Solar decision guide
How many solar panels do I need?
A national-average starting point is about 18 panels for a 6.9 kW system. That uses 855 kWh per month and 400-watt panels; your roof and usage can move the result materially.
- Starting panel count
- 18
- System size
- 6.9 kW
- Monthly use
- 855 kWh
National-average walkthrough.
Sized to the published usage basis.
National-average basis.
The count follows the load
Start with annual electricity use, size a system for local solar exposure, then divide that capacity across panels. The roof check comes last: shade and fragmented planes can reduce how much of the calculated system actually fits.
Frequently asked questions
What is a useful national starting point?
About 18 panels for a 6.9 kW system, based on 855 kWh of monthly use.
What panel output does this estimate use?
The estimate uses 400-watt panels.
Why can my count differ?
Your annual electricity use, local solar exposure, panel output, roof orientation, shade, and usable roof geometry all change the count.
Check your specific roof
General guidance is a starting point. Use your address to check orientation, shading, and usable roof area free.