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Solar Payback Calculator

Solar Payback Calculator

Estimate a grid-tied solar project's size and simple economics from electric use, utility rate, peak sun hours, system losses, installed cost, optional incentives, and annual rate changes.

22-calculator project library Reviewed 2026-07-25Calculations run privately in your browser

Enter project details

Example values are prefilled

How to use this solar payback calculator

Estimate solar system size, panel count, gross and net cost, annual savings, payback period, and 25-year cash flow.

Formula

Annual kWh = monthly bill ÷ utility rate × 12. Required kW = target annual kWh ÷ (sun hours × 365 × performance factor). Net cost subtracts only user-entered incentives and rebates.

Worked example

Example: A $180 monthly bill at $0.20/kWh implies about 10,800 kWh per year. A 90% offset targets 9,720 kWh of annual solar production before sizing for sun hours and losses.

Accuracy and limitations

This is a screening estimate, not a proposal. Roof orientation, shade, weather data, utility tariffs, export compensation, financing, taxes, equipment replacement, and incentive eligibility can dominate results.

Frequently asked questions

Why is the incentive default zero?

Programs and tax eligibility change. Enter only a percentage and rebate amount that you have independently verified for the project.

What are peak sun hours?

They summarize daily solar energy into equivalent hours at full irradiance; use a reputable site-specific estimate.

Does payback include financing?

No. It models a cash purchase. Loan interest, dealer fees, and tax treatment should be added separately.