Put your roof to work in a safe manner

​​Solar panels are becoming more cost-effective, and the large and often flat rooftops of industrial and commercial buildings are an ideal location to harvest the energy of the sun. It is a cause of great concern when the rooftops in question are constructed using combustible materials, including insulation materials.

Multiple components increase risk

Solar panel systems contain multiple components, including its module circuitry, cables, inverters and combiner boxes etc. All electrical installations, by their nature, will carry some degree of fire risk. There are a number of scenarios in which a rooftop fire with PV panels can occur. Electrical faults, such as short circuits or DC arcing in PV modules, inverters, and combiner boxes etc., can create enough heat for the combustible components to ignite.

Wrongly installed or defect equipment, such as DC/AC inverters, has also resulted in several fires in PV systems. Furthermore, faulty cable management can cause cables to overheat and ignite combustible materials on or within the roof structure.

Furthermore, the mere presence of PV panels on a roof structure will change the dynamics of a fire and may increase fire spread across a common roof assembly. If a fire occurs on a roof with PV panels the heat from the fire may radiate back and forth between the PV panel and the surface of the roof, causing the fire to spread to the combustible roof materials.

A hazard to firefighters

In addition to the many different fire scenarios that can arise when installing PV panels on combustible roof constructions, having solar panels on the rooftop can also complicate the efforts of the fire brigade in a fire-fighting situation. When the fire brigade arrive at a burning building, they seek to disconnect all life threatening utilities to the building.

However, this is not possible with solar panels, as they will continue to produce power as long as the sun is shining. Therefore, the fire fighters will have to fight the fire in the presence of significant voltage, which in addition to the risk of DC arcing, also poses a threat to their personal safety.

Therefore, when securing the utilities, it is important that firefighters identify the source of the power from the photovoltaic system and disconnect that as well. This may be difficult if you are in a building for the first time and have no idea where it may be located. In some jurisdictions, however, the utility companies and code enforcement authorities have required the installation of a disconnecting device outside of the facility near the meter to disconnect the solar power from the buildings electrical system.

Steps to take for fire safety

From a fire safety point of view, the following should be taken into account: ​

• PV arrays should be installed according to OEM (Original Equipment Manufacturer) instructions. PV panels containing expanded plastic should be avoided. Likewise, all cables should be of the low combustibility type and installed with adequate provision for expansion and contraction for extreme temperature fluctuations over a year. Also, the cable connectors should be waterproof.
• It is strongly recommended that where PV panels are to be installed on building roofs, that the roof is non-combustible.
• No panel array should be closer than 5 metres from a major fire wall (typically walls that separate warehouses from production will be considered to be major fire separation walls) and cable runs should not be installed over a fire wall, without providing fire proofing to the cables.
• The inverter and associated plant to the PV panels should be located in a dry, non-combustible enclosure, equipped with automatic fire detection and, if feasible, equipped with automatic inert gas or carbon dioxide fire extinguisher.
• Inverters on the DC and AC sides should be provided with surge protection.
• Emergency shut down of the system is highly recommended, located near the entrance of the building and at the inverter.
• Soon after the PV array is taken in to use, a thermographic inspection should be carried out on all electrical components, including cable connections. Any identified faults should be repaired immediately. Thermographic surveys should be conducted every two years, as a minimum. The panels themselves could need annual cleaning for efficiency and in order to reduce possible hotspots. These could also be detected with thermography.
• Annual maintenance should be performed in accordance with OEM specifications, and should include testing of inverters. Mechanical connections to PV panel supports should also be inspected. In addition, visual inspections are needed after every NatCat incident, e.g. storm, hail, snowfall, etc. Especially snow removal needs high attention. Continuous online monitoring becomes increasingly common and reduces the risk.
• The PV array insulation resistance should be tested every three years. ​

Martin Sörensen