Fire Risks for a Solar PV Plant Commercial Installation

Today I will focus on the PV panels and the strings and there are quite a few solutions available, as well as various methods to mitigate risk.

When installing PV panels one of the first things to check is that quality MC4 connectors are used, and if a panel has a T4 type connector then it is best to install T4 connectors on the PV string cables that connect to the PV Panels.

Tighten the PV connectors with the appropriate tools, push them in until a positive click is heard. I have had it where I get a positive click but the cable and pin move back slightly, this could cause a hot connection, now I also hold the cable at the back of the MC4 when pushing them together. If the correct tools are used to tighten the MC4’s then this should not happen. I have had an issue on an inverter where the MC4 would not connect properly and the particular connection was hotter than the rest when checking operation with a thermal imaging camera.

Next is String Cabling, I prefer to run the positive cables of the strings apart from the negative cables. Red cables are cable-tied together on one side of the steel trunking and black cables are tied together and placed on the other side of the steel trunking.

We have had one factory catch fire inside the factory due to a chemical reaction and the fire reached the roof under the PV panels. The roof burnt and so did some of the PV panels, however the fire did not spread on the roof as the red and black cables were separated and therefore none of the red and black cables short circuited, which would have resulted in the building burning down. There is also the issue of unconnected MC4 connectors from a string that touch the roof, these cause intermittent faults by arcing to the roof when it is damp. The inverter should shut down due to AFCI fault (Arc Fault Circuit Interrupter). Strings must be drawn and shown correctly on a drawing of the roof or structure and can also be shown using an excel spreadsheet and colour coding the strings. I have been on sites and spent days trying to find and rectify an AFCI fault, the contractor did not provide adequate drawings and information.

Should a fire occur on the roof, people scramble, which string could it be, how do we stop the fire from spreading, panic sets in.

There are a few options to consider. There are fire suppression systems, or a foam blanket could be sprayed onto the panels. However, these systems are only good if there is not a strong wind or if there is no precipitation which could dilute the foam, PV panels can produce power in cloudy conditions.

My preference is to install optimizers onto the PV panels with Rapid Fire Shutdown. This solution will work in rain, wind or shine, the optimizer has circuitry to check the MC4 connector temperature, loss of communication to the AC inverter, loss of Grid, Arc Fault Detection or short circuit fault. This results in each optimizer defaulting to a state where each optimizer in the string produces 1v only. Risk of shock is reduced and the risk of fire is reduced. An emergency stop button can be wired into the Rapid-Fire Shutdown controller, the customers Fire Protection panel can interface to the Rapid-Fire Shutdown controller, and any of these actions will switch the optimizers to 1v output as opposed to 700V to 1000V output. Some insurance companies insist on their client installing a solution with Rapid Fire shutdown. Where this solution may cost up to 15% more than a standard solution, the benefits outweigh the extra cost.

Risk reduction is a huge benefit, however there are more benefits, added to that, each PV Panel is monitored, if one PV panel is compromised due to shading, micro cracks or physical damage, the rest of the string is not affected. Technicians know exactly which PV Panel is not working properly, no need to lift 17 or 18 panels to find the faulty PV Panel. This results in much better annual yields, therefore the extra cost of the solution pays for itself within 1 to 3 years. This solution can also be retro fitted onto an existing plant, where case studies have shown an increase of up to 38% in annual PV Production. These are my thoughts and opinions only, this is not a white paper, many people or experts may differ and I accept that.