Solar panel sizes and weight

Residential solar panels have grown slightly over the years. The older standard format of about 1.65 by 1 metre still covers plenty of roofs, but new panels usually measure around 1.75 by 1.15 metres. That is almost exactly 2 square metres per panel, at a thickness of 3 to 4 centimetres. The power of such a panel typically sits between 400 and 450 watt-peak.

Those large panels of over 2 metres sound attractive for their power, but they rarely work on a home roof. They are heavier, harder to handle on scaffolding and leave you less room to puzzle around roof windows and chimneys. For homes, the standard format is almost always the logical pick.

A standard residential panel weighs some 20 to 25 kilos. Versions with glass on both sides sit at the top of that range; the difference between those builds is covered in glass-glass vs glass-foil. On a pitched roof the mounting system comes on top: rails and roof hooks. All in, you are looking at roughly 12 to 15 kilos per square metre of roof.

That sounds like a lot, but in proportion it is modest: the roof tiles already up there usually weigh more per square metre than the entire installation adds. The structure of a normal tiled roof can therefore almost always take solar panels. A flat roof is a different story, because ballast tiles hold the frames in place and the weight per panel quickly adds up to several dozen kilos. On light timber roofs, such as extensions and garages, we run the numbers beforehand.

How that ballast works and when a structural check is sensible is covered in our piece on solar panels on a flat roof.

On a pitched roof the maths is simple: about 2 square metres per panel, contiguous and free of obstacles. Panels are not laid right up to the edge; keep about 20 centimetres of distance from the ridge and the roof edges, in line with the layout guidance from Milieu Centraal on roof suitability (Dutch). A roof window or chimney breaks up the face and in practice often costs you one or two panels.

On a flat roof a south-facing layout needs about 2.3 square metres of roof per square metre of panel, because the rows would otherwise shade each other. Per panel that is well over double what a pitched roof needs. An east-west layout packs tighter and uses the roof better.

Want to go from roof area to an actual panel count, including your consumption? That step-by-step plan lives in how many solar panels do I need.

Panels can go on the roof portrait (upright) or landscape (sideways). On pitched roofs portrait is most common, but landscape sometimes works out better around a dormer or on a low roof face above a gutter. It changes the rail direction and the number of roof hooks, and sometimes a rotated bottom row fits exactly one panel more.

On flat roofs wind comes into play: at the same tilt, a landscape panel catches less wind than a portrait one, which improves the ballast calculation. In the layout plans we draw, we try both orientations before the final count goes into the quote.

If an awkward gap remains, filler options exist: smaller panels or non-connected dummy panels that visually complete the layout. The latter is purely cosmetic, but it does make a roof calmer to look at.

We draw a layout plan for every quote based on your roof dimensions, obstacles and shading. During the survey we re-measure the roof, check the state of the tiles or roofing and, on flat and lightweight roofs, assess the load capacity. So you know in advance exactly how many panels are coming, how they will sit and what the installation will deliver.

Not sure whether your roof can take the size and weight? Send us your roof dimensions or a photo and we will do the maths. What else to look for when buying is covered in buying solar panels.