Can shadows from lightning rods damage solar panels?

Yes, core shadows can cause hot spots and damage cells. Air-termination rods must be positioned at a calculated distance to cast only diffuse shadows.

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By Sona Brands

On December 08, 2025

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Lightning and Surge Protection for Rooftop Photovoltaic Systems

Q: Do I need an external lightning protection system for my home PV system?

It depends on building regulations and risk analysis. While not always mandatory for private homes, it is recommended if lightning strikes are likely or fire risk is unacceptable. SPDs are generally recommended regardless.

Q: What happens if I don't maintain the separation distance?

If the separation distance is breached, lightning can flash over to the PV system. You must then bond the PV frame to the lightning protection system and use Type 1 combined arresters on DC cables.

As rooftop photovoltaic (PV) systems become increasingly common for both residential and industrial applications, protecting these significant investments from the destructive power of lightning and surges is critical. This white paper outlines the necessity of comprehensive protection strategies, detailing risk assessment, separation distances, and the selection of appropriate Surge Protective Devices (SPDs) for both the DC and AC sides of PV installations.

Lightning strike over a rooftop solar panel installation

Lightning strikes pose a severe risk to PV systems, necessitating robust protection measures.

The Necessity of Lightning & Surge Protection

Risk of Direct Lightning Strikes

The energy released by a lightning discharge is a frequent cause of fire. For structures like schools, hospitals, and industrial facilities, a lightning protection system (LPS) is often mandatory. While installing PV modules doesn't inherently increase strike risk, a direct strike can cause catastrophic damage. Therefore, integrating PV systems with an existing LPS—or installing one where necessary—is crucial.

Surge Damage to Equipment

Lightning discharges induce surges on electrical conductors, potentially damaging PV modules, inverters, and connected building devices. Surge Protective Devices (SPDs) are essential to mitigate these voltage peaks. Standards like CLC/TS 50539-12 and IEC 60364-4-44 mandate SPDs unless a specific risk analysis deems them unnecessary.

Cable Routing and Earthing

Minimizing Conductor Loops

Large conductor loops increase the risk of inductive coupling from lightning. Cables should be routed to avoid large loops. DC and AC power lines, along with data lines (e.g., for radiation sensors), should be routed together with equipotential bonding conductors along their entire path.

Functional Earthing

Metal mounting systems for PV modules must be earthed. If the separation distance is maintained, a copper conductor of at least 6 mm² is required. If the separation distance cannot be maintained, the mounting system effectively becomes part of the lightning protection system, requiring a minimum 16 mm² copper conductor capable of carrying lightning currents.

Separation Distance (s)

Why Separation Distance Matters

A specific separation distance 's' must be kept between the external lightning protection system and the PV system components. This prevents uncontrolled flashovers (sparking) from the lightning protection system to the PV system, which could lead to fire. The distance depends on the class of LPS and can be calculated according to IEC 62305-3.

Avoiding Core Shadows

Air-termination rods used for lightning protection can cast shadows on solar panels. "Core shadows" (dark, clearly outlined shadows) significantly reduce yield and can damage solar cells. Sufficient distance between rods and modules is required to ensure only diffuse shadows are cast. For example, a 10mm diameter rod requires a distance of 1.08m to avoid core shadows.

Selection of Surge Protective Devices (SPDs)

Type 1 vs. Type 2 SPDs

Type 1 SPDs are required when the separation distance 's' is not maintained, or for buildings with an external LPS where direct lightning currents might enter the system. These handle partial lightning currents (10/350 µs waveform). Type 2 SPDs are suitable for buildings without an external LPS or where sufficient separation distance is maintained, protecting against induced surges (8/20 µs waveform).

Special DC SPDs for PV

PV sources have unique non-linear characteristics requiring specialized SPDs. Standard AC arresters are insufficient. DEHN offers combined arresters like the DEHNcombo YPV SCI with integrated short-circuiting technology (SCI) to safely extinguish DC arcs and prevent fire risks in case of overload.

Data Line Protection

Inverters connected to monitoring systems via RS485 or Ethernet also require protection. Devices like the BLITZDUCTOR XTU protect data interfaces from surges that could otherwise destroy communication modules and interrupt yield monitoring.

Frequently Asked Questions

Do I need an external lightning protection system for my home PV system?

It depends on national building regulations and a risk assessment. While not always mandatory for private homes, it is highly recommended if lightning strikes are expected or if the risk of fire is unacceptable. Surge protection devices (SPDs) are generally recommended regardless of an external LPS.

What happens if I don't maintain the separation distance?

If the separation distance 's' is not maintained, lightning currents can flash over to your PV system cabling, entering the building. In this case, you must bond the PV frame to the lightning protection system and use Type 1 combined lightning current arresters on the DC cables entering the building.

Can shadows from lightning rods damage my solar panels?

Yes. "Core shadows" can cause hot spots in solar cells, potentially damaging them over time and reducing system yield. Air-termination rods must be positioned at a calculated distance to ensure they only cast diffuse shadows on the modules.

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