An effective Surge protection for PV systems not only guarantees the long-term operation and value retention of the system, but also makes a significant contribution to operational safety. Whether caused by direct or nearby lightning strikes, switching operations in the power grid or internal load changes - overvoltages can severely damage the electrical components of a PV system. Defective inverters, destroyed modules or even fires are possible consequences. In addition to safety risks, considerable economic losses due to repairs and production downtime.
Disconnector and overvoltage protection
In general, overvoltage protection and Disconnector essential components of a PV system. However, they have different purposes. Disconnectors are used to safely disconnect circuits, for example for maintenance work or in the event of a fault. They disconnect the PV system electrically from the grid or the inverter and thus enable safe working on the system. These are purely mechanical switches without a protective function against overvoltages. Overvoltage protection, on the other hand, protects the electrical components from dangerous voltage peaks and discharges such brief but potentially destructive overvoltages to earth at lightning speed.
What is an overvoltage?
An overvoltage occurs when the electrical voltage in a system briefly exceeds the maximum permissible value - often by a multiple of the normal operating voltage. This Voltage peaks are only of short duration, but can considerable damage cause. The causes of overvoltage can be roughly divided into two categories:
1. atmospheric overvoltages
The atmospheric influences include above all Lightning strikes. A direct lightning strike to a PV system or its surroundings can Extreme voltage pulses cause. But even a distant impact is enough to induce dangerous voltages in the cables via electromagnetic fields. This is referred to as Lightning impulse voltages. They are particularly energy-rich and have a very steep rise time.
2. mains-related overvoltages
Grid-related overvoltages, on the other hand, are caused by processes in the power grid or within the electrical system itself. Typical triggers are switching large electrical loads, Short keye or Resonance effectswhere electrical oscillations can build up and amplify in the network. These so-called Switching impulse voltages usually have lower energies, but are also potentially harmful.
A third category is represented by so-called Temporary overvoltages (TOV - Temporary Overvoltage). They are caused by prolonged voltage increases, for example as a result of a neutral conductor failure, and can also cause considerable damage due to their duration.
Standards & guidelines for surge protection in PV systems
Surge protection for photovoltaic systems is subject to a large number of technical regulations that cover various aspects of planning, installation, operation and maintenance. At the heart of this is DIN VDE 0100-712, which is the overarching standard that summarizes all requirements for electrical installations of PV systems. It relates to both the direct current and alternating current side and refers to other relevant standards, in particular on surge protection measures, lightning protection systems and testing obligations.
It is crucial for operators, planners and installers to understand the relevant standards in context and apply them correctly - not only to comply with legal requirements, but also to ensure the technical operational safety and insurability of the system. The following table provides a structured overview of the most important standards and directives in the context of surge protection for PV systems:
| Standard / Guideline | Subject area | Area of application | Special features |
| DIN VDE 0100-712 (2019) | Electrical safety of PV systems | DC and AC side (modules, inverters, storage units, cables, disconnecting devices, etc.) | Basic standard for PV installations, also regulates the integration of surge protection |
| DIN VDE 0100-443 (mandatory since 12/2018) | Obligation for overvoltage protection | Buildings with PV systems (residential, commercial, public buildings) | Surge protection is mandatory if there is a risk to life, property or IT systems |
| DIN VDE 0100-534 | Implementation of surge protection | Selection, installation and coordination of SPDs (Surge Protective Devices) | Regulates technical details: protection level, type selection, installation location, cable routing |
| DIN EN 62305-3 / VDE 0185-305-3 | Lightning protection (external/internal) | Buildings with external lightning protection systems | Supplement 5 contains PV-specific information on integration into lightning protection systems |
| DIN EN 62305-2 / VDE 0185-305-2 | Risk analysis | All buildings, optionally before installation of a lightning protection system | Determining whether and to what extent a lightning protection system is required |
| DIN VDE 0100-600 | Initial inspection of electrical systems | Existing PV systems | Regular inspection, documentation and maintenance of the surge protection system |
| DIN VDE 0126-23-1 | Operation & maintenance | Existing PV systems | Regular inspection, documentation and maintenance of the surge protection system |
| VdS guidelines (e.g. VdS 2010, 3145) | Underwriting recommendations | Especially for ground-mounted systems or roofs with flammable building materials | Supplementary requirements of the insurance industry for risk reduction and fire protection |
Concepts for surge protection for PV systems
Effective surge protection for Insurance-compliant PV systems is not based on individual devices, but on a well thought-out overall concept. This takes into account the spatial structure of the system, the type of connection, the presence of an external lightning protection system and the individual safety and availability requirements. A central element is the so-called Multi-level protectionThe combination of different protective devices with coordinated protective behavior:
Coarse protection (type 1): Is used if an external lightning protection system is available or is required following a risk analysis. It is able to safely discharge very high lightning currents before they can reach downstream systems. Typical installation location: Main distribution board or lightning current entry point.
Center protection (type 2): Used to discharge induced or switched overvoltages and is used independently of an external lightning protection system in almost all PV systems. It protects sensitive equipment such as inverters, battery storage or control electronics. Typical installation location: Sub-distribution board, inverter or generator connection box.
Fine protection (type 3): Supplements the protection concept with local terminal device protection, especially for particularly sensitive electronics. This requires upstream coordination with type 2 arresters. Typical use: directly upstream of communication or control units
A protection concept always begins with a Risk analysisIs there external lightning protection? Is the building located in a lightning-prone area? Which protection classes are required? What are the cable lengths and potential differences? These factors are used to decide which protective measures are required and where the protective devices should be positioned.
Not only the selection of the right components is crucial, but also their professional installation: the shortest possible cable routes, correct coordination between the protection levels, proper earthing and equipotential bonding. Only if all protection levels are coordinated can the energy of an overvoltage event be effectively reduced and harmful residual voltages limited to a safe level.
