Lightning is a high energy electrical discharge that occurs when there is an imbalance between storm clouds and the ground or between the clouds themselves. Very tall building structures or objects attract lightning more frequently because they represent the shortest path from a cloud to ground. Wood and other flammable building materials can easily catch fire and lightning current travelling through wires can burn them up and damage an entire building. When there is an encounter between lightning and the home's electrical wiring, the explosive surge tends to damage even non-electronic appliances that are connected. A good lightning protection system reduces the risks of injury and fires and avoids casualties.
The components of an efficient lightning protection system include vertical protrusions (rods or a network of air terminals), conductor cables to carry lightning current from the rods to the ground and ground rods that are buried into the earth around the structure to be protected and to allow lightning current to discharge around the structure. International Electro-technical Commission standard (IEC62305), which is accepted by many countries as national standard, advocates the need of planning, erection, testing, and regular maintenance of lightning protection systems for building structures.
Solar street lights require a relatively higher investment and it is important to protect your lights from the fallout of lightning strikes. Solar street lights and related components are either mounted on poles or walls and they are surrounded by trees or tall buildings most of the times. Solar street lights are prone to lightning strikes, which can damage solar panels and other components. Most of the solar street lights are integrated devices so even when a single wire is destroyed or damaged, the entire solar lighting system can stop working. Even indirect lightning can be destructive as it generates an electromagnetic force that prompts overvoltage. Fire protection of buildings must be of utmost importance since the energy released by a lightning discharge is one of the major causes of fire. The solar lights installed on the rooftop are also susceptible to damage from lightning. Nonetheless, most lightning damages are preventable if some cost-effective techniques are followed.
Installing a low resistance and low impedance grounding system is the first smart step to be taken towards protecting your solar street lights from extensive damages caused by lightning. The installed grounding system is expected to provide safety step and touch voltage criteria suitable for a power generation facility. A surge protection device (SPD) system also should be installed after the installation of a stable grounding system. Risk analysis must also be undertaken to understand the risk parameters before setting up a lightning protection system.
Grounding system design and analysis
To design a solar grounding system, comprehensive soil resistivity measurement needs to be done. Soil resistivity test involves measurement of how much soil resists the flow of electricity. Wenner four-probe soil resistivity method is by far the most used test method, which corresponds to IEEE Std. 81. This test uses four probes spaced at equal distances to measure how much electricity is conducted between the probes through the soil. The distance between the test probes results in soil resistivity data at the equivalent depth and this test is considered to be the most reliable soil resistivity test. How soil conducts electricity is an important factor to be understood. Multilayer soil resistivity test results should be acquired and specialized grounding software helps model the best grounding system for an array. The computer model helps designers complete a comprehensive fault analysis. The ohmic value for grounding systems suggested by IEC 62305-3, UNE 21186:2011 and NF C 17-102:2011 standards is below 10Ω when isolated from any conductive element and measured at low frequency.
Surge protection system
Installing both AC and DC surge protection devices at major areas throughout a solar site to protect panel module circuits, inverter stations and critical control circuits at the combining switch gear box is another crucial aspect in addition to proper grounding and bonding. A comprehensive network of quality SPDs must be installed to protect the unit from hardware damage and from operational disruptions resulting from lightning and non-lightning related transients. The most intense surge events are caused by direct lightning; however, indirectly-coupled surge impulses originating elsewhere can also be at high voltage levels as well and can be quite threatening to the solar street light units.
It has been suggested by National Fire Protection Association (NFPA 780) and International Electro-Technical Commission (IEC-62305) standards that solar developers should take lightning risks into consideration to establish a baseline for lightning protection systems. In other words, it is either the developer’s or the property owner’s responsibility to conduct a cost-benefit analysis and decide what type of lightning protection is suitable to the particular array. To determine the need for an effective lightning protection system, the level of risks must be ascertained. The probability of direct lightning strike to the solar lights and the risk parameters of the same must be compared. Risks associated with loss of power production which can cause discontinuity of service should also be of primary concern.
One of the most common and cost-effective precautionary methods is ‘single needle lightning rod’, where the rod receives lightning and leads it down to the earth safely. This act of releasing lightning current into the ground helps protect the building from electrification. This operates without any power supply and does not need any maintenance. However, single needle lightning rod can protect your structure only from direct strike lightning. Indirect lightning can also cause huge damage to the solar LED street lamp system if it is not protected.
Power surge protectors are capable of giving protection against induction strike lightning. Power surge protectors follow international standard fixtures and advanced manufacturing technique. They can be easily installed and maintained. Power surge protectors are designed to work under any hostile environment such as acid, alkali, dust, salt, fog, severe weather conditions, etc. Temperature control circuit break technology with built-in over-current protection circuit helps to provide protection from fire disaster.
Inadequate protection from direct lightning strikes, insufficient transient protection and incorrect grounding system are some of the reasons that can work against your solar lights during a lightening. Most damage to solar street lights occurs from nearby hits and lightning protection systems offer fire protection and damage protection by stopping the surge of electrical current from passing through the materials and directing the current to the ground directly. Besides physical damage, economical damage can lead to replacement and repair costs. Lightning impulses can also cause premature ageing of the solar units, hence it is advisable to install a well-designed structural lightning protection system to safeguard your solar street lights from any type of lightning damage.