47 CATHEDRAL COMMUNICATIONS THE BUILDING CONSERVATION DIRECTORY 2025 BUILDING CONTRACTORS 2 metres to several hundred metres. PV cable is typically non-armoured so routes need to be mechanically sound and free from aspects that can damage them. PV DC connectors are a critically important part of a PV system, used to mate DC cables from PV modules to the cable connecting the inverters. They are recognised as one of the most common causal factors of PV fires. PV connectors require correct ‘making’, with correct cableto-pin crimping using the correct crimping tool, correct torquing of the gland for IP integrity and connector compatibility. DC isolators disconnect the PV string from the inverter. They are designed to isolate both the positive and negative PV strings under load and can accommodate significant arcing at the point of making or breaking the circuit when operational. PV combiner boxes are often used on larger PV systems to merge multiple PV inputs (up to 40 strings) into a single DC −/+ cable pair feeding the inverter. PV combiner boxes are more susceptible to fire risk than other components due to the large number of screw terminations and high DC currents at the point of making/breaking, with some inevitable arcing occurring whenever the switch is opened and closed. Inverters are at the core of a PV system as they convert the current from DC to AC and generally provides monitoring data on DC and AC performance. Good ventilation and regular cleaning of cooling fans/filters are essential to maintain correct operation, especially in dusty environments. Mounting systems for supporting PV panels must be designed to hold the modules securely in place in the most extreme conditions that may be expected, taking into account climate change and the increasing frequency of extreme weather events. This includes high winds, snow, lightening and hail, wherever they are located, although rooftops may be particularly vulnerable. Battery storage is now a common purchase with any PV system as it can provide a constant energy supply from a variable source of energy over a 24-hour period. Lithium-ion batteries are often used because they can store significant energy at high density in small footprint devices. Some of these are more stable and less prone to fire than others. Developments in PV systems continue apace and components may vary. One of the biggest changes is the option for every solar panel to have its own microinverter to effectively give an AC output. While currently more expensive, this can be advantageous in reducing system complexity, improving expandability, and overcoming shading issues and power loss from long DC cable runs. Similarly, AC batteries may now be chosen that cut out a conversion step leading to greater system efficiency. An AC PV system may overcome many of the fire challenges because it transports electricity at much lower currents than DC, and because the micro inverter may automatically disconnect the panel in the event of fire. The fundamental causes of most electrical fires in PV systems result from heating, arcing and induced currents that can cause local materials to combust. Physical damage from local challenges and extreme weather events also play a significant part. In a 2021 study by IEC, data on fires was analysed and showed that installation and product defect faults accounted for 72 per cent of the causal factors for fire (see graph opposite). In terms of the impact of fires involving PV panels a study of 400 incident reports from Germany between 1995 and 2012 revealed: FIRE FROM OUTSIDE – PV system affected 220 FIRE FROM PV SYSTEM – Building destroyed 10 FIRE FROM PV SYSTEM – Building damaged 65 FIRE FROM PV SYSTEM – PV system damaged 49 FIRE FROM PV SYSTEM – PV system component damaged 55 It was also identified that the majority of these fires happened in roof-mounted systems. Between 2019 and 2022 UK solar capacity grew by 10 per cent but solarpanel related fires surged by nearly 50 per cent, suggesting that in the rush to install and take advantage of good feed-in tariffs, compromises were being made in the quality of equipment and installation. PV COMPONENTS MOST LIKELY TO CAUSE A FIRE A study undertaken by BRE in 2017 found that DC isolators were the cause of almost half (49%) of all PV fires [Graphs: ‘RC62: Recommendations for fire safety with PV panel installations’, FPA and RISC Authority, 2023] CAUSES OF FIRES AFFECTING PV Installation and product defects were responsible for 72% of PV fires considered by an IEC study in 2021 PV arrays are often mounted on the roof but they can also be mounted on the ground, in gardens or over car parking spaces where they provide shade.
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