SmartCost Lab

Solar Panel Savings Calculator

Estimate the payback period and lifetime savings of rooftop solar from your expected generation, how much of it you'll use at home, your electricity price and what you're paid for exports.

Last reviewed 16 October 2026 · How we build and check calculators

System

kWh/yr

Required. Get a location-specific estimate from your installer's quote or a free official tool: NREL PVWatts (US), the EU JRC's PVGIS (UK and worldwide), Natural Resources Canada's PV potential maps, or your installer's Clean Energy Council–accredited design (Australia).

$

Required — from your quote.

How you'll use it

%

Example assumption. Homes that are empty in the day may use less; a battery, EV or heat pump can raise it. Your installer can estimate it.

¢/kWh

The price per kWh on your bill, including any taxes already built into it.

Reference rate: 18.31 ¢/kWh — U.S. average residential electricity price (average revenue per kWh, so fixed charges are already spread in; monthly, preliminary), U.S. EIA, Electric Power Monthly, Table 5.6.A, July 2026 (preliminary). Enter your own rate from your bill.

¢/kWh

Required — feed-in / export / net-metering credit from your supplier. Enter 0 if you aren't paid for exports.

Long term

$

Optional. Include an allowance for an inverter replacement if you like.

%

Default 0.5%/yr is the median degradation rate found by NREL's review of field data (Jordan & Kurtz, 2013). Use your panel warranty figure if you prefer.

%

Blank = flat prices. We don't forecast electricity prices.

Results will appear here

Fill in the highlighted fields. Anything marked as required has no verified default, so we need your own figure.

Start with a generation estimate for your roof

How much a system generates depends on location, roof direction and tilt, shading and system size — far too much to guess. That's why the generation field is required. Free official tools will estimate it from your address: NREL's PVWatts in the US, the EU's PVGIS for the UK (and anywhere else), Natural Resources Canada's solar maps, and your installer's design report. Installer quotes usually include an annual generation figure too.

Self-use is where the money is

Every kWh you use yourself saves the full price you'd otherwise pay for grid electricity. Every kWh you export earns the export, feed-in or net-metering rate, which is often much lower. So the share of generation you use at home matters as much as the size of the system. Homes that are occupied during the day, run a heat pump, charge an EV in daylight or add a battery tend to use more of their own generation.

generation(year n) = year-1 generation × (1 − degradation)^(n−1) savings(year n) = generation × self-use % × import price × (1 + price change)^(n−1) + generation × (1 − self-use %) × export price − maintenance payback = year when cumulative savings first exceed the installed cost

About the defaults

  • Degradation 0.5% a year — the median of nearly 2,000 degradation rates from field studies reviewed by NREL researchers (Jordan & Kurtz, 2013). Panel warranties often guarantee a specific minimum output after 25 years; you can use that instead.
  • Self-use 50% — an example starting point only; your installer can estimate it from your usage pattern.
  • Grid price change 0% — flat prices. If you expect prices to rise, payback shortens; we don't forecast it for you.

Worked example

A system generating 4,000 kWh a year, half used at home at 30¢ per kWh and half exported at 5¢, saves 2,000 × 0.30 + 2,000 × 0.05 = $700 in year one. If it cost $6,000 after rebates, simple payback is 6,000 ÷ 700 = 8.6 years. Over 25 years with flat prices and no degradation, the net gain would be 25 × 700 − 6,000 = $11,500.

This calculator doesn't discount future savings or include loan interest. If you're financing the system, a loan's interest can add materially to the cost — add it to the installed cost for a rough view.

Sources

Results are estimates based on the figures you enter and the stated assumptions. They are not financial, tax, legal or engineering advice. Spotted a problem? Tell us.