Updated 2026-04-30 · Methodology: named formula library

Solar Panel Calculator

Estimate how much electricity a solar panel system generates and how much money it saves you.

Monthly Electric Bill

Rate ($/kWh)

Peak Sun Hours / Day

Panel Watts

Solar Panels Needed

20 panels

You need approximately 20 solar panels (7.7 kW system) to offset your $150/month electric bill.

System Size7.7 kW

Panels Needed20

Est. System Cost$21,538

Federal Tax Credit (30%)$6,462

Net Cost$15,077

Annual Savings$1,800

Payback Period8.4 years

Data sources: CalcIntel Formula Library

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).

Worked Example

8 kW system, 5 sun-hours/day, $0.16/kWh

systemSize: 8
sunHours: 5
rate: 0.16
Result: ~$2,300/yr savings

8 × 5 × 365 = 14,600 kWh × $0.16 = $2,336.

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 does the Solar Panel Calculator work?

Enter your monthly electric bill (default: 150) and any other inputs; the calculator instantly applies its solar panel formula and shows the result with details. All math runs in your browser; nothing is sent to a server.

Is the Solar Panel Calculator accurate for solar decisions?

It uses standard, documented formulas that match published references. For high-stakes solar decisions, verify the result against an authoritative source (industry calculator, professional advisor, or government data). The calculator is a planning estimate, not a substitute for professional judgment.

What inputs does the Solar Panel Calculator require?

4 inputs: Monthly Electric Bill, Rate ($/kWh), Peak Sun Hours / Day, Panel Watts. Each has a sensible default; replace with your own values to get a result tailored to your situation.

Can I bookmark or share the Solar Panel Calculator?

Yes — the URL is stable: https://www.calcintel.com/calculator/solar-panel. Inputs reset to defaults on each visit (no input is stored), so screenshot or copy the result if you want to preserve a specific scenario.