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. Note: the 30% federal residential solar credit ended after 2025, so verify current state and utility programs. Net metering credit (%) 100 means every kWh you produce offsets a kWh at the full retail rate. Set it lower if your utility pays wholesale rates for exported power.

Assumptions (tap to view and edit)

System lifetime (years) Panel warranties commonly run 25 years. Annual electricity price increase (%) Applied to the value of the electricity your system offsets each year. System derate factor Accounts for inverter losses, wiring, soiling, and temperature. 0.80 is a standard planning value.

The calculator sizes the system to cover your annual usage and assumes no paid exports: extra production beyond what you use earns nothing here. If your utility pays well for exported power, your real numbers would be better.

Your estimate

–Estimated system size

$0Gross cost, before incentives

$0Net cost, after incentives

$0Saved per year, year 1

–Simple payback period

$0Net savings over system life

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.
Oversized systems earn little. This calculator sizes to your usage and assumes no paid exports. Bigger is not better without a good export rate.
Get at least three installer quotes. Installed cost per watt is the biggest variable in the payback math, and quotes vary widely.