Roof Solar Capacity Estimator
Estimate how many solar panels fit on your roof and what system size you can install.
Roof Requirements for Solar Installation
Setback Requirements
Building codes in most US jurisdictions require a 3-foot clear border around all roof edges. This fire access setback reduces the usable roof area significantly — a 40×30 ft roof loses 204 sq ft (17%) to setbacks alone, leaving 34×24 ft of usable space.
How Pitch Affects Panel Count
A medium-pitch roof (6–9:12) is ideal for solar because it naturally tilts panels toward the sun while still allowing easy installation. Flat roofs need ballasted racking (reducing density), and steep roofs make mounting hardware complex and reduce how many rows fit.
Roof Direction
South-facing roofs receive the most sun throughout the day in the Northern Hemisphere and are rated at 100% output. Southwest and southeast orientations produce about 95% as much energy. East/West-facing roofs produce roughly 85%, while north-facing roofs are generally not recommended (65% factor).
Shading Losses
Even partial shading from trees, chimneys, or neighboring structures significantly reduces output — especially in traditional string inverter systems. Modern microinverters and power optimizers mitigate shading losses at the panel level.
Annual Production Estimate
Annual production is estimated using 4.5 peak sun hours per day (US average) and 80% system efficiency. Adjust in our Solar System Size Calculator for your exact location.