How much space do solar panels need on the roof of your house or building?

Last updated: October 23, 2026

Solar panels require approximately 5 to 6 square meters per kilowatt on a metal roof if installed parallel to it, and 7 to 10 square meters per kilowatt on a flat concrete roof because the panels are installed at an angle in rows with spacing between them to avoid shading. The final figure depends on the actual usable area after excluding tanks, air conditioners, and walkways.

What is the area of one solar panel?

Most solar panels used today in residential and commercial projects have a power rating of approximately 540 to 600 watts, and their dimensions are around 2.3 meters long and 1.1 meters wide, which translates to approximately 2.5 to 2.6 square meters per panel. This means that one kilowatt (roughly equivalent to two panels) requires about 4.7 square meters of panel space, before accounting for any additional distances.

But the size of the panels is one thing, and the required surface area is another. The difference comes from the installation method, the spacing between rows, the passageways needed for cleaning and maintenance, and the distance from the edges of the roof.

How many square meters do you need per kilowatt depending on the type of roof?

Metal surface (sheet metal)

In warehouses and factories with metal roofs, the panels are often installed parallel to the roof slope, almost touching each other with minimal gaps. Therefore, the required space is close to the area of the panels themselves, with the addition of maintenance passageways. This type is used Metal surface mounting structure Lightweight and fixed to the sheet metal.

flat concrete surface

In houses and buildings with concrete roofs, panels are installed at a south-facing angle to improve production. The problem is that the front row casts a shadow on the row behind it, especially in winter when the sun is low. Therefore, a gap is left between the rows, and the greater the angle of inclination, the greater the required gap. Here, [the following is used] Inclined structure for concrete surfaces.

High structure and carports

When the roof is cluttered with tanks and air conditioning units, panels can be raised above them on a raised structure, utilizing the upper space without removing anything. In facilities with parking, the parking spaces themselves are transformed into production space. car sunshades.

These are estimated figures that include spacing between rows and simple aisles, and vary according to board size, width, and structure design.

How is the distance between rows calculated on a concrete surface?

The idea is that the height of the back edge of the slanted panel casts a shadow whose length depends on the sun's altitude. The distance is usually calculated based on the worst time of year acceptable for the design, which is winter mornings and evenings.

Illustrative example: Arrange boards at a 25° angle on a roof in Riyadh

The following figures are approximate and assume a 2.28-meter longitudinally mounted panel and a design sun height of approximately 30°:

• Horizontal span of the inclined plate = 2.28 × cos 25° ≈ 2.07 meters.
• Height of the back edge = 2.28 × s 25° ≈ 0.96 m.
• Length of shadow behind row = 0.96 ÷ tan 30° ≈ 1.67 m.
• The distance from the beginning of one row to the beginning of the next row is ≈ 2.07 + 1.67 ≈ 3.74 meters.
• Area per panel = 3.74 × 1.13 (panel width) ≈ 4.2 m², which is approximately 7.7 m² per kilowatt before the corridors.

If we reduce the angle to 15°, the horizontal span becomes approximately 2.20 meters, the shadow about 1.02 meters, and the distance between row beginnings about 3.22 meters, thus reducing the area to approximately 6.6 m² per kilowatt. Therefore, some designers choose a slightly less-than-ideal angle when space is limited, as the gain of an additional panel can compensate for the small difference in output per panel. For complete details, see the article on spacing between solar panel rows, and the article on choosing the angle itself. Best orientation and tilt angle for panels.

How do you determine the usable area on your roof?

The most common mistake is calculating the system based on the total surface area. The surface is actually filled with things that cannot be installed directly on top of it:

• Water tanks and their bases, stairwell, and ventilation outlets.
• Outdoor units of air conditioners and their extension routes.
• The edges closest to the parapet (the surrounding wall) because its shadow falls on the nearby panels.
• The necessary passageways to access the panels for cleaning and maintenance.
• A safe distance from the edges of the roof, especially in tall buildings exposed to wind.

Practical method: Draw a simple plan of the surface in meters, mark each obstacle on it, then calculate the empty rectangular areas facing south or where rows can be arranged facing south.

Illustrative example: A house with an area of 300 square meters

Let's assume a concrete roof with a total area of 300 m². After excluding the tanks, stairwell, air conditioners, corridors, and parapet edges, approximately 60% remains usable. These figures are approximate.

• Usable area ≈ 300 × 0.6 = 180 m².
• At an angle of 25° and an area of 8 m² per kilowatt approximately including corridors: 180 ÷ 8 ≈ 22 kilowatts.
• That is, approximately 40 panels with a power of 550 watts.
• At an angle of 15° and an area of 7 m² per kilowatt: 180 ÷ 7 ≈ 25 kilowatts, i.e., approximately 46 panels.

Then compare this figure to your consumption. If the space accommodates more than you need, choose the optimal angle for production; if it's less, use the solutions in the next section.

What do you do if the surface area is not enough?

1. Choose higher power panels: The higher-capacity board produces more than approximately the same area.
2. Reduce the angle of inclination slightly: To bring the rows closer together, as in the example.
3. Use a high structure: High structure of solar panels The panels are raised above the tanks and air conditioners, and provide shade for the roof below.
4. Utilize other spaces: Parking lots or an adjacent ground-level yard suitable for ground installation.
5. Reduce consumption first: Improving insulation and replacing old equipment reduces the size of the system required.

Before all else, ensure the structural integrity of the roof can withstand the weight of the panels, the frame, and wind loads, especially in older buildings. This is a design aspect that should be reviewed by a professional.

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