Solar photovoltaic (PV) installations are often exposed, elevated, and spread across large rooftop or ground-mounted areas, making them inherently vulnerable to lightning activity. To mitigate this risk, a Lightning Protection System (LPS) must be carefully coordinated with the solar PV earthing system. The image illustrates best-practice principles for bonding, separation, and earthing coordination between PV arrays, mounting structures, inverters, distribution boards, and lightning earth electrodes.
1. Why Lightning Protection Is Critical for Solar PV Plants
Lightning strikes can introduce:
- Extremely high surge currents
- Dangerous step and touch voltages
- Severe damage to PV modules, inverters, and electronics
A well-designed LPS safely intercepts lightning current and directs it into the ground, while the earthing system ensures personnel safety and equipment protection. Poor coordination between these systems can inadvertently route lightning currents through sensitive PV equipment.
2. PV Array and Mounting Structure Earthing
The upper portion of the diagram shows PV modules and mounting rails:
- Module Frame Bonding (PE)
All module frames must be bonded using protective earth conductors. - Mounting Rail Bonding
Metallic mounting rails are bonded to the same system earthing network. - Conductor Identification
Protective earth conductors are typically green/yellow, with sizing based on standards and risk assessment.
This bonding ensures all exposed metallic parts remain at the same potential, reducing shock risk during fault or lightning events.
3. Lightning Protection System (LPS) Down Conductor
The LPS down conductor:
- Provides a direct, low-impedance path for lightning current
- Connects air terminals to the lightning earth electrode
Key rules highlighted include:
- Do not bond PV module frames directly to the LPS down conductor unless required by risk assessment
- Maintain separation distance (S) as per IS/IEC 62305
This separation prevents lightning current from coupling into the PV electrical system.
4. System Earthing and Equipotential Bonding
The diagram emphasizes equipotential bonding using an Equipotential Bonding Bar (EBB):
- Inverter PE, DCDB, and ACDB earth connections terminate at the EBB
- Bonding equalizes potential between system components
- Reduces touch voltage risk during fault conditions
Where required by design, bonding between system earth and LPS earth may be implemented via the EBB.
5. Independent Earth Electrodes: System Earth vs LPS Earth
A critical design principle shown is the use of independent earth electrodes:
- System Earth Electrode (PE) for electrical equipment
- Lightning Earth Electrode (LPS) for lightning current dissipation
Maintaining separation between these electrodes:
- Prevents high lightning currents from entering equipment earthing
- Improves safety and equipment longevity
A minimum separation distance is recommended unless bonding is mandated by standards or risk assessment.
6. Cable Routing and Separation
To avoid electromagnetic coupling:
- Do not route PE cables parallel to LPS down conductors
- Maintain physical separation wherever possible
- Cross conductors at right angles if unavoidable
These measures significantly reduce induced surges in PV cabling during lightning events.
7. Conductor Sizing and Materials
The diagram specifies:
- 6–16 sq.mm green/yellow PE conductors for system earthing
- Appropriately sized LPS conductors for lightning currents
Conductor sizing must follow applicable standards and site-specific lightning risk analysis.
8. Standards and Risk Assessment
Key standards referenced include:
- IEC / IS 62305 for lightning protection
- IS 3043 for earthing
A formal lightning risk assessment determines:
- Need for bonding between system and LPS earth
- Conductor sizing
- Separation distances
Design decisions must be documented and justified.
9. Inspection, Testing, and Maintenance
Lightning protection and earthing systems require:
- Visual inspection of conductors and bonding points
- Periodic earth resistance testing
- Verification of separation distances
Any modification to the PV system must be reviewed for LPS impact.
Conclusion
Effective lightning protection in solar PV systems depends on correct coordination between PV earthing and the lightning protection system. By maintaining separation, implementing equipotential bonding, and following applicable standards, lightning energy can be safely dissipated without endangering equipment or personnel. Proper design, installation, and maintenance ensure long-term resilience of solar PV installations in lightning-prone environments.
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