How Much Roof Area Does Your Company Need for Solar Panels? A Sizing Guide

“How much roof do I need?” and “what plant fits?” are the same equation solved in opposite directions: one starts from a target capacity and calculates the area; the other starts from the area and calculates the maximum capacity. A serious proposal does both and lets the lower one govern.

Converting consumption into kWp is covered in the guide on how many panels you need and is taken as given here. What changes for a company is that consumption is an hourly curve, not a number, and that the roof is not a free rectangle but a surface with edges, equipment and shade.

For an industrial plant, when the energy is consumed matters, not just how much. A building on a daytime shift consumes a lot at midday and little on Sundays; a cold store consumes almost the same all day. What is produced when the load is low goes to the grid, and an exported kWh is not recognised in the same way as a self-consumed one, as the article on surplus sales explains.

That is why it is worth calculating capacity with three limits and keeping the lowest. The energy limit divides the annual energy you want to cover by the site’s specific yield (kWh per kWp per year). The load limit compares the daytime power on working days with the plant’s maximum instantaneous output, which is below the installed kWp. The area limit is what fits on the roof, the subject of the rest of this guide.

As a yield reference, PVGIS calculates for 10° facing south, with 14 % system losses, about 1,322 kWh per kWp per year in Bogotá, 1,445 in Medellín, 1,268 in Cali and 1,572 in Barranquilla (ERA5 reanalysis, 2005-2023, no nearby shading). These are indicative values; a proposal should carry its own simulation. The IDEAM solar radiation atlas is the national reference to consult.

Two regulatory limits intersect with area. For the 1 MW ceiling of a small-scale self-generator, when the plant connects through inverters, what counts is the sum of their nominal AC capacities, not the kWp of modules (article 3 of Resolución CREG 174 de 2021, which refers to the 1 MW limit of Resolución UPME 281 de 2015). And if the plant delivers surplus energy at voltage level 1, before requesting the connection you must check that the grid has availability under the parameters of article 6 of that resolution (self-generators that do not deliver surplus are not subject to those limits); if they are not met, the process of article 17 is followed. To see which category applies to a large plant, read the article on self-generation and distributed generation.

Four modules from three manufacturers, from 575 to 720 Wp, consulted on 7 November 2026, give the dimensions and occupancy in the list that closes this section (power at standard test conditions, STC; the power range is the one on the datasheet).

The conclusion is counterintuitive: a 700 Wp module does not occupy less area per kWp than a 580 Wp one. The four datasheets are between 217 and 232 W per square metre of module, that is, between 4.3 and 4.6 m² per kWp. Raising the power per unit reduces the number of modules and connections, not the area; to gain square metres you have to raise efficiency, and among current commercial modules the margin is a few points.

Two practical warnings. Weight: about 12 kg per square metre in glass and aluminium alone, without mounting structure or ballast, and between 31 and 38 kg per module 2.3 to 2.5 m long, which affects how it is handled on the roof. And compatibility: K2 Systems, for example, publishes for its Dome 6 flat roof system (tilted at 10°) modules up to 2,390 × 1,170 mm, and for its Dome Zero system (mounted parallel to the roof, at 0°), up to 2,390 × 1,305 mm. A module 1,303 mm wide, like the 700 Wp one on the list, fits the second and not the first, but the second does not tilt the module, with the consequences for cleaning seen below.

Module area is not roof area. On a pitched roof, with the array parallel to the plane, almost all of it is used: the NREL technical-potential study assumes the modules cover 98 % of the plane, with 1.27 cm between modules. On a flat roof with a tilted structure, each row shades the next and they must be spaced apart: with NREL’s criterion for the United States (15°, modules facing south) the modules cover 70 % of the surface, which is why flat roofs on large buildings are used less efficiently.

That 70 % reflects a different criterion (annual self-shading losses of about 2.5 %) and US latitudes; near the equator the sun is higher on the worst day, shadows are shorter and rows can be closer together. Shade-free spacing comes from simple geometry: row pitch = L × (cos β + sin β ÷ tan γ), with L the module length along the slope, β the tilt and γ the sun’s profile angle (its elevation in the north-south plane) at the least favourable hour you want to cover. In Medellín (6.2° N), on 21 December it is about 52° at 9:00 and 15:00 solar time, and about 43° at 8:00 and 16:00.

For a 2,382 mm module in portrait, with no shade from 9:00 to 15:00 that day, the pitch is 2.67 m at 10° and 2.78 m at 15°: the modules cover 89 % of the field at 10° and 86 % at 15°. In Bogotá, Cali and Barranquilla, at 10°, it comes to between 5.0 and 5.2 m² per kWp. This is our own calculation with a declared shading criterion, so the comparison with NREL’s 70 % is indicative, not like-for-like; a real plant is designed with a shading simulation. To minimise reverse currents, RETIE requires guaranteeing the absence of partial shading by means of protections that may be built into the equipment (item n, number 2, of article 3.17.23); it does not set a spacing between rows.