Components for surge protection in PV systems
Various technical components are used to effectively protect PV systems against surges and lightning effects. They are specially adapted to the requirements of the DC and AC side as well as to communication and data lines. The so-called Surge arrester (SPD - Surge Protective Devices) according to type 1-3 are among the most important devices.
External lightning protection (if required)
External lightning protection is used if a risk analysis requires it or if the building already has an appropriate system. The aim is to specifically intercept direct lightning strikes and conduct them safely to earth. This includes interception devices such as rods or wires at exposed points, down conductors for safe current routing and a well-dimensioned earthing system. These measures primarily protect the fabric of the building and serve the structural fire protection - Sensitive electronic components of the PV system require additional internal surge protection. Protection against overvoltage damage for communication and data lines
Surge protection devices (internal lightning protection)
Surge protective devices (SPDs) protect Electrical equipment against the consequences of indirect lightning strikes and switching surges. A distinction is made between three types depending on the place of use and protection requirements: Type 1 (lightning current arrester) dissipates high lightning currents and is mainly used at the building entrance. Type 2 (surge arrester) protects against switching and remote overvoltages and is used in meter cabinets, distribution boards or on inverters. Type 3 (fine protection) supplements type 2 to protect particularly sensitive devices, such as communication components. In PV systems, a coordinated combination of all three types is usually required.
Differences between protective devices on the DC and AC side of PV systems
Photovoltaic systems work both with direct current (DC) on the side of the solar modules and with alternating current (AC) after conversion in the inverter. Overvoltage protection is required on both sides. always mandatory. Depending on the type of voltage, the protective devices differ significantly in terms of their design, functionality and technical requirements.
On the DC side - i.e. between the solar modules, the strings and the inverter - the current flow remains constant in one direction. When switching off, this can result in a stable arc that is difficult to extinguish. DC protection devices must therefore have larger contact distances, special arc extinguishing chambers or other technical measures to safely interrupt this arc. In addition, DC devices are polarized, i.e. they are clearly marked with "+" and "-" and must be installed according to the direction of the current. Typical installation locations are generator junction boxes or string boxes in the immediate vicinity of the modules. For longer cable runs - over 10 meters, for example - between the solar generator and inverter, the use of additional protective devices is recommended.
On the AC side - downstream of the inverter, i.e. in the area of the grid feed, the periodic zero crossings of the alternating current make it easier to extinguish the arc. Protective devices such as miniature circuit breakers or surge arresters are therefore usually of a more compact design in this area. They are generally not polarized and are often marked with "Line" and "Load" to differentiate between the input and output sides. They are typically installed in the meter cabinet, in sub-distribution boards or directly at the AC output of the inverter.
Additional components
On the DC side upstream of the inverter, there are usually Generator junction boxes with integrated overvoltage protection. Residual current circuit breaker (RCD) are installed on the AC side to ensure personal and system protection in the event of fault currents. So-called Combined arrester (type 1+2+3) offer lightning current and surge protection in one device and are installed on the AC side, particularly in buildings with an external lightning protection system. Finally, a built-in Overvoltage protection for data cables Damage and voltage peaks on the monitoring, control and communication lines.
Selection criteria for surge protection components for PV systems
The selection of suitable surge protective devices (SPDs) requires careful coordination with the technical conditions of the PV system. Several criteria are decisive here: The Rated voltage (Uc) must match the system voltage - whether on the DC or AC side - and take into account possible voltage peaks in the event of a fault. The Surge current carrying capacity (Iimp for type 1, Imax for type 2) indicates the lightning or surge currents that the device can discharge without damage. Equally important is the Protection level (Up)The maximum voltage that the device allows to pass when it responds - this value must be below the dielectric strength of the terminal devices to be protected. In addition, the transformer used should conforms to standards and comply with DIN EN 61643-11. Especially for photovoltaic systems DC-CNC which are designed for the respective string voltages and the required current carrying capacity.
Installation & placement
Correct installation and positioning of the devices is crucial for effective protection. The following applies in principle: The shorter the cable routes between the protective devices and the components to be protected, the lower the risk induced overvoltages. Particularly on the DC side, a Low impedance earth connection are essential in order to be able to reliably conduct discharged currents to earth. The installation locations depend on the respective protection requirements: On the DC side transducers are typically installed in the string box and at the input of the inverter. On the AC side they find their place in the meter cabinet and - depending on the size of the system - in sub-distribution boards. Also Communication linessuch as for Ethernet or RS485 connections, should be protected by Separate protective devices to protect data loggers, controllers or remote monitoring units from overvoltage damage.
Maintenance of the surge protection
Surge protection for PV systems is Low maintenancebut not maintenance-free. As the components dissipate electrical energy with every overvoltage event, they are subject to natural wear and tear. Regular visual inspections and functional tests are therefore essential to ensure long-term protection. Modern systems have optical or Electronic status displayswhich indicate the current status of the device. Particularly after thunderstorms or known grid faults, it is advisable to carry out a targeted check of the protection devices, especially for systems in lightning-prone regions. The Documentation is important: it helps to identify potential weak points at an early stage and at the same time meets the requirements of standards and insurance policies. A forward-looking maintenance concept therefore increases the operational reliability and service life of the entire PV system.
Conclusion
Effective surge protection is not only essential for the safe and economical operation of PV systems - it is often also a basic prerequisite for their realization. Insurers require a well thought-out surge protection concept as early as the planning phase, especially for large commercial systems. This is the only way to technically control and economically insure against risks from lightning strikes, grid events or internal faults. A multi-level, standard-compliant protection concept, combined with professional installation and regular maintenance, ensures long-term operational safety, availability and value retention of the system.