Home energy usage
The number of solar panels needed depends on how much electricity the home uses on average. A typical home uses 800-1500 kWh per month. More energy efficient homes will need fewer panels.
Panel wattage
Residential solar panels are typically 250-400 watts. More efficient panels with higher wattage require fewer panels.
Roof space and sunlight
The physical roof size and unshaded area limits the number of panels. Panels are usually spaced for optimal sunlight capture.
Location
The average sunlight hours per day determines output. More sunlight equals more energy production with fewer panels needed.
Net metering limits
Some states limit the amount of energy that can be net metered or sent back to the grid. More panels may be needed to maximize use of solar energy produced.
Budget
The number of panels comes down to how much a homeowner can reasonably spend. Panels range from $150-$400 each fully installed.
As a general guideline, most homes install 10-25 panels for adequate solar energy production, with solar providing 40-80% of total use. Actual needs depend on the specific home's details.