How Much Roof Area Do You Need for Solar? A Sizing Guide

“Will my roof take a 5 kW system?” is the first question in most site surveys. The rule of thumb is simple; the exceptions are where projects go wrong.

The rule of thumb

Plan for roughly 100 square feet of shadow-free roof per kilowatt: about 300 square feet for 3 kW, 500 for 5 kW and 1,000 for 10 kW, including the walking space needed between rows for cleaning and maintenance.

Why usable area is smaller than roof area

• Water tanks, stair headrooms and parapet walls, plus the shadows they cast
• A neighbour's rising wall or a tree that shades part of the day
• Dish antennas, vents, ducts and any area you must keep clear for access
• Row spacing, so a tilted row does not shade the row behind it in winter

Shadow analysis beats arithmetic

Shading is not constant. A parapet that casts no shadow in June can cover half the array at 10 a.m. in December, when the sun is lowest and every unit counts. During a survey we map shadows across the day and across seasons, then place the array where it stays clear in winter, not just in summer.

When the roof is genuinely tight

• Move to higher-efficiency modules to fit more kilowatts into the same area
• Use an elevated structure so the terrace stays usable underneath and parapet shading is cleared
• Extend over a car park or walkway with an engineered structure
• Split the array across two roof faces using an inverter with independent MPPT inputs

Roof type changes the structure

RCC roofs take ballasted or chemically anchored structures without waterproofing problems. Metal sheet roofs use clamps matched to the sheet profile and need no drilling. Asbestos needs careful load assessment and usually a supporting frame. We quote the structure to your roof instead of applying one design everywhere.

Send us a rooftop photo and your monthly bill, and we will tell you what size actually fits before anyone visits.