Science

Solar Panel Calculator

Estimate the solar system size, number of panels, installation cost, payback period, and 25-year savings based on your electricity bill and location.

Quick Answer

A typical US home ($150/mo bill) needs a ~6 kW system (15 panels at 400W). Cost: ~$18,000 before the 30% federal tax credit (~$12,600 after). Payback: ~7 years. 25-year savings: ~$32,000+.

Disclaimer: This calculator provides rough estimates for educational purposes only. Actual costs, savings, and system sizing depend on roof orientation, shading, local utility policies, net metering rules, equipment quality, and installation specifics. Consult a licensed solar installer for an accurate quote. Tax credit eligibility depends on your individual tax situation; consult a tax professional.

Estimate Your Solar System

Enter your electricity bill details and select your region.

System Size
7.7 kW
Panels Needed
20
@ 400W each
Monthly Usage
1,154 kWh
Cost Breakdown
Gross Cost$23,077
Federal Tax Credit (30%)-$6,923
Net Cost$16,154
Savings & Payback
Annual Savings$1,800
Payback Period9 years
25-Year Net Savings$28,846

Average Peak Sun Hours by Region

Region / StatePeak Sun Hours/Day
Arizona / Nevada6.5 hrs
California / Texas5.5 hrs
Florida / Colorado5 hrs
North Carolina / Georgia4.8 hrs
New York / Pennsylvania4 hrs
Ohio / Michigan3.8 hrs
Oregon / Washington3.5 hrs
Alaska3 hrs

About This Tool

The Solar Panel Calculator provides a quick estimate of what size solar system your home needs, how many panels that requires, the approximate cost after federal tax credits, and how long it takes to recoup your investment. It uses your monthly electricity bill, local electricity rate, and average peak sun hours to generate personalized estimates.

How Solar Panel Sizing Works

Solar system size is determined by your electricity consumption divided by the average daily peak sun hours in your area. If you use 1,000 kWh per month (about 33 kWh per day) and get 5 peak sun hours, you need a system that produces 33/5 = 6.6 kW. At 400W per panel, that is approximately 17 panels. Real-world factors like panel orientation, roof angle, shading, and system losses (typically 15-20%) may require a slightly larger system.

Understanding the Federal Tax Credit

The federal solar Investment Tax Credit (ITC) allows homeowners to claim 30% of the total system cost as a tax credit. This is a dollar-for-dollar reduction in federal taxes owed, not merely a deduction. The 30% rate applies through 2032. Many states offer additional incentives, rebates, or performance-based incentives that can further reduce the net cost. Some utilities also offer net metering, which credits you for excess electricity sent back to the grid.

Long-Term Value

Solar panels typically come with 25-year performance warranties guaranteeing at least 80% of original output. Many panels continue producing well beyond 25 years. With electricity rates historically increasing 2-3% annually, the value of solar energy increases over time. A system that saves $1,800 per year now may save $2,500+ per year in 10 years, accelerating the return on investment after the payback period.

Frequently Asked Questions

How many solar panels do I need for my home?
The number depends on your electricity usage, local sun hours, and panel wattage. Divide your monthly kWh usage by 30 (days) to get daily kWh, then divide by your area's average peak sun hours to get the system size in kW. Divide the system size in watts by your chosen panel wattage (typically 350-450W). A typical US home using 900 kWh/month in an area with 5 sun hours needs about a 6 kW system, or approximately 15 panels at 400W each.
How much does a solar panel system cost?
As of 2025, residential solar costs $2.50-3.50 per watt before incentives. A typical 6 kW system costs $15,000-21,000 before the federal tax credit. The 30% federal Investment Tax Credit (ITC) reduces this to $10,500-14,700. Many states offer additional rebates and incentives. Costs have dropped over 70% in the last decade and continue to decline. Financing options include loans, leases, and power purchase agreements (PPAs).
What is the solar panel payback period?
The payback period is typically 6-10 years depending on your electricity rate, sun hours, system cost, and incentives. In high-rate states like California or Hawaii, payback can be as fast as 4-6 years. In lower-rate states, it may be 8-12 years. After payback, solar electricity is essentially free for the remaining panel life. Solar panels typically have 25-year warranties and can last 30+ years with minimal degradation.
What is the federal solar tax credit?
The federal Investment Tax Credit (ITC) allows you to deduct 30% of the total solar system cost from your federal taxes. This applies to systems installed through 2032, then steps down to 26% in 2033 and 22% in 2034. The credit applies to the full system cost including equipment, labor, and permitting. It's a dollar-for-dollar tax reduction, not just a deduction, making it one of the most valuable solar incentives available.
How many peak sun hours does my area get?
Peak sun hours vary by location. The US Southwest (Arizona, Nevada) gets 6-7 hours, the South and California get 5-6 hours, the Mid-Atlantic and Midwest get 4-5 hours, and the Pacific Northwest gets 3.5-4.5 hours. Peak sun hours represent the equivalent hours of full-intensity sunlight (1,000 W/m²), not total daylight hours. Even cloudy areas can benefit from solar — Germany, which gets less sun than most US states, is one of the world's largest solar markets.

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