Atmospheric discharges pose a huge danger to photovoltaic solar generation plants. It is believed that approximately 26% of all damage suffered by photovoltaic systems in the world is caused by direct or indirect atmospheric discharges.
Taking into account that many Brazilian cities have a density of atmospheric discharges to the earth (NG)2 between 5 and 10 lightning strikes/km2 per year, we will soon have in Brazil numerous plants hit annually by a significant number of direct atmospheric discharges, something for which we must prepare with great dedication.
In addition to this fact, an atmospheric discharge induces voltages and currents up to 2 kilometers away from its point of impact.
As photovoltaic plants are normally located in isolated locations, we can imagine the amount of energy transferred to them by lightning strikes that reach an area equivalent to a radius of 2 km from the center of the plant.
The reduction of risk of damage is directly proportional to the knowledge we have about them. Therefore, it is necessary to divide those associated with atmospheric discharges in photovoltaic plants into three categories:
- Direct impacts of discharge on the plant;
- Voltage or current surges caused by direct or indirect discharges in your installations, including photovoltaic modules;
- Injury or death of workers who are in the open areas of the plant.
Currently, Brazil has two specific technical standards for protection against atmospheric discharges: ABNT NBR 5419-13/24/35/46:2015 “Protection against atmospheric discharges” and ABNT NBR 16785:20197 “Protection against atmospheric discharges – Systems of warning of electrical storms.”
The two standards are complementary and equally important, and must be followed in all photovoltaic plant projects.
Part 2 of the ABNT NBR 5419:2015 standard presents 4 types of risks for a structure:
- R1, risk of loss of human life, including permanent injuries;
- R2, risk of loss of service to the public;
- R3, risk of loss of cultural heritage;
- R4, risk of loss of economic values.
Protecting people in photovoltaic plants against the effects of lightning involves step and touch voltages more than other risks such as fires, for example.
As photovoltaic plants are basically open areas, it is essential to move all people from the plant to sheltered locations, preventing the atmospheric discharge, wherever it falls, from reaching people with potential differences between parts of their body while the electrical discharge current travels through the ground.
The existence of a capture subsystem in this case will protect the modules and their structures, but never human beings.
Therefore, R1 must be minimized by lightning detection and warning systems, based on the ABNT NBR 16785:2019 standard.
In photovoltaic plants, special attention is required to R2, due to the total or partial interruption of the energy supply to a location and to R4 due to the losses caused by this interruption.
Although R2 and R4 appear to represent the same risk, R2 corresponds to the inconvenience caused to users of the energy supplied by the plant and R4 to the economic losses of its owners, because they will no longer supply their product, electrical energy, and may have to compensate their customers.
Photovoltaic systems depend on the area formed by their modules to capture solar radiation. The larger this area, the greater the energy converted, but also the greater the exposure of the photovoltaic system to atmospheric discharges.
As the sensors intercept rays and sunlight, the design of the capture subsystem must be very well studied, so that the shading caused by the sensors is as small as possible, as shown in Figure 2.
Induced voltages and currents caused by atmospheric discharges can cause permanent or temporary failures in solar inverters and photovoltaic cells, in addition to accelerating the degradation of these components, something that is still little considered.
Therefore, the vulnerability of photovoltaic systems to indirect discharges, whose probability of occurrence is much greater than that of direct discharges, is significant.
This justifies a strong investment in surge protection measures (MPS), something far beyond the simple installation of surge protection devices (DPS) 8 in junction boxes, just to comply with regulatory requirements.
So that transient overvoltages do not compromise the techno-economic viability of photovoltaic plants, it is necessary that all their characteristics, such as the type of modules, the design of the cables and the position of the grounding electrodes, for example, are optimized in order to reduce their vulnerability. to atmospheric discharges.
The study of the protection of solar plants against atmospheric discharges is still in its initial stages.
Researchers around the world have analyzed specific aspects of this topic, to find more efficient protection solutions, in addition to accounting for the costs associated with damage caused by lightning in photovoltaic systems, as reducing investments in protection during the plant's construction phase can mean spending additional costs with maintenance during its operation – the well-known trade-off between CAPEX and OPEX9.
Simply installing detectors and DPS will not be enough to guarantee the protection of photovoltaic plants against atmospheric discharges.
It will also be necessary to use its metallic structures as indirect shields, an adequate relationship between the detectors and the grounded pillars (Figure 3) and, ultimately, the development of photovoltaic cells with greater withstandability to transient overvoltages.
Atmospheric discharges represent a serious challenge for photovoltaic plants. When installed in places with a high density of lightning, they can be hit annually by several direct or indirect discharges.
To reduce this vulnerability, it is necessary to install lightning protection systems (SPDA) and carry out surge protection measures (MPS) within the recommendations of the ABNT NBR 5419:2015 standard, with characteristics appropriate to the peculiarities of a photovoltaic solar plant.
References
ZHANG, Y.; CHEN, H. Considerations of photovoltaic system structure design for effective lightning protection. IEEE Transactions on Electromagnetic Compatibility. May, 2020;
Atmospheric Discharge Group (ELAT), INPE (National Institute for Space Research);
ABNT NBR 5419-1:2015, Protection against atmospheric discharges Part 1: General principles;
ABNT NBR 5419-2:2015 Corrected Version:2018, Protection against atmospheric discharges Part 2: Risk management;
ABNT NBR 5419-3:2015 Corrected Version:2018, Protection against atmospheric discharges Part 3: Physical damage to structures and dangers to life;
ABNT NBR 5419-4:2015 Corrected Version:2018, Protection against atmospheric discharges Part 4: Internal electrical and electronic systems in the structure;
ABNT NBR 16785:2019, Protection against atmospheric discharges – Electrical storm warning systems;
DPS: The airbag of photovoltaic systems;
Let sunlight illuminate your electrical installation.
Comments (2)
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Hello
Does NBR 5419 apply to ground-based PV plants in open areas? How does it address these installations?
As an electrical technician – factory floor, I read the material, which instructs me more on understanding the systems and dealing with them, as well as updating myself on personal protection and understanding technical standards. excellent article.