Solar Panels
Panel brands, wattage, price per watt and what suits Karachi conditions.
Solar panels · Size and layout
Solar Panel Size Calculator
How much roof does a system need? This page works it out from the panel dimensions and the sun angle in Karachi, with sums you can repeat.
- ✓ Panel dimensions and area
- ✓ Row spacing for flat roofs
- ✓ Free estimate on WhatsApp
Two sizes people mix up
A panel has an electrical size, in watts, and a physical size, in metres. The first decides how much power you get. The second decides how many panels fit on your roof.
This page covers the physical side. For the electrical side, see our solar system calculator.
Typical panel sizes
Approximate figures. Always read the datasheet for the model on your quote.
| Panel class | Approximate size | Area per panel |
|---|---|---|
| Small, 150 W | about 1.5 m by 0.7 m | about 1.0 m² |
| Mid, 450 W | about 1.9 m by 1.1 m | about 2.1 m² |
| Large, 585 W | about 2.3 m by 1.1 m | about 2.5 m² |
Sizes are rounded from common datasheets and vary by maker. Allow for frame clamps and walking space.
Roof area for a system
Use the 585 W class as the example.
- 1
Count the panels
Divide the system size by the panel watts. A 5 kW system with 585 W panels needs 5 divided by 0.585, which is about 9 panels.
- 2
Find the area of one panel
About 2.3 m times 1.1 m is 2.5 m². Add walking and clamp space and plan for about 2.6 m² each.
- 3
Multiply
Nine panels need about 23 m² of clear roof. That is roughly 4.7 m² per kW.
- 4
Subtract what is in the way
Water tanks, stairwell heads, parapet shade and satellite dishes all take space or cast shade. Mark them on a sketch.
Row spacing on a flat roof
On a flat roof, panels sit on tilted frames in rows. If rows are too close, the front row shades the one behind it, and the shaded panels drag down the output of the whole string.
The rule is simple geometry. The shadow of a panel is its raised height divided by the tangent of the sun's elevation. Use the lowest sun you care about, which is noon on the winter solstice.
Karachi lies at about 24.86 degrees north. The noon sun on 21 December stands at 90 minus 24.86 minus 23.44, which is about 41.7 degrees above the horizon.
Worked row-spacing example
A 585 W panel in portrait, 2.3 m long, tilted at 25 degrees. An invented layout to show the arithmetic.
- 1
Raised height
Height equals 2.3 times the sine of 25 degrees. That is 2.3 times 0.423, or about 0.97 m.
- 2
Shadow length
Divide by the tangent of 41.7 degrees, which is about 0.89. The shadow is about 1.09 m.
- 3
Footprint of the tilted panel
The panel covers 2.3 times the cosine of 25 degrees along the ground. That is 2.3 times 0.906, or about 2.08 m.
- 4
Row-to-row distance
Add the footprint and the shadow. The front edge of one row to the front edge of the next is about 3.2 m for shade-free noon in winter.
Noon is the minimum, not the target
The sun is lower at nine in the morning and three in the afternoon, so a layout that clears shade at noon still shades in the early and late hours. Wider spacing gives more morning and afternoon output but fits fewer panels. A flatter tilt shortens the shadow. The trade-off is covered in our panel angle guide.
Wind, weight and access
A panel is a sail. On a flat roof in a coastal city, the structure, the bolts and the ballast or anchors matter as much as the layout. Our panel stand guide covers the frame types.
Leave a walking path between rows and around the edge so that cleaning and repair are possible without stepping on the panels. A layout that cannot be reached will not be cleaned.
FAQs
Questions people ask us
Short answers. For your own property, send us your electricity bill and roof details.
Ask on WhatsAppAbout 2.3 m by 1.1 m, which is about 2.5 m². Check the datasheet for the model on your quote.
About 4.5 to 5 m² per kW with 585 W panels, including walking space. Flat roofs with tilted rows need more.
For a 2.3 m panel tilted at 25 degrees in Karachi, about 3.2 m from the front of one row to the front of the next clears noon shade in winter.
At noon on 21 December the sun is about 41.7 degrees above the horizon, from a latitude of about 24.86 degrees north.
Yes. Send a roof photo and rough measurements on WhatsApp, or we can visit. The estimate is free.
Sources
Related pages
Solar System Calculator
Size a whole solar system on paper: panels, inverter, battery, cost and payback.
Solar Panel Angle
Best tilt and direction for solar panels in Karachi, with the sun angle by season.
Panel Stands
Solar structure choices for Karachi: material, tilt, height and anchoring.
Not sure it fits your roof?
Send a photo of the roof with rough measurements. We will draw a layout and tell you how many panels fit. The estimate is free.