Do you worry that your expensive solar PV system could one day be easily damaged? However, the reality is without surge protection, even the slightest voltage spike can damage every electronic device that draws power from the solar panel array. Additional to that, without lightning protection, any investment you make in energy efficiency will be useless, as lightning is one of the leading causes of solar panel failure.

Selecting the appropriate Surge Protective Device (SPD) is a critical decision for ensuring the longevity and reliability of your solar power system.

A solar surge SPD is designed to protect your solar panels and associated equipment from power surges and transient voltage spikes. It diverts excess voltage and surges current to the ground, safeguarding your system from damage.

Why Do Solar Power/PV Systems Need Surge Protection?

As you know, solar panels are installed outdoors. It makes them directly exposed to harsh conditions like rain, wind, and dust. Among the weather conditions, lightning strikes require specific attention as they can severely affect the safety and performance of a PV system.

Solar power systems are particularly vulnerable to surge damage for several reasons:

- Exposed location: Solar arrays are typically installed in elevated, exposed positions.
- Extended cable runs: DC power cables can act as antennas for induced surges.
- Sensitive electronics: Inverters, monitoring systems, and control equipment contain vulnerable components.
- Lightning attraction: Solar panel arrays can be attractive paths for lightning strikes.

When the lightning strike hits the ground, it discharges energy, affecting the electrical field on the ground. For the solar PV plant, this poses two risks:

- A direct impact that can physically destroy the solar equipment on a rooftop
- Transitory overvoltages passing through cables by magnetic coupling, which can lead to the damage of sensitive components such as printed circuit boards (PCB).

Unprotected PV systems will sustain repeated and significant damage in areas where lightning strikes frequently. This can result in a significant repair and replacement costs, system downtime, and revenue loss.

Solar surge protection(SPD) is designed to limit the transient overvoltages and divert the waves of current to the earth. Additionally, it restricts the overvoltage’s amplitude to a value that is safe for the electrical infrastructure and switchgear.

How Many Solar Surge Protectors are Required for A Photovoltaic/PV System?

The number of PV surge protectors required for a photovoltaic or PV system depends on the specific configuration and components of the system. Below are some general guidelines to keep in mind.

Main Service Entrance DC SPD:

A Type 1 DC SPD is recommended to be installed at the main entrance of the power supply of the building where the PV system is installed. This solar surge protector device provides complete protection for the entire electrical system including solar panels and related equipment. It protects against overvoltages from both mains and external sources such as lightning strikes. The main power input DC SPD 1000V should be rated to handle the maximum voltage and surge current expected in the system.

Subdistribution DC SPD:

In large photovoltaic systems there are often sub-distributors or collection boxes that combine the electrical output of multiple solar strings. It is recommended that Type 2 DC SPDs be installed in these sub-panels to provide localized surge protection to circuits connected to these panels. These DC SPDs protect against grid-induced overvoltages and limit the propagation of overvoltages within the system.

It is important to note that the specific requirements for DC SPDs in photovoltaic installations may vary depending on factors such as system size, installation site, local electrical codes, and industry standards. It is best to consult a qualified solar installer or electrician who can evaluate your system and provide specific advice on the number and type of DC SPDs required for optimal surge protection.

Also, make sure the DC SPD 1000V you choose has the voltage and surge current ratings and the necessary certifications to meet local safety standards. It is also recommended that DC SPDs be maintained and inspected regularly to ensure that they continue to be effective in protecting our solar system.

The number of SPDs installed in a solar PV system varies depending on the distance between the panel and the inverter. When the cable length between solar panels is under 10 meters: 1 SPD should be installed by the inverter, combiner boxes, or closer to the solar panels. When DC cabling is over 10 meters: more surge protectors are required at both the inverter and solar modules end of the cables.

For larger systems, consider protection at these key points:

- Array level: Install SPDs at combiner boxes for distributed arrays
- Inverter DC input: Install SPDs immediately before inverter DC inputs
- String level: For systems with multiple strings, consider string-level protection

Different grounding configurations require specific SPD connection schemes:

DC Side Configurations:

- Functionally earthed: One DC pole connected to earth
- High-resistance earthed: DC pole connected to earth through resistance
- Unearthed/floating: Neither pole directly connected to earth

AC Side Configurations:

- TN-C, TN-S, TN-C-S systems
- TT systems
- IT systems

- Each configuration requires a specific SPD connection scheme to ensure effective protection. For example, ungrounded (IT) PV systems often need SPDs with “Y-configurations” for comprehensive protection.

SPD Bypass Excess Voltage and Limit the Impact of Power Surges and Transient Spikes on Your PV System.

Voltage Adjustment:

DC SPD continuously monitors the voltage level of the electrical system. When the voltage exceeds a predetermined threshold, indicating that a surge or transient has occurred, the DC SPD activates to provide protection.

Deriving the Overvoltage:

DC SPDs provide a low impedance path to shunt excess voltage away from the protected device. Metal oxide varistors (MOVs) or gas discharge tubes (GDTs) are typically used as the primary protective element. These components have high resistance under normal operating conditions, but become conductive when voltage exceeds the rated threshold.

Absorbs and Dissipates Energy:

In the event of an overvoltage, the DC SPD 1000V immediately conducts the excess voltage to ground, bypassing sensitive equipment in the system. MOVs or GDTs in DC SPDs absorb surge energy by limiting the voltage to safe levels. This prevents excessive voltage from reaching the connected solar panels, inverters and other electronic components.

Voltage Limits:

DC SPDs are designed to limit surge voltage levels to safe thresholds. This voltage limit ensures that overvoltages do not exceed the load capacity of the device. By keeping the voltage within a safe range, the DC SPD protects the system from damage and helps prevent equipment failure.

Reaction Time:

The DC SPD’s response time (usually in nanoseconds) indicates how quickly the DC SPD 1000V can wake up when an overvoltage condition occurs. A fast response time is important to effectively dissipate the surge before it reaches the device. For optimal protection, look for DC SPDs with fast response times. Multiple levels of protection: Different types of DC SPDs can be used in photovoltaic systems to provide multiple layers of protection. A Type 1 lightning arrestor is installed at the front door to protect against external surges. A lightning strike is installed. A type 2 DC SPD is connected to the subdistributor to protect against overvoltage from the network.

How Does an SPD Work to Protect the Solar PV System?

In the simplest terms, a solar SPD controls the transient voltage and directs the current back to its source or ground when a transient voltage arises on the protected circuit.

To ensure that energy flows to the ground first to prevent overvoltages, the most important component is the Metal Oxide Varistor (MOV). which under different conditions transitions between a high and low impedance state.

The solar surge protection device is in a high-impedance state and has no impact on the solar PV system at typical operating voltages. When a transient voltage occurs on the circuit, the SPD moves into a state of conduction (or low impedance) and diverts the surge current back to its source or ground. This limits or clamps the voltage to a safer level. After the transient is diverted, the SPD automatically resets back to its high-impedance state.