Lightning and surge protection for rooftop PV systems (MASTER)

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Professional planning with an approved concept

The most commonly used PV systems are rooftop systems. They are particularly prone to damage caused by direct and indirect lightning effects due to their exposed location.

Since the PV system is directly connected to the electrical installation of the building, lightning effects can have severe consequences:

Damage to the building resulting from direct lightning effects or fire
Injury of people inside the building
Destruction of or damage to electronic devices caused by direct or indirect lightning effects

Comprehensive protection is therefore necessary and should be planned carefully.

Risk analysis – Prerequisite for professional planning

Professional planning including a risk analysis is indispensable to the safe and reliable operation of PV systems. This risk analysis is performed according to EN 621305-2. It must be adapted to the relevant building and include lightning and surge protection.

Good coordination between the different trades is important

The most important goal of PV installers is to optimise the use of the roof area. Lightning protection installers, however, have to observe the separation distance¹ for the lightning protection system. Lack of coordination may cause considerable problems. Therefore, coordination between roofers / lightning protection installers and installers of photovoltaic systems / electricians is essential not only when constructing a new building, but also when retrofitting roof-mounted systems.

¹What is separation distance? It's the necessary distance between the down conductor and another earthed metal part of the building.

Application examples for rooftop systems

No external lightning protection

Example 1

What is the situation when a photovoltaic system is newly or retrofitted?
Does the new system make lightning protection measures necessary for the entire building?

Normative requirements and notes:

If no external lightning protection system is installed (and is not required according to the risk analysis in conformity with IEC 62305-2), Supplement 5 to DIN EN 62305-3 recommends installing a type 2 surge protective device on the DC and AC side to protect PV systems from inductive and conducted interference. Similarly, the data interfaces should be protected by adequate surge arresters.

Comprehensive protection

Comprehensive protection of a rooftop system on a building without a lightning protection system requires protection of the DC and AC side as well as the data interfaces. Equipotential bonding must also be established.

A - DEHNshield Basic

Main distribution board: The combined arrester is mounted on the busbar directly at the entrance point to the building. It protects electrical installations in the immediate vicinity. Ideal for retrofitting existing buildings.

A - DEHNguard modular

Main distribution board: Protects against overvoltages from inductive couplings by distant lightning strikes and from switching overvoltages. It must be installed downstream of the electricity meter and therefore does not protect the Smart Meter and Smart Meter Gateway.

C - DEHNguard M YPV

PV Installation: Type 2 arrester specially designed for application in PV systems. Protects the DC side of the inverter against surges from inductive couplings. If there is more than 10 metres of cable between the PV system and the inverter, a further arrester is necessary in the roof area.

C - DEHNcube YPV SCI 1000

Alternative | PV Installation: Type 2 in enclosure. It is mounted directly upstream of the inverter - available in 2 versions, 1 MPPT and 2 MPPT. If there is more than 10 metres of cable between the PV system and the inverter, a further arrester is necessary in the roof area.

D - DEHNguard M

AC side inverter: Protects against overvoltages from inductive couplings by distant lightning strikes and from switching overvoltages. If there is more than 10 metres of cable between the service entrance box and the inverter, a further type 2 surge arrester is required at the inverter.

E - UNI earthing clamps/saddle clamps

Clamps suitable for integrating the mounting systems of PV installations in functional equipotential bonding / functional earthing or the lightning equipotential bonding.

External lightning protection AND sufficient separation distance

Example 2

What does a protection concept for a building with an external lightning protection system and a separation distance that can be maintained look like?

Normative requirements and notes:

According to Supplement 5 to DIN EN 62305-3, a lightning protection system should be preferred which does not have a direct connection to the PV power supply system while maintaining the necessary separation distances. The modules must be located in the protected volume of the isolated air-termination system.

