Solar Roof Area Calculator

1 kW of solar needs roughly 70 sq ft (6.5 m²) of shadow-free south-facing area with standard 540W Mono PERC panels. A 3 kW system needs ~210 sq ft, 5 kW ~350 sq ft, 10 kW ~700 sq ft. Our calculator factors in roof shape and obstructions.

Usable area excludes: walkways (1m buffer around the perimeter), AC outdoor units, water tanks, stairs, ventilation shafts, and shadow zones. Typically 60-80% of gross roof area is usable for panels. Irregular or L-shaped roofs have lower usable fractions.

30x40 ft = 1200 sq ft. After 20% obstruction and rectangular shape (95% usable), you get ~912 sq ft usable. At ~24 sq ft per 540W panel (including tilt separation), that's ~38 panels = ~20.5 kW. Large system — likely DISCOM sanction limits kick in before roof area does.

Yes. Sloped roofs save mounting cost (panels sit flush to the slope) and typically give 85-95% of optimal yield if the slope faces south. Our calculator works the same way — measure the sloped roof surface area, not the ground-projection.

Our calculator accounts for this with a shape factor. L-shaped roofs lose ~25% of usable area to cutouts. Irregular roofs lose ~40%. Always get an on-site survey for complex roofs — an installer can often recover 10-20% more area with custom sub-frames.

Row spacing depends on tilt angle and latitude. Rule of thumb: row spacing = panel length × tilt_factor, where tilt_factor ≈ 1.25 for 25° tilt. Too-close rows cast winter-morning shadows on each other, reducing yield by 5-15%.

A typical 5 kW system weighs ~250 kg spread across ~350 sq ft — roughly 0.7 kg/sq ft, well within the design load of modern RCC roofs. Older tin sheet or asbestos roofs may need a structural assessment. Ballasted mounts (no penetration) add 50-100 kg/panel and need stronger roofs.

Three options: (1) ground-mount solar if you have open land, (2) solar carport / pergola on the driveway, (3) elevated structure (BIPV) that shades the roof while generating power. Our team designs all three — ask during your site survey.