Lightning and surge protection for photovoltaic systems

No, the risk of a lightning strike is not increased by the installation of a standard PV system on or near a building. 

Surge protection for photovoltaic systems is crucial to protect the system from damage caused by unexpected voltage peaks. These can be caused by external events such as direct lightning strikes, indirect lightning strikes in the vicinity or switching operations.  

Here is a simplified explanation of how it works:  

• Detection of surges: surge protective devices (SPDs) are designed to continuously monitor the voltage and react to unusual peaks.  
• Dissipation of the overvoltage: in the event of a surge, the SPDs safely discharge the excess energy to the ground before it can reach the sensitive parts of the photovoltaic system.  
• Protection of system components: by discharging the overvoltage, the SPDs protect the solar modules, the inverter and other electronic devices.  

There are two main types of surge protection:  

• AC-SPD: protects the AC side of the system.  
• DC-SPD: protects the direct current side, in particular the solar modules and the inverter. 

Without surge protection, the consequences for a photovoltaic system in the event of a lightning strike can be serious. Here are some possible scenarios:  

• Total loss: a direct lightning strike to the system can lead to a total loss, whereby the solar modules, the inverter and other electronic components can be irreparably damaged.  
• Indirect damage: indirect lightning strikes that hit other parts of the building or cables can also cause overvoltages that lead to damage to the photovoltaic system.  
• Failure of technical equipment: surges can cause technical devices to fail, which can lead to costly repair work.  
• Fire hazard: there is also a risk of fires being caused by the overvoltage. This not only jeopardises the system, but also the building.  

It is therefore important to install suitable surge protection to minimise these risks and ensure the safety and longevity of the photovoltaic system. 

Surge arresters are divided into three classes: Type 1, 2 or 3. The arresters differ in their discharge capacity and protection level. The protection level indicates the maximum voltage that occurs in the event of a discharge process.  

Class 1 = primary protection
The arresters have the highest impulse current capability and are designed for the load of a direct lightning strike. If the protection level of the Type 1 arrester is higher than the dielectric strength of the downstream devices to be protected, a Type 2 arrester must be connected downstream.   

Class 2 = Medium-level protection
The arresters are designed for surge currents that are to be expected in the event of indirect lightning strikes.  

Class 3 = Secondary protection
These arresters have the lowest impulse-current-carrying capacity and protect sensitive devices such as PCs, TVs, etc. 

This depends on whether an external lightning protection system is present and, if so, whether or not the separation distance between the lightning protection system and the PV components has been maintained. In this regard, see the protection proposals in WPX029.

In addition to the arrester types, DEHN also differentiates between Red/Line and Yellow/Line arresters.  

• Red/Line arresters describe all types for the energy part of a photovoltaic system.  
• Yellow/Line arresters are intended for use in the area of signalling and communication lines. 

No. Surge arresters from DEHN can discharge lightning currents several times. This has been proven by various laboratory tests and also confirmed by our many years of experience in the field.  

However, you should regularly check whether the arresters are still functional. You can determine whether the device is functioning or defective by the green-red marking in the inspection window. 

• DC voltage cable: If the DC cable is longer than 10 metres, a Type 2 surge protective device should be installed at the connection to the photovoltaic modules.  
• Inverter: Installation of Type 2 surge protective devices upstream and downstream of the inverter.  
• Electrical installation of the building: To protect the electrical devices in the building, a Type 1 surge arrester should be installed in the power grid feed. 

• Inverter: Installation of Type 1 surge protective devices upstream and downstream of the inverter.  
• Electrical installation of the building: To protect the electrical devices in the building, a Type 1 surge arrester should be installed in the power grid feed. 

For lightning protection reasons, it is not necessary to integrate the module frames into the earthing system. Only the mounting system needs to be integrated for this. That being said, certain module types require earthing; please refer to the module manufacturer's instructions in this regard.

When earthing photovoltaic systems, certain components must be earthed to prevent personal injury and damage to the system. Here are the essential elements that need to be earthed:  

• Frame of the solar modules: For lightning protection reasons, it is not necessary to integrate the module frames into the earthing system. Only the mounting system needs to be integrated for this. That being said, certain module types require earthing; please refer to the module manufacturer's instructions in this regard.   
• Mounting system: The frame on which the solar modules are mounted, especially if it is made of steel or aluminium, must also be earthed.  
• Metal cable trays and cable conduits: All metal parts that are connected to the cabling of the system should be included in the equipotential bonding.  
• Inverter housing: If the housing of the inverter is made of metal, it must also be earthed.  

