Solar Panel Calculator
How many solar panels does your home need? Enter your bill — get your answer.
How to Use This Calculator
Start with your electricity bill
Enter your monthly electricity bill in dollars and your electricity rate per kWh. The calculator divides your bill by the rate to find your monthly energy consumption in kilowatt-hours. If you don't know your rate, check your utility bill — it's usually listed as "price per kWh" or "energy charge." The US average is about $0.15/kWh, but it ranges from $0.10 (Louisiana) to $0.35+ (Hawaii).
Set your location's sun hours
The peak sun hours field is the most important factor after your bill. It represents the equivalent hours of full-strength sunlight your location gets per day, averaged over the year. Phoenix gets ~6.5, Seattle ~3.5, Miami ~5.5, Denver ~5.0. This isn't the same as daylight hours — a cloudy day might have 10 hours of light but only 2 peak sun hours.
Pick your panel wattage
Modern residential panels range from 350W to 450W. Higher-wattage panels mean fewer panels needed but cost more per panel. The 400W default is the current sweet spot for residential installations in 2026.
Use scenario buttons
Not sure where to start? Click a scenario button — Small home, Average home, Large home, or All-electric home — to pre-fill realistic values. Adjust from there.
Expand "More options"
For precise sizing, expand More options. The bill offset controls what percentage of your bill you want to cover (100% is typical, 110% if you want to sell excess). System efficiency accounts for real-world losses — temperature, shading, inverter conversion, wiring resistance, and dust. The 86% default is conservative and works for most installations.
The Formula
The calculator uses this sizing formula:
The key insight: peak sun hours and system efficiency are the multipliers that turn theoretical output into real-world production. A 400W panel doesn't produce 400W for 8 hours — it produces the equivalent of 400W for your location's peak sun hours, minus system losses.
When you change peak sun hours in the calculator, you can see how dramatically location affects the number of panels needed. Moving from Seattle (3.5 hours) to Phoenix (6.5 hours) nearly halves your panel count.
Example
The Johnson family — Austin, TX
The Johnsons pay $180/month for electricity and want to offset 100% of their bill with solar. Austin gets about 5.0 peak sun hours per day. They're looking at 400W panels.
Result
The 27-panel system at 10.6 kW produces enough to cover their annual usage of 16,620 kWh. At current Austin installation costs of ~$2.80/W, this system would cost approximately $29,680 before the 30% federal tax credit, bringing the net cost to about $20,776. At $180/month savings, the payback period is roughly 9.6 years — with the panels producing clean energy for 25+ years.