Thinking about going solar? This estimator gives you a ballpark panel count and system size based on your available roof space and electricity usage. It's a starting point for conversations with solar installers.
Roof & Usage
sq ft
kWh
Solar Resource
hrs
Scenario: You have 400 sq ft of usable roof, use 900 kWh per month, and get 5 sun hours per day.
Result: Roof fits up to 22 panels (at 18 sq ft each). To offset 900 kWh, you need about 15 panels, producing a 6 kW system. Recommended: 15 panels.
Divide your monthly kWh by 30 days, then by your sun hours, then by panel wattage (400W). For 900 kWh/month with 5 sun hours: 900/30/5 = 6 kW needed, or about 15 panels at 400W each. Actual sizing varies with shading, roof angle, and local weather.
Each 400W panel needs about 18 square feet. A 6 kW system (15 panels) needs about 270 sq ft of unshaded, south-facing roof. East and west-facing roofs work but produce 10-20% less energy.
A system that offsets 100% of your usage eliminates your electric bill except for minimal grid connection fees ($10-$20/month). At $0.15/kWh, a 6 kW system producing 900 kWh/month saves about $135/month, or $1,620/year.
Most solar panels are warrantied for 25 years and produce electricity for 30-40 years. They degrade about 0.5% per year, so after 25 years they still produce about 87% of their original output. Inverters last 10-15 years and may need replacement.
Want to learn more before you start your project?
Read the full guide →
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