In square metres per kWp of field (array and gaps between rows, without edges or walkways): about 4.6 with the array parallel to a pitched roof, about 5.0 at 10° and 5.3 at 15° on a flat roof with the criterion above, and about 6.4 with NREL’s 70 %. The gross roof needs more, as the example shows.

In the east-west configuration the rows go in pairs, back to back, at 10°, and the spacing against shade is reduced to a maintenance walkway: more modules fit per square metre, with slightly lower yield per kWp (between 97.1 % and 99.4 % of south at 10°, according to PVGIS). How many more fit depends on the structure and should be read from its datasheet.

Near the equator, orientation and tilt matter much less than at high latitudes. In four cities, PVGIS gives between 99.1 % and 100.4 % of the 10° south yield for tilts of 5° to 15° facing south; between 98.0 % and 100.3 % for the horizontal plane; between 97.8 % and 99.8 % at 20°, and between 93.5 % and 97.4 % at 30°. Facing south, the tilt PVGIS optimises ranges from 3° in Cali and 5° in Medellín to 14° in Barranquilla (6° in Bogotá).

At 10°, an east-facing array produces between 98.0 % and 101.2 % of what the south-facing one produces; west-facing, between 96.3 % and 99.1 %; with half the rows on each side, between 97.1 % and 99.4 %; and north-facing, between 93.7 % and 98.5 %.

The minimum tilt has a practical reason. LONGi’s manual suggests not going below 10° so that rain washes the dust off and water does not pool on the glass; Trina recommends the same and warns that horizontal modules, at 0°, have no self-cleaning and must be cleaned more often. That is why 10° is the usual compromise on a flat roof: it costs almost no energy and avoids the problems of the horizontal plane. Before going below 10° to gain area, check the module warranty.

With several orientations on the same roof, RETIE sets an electrical condition: in the same array or string associated with the same inverter maximum power point tracker, modules must not be given different orientations unless DC-DC converters or module-level power electronics are installed (item n, number 3, of article 3.17.23 of Book 3 of Resolución 40284 de 2026; works begun before 1 January 2026 may demonstrate conformity under Resolución 90708 de 2013, according to article 3 of 40284). LONGi asks the same for modules in a string.

On a pitched roof, orientation and tilt are already given and what is decided is which slopes to use. With the array parallel to the plane, occupancy is 4.4 to 4.7 m² per kWp of covered plane (with NREL’s 98 %). LONGi also asks for 10 cm between the frame and the roof when installed on parallel brackets, so that air can circulate.

It is not advisable to discard a slope just because it is not the ideal one: at 20° facing east or west, yield is between 93 % and 100 % of that at 10° facing south. On a steep slope (30°) the loss is larger: between 88 % and 98 % of the 10° south yield facing east or west, and between 79 % and 89 % facing north (PVGIS, depending on the city and the side).

The type of roof, its condition and its load capacity are covered in outline by the article on whether panels damage the roof. Here it is enough to remember that the design must check that the roof can carry the weight of the array and its structure (RETIE requires taking the panel’s weight and dimensions into account so it does not damage the building, item o of article 3.17.23) and that NSR-10 (Decreto 926 de 2010, as amended) sets out the design loads in its Title B.

Gross roof area is almost never usable area. These deductions recur on a factory or warehouse roof, though none is universal:

Edges. K2 Systems sets 600 mm as the minimum distance to the roof edge in its ballasted flat roof systems; that strip also serves for drainage, anchoring and safety.

Walkways. RETIE requires the design to define the physical means of access and movement for assembling, inspecting, operating and maintaining the panels (walkways, corridors, access points, circulation areas), and that they be built into the finished installation and be physically verifiable by the inspection body (additional paragraph of item o of article 3.17.23). It does not set widths, and every metre of walkway is a metre without modules.

Equipment and obstacles. Air-conditioning units, extractors, tanks, ducts, skylights and roof hatches take up area and cast shade towards the north in December and January at these latitudes. With the 52° profile angle from the section on row spacing, a parapet, tank or duct 2 m high casts about 1.5 m of shadow in the north-south direction at 9:00 and about 2.15 m at 8:00 (the actual shadow is longer, 2.65 m at 9:00, and slants westwards in the morning).

Nearby power lines. Title 10 of Book 3 of RETIE sets minimum safety distances between energised parts of power lines and buildings (article 3.10.1 and Table 3.10.1.a). Among the explanatory notes of the title, note 4 specifies that the horizontal distance “b” is measured from the nearest energised part, taking into account the real possibility of vertical expansion of the building and that the line must never end up above the construction. If an overhead line runs next to the roof, check with the designer and the grid operator that those distances are maintained.

Lightning protection. Photovoltaic installations on roofs, rooftops or open ground must undergo a lightning risk-level assessment under Title 13 of Book 3 and the IEC TR 63227 standard or GTC-IEC-TR 63227 (item p of article 3.17.23). The protection may require elements on the roof, which also take up space.

