Is Solar PV a fire hazard?
Posted by Paul Hutchens on 7 January 2013 at 9:50 am
Q: Are you aware of Times article and web site pvsolardoctor.com which claims PV panels are a fire risk if water enters the wiring system?
A: This question has resulted in a lot of research and investigation and the answer is, unfortunately, a bit involved.
Generating your own electricity using solar power is a great way to save money and reduce your impact on the environment. As growing numbers of households and businesses install solar panels the potential risk of fire, theft or electrical faults must be considered.
1. The first issue relates to safe and effective installation. All cables and wires should be terminated properly and signed off for building control purposes. This normally happens through the qualified electrician’s or installation company's competent persons scheme e.g. NICEIC or NAPIT. Ensuring that you use an installation company with a good track record will help with this – recommendations on YouGen are a good start!
2. There have also been issues with incorrectly specified DC isolator switches. According to Steve Pester from BRE in a recent article in Renewable Energy Installer "BRE was sent an example of a DC isolator (switch) which had filled up a room with smoke in a few seconds. It burnt through the side of the enclosure before it could be disconnected. The cause? Almost certainly an incorrectly specified isolator. All installers will know that DC is much more dangerous than AC and requires special components.
"You may think, therefore, that it’s a clear-cut case of the installer not doing their homework, or deliberately using a cheaper AC switch instead of a DC type but that is not necessarily true. We have been made aware of a worrying practice whereby one or two manufacturers are 'redefining' isolators originally designed for AC use as suitable for DC, with or without minor modifications. Occasionally, distributors have incorrectly advised installers on this issue as well. The advice ranges from using a 'rapid action' when turning the switch to wiring two poles in series in order to increase the switch gap in the 'off' position. If you hear this kind of thing, be suspicious! Purpose-designed DC isolators will rapidly suppress switching arcs and are of a different design from AC types."
Please ask your installer about this and ensure they are using proper DC isolators such as those provided by IMO and Santon who make 'true' DC switches and are equally passionate about the issues surrounding poorly specified AC isolators being used to protect DC circuits.
3. Lastly when a fire occurs, fire fighters across the country are concerned with faulty installations and attending fires with ‘live’ solar installations. Without safe and effective array shutdown fire crews are reluctant to enter burning properties with solar installations. This may be the case whether the fire was caused by the PV installation or not; in fact in most cases the fire may have been caused independently.
Actually there is potentially a little scaremongering going on here; the risk of grounding to a fire fighter via their hose and the stream of water is minimal.
However, it is true that, whilst you can isolate the DC and AC current via the isolators that will be present (although probably in the roof space and may not be accessible in the event of a fire), switching the system off at this point will not stop the DC current flowing from the panels which are 'live' during daylight hours.
The solution could be the installation of a fireman’s switch – which is a motorised disconnector wired into the DC connection. It actually breaks into the strings when the switch is activated – which can be done via a remote control panel (e.g. outside the property) or even by mobile phone! Some systems can detect fire and smoke, and alert users with an audible alarm and automatically shut down the solar array removing the risk of follow-on electrical fires and enabling fire crews to tackle fires safely.
This solution will not stop the panels generating voltage (we cannot turn off the sun) but will stop the flow of current by creating an open circuit.
Santon produce a commercial grade switch – click here for a description of how they work. Area Energy produces Solace a system suitable for domestic installations. These systems can be retro-fitted but are likely to be expensive at £600 - £1,000 depending on the size and complexity.
This is by no means a regulatory requirement – although potentially it could become one – so should these switches be fitted in all cases? They are certainly a contribution to the safety of fire crews, or anyone else trying to access the property or extinguish the fire, but if these are to be deployed there needs to be a concerted training and awareness campaign for fire fighters – otherwise they may still refuse to act and, whilst managing the danger to people, allow the fire to burn itself out!
Photo by Andrew Becraft
If you have a question about anything in the above blog, please ask it in the comments section below.
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