Comprehensive protection for the DC side

If the separation distance calculated according to IEC 62305-2 is maintained, type 2 surge arresters are used to protect the inverter on the DC side and for the modules. The number of surge protective devices (SPDs) depends on the distance to the device to be protected. An additional protective device is required every 10 m.

Comprehensive protection for the AC side

The AC side is protected by a combined arrester near the grid connection. If the distance between the grid connection and the inverter is more than 10 m, the installation of a further type 2 arrester on the AC side of the inverter is recommended.

A - DEHNventil

Main distribution board: Mounted directly at the entrance point to the building. Protects the electrical installation in the direct environment. The patented RADAX Flow Technology, offers high follow current limitation and thus maximum system availablity.

B - BLITZDUCTOR XTU

Data interface: Protects balanced data interfaces (e.g. RS 485). Integrated actiVsense Technology - the arrester automatically detects the operating voltage of the useful signal and optimally adapts the voltage protection level to it.

C - DEHNguard M YPV

PV installation: Type 2 arrester specially developed for use in PV installations. Protects the DC side of the inverter against surges from inductive couplings. If there is more than 10 metres of cable between the PV system and the inverter, a further arrester is necessary in the roof area.

C - DEHNcube YPV SCI 1000

Alternatively | PV installation: Type 2 arrester in an enclosure. It is mounted directly upstream of the inverter. Available in 2 versions, 1 MPPT and 2 MPPT. If there is more than 10 metres of cable between the PV system and the inverter, a further arrester is necessary in the roof area.

D - DEHNguard M

AC side: Protects against overvoltages from inductive couplings by distant lightning strikes and from switching overvoltages. If there is more than 10 metres of cable between the service entrance box and the inverter, a further type 2 surge arrester is required at the inverter.

E - UNI earthing clamps/saddle clamps

Equipotential bonding: Clamps suitable for integrating the mounting systems of PV installations in the functional equipotential bonding - functional earthing or lightning equipotential bonding.

F | Lightning Protection

HVI®Conductor, makes it easier to keep the separation distance from conductive parts. Optimum use of the roof surface.

External lightning protection WITHOUT sufficient separation distance

Example 3

What does a protection concept for a building with external lightning protection where the sufficient separation distance CANNOT be maintained, e.g. metal roofs, look like?

Normative requirements and notes:

According to Supplement 5 of DIN EN 62305, a lightning protection system should be preferred which does not have a direct connection to the PV power supply system while maintaining the necessary separation distances.
If the separation distance calculated according to IEC 62305-2 cannot be maintained, it is recommended to establish lightning equipotential bonding and connect the PV frame directly to the lightning protection system.

Comprehensive protection for the DC side

Type 1 combined arresters are used for protecting the inverter on the DC side and the modules. The number of surge protective devices (SPDs) depends on the distance to the device to be protected. An additional protective device is required every 10 m.

Comprehensive protection for the AC side

The AC side is protected by a combined arrester near the grid connection. If the distance between the grid connection and the inverter is more than 10 m, it is recommended to install an additional type 1 arrester on the AC side of the inverter.

A - DEHNventil

Main distribution board: Mounted directly at the entrance point to the building. Protects the electrical installation in the direct environment. The patented RADAX Flow Technology, offers high follow current limitation and thus maximum system availablity.

B - BLITZDUCTOR XTU

Data interface: Protects balanced data interfaces (e.g. RS 485). Integrated actiVsense Technology - the arrester automatically detects the operating voltage of the useful signal and optimally adapts the voltage protection level to it.

D - DEHNshield Basic FM

AC side inverter: If the cable length between the grid connection and the inverter is longer than 10 metres, an additional combined arrester is required at the inverter. The combined arrester fulfils the requirements of LPS class III at the point of installation and protects the inverter against any partial lightning currents and surges.

E | UNI earthing clamps/saddle clamps

Equipoetential bonding/earthing: Clamps suitable for integrating the mounting systems of PV installations in the functional equipotential bonding/functional earthing or lightning equipotential bonding.