Factory roof solar capacity
A 100 m × 50 m factory roof (5 000 m² footprint) at a 5° pitch fits 1 548 panels — 967.5 kWp in Red Energy's layout engine, producing roughly 1 619 000 kWh a year in Johannesburg. This page shows how that figure is reached, and why the same building pitched at 15° holds 860.
Hypothetical building, real engine. The roof below is not a customer site. Its dimensions were chosen to be typical of a South African light-industrial building. Every panel count and production figure is the actual output of the same layout and production code My Solar Plan runs on a customer's roof, regenerated whenever that code changes.
The roof
A rectangular shed with an east–west ridge has two faces: one sloping to the north and one to the south, each 2 500 m² in plan. Low-pitch metal-sheeting roofs are common on industrial buildings, so the example is run at two pitches. The location is a city-level reference point for Johannesburg, Gauteng.
Result at a 5° pitch
- 1 548panels (625 W each)
- 967.5 kWpmaximum roof capacity
- 1 619 000 kWhestimated production per year
- 1 674 kWh/kWpaverage specific yield
| Face | Plan area | Used for panels? | Panels | Capacity | PVGIS yield |
|---|---|---|---|---|---|
| North-facing | 2 500 m² | Yes — flat enough that direction does not matter | 774 | 483.75 kWp | 1 739 kWh/kWp/yr |
| South-facing | 2 500 m² | Yes — flat enough that direction does not matter | 774 | 483.75 kWp | 1 608 kWh/kWp/yr |
At 5° both faces are close to flat. Red Energy treats a face pitched at 10° or less as flat, so its direction does not exclude it. The south-facing side still produces less per kilowatt-peak (1 608 against 1 739 kWh/kWp a year), which the production estimate reflects face by face.
Result at a 15° pitch
Pitch the same building at 15° and the picture changes. The north face holds 860 panels (537.5 kWp), more than the 774 at 5°: the engine packs on the true sloped surface, and at 15° that slope is long enough for one more row of panels. The south face is now a genuine south-facing slope, so it is kept in the plan but given no panels. The roof as a whole drops to 860 panels and 537.5 kWp, producing about 982 000 kWh a year, although each north-facing kilowatt-peak now yields more (1 827 kWh/kWp).
How the layout is calculated
- Module: the Jinko Tiger Neo JKM625N-66HL4M-BDV, 625 W, 2 382 × 1 134 mm — the panel Red Energy installs, not a generic size.
- Orientation: roof panels are laid portrait, with the long edge running up the slope, on a grid aligned to the face's eave (or its longest edge when the face is too flat for its direction to be meaningful).
- Clearances: 0.3 m from every roof edge, 20 mm between panels, and a continuous 300 mm access gap after at most three rows. The edge and panel spacing are layout placeholders, not a fire-access, structural or regulatory requirement.
- Capacity: panel count × 625 W, with no derating.
- Production: PVGIS (the European Commission's Photovoltaic Geographical Information System, SARAH-3 satellite radiation data) for each face's own pitch and direction, modelled as free-standing mounting with Red Energy's 7% system-loss allowance and the distant terrain horizon, but no local shading, retrieved 2026-10-13. On a real property My Solar Plan uses Google Solar's own measurement of a roof face where one exists.
What reduces the count on a real roof
These figures are an upper bound for a clear roof. The layout does not yet account for shading from nearby buildings, parapets or plant; skylights, vents, air-conditioning units and other roof fittings; fire-access routes; or the roof's structural capacity and condition. Old or fragile sheeting may need attention before an installation. Each of these is checked during Red Energy's site inspection.
A larger roof is also not automatically a better system. How much of it is worth covering depends on how much electricity the business uses during the day — see commercial solar system sizing and the warehouse savings example.
Frequently asked questions
How many solar panels fit on a factory roof?
It depends on the usable roof area, its pitch and direction, and what is on the roof. In Red Energy's layout engine an unobstructed 5 000 m² low-pitch factory roof takes 1 548 panels of 625 W (967.5 kWp). Skylights, plant, fire-access routes and structural limits reduce that on a real roof.
Can a south-facing roof be used for solar in South Africa?
Red Energy never places panels on a pitched roof face that points south (within 45° of due south), because in the southern hemisphere it faces away from the sun. Roofs pitched at 10° or less are treated as flat and can be used whatever their direction.
Is the panel count in this example a quote?
No. It is the output of Red Energy's layout engine for a hypothetical, unobstructed roof. A real design is confirmed after a site inspection and matched to an approved equipment configuration, which can lower the panel count.
Build an indicative plan for your own site
My Solar Plan runs the same engine on your property: start with the address, confirm the roof, describe how the business uses electricity, then save the plan privately and refine it with Red Energy.
Start with my propertyLast reviewed 2026-10-13.