Solar Panel Size Calculator
Estimate how many solar panels you need based on your electricity usage and location
Your Information
Rate will auto-fill based on state average
Your Solar System
System Size
0kW
Number of Panels
0
Roof Space Needed
0sq ft
Annual Production
0kWh
Estimated Cost
$0
After 30% Tax Credit
$0
💡 How we calculate: We use your electricity bill (or kWh), state average sun hours, roof direction efficiency, and panel wattage to estimate the system size, panels needed, roof space, and costs. Results are estimates—get quotes from solar installers for accurate numbers.
Frequently Asked Questions
How many solar panels do I need?
The number of panels depends on your electricity usage, location, roof direction, and offset goal. Our calculator estimates panels by dividing your needed system size (in kW) by the wattage of each panel. A typical 400W panel system for an average home might need 20-25 panels.
What does "offset percentage" mean?
Offset is how much of your electricity bill solar covers. 50% offset means solar generates half your usage; 100% means it covers all your electricity needs. Higher offset requires more panels and costs more, but gives better long-term savings.
Why does my state matter?
Different states have different amounts of daily sunlight (sun hours), affecting how much energy panels produce. Sunny states like California need fewer panels; cloudier states like Washington need more. We use state average sun hours in our calculation.
What's the 30% tax credit?
The federal Investment Tax Credit (ITC) allows homeowners to claim 30% of solar installation costs on their taxes. This is a federal incentive available through 2032. Many states and utilities offer additional rebates—check with your local programs.
How much roof space do I need?
A typical 400W solar panel is about 18 sq ft. For a 10kW system (25 panels), you'd need roughly 450 sq ft of unshaded roof space. Check if your roof can fit the system and has good sun exposure all day.
What's annual production?
Annual production is how much electricity your system generates per year. It's calculated using system size, state sun hours, 80% system efficiency, and roof direction. This helps estimate savings and payback period.
How accurate is this calculator?
This is an estimate based on averages. Actual results depend on roof angle, shading, local weather, panel efficiency, and inverter losses. Get quotes from solar installers for precise system designs and costs tailored to your home.
What if my roof can't fit the panels?
If roof space is limited, you can reduce your offset goal (50% instead of 100%), use higher-wattage panels, or explore alternative installations like ground-mounted systems or canopies. Consult a local solar installer.
Does shading affect results?
Yes. Our 80% system efficiency accounts for typical losses (inverter, wiring, temperature). If your roof has significant shading from trees or buildings, actual production will be lower. A solar consultant can do a detailed shading analysis.
When should I get a professional quote?
After using this calculator to understand system size and costs, contact 2-3 local solar installers. They'll do a roof inspection, analyze shading, discuss financing options, and provide accurate quotes. Most consultations are free.