Page 378 - 35_DS702_E_2014_Lightning_Protection_Guide

air-termination air-termination
system pile-driven foundation system screw-in foundation

lightning lightning
current current
carrying carrying
connection connection

Figure 9.19.4 Pile-driven and screw-in foundation with a lightning current carrying connection between the air-termination system and the
earth-termination system

Solar generator and systems of the external
lightning protection system
The air-termination systems of the external lightning protec-
tion system are vital. In case of an uncontrolled lightning
strike to the PV system, lightning currents will flow into the
electrical installation and cause severe damage to the system.
When installing the external lightning protection system, it
must be observed that solar cells are not shaded, for example,
by air-termination rods. Diffuse shadows, which occur in case
of distant rods or conductors, do not negatively affect the PV
system and the yield. Core shadows, however, unnecessarily
stress the cells and the associated bypass diodes. The required
distance can be calculated and depends on the diameter of
the air-termination rod. For example, if an air-termination
Figure 9.19.5 UNI saddle clamp
rod with a diameter of 10 mm shades a module, only a dif-
fuse shadow is cast on the module if a distance of 1.08 m
lightning currents. If the modules, cables and the opera- is maintained between the module and the air-termination
tions building with the weather station are located in the rod. Annex A of Supplement 5 of the German DIN EN 62305-3
protected volume of the external lightning protection standard provides more detailed information on the calcula-
system, it is not to be expected that direct lightning cur- tion of core shadows.
rents are injected into the lines. If the connection to the
distribution network operator (DNO) is established on the Cable routing in PV systems
low-voltage level, this point is connected to the main earth- All cables must be routed in such a way that large conduc-
ing busbar (MEB) via type 1 lightning current arresters (e.g. tor loops are avoided. This must be observed for the single-
DEHNventil) since partial lightning currents are present. The pole series connections of the d.c. circuits (string) and for the
same applies to the incoming telecommunication cables for interconnection of several strings. Moreover, data or sensor
which type 1 arresters such as BLITZDUTOR or DEHNbox lines must not be routed across several strings and form large
(Figure 9.19.6) must be installed. conductor loops with the string lines. For this reason, power

www.dehn-international.com LIGHTNING PROTECTION GUIDE 377