The accelerated expansion of photovoltaic generation in Brazil has consolidated solar energy as one of the pillars of the energy transition, comprising approximately 23,2% of the electricity matrix. Increasingly powerful, distributed, and grid-connected systems have begun to be integrated into homes, industries, businesses, and large power plants.
However, this technological advancement has also brought a critical challenge: how to ensure the safety, operational continuity, and durability of these systems in the face of extreme electrical events.
Among the main risks faced by photovoltaic systems are electrical surges, frequently associated with lightning strikes, grid switching, and electromagnetic interference.
According to INPE (National Institute for Space Research), Brazil receives an average of 78 million lightning strikes per year, being considered a country with a high keraunic level. When not properly managed, these phenomena can cause premature failures, significant financial losses, and even risks to the safety of facilities and people.
It is in this context that surge protection ceases to be an accessory item and begins to occupy a strategic role in the design, installation, and maintenance of photovoltaic systems. More than just meeting technical standards, it is about adopting a conscious engineering approach capable of raising the level of reliability and robustness of solar power plants.
O new ebook It was developed by CLAMPER to present, in a clear and practical way, the fundamental concepts, protection mechanisms, relevant standards, and best practices related to surge protection in photovoltaic systems, contributing to safer technical decisions and more resilient designs.
What are electrical surges?
Normal voltage and current variations are expected in network operation. An electrical surge is also a voltage variation, but a transient one of short duration and high energy, usually caused by lightning strikes or network switching operations.
A power surge lasts on the order of microseconds and is capable of damaging sensitive components such as photovoltaic inverters, since their electronics are only able to withstand small, transient impulses. Without external protection, it can fail after just a few surges.
Surges can occur conductively (through cables), inductively (magnetic fields), capacitively (electric fields), or resistively (potential difference in the ground).
Where do electrical surges occur in a PV system?
In a photovoltaic system, the surge finds more than one point of entry:
- Direct Current Side: cables forming large loops at the module string connections favor the induction of high-intensity current, in addition to long cable lengths between modules and inverters.
- Alternating Current side: lightning strikes or network switching operations propagate surges to the AC side of the inverter.
Therefore, both national and international standards recommend the use of Surge Protection Devices (SPDs) in photovoltaic systems, given their exposure to the various components of the system.
What are the types of lightning strikes?
There are two ways a lightning strike can hit a piece of equipment:
- Direct discharges: These are the most dangerous, as they directly affect the system, usually the photovoltaic module, the most exposed component. The affected module shows signs of burning on the frame and upper parts, and may even have broken glass.
- Indirect discharges: These strikes are milder, since the lightning struck in another location and only induced a current in the string cables. On the other hand, it can damage dozens of bypass diodes at once. This causes a loss of voltage in the module and consequently a loss of generation. In general, it affects modules connected in the same string and closer to each other. This high voltage can reach the inverter and damage it as well. In addition, indirect discharges can also travel through the utility grid to reach the inverter on the AC side.
In none of the cases mentioned above would the warranty cover the impacts caused, since it is not a manufacturing or product performance problem. Only insurance policies specifically designed for this purpose could compensate for the damages caused.
What is a DPS?
A surge protection device (SPD) is a piece of equipment used in electrical installations to protect equipment against transient overvoltages, usually caused by lightning strikes, switching operations on the electrical network, or switching of inductive loads.
The surge protection device (SPD) acts as a voltage limiter, diverting high-voltage surges that could damage sensitive equipment to the grounding system. It does this by using a varistor, which is a non-linear resistance component whose resistance varies according to the applied voltage.
How does a surge protector work?
Under normal operating conditions, the surge protection device (SPD) remains inactive, exhibiting high impedance and not interfering with the circuit.
When a voltage surge occurs and the value exceeds the tripping level of the surge protection device (SPD):
- The device starts conducting, reducing the impedance;
- Excess energy is quickly diverted to the ground;
- The voltage in the circuit is limited to a level that is safe for the equipment;
- After the surge, the SPD returns to a high-impedance state, blocking the current from flowing to ground.
Why use a surge protector?
Many people may wonder, "Lightning doesn't strike the same place twice, what are the chances of it hitting my power plant?" And in fact, it's not very common for lightning to strike the same place twice, unless the shape and height make it possible. However, even if the lightning doesn't strike your power plant directly, it can affect it indirectly. For example:
A lightning strike occurs on a tree near the power plant; signs of burning are found on the tree, but no visual defects are noticed on the modules.
However, a nearby lightning strike induces current in the string cables, damaging the bypass diodes and causing these modules to lose voltage by one-third at a time. Furthermore, this sudden voltage drop on the DC side can damage the inverter.
Is there a DPS for specific use in photovoltaics?
These surge protection devices (SPDs) are specifically designed for use in photovoltaic systems, and they have important differences compared to conventional alternating current (AC) SPDs.
The main difference lies in the electrical behavior of direct current, which does not cross zero as it does in AC. For this reason, photovoltaic surge protection devices (SPDs) use varistors specially designed for DC, with a greater capacity to withstand high DC voltage and prevent permanent conduction.
Furthermore, it is common to find internal thermal decoupling circuits (fuses or circuit breakers) that disconnect in case of a short circuit, reducing the risk of overheating and fire.
CLAMPER has developed a specific surge protection device (SPD) for photovoltaic systems on the DC side, the CLAMPER Solar SB line, which features integrated DC disconnectors or in-line fuses in the CLAMPER Solar CB models, a flame-retardant plastic housing resistant to weathering, and a visual status indicator.
How much does it cost to not install a surge protector?
A surge protection device (SPD) represents on average 8% of the total cost of a PV system. To reduce the system's cost, some installers choose not to add protection.
However, this can cause damage of much greater proportions, such as inverter failure (10x the protection value), generation interruption (varies with the downtime, but is much greater than the protection value), corrective maintenance costs to replace damaged equipment, and loss of warranty, since some manufacturers do not accept warranty for inverters without protection or do not cover external damage such as surges.
Conclusion
As explained earlier, surge protection devices (SPDs) are essential for protecting photovoltaic system assets, and knowing how to choose the appropriate SPD parameters is crucial for them to function properly and filter the voltages for which they were designed. The ebook provided by CLAMPER describes each of these parameters, serving as a complete guide to choosing the right SPD.
The opinions and information expressed are the sole responsibility of the author and do not necessarily represent the official position of the author. Canal Solar.
