Surge protection for PV plants

Today, almost everyone has heard about photovoltaics – the use of solar radiation to generate electricity. When properly implemented and adhering to specific principles, installing a PV system (photovoltaic power plant) can significantly reduce annual electricity costs.

Different systems covering different requirements can be encountered, ranging from small off-grid systems in garden colonies to residential on-grid systems (connected to the distribution power supply system) that decrease household energy bills, and large-scale PV installations. Despite their differences, all these systems share one crucial aspect: the need for protection against atmospheric influences and switching overvoltage in the distribution power supply system. Whether it’s a comprehensive surge protection setup for a large PV installation or the protection of a small residential PV system, safeguarding your investment is essential. Even with its relatively low upfront cost, surge protection for PV systems can save you hundreds of thousands of crowns in the long run.

A lightning rod, technically known as an LPS (Lightning Protection System), installed on the building's roof, is commonly associated with protection against lightning strikes. This is referred to as the external lightning protection system. However, not every building is equipped with an LPS, leading to the question: “Is a lightning rod mandatory for photovoltaics?” Generally, the answer is no. However, each building must be assessed individually using the risk management system outlined in EN 62305-2 ed.2. Based on the risk evaluation, buildings can be classified into those with an LPS and those without.

We must not forget about internal lightning protection (surge protection device), which is mandatory under our legislation. Surge protection device protects the building or equipment not only against external atmospheric influences but also against electromagnetic effects and switching overvoltage in the power supply system, which can also damage sensitive equipment such as inverters. The proper selection and application of surge protection are defined by the IEC 61643-32:2017 standard.

Photovoltaic system with Lightning Protection System (LPS): If a building is required to have a lightning protection system (LPS) according to risk management system (EN 62305-2 ed.2), it is necessary to consider the possibility of a direct lightning strike (current impulse with parameters 10/350 µs) to the building or even the PV system. In such cases, it is important to distinguish between systems where the separation distance "s" between the lightning protection system and the PV panels is maintained, and systems where the separation distance "s" is not maintained.

If a structure is equipped with a lightning protection system and the separation distance between the lightning protection system and the PV panels is maintained, there is not a risk of a direct lightning strike to the building and the PV system. In this case, an SPD type T2 is sufficient protection. A suitable SPD for position A (or for positions A and D if the distance between the inverter and the panels exceeds 10 m) is the HSA PV 600 M, which is suitable for all LPL levels. This product is specifically designed for U_CPV = 600 V DC, but the HSA series offers variants ranging from 200 V DC to 1500 V DC. The product features a Y-connection, which, thanks to the integrated spark gap, is resistant to to the earth connection of the working conductors and has zero residual (leakage) current through the PE conductor.
 

Fig. 1 – PV system with a Lightning Protection System, where the separation distance "s" is maintained

If a structure is equipped with a lightning protection system and the separation distance between the lightning protection system and the PV panels is not maintained, there is a risk of a direct lightning strike to the building and the PV system. In such cases, it is necessary to install an SPD type T1 , or preferably a combined SPD type T1 + T2. A suitable representative for SPD at position A (or at positions A and D if the distance between the inverter and the panels exceeds 10 meters) could be the HLSA6,5 PV 600 M. This device is designed for a voltage of U_CPV = 600 V DC, but the HLSA series also offers variants ranging from 200 V DC to 1 000 V DC. A typical residential building usually falls under LPL III-IV (Lightning protection levels III and IV), which require an SPD for PV applications with a minimum discharge capacity of 5 kA per pole. This product is therefore particularly suitable for LPL III and IV. It is also configured in a Y-connection. For LPL I and II, the HLSA12,5 PV series is more suitable, available in voltage levels of 1000 and 1500 V DC. 

Fig. 2 – PV system with a Lightning Protection System, where the separation distance "s" is not maintained

If the structure is equipped with a lightning protection system, it is necessary to install an SPD type T1 in the main distribution switchboard at position C. Alternatively, a fast-reacting, varistor-based, combined SPD type T1+T2+T3 is recommended. If the inverter is located more than 10 meters away from the main distribution switchboard, an SPD type T2 (if the separation distance is maintained) or an SPD type T1 (if the separation distance is not maintained) must be installed directly in front of the inverter at position B.

PV system without a lightning protection system: If the structure is not required to have a lightning protection system (LPS) according to risk management system (EN 62305-2 ed.2), there is no risk of a direct lightning strike to the building or the PV system. 

Fig. 3 – PV System without a Lightning Protection System

In this case, as a minimum requirement according to the standard, an SPD type T2 can be installed. A suitable SPD for position A (or positions A and D, if the distance between the inverter and the panels exceeds 10 meters) could be the HSA PV 600 M, which is suitable for all LPL levels.

If the risk assessment does not specify otherwise, an SPD type T2 is suitable for position C. If the inverter is more than 10 meters away from the main distribution switchboard, an SPD type 2 must be installed again directly in front of the inverter (position B). 

If the structure does not have a lightning protection system and no risk assessment is available, it is necessary to conduct one or assume the worst-case scenario, selecting lightning and surge arrester LPL I.

For all products in this series, we offer a more economical option without a spark gap across the entire voltage range, marked by "/2" at the end of the product name in a U-connection configuration. 

The entire product line also features the benefit of replaceable modules - products marked by the letter M.

If remote monitoring of the surge protection status is required, products marked by the letter S can be used. The potential-free contact of this remote monitoring can be connected to a smart home system (typically as an input for the control PLC), providing continuous information to the investor about the status of the surge protection without needing a physical inspection of the distribution switchboard.

Detailed information regarding the connection of surge protection for photovoltaic systems in residential buildings is available