This calculator deliberately applies a usable-area percentage instead of assuming every square foot can hold modules. It still cannot see setbacks, obstructions, separate roof planes, shading or exact panel geometry. Orientation is represented with a simple planning factor; use the address-level Roof Analyzer for building-specific solar data.
Why we ask for usable roof percentage
A roof can have plenty of total area but much less installable area. Fire setbacks, ridges, hips, valleys, vents, skylights, chimneys and shaded roof planes all reduce practical panel capacity.
Roof direction changes when the panels produce
A south-facing plane usually maximizes annual production in the northern hemisphere, while east and west planes shift more generation toward morning or afternoon. See the visual orientation guide before treating all usable roof area as equivalent.
Roof material changes the installation method
Panel fit is only one part of rooftop solar. Asphalt shingles, standing-seam metal, tile and flat roofs can require very different mounting hardware and waterproofing details.
When to use the address-level analyzer
If you know the property address, use the Solar Roof Analyzer. It can use Google Solar API building insights where coverage is available. Then use the Solar Panel Calculator to compare roof capacity with the number of panels needed for your electricity use.