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At present, about one million PV systems are installed in sult which is understood by all parties involved. The software
Germany. Based on the fact that self-generated electricity compares the risk with the technical expenditure and provides
is generally cheaper and provides a high degree of electri- economically optimised protection measures.
cal independence from the grid, PV systems will become an Section 4.5 (Risk Management) of Supplement 5 of the
integral part of electrical installations in the future. How- German DIN EN 62305-3 standard describes that a light-
ever, these systems are exposed to all weather conditions ning protection system designed for class of LPS III (LPL III)
and must withstand them over decades. meets the usual requirements for PV systems. In addi-
The cables of PV systems frequently enter the building and tion, adequate lightning protection measures are listed
extend over long distances until they reach the grid connec- in the German VdS 2010 guideline (Risk-oriented light-
tion point. ning and surge protection) published by the German In-
Lightning discharges cause field-based and conducted surance Association. This guideline also requires that
electrical interference. This effect increases in relation with LPL III and thus a lightning protection system accord-
increasing cable lengths or conductor loops. Surges do not ing to class of LPS III be installed for rooftop PV systems
only damage the PV modules, inverters and their monitor- (> 10 kW p ) and that surge protection measures be taken.
ing electronics, but also devices in the building installation. As a general rule, rooftop photovoltaic systems
More importantly, production facilities of industrial build- must not interfere with the existing lightning pro-
ings may also easily be damaged and production may come tection measures.
to a halt.
If surges are injected into systems that are far from the pow- Necessity of surge protection for PV systems
er grid, which are also referred to as stand-alone PV systems, In case of a lightning discharge, surges are induced on elec-
the operation of equipment powered by solar electricity (e.g. trical conductors. Surge protective devices (SPDs) which
medical equipment, water supply) may be disrupted. must be installed upstream of the devices to be protected
on the a.c., d.c. and data side have proven very effective in
Necessity of a rooftop lightning protection system protecting electrical systems from these destructive voltage
The energy released by a lightning discharge is one of the peaks. Section 9.1 of the CENELEC CLC/TS 50539-12 stand-
most frequent causes of fire. Therefore, personal and fire ard (Selection and application principles – SPDs connected
protection is of paramount importance in case of a direct to photovoltaic installations) calls for the installation of
lightning strike to the building. surge protective devices unless a risk analysis demonstrates
At the design stage of a PV system, it is evident whether a that SPDs are not required. According to the IEC 60364-4-44
lightning protection system is installed on a building. Some (HD 60364-4-44) standard, surge protective devices must
countries’ building regulations require that public build- also be installed for buildings without external lightning
ings (e.g. places of public assembly, schools and hospitals) protection system such as commercial and industrial build-
be equipped with a lightning protection system. In case of ings, e.g. agricultural facilities. Supplement 5 of the German
industrial or private buildings it depends on their location, DIN EN 62305-3 standard provides a detailed description of
type of construction and utilisation whether a lightning the types of SPDs and their place of installation.
protection system must be installed. To this end, it must be
determined whether lightning strikes are to be expected or Cable routing of PV systems
could have severe consequences. Structures in need of pro- Cables must be routed in such a way that large conductor
tection must be provided with permanently effective light- loops are avoided. This must be observed when combining
ning protection systems. the d.c. circuits to form a string and when interconnecting
According to the state of scientific and technical knowledge, several strings. Moreover, data or sensor lines must not be
the installation of PV modules does not increase the risk of a routed over several strings and form large conductor loops
lightning strike. Therefore, the request for lightning protection with the string lines. This must also be observed when con-
measures cannot be derived directly from the mere existence necting the inverter to the grid connection. For this reason,
of a PV system. However, substantial lightning interference the power (d.c. and a.c.) and data lines (e.g. radiation sensor,
may be injected into the building through these systems. yield monitoring) must be routed together with the equipo-
Therefore, it is necessary to determine the risk resulting from tential bonding conductors along their entire route.
a lightning strike as per IEC 62305-2 (EN 62305-2) and to take
the results from this risk analysis into account when installing Earthing of PV systems
the PV system. For this purpose, DEHN offers the DEHNsupport PV modules are typically fixed on metal mounting systems.
Toolbox software which allows to determine the risk. A risk The live PV components on the d.c. side feature double or
analysis performed by means of this software provides a re- reinforced insulation (comparable to the previous protective

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