feed-in rate.
Payback divides installed cost by annual savings; the 25-year figure extrapolates undiscounted.

Worked example

A 6 kW system at 4.5 PSH, 0.8 derate: 7,889 kWh/yr. At 60% self-consumption ($0.18) and 40% export ($0.05): savings = 4,733 × 0.18 + 3,156 × 0.05 = $1,010/yr. At $2.50/W ($15,000): 14.9-year payback — or ~9 years with a 30% incentive.

Interpreting the result

Self-consumption is the economic lever: every kWh you use yourself is worth the full retail rate; exports often earn 20–30% of that. Battery storage shifts export to self-consumption but adds capital. The payback figure ignores rate inflation (real-world paybacks shrink as rates rise), degradation (~0.5%/yr) and inverter replacement (~year 12).

Assumptions

Fixed rates; no escalation or degradation applied.
No incentives, rebates or tax credits included — subtract them from installed cost for real payback.

Limitations

Net-metering policy changes are the biggest real-world risk to export economics.
Roof age, orientation and shading shift production; use site-specific PSH.

Frequently asked questions

What is a good solar payback period?

6–10 years is excellent and typical where rates are high and incentives exist; 12–15 years is marginal but still positive over a 25+ year system life.

Do solar panels increase home value?

Studies (e.g. Zillow/LBNL) find owned (not leased) systems add roughly the discounted value of remaining savings — typically $10–20k for a standard residential system in the US.