Solar Panel Calculator
Estimate how much electricity a solar panel system generates and how much money it saves you.
You need approximately 20 solar panels (7.7 kW system) to offset your $150/month electric bill.
Why This Calculation Matters
The Solar Panel Calculator helps you screen a solar investment before spending serious money on a formal quote. It captures the core economics; to finalize a decision, combine these numbers with installer-specific proposals, tax credits, and utility rate plans.
How to Use This Calculator
- Enter your values in the input fields, each one has a label and help text explaining what to type.
- Results appear instantly as you type; there's no "calculate" button to press.
- Change any input to compare scenarios side by side.
All math happens in your browser. Nothing you type is sent to a server, saved, or shared.
Beyond the Calculator
Real-world performance depends on local climate, shading, equipment efficiency, and rate structure. Use this number as a screen, then get 2-3 installer quotes for the definitive answer.
Solar Panel Estimation
Daily production = System size (kW) × Peak sun hours × 0.85 (efficiency factor)
Average Peak Sun Hours by Region
- Southwest US: 6-7 hours
- Southeast US: 4-5 hours
- Northeast US: 3.5-4.5 hours
- Midwest US: 4-5 hours
- Pacific Northwest: 3-4 hours
Federal Tax Credit
The federal solar Investment Tax Credit (ITC) covers 30% of installation costs through 2032.
Formula
Daily generation (kWh) = system size (kW) × peak sun hours × 0.8 derate factor. U.S. peak sun hours range from ~3 (Pacific Northwest) to ~6 (desert Southwest).
When to Use This Calculator
- Screen a solar, battery, or EV investment for payback period.
- Model what-if scenarios as utility rates, tax credits, or panel costs change.
- Compare vendor proposals on a consistent basis.
Limitations & Common Mistakes
- Actual system output depends on shading, panel orientation, local weather, and equipment losses.
- Tax credits and utility rate plans change, verify with your installer and utility provider.
- Payback calculations ignore financing costs and opportunity cost of capital.
Frequently Asked Questions
How many solar panels do I need?
The average US home uses about 900 kWh/month. A standard 400W panel produces about 1.5-2 kWh/day in most areas. You'd need 15-20 panels (6-8 kW system) to offset most of your electricity. Exact numbers depend on your location, roof angle, and energy usage.
How long does it take for solar panels to pay for themselves?
Most residential solar systems pay for themselves in 6-10 years through electricity savings and the federal tax credit. After payback, you're essentially getting free electricity for another 15-20 years (panels last 25-30 years).
Does this include tax credits and rebates?
Use the input fields for any incentives that apply to you. Federal, state, and utility incentives change often, verify current programs with your installer and local utility.
Is this calculator free to use?
Yes. The Solar Panel Calculator is free, requires no signup, and runs entirely in your browser, your inputs are never sent to a server.
How often is this calculator updated?
Formulas are reviewed against authoritative sources, and any rate or price data is refreshed on an automated schedule. Check the "as of" date on any live data panel for the most recent refresh.
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