1. Introduction: Why PV SPDs Are Essential

Solar photovoltaic (PV) systems are exposed to environmental risks, particularly lightning
and switching surges. These events can generate transient overvoltages that damage sensitive
components such as inverters, monitoring equipment, and even PV modules themselves.

A PV surge protective device (SPD) is a critical safeguard that prevents
these damaging voltages from reaching system components. In this article, we explore how
PV SPDs work, their role in solar projects, and the best practices for applying them effectively.

2. What Is a PV Surge Protective Device?

A surge protective device is an electrical component designed to limit transient overvoltages
by diverting surge current to ground. In PV systems, SPDs are specifically engineered to handle
the unique conditions of direct current (DC) circuits with high voltages (up to 1500V).

• Protective Role: Prevents damage from lightning-induced surges and grid switching spikes.
• System Placement: Installed at key junctions such as combiner boxes, DC distribution, and inverter inputs.
• Core Components: Typically use metal oxide varistors (MOVs) or gas discharge tubes (GDTs).

3. The Working Principle of PV SPDs

PV SPDs function as “voltage clamps.” Under normal operating voltage, they remain passive
and non-conductive. When a surge event occurs:

1. The surge voltage exceeds the SPD’s threshold.
2. The SPD rapidly transitions to a low-impedance state.
3. Excess energy is diverted to ground, limiting the voltage seen by downstream equipment.
4. After the event, the SPD returns to its non-conductive state.

This fast response—measured in nanoseconds—prevents insulation breakdown, semiconductor
damage, and premature aging of PV components.

4. Key Application Scenarios

PV SPDs must be strategically deployed to provide comprehensive system protection:

• At the PV Array: Protects strings and modules from direct lightning surges.
• Inside Combiner Boxes: Shields multiple strings before they are aggregated.
• At the Inverter DC Input: Prevents high-voltage transients from damaging power electronics.
• On the AC Side: Guards inverters and grid connections from utility surges.
• At Communication Interfaces: Protects monitoring and SCADA systems from induced surges.

5. Types of PV SPDs

PV SPDs are classified by their construction and performance levels:

• Type 1: Designed for direct lightning strikes; often used at service entrances.
• Type 2: For indirect lightning and switching surges; most common in PV systems.
• Type 3: Provides localized protection for sensitive electronics.

In solar systems, a coordinated approach often combines Type 1 and Type 2 SPDs for layered defense.

6. Standards and Certifications

PV SPDs must comply with international standards to ensure safety and performance:

• IEC 61643-31: Specific to DC surge protection for photovoltaic applications.
• UL 1449: North American standard for surge protective devices.
• NEC Article 690: Outlines SPD requirements in PV installations in the U.S.

Selecting certified devices ensures compliance and reliable operation under real-world conditions.

7. Benefits of Using PV SPDs

Integrating SPDs provides measurable benefits:

• Extends lifespan of inverters and PV modules.
• Reduces downtime and costly repairs.
• Improves system reliability, especially in lightning-prone regions.
• Ensures compliance with insurance and regulatory requirements.

8. Common Misconceptions About PV SPDs

• “SPDs eliminate all risks.” In reality, they reduce but do not completely remove surge risks.
• “One SPD is enough.” Proper protection requires multiple SPDs at different system levels.
• “SPDs last forever.” They degrade over time and must be inspected or replaced periodically.

9. Best Practices for Applying PV SPDs

To maximize effectiveness, follow these best practices:

• Install SPDs as close as possible to protected equipment.
• Ensure proper grounding and bonding of the entire PV system.
• Use SPDs rated for the correct DC system voltage (1000V, 1500V).
• Regularly inspect and test SPD health indicators.
• Coordinate multiple SPDs to create a layered protection scheme.

10. Conclusion

A PV surge protective device is a vital investment in the safety and reliability
of solar energy systems. By understanding how SPDs work, where they should be applied, and how
to maintain them, solar project owners and engineers can ensure long-term system performance,
reduce risks, and achieve higher returns on investment.