Earthing is required by law and must be carried out in accordance with standards such as IEC 60364-5-54 and IEC 62305-3. 

Earthing is used to safely discharge excess electrical charges. If a photovoltaic system is not properly earthed, this can lead to several serious problems:  

• Electric shocks: there is an increased risk of electric shock. 
• Fire hazard: inadequate earthing can lead to a fire.  
• System damage: the efficiency and performance of the photovoltaic system can be impaired, as earthing also helps to protect the system from overvoltages.  
• Electromagnetic interference: without earthing, electromagnetic interference can disrupt the function of the system and reduce energy production.  

Earthing is therefore a critical safety aspect that should not be neglected. 

Equipotential bonding is an important safety measure for photovoltaic systems that serves to compensate for voltage differences between different conductive parts of the system.  

• Prevention of electric shocks: equipotential bonding balances dangerous voltages between the parts of the system, which reduces the risk of electric shocks.  
• Protection against surges: equipotential bonding helps to protect the system from electrical surges that can be caused by indirect lightning strikes or switching operations in the grid.  
• Minimisation of fires and short circuits: correct equipotential bonding minimises the risk of fires and short circuits that can be caused by unequal voltages.  
• Reduction of electromagnetic interference: electromagnetic interference can impair the performance of the system. Equipotential bonding helps to minimise this interference. 

Earthing the inverter of a photovoltaic system is an important step in ensuring the safety of both the system and people. The following steps are required for earthing an inverter:  

• Selecting the right earthing system: An earthing system must be selected that complies with standards such as IEC 60364-5-54 and IEC 62305-3.  
• Connection with the main earthing busbar: The inverter should be connected to the main earthing busbar, which in turn is connected to the main earthing conductor (foundation earth electrode).  
• Connection of the protective conductor: A protective conductor must be routed from the inverter to the main earthing busbar in order to safely discharge potential residual currents or overvoltages to earth.  
• Testing the system: After installing the earthing system, the system should be tested to ensure that the earthing has been implemented correctly and in accordance with standards. 

Cables that comply with the standards and requirements for electrical installations are generally used for earthing a photovoltaic system.  

Cable type: It is recommended to use cables according to IEC 62930, which are specified for the cabling of photovoltaic systems.  

Conductor cross-section: The conductor cross-section of the earthing cable should be sufficiently dimensioned to safely conduct the expected current. A 1 x 16 mm² green-yellow wiring cable is often used for earthing the mounting system of the photovoltaic system. There are differences here with regard to the differentiation criteria:   

• Buildings with PV systems, without external lightning protection   
• Buildings with PV systems, with external lightning protection and sufficient separation distance  
• Buildings with PV systems, with external lightning protection, without sufficient separation distance  

It is important that the cables are selected and installed in accordance with the applicable regulations and standards such as IEC 60364-5-54 and IEC 62305-3. 

The depth of the earthing for a photovoltaic system depends on the local conditions and must ensure that it is frost-free. An installation depth of at least 0.5 m is required. This depth ensures that the earthing system is protected from frost and can fulfil its function reliably. The installation depth should be selected so that the effects of frost, soil dryness and corrosion are minimised. Earth electrode lengths of 9 m have proven to be advantageous.

A cable cross-section that meets the safety requirements and standards is required for earthing a photovoltaic system. According to IEC 60364-5-54, the cross-section for earthing should be at least 6 mm² of copper. If the earthing also fulfils an overcurrent function, such as for lightning protection, a cable cross-section of at least 16 mm² is required.

• Photovoltaic modules, mounting system, cabling: Air-termination systems are installed in such a way that these system components are located in the protected volume and a direct lightning strike to the system components is prevented. The cables of the lightning protection system must be laid at a distance from all parts of the photovoltaic system that prevents flashover (separation distance). This must be calculated precisely by a lightning protection specialist, for example.  
• Mounting system: The metal mounting system is connected to the main earthing busbar. In the case of extensive systems, the connection can also end at an equipotential bonding bar. [Textumbruch]Important: A direct connection between the mounting system and the lightning protection system cables must be avoided at all costs.  

• Photovoltaic modules, mounting system, cabling: Air-termination systems are installed in such a way that these system components are located in the protected volume and a direct lightning strike to the system components is prevented. The air-termination systems are connected to the modules or the mounting system several times. These connections must be designed for partial lightning currents. 
• Module frame, mounting system: The metal parts must be suitable for the conducting of partial lightning currents in terms of material and connection technology.