How does this solar calculator work?

Sun-Calc uses your home's address to pull real roof geometry and orientation data from the Google Solar API, then runs that through NREL PVWatts — the same model used by the U.S. Department of Energy — to estimate how much electricity your panels would produce each month. It factors in your local electricity rate, installation cost, and the federal Investment Tax Credit to give you an estimated payback period and 25-year ROI.

How long does it take for solar panels to pay for themselves?

The average solar payback period in the U.S. is 7–10 years, but it varies widely based on your location, roof orientation, local electricity rates, and installation cost. Homes in sunny states like California, Arizona, and Florida often see payback in 5–7 years, while cloudier regions may be closer to 10–12 years.

What is the federal solar tax credit (ITC)?

The federal Investment Tax Credit (ITC) may let you deduct 30% of your total solar installation cost from your federal income taxes. For example, a $20,000 system would qualify for a $6,000 tax credit, bringing your net cost to $14,000. The 30% rate is currently scheduled to remain through 2032, then step down to 26% in 2033 and 22% in 2034.

How much does a home solar system cost?

As of 2025, the average cost of a residential solar installation is $2.50–$4.00 per watt before incentives. A typical 6 kW system runs $15,000–$24,000 before the 30% federal tax credit, which brings it down to $10,500–$16,800. Prices vary by installer, panel brand, and region.

How many solar panels does my home need?

The number of panels depends on your energy usage, your roof's available area, and the wattage of the panels you choose. Most homes use 15–25 panels for a system that offsets 80–100% of their electricity bill.

What affects solar panel energy production?

The main factors are: roof tilt and azimuth (south-facing roofs at a 30–35° tilt are ideal in the U.S.), shading from trees or nearby buildings, your geographic latitude, local weather patterns, and panel efficiency.

Is solar worth it without a south-facing roof?

Yes, in most cases. East- and west-facing panels typically produce 15–20% less energy than south-facing panels, but the economics still work out in most states — especially where electricity rates are high.

What data sources does Sun-Calc use?

Sun-Calc combines three authoritative sources: the Google Solar API for roof geometry and solar irradiance data, NREL PVWatts v8 for energy production modeling, and SunCalc for solar path visualization.

Solar Home Calculator

1

Enter Your Address

Calculate surface area and angles automatically for your home.

2

Roof Analysis

Sections of the roof in size, pitch and angle which are rated based on potential solar production. Low producing areas are excluded in System Configuration, below.

Sun Path at Your Location

Yellow = sun path on summer solstice · Orange = equinox · Red = winter solstice

3

System Configuration

Recommended default solar system settings. Change these values to meet your needs. When ready, press Calculate Solar Output to see cost, return-on-investment and production estimates for your home.

System Size (kW)

Panel Type

Mount Type

System Losses (%)

Panel Tilt (°)

Panel Azimuth (°) 180° = South

Electricity Rate ($/kWh)

Install Cost ($/Watt)

4

Estimated Results

            Annual Energy
            —
            kWh/year
          

Annual Savings

— per year

System Cost

— before incentives

After 30% ITC

— net cost

            Payback Period
            —
            years
          

25-Year ROI

— return on investment

Monthly Energy Production

Approximate Monthly Breakdown

Month	Solar Radiation (kWh/m²/day)	AC Energy (kWh)	Savings ($)

How Solar Panel ROI Works

What Is Solar Panel ROI?

Return on investment (ROI) for solar panels measures how much money you get back — in the form of electricity bill savings — relative to what you paid for the system. A typical residential solar installation in the U.S. costs $15,000–$24,000 before incentives. After applying the 30% federal Investment Tax Credit, most homeowners pay $10,000–$17,000 out of pocket. Over a 25-year panel lifespan, that same system can generate $30,000–$60,000 in electricity savings depending on local rates and sunlight, making solar one of the highest-return home improvements available.

How Payback Period Is Calculated

Your solar payback period is the number of years it takes for cumulative electricity savings to equal your net system cost. For example, if your system costs $14,000 after incentives and saves you $1,600 per year on electricity, your payback period is about 8.75 years. After that point, every kilowatt-hour your panels produce is pure savings. Sun-Calc calculates this using your actual roof geometry, local solar irradiance data from NREL, and the electricity rate you enter — so the estimate reflects your specific home, not a national average.

Why Location Matters So Much

Solar production varies dramatically by geography. A 6 kW system in Phoenix, Arizona might produce 10,000 kWh per year, while the same system in Seattle, Washington might produce only 6,500 kWh — a 35% difference. But production is only half the equation. Electricity rates matter just as much: at $0.28/kWh (typical in California or Massachusetts), those 6,500 kWh are worth $1,820/year. At $0.12/kWh (typical in parts of the South), the same output is worth only $780/year. This is why two homeowners with identical systems in different states can have very different payback periods.

How Roof Orientation Affects Output

In the Northern Hemisphere, south-facing roof surfaces receive the most direct sunlight throughout the year, making them ideal for solar panels. A roof pitched at 30–35° facing due south (180° azimuth) typically captures 10–15% more energy than east- or west-facing alternatives. However, east and west orientations are still viable — they produce energy during morning and afternoon peak usage hours, which can actually be advantageous in states with time-of-use electricity pricing. Sun-Calc analyzes every segment of your roof individually using Google's Solar API, so you see the production potential for each surface, not just the best-case scenario.

What the 30% Federal Tax Credit Means for You

The Residential Clean Energy Credit (also called the Investment Tax Credit, or ITC) allows you to deduct 30% of your total solar installation cost directly from your federal income tax bill — not just as a deduction, but as a dollar-for-dollar credit. On a $20,000 system, that's $6,000 off your taxes. The credit applies to panels, inverters, labor, and permitting costs. It is currently scheduled at 30% through 2032. Importantly, you must have sufficient federal tax liability to use the full credit in one year; if not, the unused portion can be carried forward to the following tax year. Consult a tax professional to understand how the credit applies to your specific situation.

Understanding the Sun-Calc Estimates

Sun-Calc uses three professional-grade data sources to generate its estimates. The Google Solar API provides roof geometry, tilt, azimuth, and hourly irradiance data for your specific address using aerial and satellite imagery. NREL PVWatts v8 — the National Renewable Energy Laboratory's industry-standard model — translates that irradiance data into monthly and annual energy production estimates based on your panel type, system size, and losses. SunCalc visualizes the sun's path across your specific location throughout the year. All estimates are approximations. Actual production can vary due to shading changes, weather variation, equipment degradation, and installation quality. Always get quotes from licensed installers before making purchasing decisions.

Frequently Asked Questions

Question	Answer
How does this solar calculator work?	Sun-Calc uses your home's address to pull real roof geometry and orientation data from the Google Solar API, then runs that through NREL PVWatts — the same model used by the U.S. Department of Energy — to estimate how much electricity your panels would produce each month. It factors in your local electricity rate, installation cost, and the federal Investment Tax Credit to give you an estimated payback period and 25-year ROI.
How long does it take for solar panels to pay for themselves?	The average solar payback period in the U.S. is 7–10 years, but it varies widely based on your location, roof orientation, local electricity rates, and installation cost. Homes in sunny states like California, Arizona, and Florida often see payback in 5–7 years, while cloudier regions may be closer to 10–12 years. Use this calculator to get an estimate specific to your address.
What is the federal solar tax credit (ITC)?	The federal Investment Tax Credit (ITC) may let you deduct 30% of your total solar installation cost from your federal income taxes. For example, a $20,000 system would qualify for a $6,000 tax credit, bringing your net cost to $14,000. The 30% rate is currently scheduled to remain through 2032, then step down to 26% in 2033 and 22% in 2034.
How much does a home solar system cost?	As of 2025, the average cost of a residential solar installation is $2.50–$4.00 per watt before incentives. A typical 6 kW system runs $15,000–$24,000 before the 30% federal tax credit, which brings it down to $10,500–$16,800. Prices vary by installer, panel brand, and region.
How many solar panels does my home need?	The number of panels depends on your energy usage, your roof's available area, and the wattage of the panels you choose. Most homes use 15–25 panels for a system that offsets 80–100% of their electricity bill. This calculator automatically sizes a system based on your roof's usable area and adjusts for your local solar resource.
What affects solar panel energy production?	The main factors are: roof tilt and azimuth (south-facing roofs at a 30–35° tilt are ideal in the U.S.), shading from trees or nearby buildings, your geographic latitude, local weather patterns, and panel efficiency. This calculator accounts for all of these using real data for your specific address.
Is solar worth it without a south-facing roof?	Yes, in most cases. East- and west-facing panels typically produce 15–20% less energy than south-facing panels, but the economics still work out in most states — especially where electricity rates are high. The calculator will show you production estimates for your actual roof orientation so you can judge for yourself.
What data sources does Sun-Calc use?	Sun-Calc combines three authoritative sources: the Google Solar API for roof geometry and solar irradiance data, NREL PVWatts v8 for energy production modeling, and SunCalc for solar path visualization. These are the same tools used by professional solar installers and energy researchers.