Solar Panel Calculator
Estimate solar system size, panel count, and roof area needed
Average monthly electricity consumption
Daily peak sun hours at your location
Wattage per single solar panel
Panels Needed
—
panels
System Size
—
kW
Roof Area Needed
—
sq ft
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Planning a solar installation? Sizing your system correctly is the key to offsetting your electric bill without overpaying for capacity you don't need.
- Find your monthly kWh usage on a recent electric bill
- Look up your local peak sun hours (4-6 for most of the US)
- Enter the wattage of the panel model you plan to buy
- Use the roof area result to confirm you have enough unshaded space
Expert Insights
Smart analysis for your Solar project
Sun Hours Mapping
Peak sun hours vary from 3 in the Pacific Northwest to 6-7 in the Southwest. Our calculator pairs your usage with local sunlight to right-size the array.
System Loss Factor
The 0.8 efficiency factor accounts for inverter losses, wiring resistance, soiling, and temperature derating — real-world conditions that cut output 15-25%.
Panel Orientation
South-facing panels at a 30° tilt produce the most annual energy. East/west arrays need roughly 15-20% more panels for the same output.
Calculation Formula
Daily kWh = Monthly usage / 30
System size (kW) = Daily kWh / Peak sun hours / 0.8 (system losses)
Panels needed = ceil(System size * 1000 / Panel wattage)
Roof area = Panels * 18 sq ft per panel
Solar Panel Type Comparison
| Panel Type | Efficiency | Cost per Watt | Power Output | Roof Area/Panel |
|---|---|---|---|---|
| Monocrystalline | 18-22% | $1.00-1.50 | 350-450W | 17-19 sq ft |
| Polycrystalline | 15-17% | $0.70-1.00 | 250-350W | 18-20 sq ft |
| Thin-Film | 10-13% | $0.50-0.80 | 100-200W | 20-25 sq ft |
| Bifacial Monocrystalline | 20-24% | $1.20-1.80 | 400-500W | 17-19 sq ft |
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- National Renewable Energy Laboratory (NREL) — Solar Resource & PV System Modeling. Learn more
- Solar Energy Industries Association (SEIA) — Residential Solar Guides. Learn more
- U.S. DOE Office of Energy Efficiency & Renewable Energy — Homeowner's Guide to Going Solar. Learn more
Frequently Asked Questions
How many solar panels do I need?
Divide your system size in watts by the wattage of a single panel. For example, a 6 kW system using 400W panels needs 15 panels (6000 / 400 = 15).
How much roof area do I need for solar panels?
Each standard residential panel needs about 18 sq ft. A 6 kW system with 15 panels requires roughly 270 sq ft of unshaded, south-facing roof space.
What are peak sun hours?
Peak sun hours measure the daily sunlight equivalent at 1000 W/m2. Most US locations receive 4-6 peak sun hours per day; the Southwest can reach 6-7.