Solar PV system
Panel layout, kWp, PVGIS production and self-consumption
How the calculation works
Enter the location (latitude and longitude), the panel (dimensions and power) and one or more roof planes: length along the eaves, depth along the slope or in plan, pitch, orientation, edge distances, gaps and obstacles. The calculator lays out the panels, calculates kWp and sends each plane to the official PVGIS (JRC) for monthly and annual production. With annual consumption and a selected profile it calculates an hourly balance.
Formula and assumptions
Panels per row = ⌊(B − 2·edge + gap) ÷ (b + gap)⌋; rows = ⌊(D − edges + gap) ÷ (h + gap)⌋. kWp = number × Wp ÷ 1000. Slope length = plan depth ÷ cos(pitch). Flat roof: footprint = h·cos β, row pitch = h·cos β + h·sin β ÷ tan α (α = sun altitude at noon on 21 Dec).
Worked example
Plane 10 m along the eaves and 6 m along the slope, 0.3 m edge distances, 1.134 × 1.762 m panels (440 Wp) in portrait with 2 cm gaps: 8 × 3 = 24 panels, 10.56 kWp. Production for the location comes from PVGIS; with a manually entered yield of 1200 kWh/kWp the estimate would be 12,672 kWh per year (not a PVGIS result).
More worked examples
- Pitched roof with a plan depth of 5.2 m and 30° pitch: length along the slope 5.2 ÷ cos 30° = 6.0 m.
- Flat roof 10 × 12 m, panels tilted 15° at 45.8° N: row footprint 1.70 m, row pitch 2.91 m, 28 panels (12.32 kWp).
Number of 1.134 × 1.762 m panels (440 Wp, portrait, 0.3 m edge distances, 2 cm gap)
| Plane along eaves × along slope (m) | Panels | kWp | Panel area (m²) |
|---|---|---|---|
| 6 × 4 | 4 | 1.76 | 8.0 |
| 8 × 5 | 12 | 5.28 | 24.0 |
| 10 × 6 | 24 | 10.56 | 48.0 |
| 12 × 7 | 27 | 11.88 | 53.9 |
What affects real consumption
- Orientation and pitch of the roof plane.
- Edge distances, obstacles and local shading.
- Location and system losses.
Common mistakes
- Plan depth of the roof used as the length along the slope.
- System losses subtracted twice – in PVGIS and again in the calculation.
- Azimuth entered into PVGIS without conversion (PVGIS uses 0° for south).
Frequently asked questions
How many solar panels fit on a roof?
It depends on the actual dimension of the plane along the slope, edge distances, gaps and obstacles. The calculator lays out the panels in a grid and removes those touching the zone around an obstacle.
Where does the production data come from?
From the official PVGIS of the European Commission's Joint Research Centre, separately for each plane by tilt and orientation. If PVGIS is not available, the calculator shows this clearly.
Why is there no self-consumption share without a profile?
The self-consumption share depends on whether electricity is used in the same hour it is produced. This cannot be determined accurately from annual consumption alone, so it is only calculated as a labelled scenario with a selected profile.