East–west or south on flat roofs.

South-facing rows are tilted towards the south – 10–20° for the flat-roof systems in Ritwerk’s catalogue. Each row casts a shadow behind it, so the rows need clear space between them. SOLTOP gives a c/c spacing of 1.60, 1.80 and 2.00 m between rows for its south system at 10°, 15° and 20°, and describes these dimensions as flexible.

East–west sets the panels in pairs, back to back, one facing east and one facing west. With SOLTOP and Nordmount they are tilted at 10°. Between the pairs there is only a narrow valley gap, and SOLTOP’s east–west datasheet works with 2.35 m c/c per pair. The area is used more densely, but every panel tilts away from the south.

The ratio between the panels’ power and the inverter’s rated output is called the DC/AC ratio. With east–west, the two sides see their peak irradiance at different times, and the array’s peak is lower. The same ratio therefore clips less than with a south-facing array. How much is clipped depends on the location and the array, so calculate it rather than reaching for a rule of thumb.

Ritwerk simulates each panel orientation separately, hour by hour, and clips at the inverter’s rated output. Clipping appears in the loss chain, the ratio appears in the report, and the designer warns when the ratio is above 1.5.

The manufacturer’s c/c spacing is a compromise between shading and area. In Madrid and Rome, south-facing rows at 15° with 1.80 m c/c are unshaded at midday all year. In Kassel and Stockholm they shade each other in winter, but that is also when yield is at its lowest. What the shading costs over the year is worked out with an hour-by-hour shading calculation.

In Ritwerk, rows on racking shade each other in the shading analysis, both south-facing rows and east–west pairs. If you change the row spacing or the valley gap, the panels are laid out again straight away, and the shading loss per panel shows in the report.

Soltop and Nordmount Flow are ballasted without penetrating the roof, while Weland’s low-pitch system is fixed mechanically through sealing plates. SOLTOP writes that its east–west system needs no or only a little extra ballast, while its simpler south system needs more ballast than the version with side spoilers and wind deflectors. Ballast is determined per project, and the edge and corner zones need the most.

The denser layout weighs more per m². SOLTOP gives the distributed load as about 13.1 kg/m² for east–west at 2.35 m c/c and 9.3 kg/m² for south at 15° with 1.80 m c/c, based on 19 kg panels. For east–west the value is without extra ballast. The roof’s load capacity for self-weight, ballast and snow needs to be checked.

Ritwerk does not calculate the ballast. When you choose Soltop or Nordmount, the designer refers you to the manufacturer’s calculation – SOLTOP’s Systemstatik or NM Planner – and marks the panels in the edge and corner zones.

Sweden. Several aspects of how PV affects fire safety are not regulated directly in the building regulations, writes Storstockholms brandförsvar (the Greater Stockholm fire and rescue service) in its guidance (revised 2026). It applies to the service’s eleven municipalities and recommends at least 2.5 m to a fire wall or fire compartment boundary, continuous arrays of no more than 40 × 40 m with 5 m between them, and keeping panels away from roof edges and smoke vents. Loads are calculated to BFS 2024:6.

Germany. Musterbauordnung § 32 (5), in the wording adopted by the Bauministerkonferenz on 22–23 September 2022, requires at least 0.50 m from fire walls for solar systems mounted no more than 30 cm above the roof surface or integrated into the roof, and at least 1.25 m for others, such as racking higher than that. No distance is required if the fire wall protects against the spread of fire. The building code of the federal state is what is binding.

Spain. Wind load on flat roofs (5° or less) is calculated to CTE DB SE-AE with zones F, G, H and I in table D.4, and the pressure coefficients in EN 1991-1-4 may be used (D.3.6). The snow load uses a shape coefficient of 1 up to a 30° pitch. The CTE fire safety document DB SI does not mention PV systems specifically.

Italy. Snow and wind are calculated to NTC 2018. The snow shape coefficient is 0.8 up to a 30° pitch, and in snow zone III, where Rome lies, the ground snow load is 0.60 kN/m² up to 200 m above sea level. With Rome’s solar elevation, 1.80 m c/c is enough for south-facing rows at 15° to stay unshaded at noon all year round.