Fire safety for PV systems

Poor design or installation can lead to fire as there is increased risk of electrical arcs. Arcs commonly occur where there is an unintentional break in the electric circuit. This is what a DC arc looks like:

In Germany, Australia and the UK, the majority of faults have occurred in the DC side of the circuit (PV modules, DC wiring, DC isolators, etc) [1] [3] [4]. The probability here is high because there are many components and connections on the DC side. That means there are more chances for something to go wrong: for e.g. one of the components is faulty or one of the connections is not properly made.

DC isolators are a particularly common root cause for PV system fires. As much as 50% of fires caused by PV in WA were caused by rooftop DC isolators between 2009-2015 [3]. The story is similar in the UK, with 40% caused by the DC isolator and over 20% caused by DC connections. Based on statistics from these fire cases, a large portion of fires could have been avoided if manually installed DC isolators were eliminated, and the number of DC connections were minimised. In support of this, SMA provides DC isolators already inbuilt into our inverters, which avoids the risks associated with manual wiring and installation of external DC isolators.

3. Firefighters can still attend a home with a PV-system

When appropriate precautions are taken, firefighters can still extinguish fires on homes with PV systems [1]. These precautions include keeping a minimum distance between the nozzle and PV array such that there is no risk of electrocution to the firefighter.

4. Are module-level shutdown devices needed?

In short, no. Here’s why:

PV system safety has improved over time with the introduction of new safety devices. You may think that adding additional safety devices would reduce the chances of a problem. However, adding more devices increases the number of connections and components that could fail. In the case of adding module-level shutdown devices, the number of DC connections roughly doubles! This increases the number of sites for a potential problem, whether it is component failure or an installation mistake like not properly making connections.

Module-level shutdown devices are also unnecessary for firefighters to safely attend an incident involving a PV system. The independent testing institute TÜV does not propose the mandatory inclusion of module-level shutdown devices: “reasoning has led fire departments to shift away from the general demand for a shutdown on the grounds that theoretically any switch-off device can fail” [1].

With SMA you can choose whether module level power electronics are needed. In some systems, such as those that have persistent shading during the day, the TS4-R Optimiser can be used to maximize yield from the PV system and minimize stress on the shaded module. The TS4-R system can be selectively deployed only to affected shaded-modules to minimise the number of components and connections.

Conclusion

Fires are extremely unlikely in PV systems when they are properly designed and installed. Analysing previous fires at PV systems has confirmed this. PV systems can be made even safer by addressing the most frequent root causes of DC arcs, which are mostly related to human errors during the design and installation stage. There is no need for module-level-shutdown devices as firefighters may already manage risks onsite and they do not address the common root causes for PV system fires.

If you would like to learn more on this topic, you can watch a recorded webinar on this topic which SMA participated in with PV Magazine in December 2018. You can access the webinar at the following link:

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