Solar Calculator

Estimate rooftop solar bill savings, payback period and net present value over the selected period.

Solar panels only, paid upfront. Use an installed quote after rebates and your electricity plan. Generation and tariffs are editable estimates.

How this tool works

Reviewed 22 September 2026. User-supplied solar quote and electricity tariffs.

Calculation outline

Year-one generation equals installed kW × daily kWh per kW × 365. Generation falls by the selected decline rate each year.
Value solar used at home at the import tariff, capped at annual household usage. Value remaining generation at the feed-in tariff. Deduct upkeep and the selected inverter replacement.
Subtract installation cost from cumulative savings. Estimate first cash payback within a year assuming even savings. Discount each year-end net saving to calculate net present value (NPV).

Worked example

A 1 kW system producing 4 kWh per kW daily generates 1,460 kWh a year. Using half at home at 30c/kWh saves $219, and exporting half at 10c/kWh earns $73. With no upkeep or decline, $1,000 upfront pays back in about 3.4 years.

Limits

No battery, financing, tax, energy-price growth or property resale benefit. Daily supply charges remain payable and are excluded. Enter the final installation price after rebates; no rebate is added again.
Self-consumption is a share of solar generation, not household demand. An annual cap is only an approximation: shading, roof orientation, seasonal and hourly demand, export limits and tariff changes affect actual results. Use an installer estimate or SunSPOT for generation.
Assumes every unused kWh can be exported at the entered rate. Export charges, curtailment and time-of-use rates are not modelled. Net savings may be negative. First payback can precede later replacement costs; check the full cash-flow table and final NPV.

Sources

General information and estimates only, not personal financial, tax or legal advice. Replace example inputs with your own quotes and budget.