Lightning and surge protection for rooftop PV systems
DEHN protects rooftop PV systems

Lightning and surge protection for rooftop PV systems

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.

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.

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.

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