Strings, Cables, Penetrations: How are they Connected?
String planning is the foundation of every PV system. It determines how the modules are connected, how many cables run across the roof, and how many of them need to be routed through the roof into the building. For selecting the correct roof penetration, the number of cables is the decisive factor.
Basics of String Planning
A string consists of several PV modules connected in series. Each string has two connection cables: a positive cable and a negative cable. These two cables must be routed from the roof to the inverter.
- 1 String = 2 PV cables (positive + negative)
- 2 Strings = 4 PV cables
- 3 Strings = 6 PV cables
Additionally, in many cases, an earthing cable (PE) is routed from the mounting frame into the building.
Practical Examples
Small Detached House (5-8 kWp)
Typically: 1 string with 12-16 modules. Requires 2 PV cables plus an optional PE cable. Suitable penetration: 2 PV or 2 PV+PE.
Medium Detached House (8-12 kWp)
Common: 2 strings. This results in 4 PV cables plus optional PE. Suitable penetration: 4 PV or 4 PV+PE.
Large Residential Building or Commercial (12-20 kWp)
Frequent: 3 strings with 6 PV cables plus PE. Suitable penetration: 6 PV or 6 PV+PE.
One Penetration or Several?
Generally: Fewer penetrations mean fewer potential leaks on the roof. A single penetration with sufficient cable openings is therefore preferable to a solution with several small penetrations.
NEXCAPE therefore offers variants with up to 6 PV penetrations plus PE in one component. This allows even larger systems to be realized with only one roof penetration.
Don't Forget Penetration Length
In addition to the number of cables, the length plays a role. It must bridge the distance between the tile surface and the inside of the roof. NEXCAPE penetrations are available in 105 mm, 125 mm, and 150 mm – suitable for the most common roof structures in Germany.
Conclusion: Plan First, Then Order
String planning determines the penetration – not the other way around. Solar installers should determine the number of cables early and select the penetration accordingly. All NEXCAPE penetrations made of UV-resistant TPU are manufactured in Germany using 3D printing and allow for tool-free installation without disassembling MC4 connectors.
Find the right penetration for every string plan: to the TPU roof penetrations for solar cables
Further reading: Select the appropriate variant by string count (2 PV / 4 PV, ± earthing)
