Rooftop Solar PV Plants which are placed at the top of buildings making them susceptible to direct lightning strikes require protection using correctly designed lightning protection using lightning arresters and surge protection to ensure long working lives.
Solar plants have quickly become one of the fastest-growing sources of renewable energy in many parts of the world because of the sharp drop in panel costs and the increase in the efficiency of these systems. These PV plants are becoming integral to many electrical networks where they provide independence from the central grid but at times also cheaper generation rates. In urban areas, solar rooftop systems are especially popular because of the empty rooftop real estate that many building societies wish to now monetize and provide cheaper electricity for their residents. However, the location of these rooftop solar projects on exposed rooftops makes them susceptible to the impact of lightning especially in high lightning prone cities in India such as Mumbai or Bangalore which have many Rooftop Solar Plants. It is also important to note that as per today’s scientific knowledge, the construction of Rooftop Solar projects does not increase the risk of lightning.
Lightning Risk Assessment and Design
You can read about the procedures of lightning risk assessment and lightning protection system design in more detail in our blog ‘3 Steps to Install a Safe & Reliable Lightning Protection System’. To summarise, Lightning Risk Assessment uses a range of factors from the structure such as the height of the structure, number of incoming power and telecommunication lines, electrical systems, number of people occupying the structure, sensitivity of the equipment inside, and many other factors to determine the risk that the structure faces. Using the class of lightning protection decided from the Risk Assessment step, lightning protection system design can be done using the Rolling Sphere, Protection Angle method, or the Mesh method. The system design will provide information such as the location of the lightning arresters, down conductors, earth electrodes, other equipment, and the complete Bill of Material.
It requires many measurements, calculations, and years of experience to execute Lightning Risk Assessment and Design perfectly. In addition to the products and 25 years of experience that Axis offers, we also offer a software suite that will help simplify all your lightning protection calculations so that you can put your head towards providing the best service for your clients. Axis can also help you with the entire process from Risk Assessment to Lightning Protection System Design and all the way through supply of internationally approved products. Our engineers will be on the field with you to make sure that they provide the most precise protection for your structure! For more information on our Software Solutions or our Risk Assessment and System Design, please contact us!
External Lightning Protection System
Air Termination System:
A variety of air termination systems can be used in conjunction with the rooftop solar plant depending on the dimensions and materials of the space. As mentioned above, three methods can be used as per the international standards to design the air termination, namely the rolling sphere method, the protection angle method, and the mesh method. Depending on the designs obtained from the different methods, the franklin rods, early streamer emission (ESE) lightning arresters or conductors for a mesh can be used in order to protect the building. The down conductors that are used in conjunction with the lightning arresters have to be distributed around the structure keeping the separation distance as defined by the class of LPS.
The person designing air termination should also take extra precautions to take into account the solar modules. Some specific issues include:
- Space Optimisation: The final goal of rooftop solar plants is to maximize the use of the limited area available. There needs to be coordination between the designers/installers of the lightning protection system and the rooftop solar system to make sure that space is optimized while still meeting minimum requirements such as separation distance.
- Solar Tracking: Modern solar farms include tracking which makes the PV modules move along with the movement of the sun. The designer needs to cognizant of this movement and make sure that the modules are protected throughout the day regardless of the position of the modules.
- LPS Shadows: The efficiency of the plant can be affected if the LPS, especially the lightning arresters, cast a shadow on the modules. Thus, the designer should make sure that they minimize the impact of shadows.
- Separation Distance: The separation distance between the modules and the lightning protection should be considered. This is the minimum distance required as per the standard to make sure that uncontrolled flashovers to adjacent metallic surfaces (PV modules or frames) do not occur during a lightning strike. If separation distance is not maintained, in the worst-case scenario, it could lead to a fire in the system.
- Fall of Lightning Arresters: If the long metallic lightning rods or Early Streamer Emission (ESE) lightning arresters are not designed or installed correctly, there is a possibility of significant financial losses if they fall onto the modules.
Down Conductors:
The down conductors also need to maintain a minimum separation from any doors, windows, balconies, or any other point where they might be within human reach during stormy periods.
Earth Termination System:
The earthing system used for the protection of rooftop solar plants can be either Type A or Type B earthing. Type A earthing usually uses either vertical or horizontal earth electrodes, or sometimes a combination of both. This could mean connecting the down conductors to a copper bonded earth rod that is buried in the ground. Type B earthing or ring earthing involves using a closed ring of conductors around the building maintaining at least 1 meter from the structure. For Type A Earthing, depending on the class of LPS defined during the risk assessment stage, the length of the vertical and/or horizontal earth electrodes to be connected to each down conductor will be defined in the standard. For Type B Earthing, if the radius of the ring electrode is less than the length of vertical or horizontal earth electrodes required for Type A Earthing then additional horizontal or vertical earth electrodes can be connected to the ring.
Internal Lightning Protection System
While the External LPS helps protect the rooftop solar plant and the building from direct lightning strikes, the system can still be vulnerable to indirect effects of nearby lightning strikes without the use of adequate Internal lightning protection systems using equipotential bonding and surge protection devices (SPD’s). Indirect surges can be caused, for example, by lightning striking a power line that is entering the building thus causing a power surge that affects all electrical systems connected to the power line including the rooftop solar plant. Bonding metallic surfaces at the border of each Lightning Protection Zones (LPZ) using equipotential bonding or surge protection devices (SPD’s) can protect the next LPZ from the surge.
Conclusion
Solar Rooftop plants require well-designed lightning protection systems and products to ensure that they meet their advertised working life. You should only procure products certified according to international or national standards for your lightning protection requirements to ensure that the products perform according to the requirements of the design of the lightning protection system. Axis supplied the entire range of products for Lightning Protection for over 25 years to hundreds of projects across the world. View our catalogue for our Lightning Protection Products or contact us for more information.
This article is part of our series of articles on Lightning Protection, Surge Protection & Earthing, you can read more with the following links:
Introduction to the basics of Lightning Protection and Earthing and the Standards (IEC 62305 and UL 467)
Surge Protection Devices (SPD)
Lightning Protection Zones and their Application to SPD Selection
How does a Lightning Arrester work?
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