Solar ROI Calculator | The Greener Electron

See whether rooftop solar pays off for your home. Enter your electric bill and your local sunshine and the calculator estimates your system size, costs, payback period, and long term net savings. Every assumption is visible and editable, because honest math beats marketing math.

Your electricity use

Average monthly electric bill ($) Your average over a full year if you can. Check past bills for your best estimate. Electricity price ($ per kWh) Find this on your electric bill. US average is around $0.17 per kWh. Peak sun hours per day Average for your roof over the year. Roughly 3.5 to 4 in cloudy northern areas, 5.5 to 6.5 in the sunny southwest. Search your state plus “peak sun hours” for a local figure.

The solar option

System cost per watt ($) Installed price per watt of panels, before incentives. US average is roughly $2.50 to $3.00. Use a real quote here when you have one. Incentives and rebates ($) Total tax credits, state rebates, and utility incentives you expect to receive. If they exceed gross cost, the estimate shows a negative net cost and immediate payback. Note: the 30% federal residential solar credit ended after 2025, so verify current state and utility programs. Solar self-consumption (% of production) Share of your solar production used in your home as it is generated. 40% is an example starting value, not a measured default; estimate it from utility or interval data. The model caps on-site use at annual electricity consumption. Export credit (% of retail rate) Applied only to exported kWh. 100 means exports earn the same per kWh as the avoided retail rate; 25 means one quarter of it. Use your utility’s export tariff if available.

Assumptions (tap to view and edit)

System lifetime (years) Panel warranties commonly run 25 years. Annual electricity price increase (%) Applied uniformly to the combined on-site savings and export credit estimate each year; actual tariffs may change differently. System derate factor Accounts for inverter losses, wiring, soiling, and temperature. 0.80 is a standard planning value.

The calculator sizes the system to approximately your annual usage. It values the estimated on-site share at the avoided retail rate and remaining annual production at the export credit. This annual estimate cannot match solar generation and household use hour by hour; actual self-use and utility tariffs can differ.

Your estimate

–Estimated system size

$0Gross cost, before incentives

$0Net cost, after incentives

$0Saved per year, year 1

–Simple payback (no escalation)

$0Net savings over system life

Simple payback uses year-one savings and excludes future rate increases. Net savings over system life includes the entered annual increase assumption.

Simple-payback point25 year system life

Before you decide

This is an estimate, not a quote. Production assumes a suitable, unshaded roof facing the right way. Shading, roof angle, and roof condition can cut output a lot.
Utility rules change. Rates and net metering policies shift over time, and what your utility pays for exported power makes or breaks the math.
Panels degrade slowly. Output falls roughly 0.5% per year. This simple math does not model that, so treat the long term savings as slightly optimistic.
Exports may be worth less. Production that is not used in the home is valued at your export-credit assumption, which may be below the retail electricity price.
Get at least three installer quotes. Installed cost per watt is the biggest variable in the payback math, and quotes vary widely.

Comparing installer quotes? Get the free printable Solar Quote Checklist.