As an order-of-magnitude reference for walkways, the 2021 International Fire Code (IFC) is a model code of the International Code Council (United States) that each jurisdiction adopts on its own and that does not apply in Colombia. For buildings other than those containing Group R-3 occupancies (single-family and two-family dwellings) it requires a clear perimeter of 1.83 m (6 ft), reducible to 1.22 m (4 ft) if either axis of the building is 76 m (250 ft) or less; interior pathways between array sections at intervals of no more than 45 m (150 ft) across the length and width of the roof; and pathways at least 1.22 m (4 ft) wide to standpipes and ventilation hatches, around roof access hatches and around smoke vents. It exempts carports and similar detached structures. If the insurer or the fire brigade ask for similar criteria, those metres are subtracted from usable area.

To give an idea of what “usable” means in a potential study, NREL excludes surface that, because of shade, would produce less than 80 % of the energy of an unshaded system, and treats a roof as suitable only if it has at least one contiguous plane of 10 m² or more meeting those criteria (it also excludes north-facing planes and tilts above 60°). It is a statistical US study, but it leaves a useful idea: usable area is the area that produces well, not the area that is free.

The example is modelled, not a real project. Every input is declared in the list of assumptions at the end of this section, so that it can be replaced with your company’s figures.

Step 1, energy limit: 40 % of consumption is 288 MWh, and at 1,400 kWh per kWp per year it gives 206 kWp. Step 2, load limit: the 150 kW of daytime load, divided by 0.8 (maximum instantaneous output over installed kWp), gives 187.5 kWp; with more, at midday on working days the plant would export. Step 3, take the lower one: 312 modules of 600 Wp, 187.2 kWp, producing about 262 MWh a year, 36 % of consumption. In PVGIS’s hourly simulation for Medellín that plant barely exports except on Sundays, when it delivers about 17 MWh a year, a little over 6 % of what it produces.

Step 4, modules: 312 × 2.70 m² = 843 m², or 4.50 m² per kWp. Step 5, field: 943 m² at 10° facing south with the no-shade criterion from 9:00 to 15:00 (5.04 m² per kWp), 983 m² at 15° (5.25) and 1,204 m² with NREL’s 70 % (6.43). Step 6, gross roof: if 30 % is lost to edges, walkways, equipment and shade (an assumption of the example, not a reference figure), about 1,350 m² are needed at 10°, 1,400 m² at 15° and 1,720 m² with NREL’s 70 %: between 7.2 and 9.2 m² per gross kWp. That is why the short rule of 5 to 7 m² per kWp of usable roof in the how-many-panels guide works for the field or a pitched roof, but falls short for the gross roof of a flat building.

Step 7, the inverse reading: with only 1,000 m² gross and the same 30 % deduction, 700 m² would be usable and between 181 and 231 modules would fit (109 to 139 kWp), producing between 152 and 194 MWh a year, 21 % to 27 % of consumption. A partial plant is not a bad plant: it is the one that fits. The example does not say how much your company should cover; it shows how area changes with the shading criterion and the deduction.

When the lowest of the three limits is area, there is a reasonable order of options.

Partial self-consumption. It is the simplest way out: since an exported kWh is not recognised in the same way as a self-consumed one (see the article on surplus sales), it can also be a well-proportioned plant for the load. It is sized for the part of the roof that produces well and the rest of consumption stays on the grid.

Rearranging the roof. Moving a unit or grouping skylights can free more usable area than changing the module. The row spacing can also be reviewed, with a shading simulation and not by eye, and an east-west configuration at 10° evaluated.

Carports over parking lots or yards. NREL mentions them, along with façade integration, as surfaces additional to the roof. Their structure (foundations, clearance height, wind) is calculated separately.

Façade. It is the option with the lowest yield per kWp: compared with a roof at 10° facing south, PVGIS calculates 35 % to 42 % facing south, 47 % to 52 % facing east, 41 % to 50 % facing west and 21 % to 31 % facing north. It only makes sense when there is no other surface or the façade is part of the building’s design.

Land. A ground-mounted plant uses the row calculation of a flat roof, plus access roads, fencing, an inverter area and setbacks. The regulatory category that applies depends on the installed or nominal capacity, on whether surplus is delivered and on the grid it connects to, and is confirmed with the grid operator. If one company splits its capacity across roof, carport and land, keep in mind article 29 of Resolución CREG 174 de 2021: the capacity of an AGPE, AGGE or distributed generator cannot be split in order to report it as independent plants and apply the resolution as if they were. If your company’s split falls under that case, the grid operator or an adviser should confirm it.

A proposal that has looked at the roof answers with numbers what this guide raises. It helps to arrive at the site visit with twelve months of consumption, the hourly load curve if the operator provides it, and a plan or photos of the roof with the equipment marked.

If you want your roof area reviewed with these criteria, you can request a business quote from Nodosolar. Whoever prepares it, it should return: