Solar Panel Calculator
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What Your Result Means
- System Size (kW): The total capacity of solar panels needed to offset your annual electricity usage. A typical U.S. home installs 6–10 kW.
- Number of Panels: How many individual panels (at your chosen wattage) make up the system. Standard 400 W panels are about 6 × 3.5 feet each.
- Payback Period: How many years of savings it takes to recoup the install cost. Under 10 years is generally considered a strong investment.
- 25-Year Savings: Net savings over the typical panel warranty life after subtracting install cost. Does not include maintenance, inverter replacement, or rate increases.
How This Calculator Works
You enter your monthly electric bill, the rate you pay per kWh, average daily sun hours for your area, and your preferred panel wattage. The tool divides your bill by the rate to estimate monthly usage, scales to annual kWh, then sizes a system to match that output given your sun hours. Install cost uses a $3/W national average. It does not factor in tax credits, net metering, or panel degradation.
Quick Questions
How do I find my area's sun hours?
The NREL PVWatts tool or the Global Solar Atlas provides peak sun hours by location. In the U.S., values typically range from 3.5 hours in the Pacific Northwest to 6+ hours in the Southwest.
Does this include the federal tax credit?
No. The federal Investment Tax Credit (ITC) can reduce your net cost by 30% through 2032. Apply it to the install cost shown here for a more accurate out-of-pocket figure.
Why does the calculator use $3 per watt?
$3/W is a commonly cited national average for fully installed residential systems including equipment, labor, and permitting. Actual prices vary widely by state, installer, and roof complexity — quotes typically range from $2.50 to $4.00/W.
Will solar panels produce the same amount every year?
Panels degrade roughly 0.5% per year, so output in year 25 is typically about 87–90% of year-one production. This calculator assumes constant output for simplicity.
What about battery storage?
This calculator estimates grid-tied solar without batteries. Adding a battery (typically $10,000–$15,000) extends payback but provides backup power and may help with time-of-use rate savings.
Sources
- U.S. Department of Energy — Homeowner's Guide to Going Solar (system sizing, costs, incentives)
- NREL PVWatts Calculator (sun hours and production estimates by location)
- DOE — Federal Solar Tax Credits (ITC details and timeline)
Method & review
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.