Photo-voltaic (PV) electricity and FRA

[SamFIRT]

With the increasing prevalence of PV panel based domestic (and commercial) electricity creation; usually from roof mounted modules or panels, I thought I would share some thoughts arising from some research I am doing.

PV panels create Direct Current (DC) electricity. Each panel may create up to 40 Volts DC. The panels are interconnected in series, meaning that the end of the supply cable to the next part of the circuit can have hundreds of volts DC potential. The DC supply cable then is connected to a isolator switch (DC specific double pole). The DC electricity then flows into an Inverter, where it is altered into 240 volts Alternating Current (AC) at 50 hertz. This then enters a smart meter, (sometimes constructed to be part of the inverter package). Sometimes this is all mounted on a timber backboard. The electricity then flows through a double pole AC isolator switch. It is then connected to the internal wiring of the property with a feed back into the supply grid. The smart meter will feed over supply into the grid and calculate the tariff. It will also disconnect the supply from the grid should there be an incoming grid supply failure in order to prevent electrocution of linesmen.
 
Obviously there is no greater danger of fire from all this as compared to any other electrical installation (if correctly installed and constructed out of suitable components). However, there is a greater fire loading in a loft because of the installation, a greater weight loading on the roof construction ( a cause for concern of earlier failure due to fire damage). Along with the danger of electrocution of firefighters from the live DC supply. Should a fire develop in the loft then the occupier is unlikely to detect it early until the products of combustion are smelt downstairs or seen from the street.

Discussion….. Notwithstanding building codes / regulations; I believe where PV panels are installed on roofs of premises, consideration should be given to the installation of smoke detection in the roof space in order to allow for early detection of incipient fires, especially those caused by high resistance faults?

Comments please?
 
Sam

[kurnal]

Is there any documented history of fires involving PV panels?

[SamFIRT]

Yes.

But thereby hides the rub. As I said before, I believe there is no problem per se with PV panels. The problem for the occupier is the same as with any electrical work. Inappropriate or badly made connections or poorly made components or inappropriate components; may lead to incipient fire development. However, I believe for a small cost (a single point interconnected or remote sounder smoke alarm) the extra potential ( no pun intended) for fire loading in a loft could be protected and early faults detected..

As to the potential problems for firefighters, with permanently live DC voltage (presupposing there is light outside) circuitry; well that is a different matter. This however will also be negated by early detection, thereby eliminating the problem.
 
The extra imposed loading on the roof members is another matter.

[jokar]

So we have a fire in the roof and it is detected early by the provison of AFD.  The fire then grows although the occupants are now aware of it and are out of the building, hopefully.  The fire brigade turn up and apply some type of intervention.  Hopefully, dur to the danger of the AC current there will be a firefighters switch to isolate the array from the array into the builidng.  However, the DC current will still be live and the intervention will need to handled quite carefully, without danger to the staff involved.  Lots of water, risk of shock, let it burn and cover the surrounding risk! Whatever stance is taken including
the AFD, you will probably lose the array and the roof but the AFD will keep the people safe.

[Midland Retty]

A few chums of mine from different brigades have said that standard operating procedures have now been issued in relation to PV units / panels and associated gubbins. They all pick up on the hazards you mentioned (for firefighters)

In terms of the safety of residents. I dare say that some of the issues you highlight are negated in new build houses fitted with PV panels incorporated into their original design.

In existing properties however where PV panels have been retrofitted I can see the risks. One in particular being the structural integrity of roof in the event of fire. Early warning, then, seems a sensible idea.   

[wee brian]

I went along to this last year

http://www.cfoa.org.uk/11986

came to the conclusion that there wasn't much to worry about. A chap from the German fire service explained how they deal with PV and I expect this is what the guidance that UK FRSs is based on (or they've just used a bunch of mumbo jumbo like they usually do)

I cant quite see where the increased fire load argument comes from. A pile of suitcases and a Christmas tree will have more energy in them than the bits and pieces associated with a PV installation.