Schools' Fire Safety - Eliminating The Risks From Rooftop Solar PV Systems
Jim Wallace of Seaward Solar, looks at the fire safety implications of rooftop installed solar PV systems on schools and other public or commercial buildings.
Along with many other countries, the UK is seeking to increase the proportion of energy that is obtained from “renewable” sources, such as those that exploit wind, biomass or solar energy. One of the most popular of these involves producing electricity from solar energy using solar photovoltaic (PV) panels.
The uptake of these systems has been encouraged by government incentives and the number has grown rapidly in recent years – and particularly more recently on public, commercial and industrial buildings, where different grant funded schemes enable the building owner to benefit from free solar PV system installation and electricity.
However, all new technologies can introduce new risks and evidence is emerging of the fire risks associated with some new energy generation and handling systems.
In particular, and although still comparatively rare, examples are emerging of the potential fire hazards that can be associated, directly or indirectly, with some rooftop PV systems.
The latest example of this risk came with national newspaper reports of a rooftop fire at a primary school in Nottinghamshire that damaged two classrooms.
The blaze was reported to be the third such incident of its type involving solar PV panels installed as part of British Gas's Generation Green project, which gives schools free equipment in return for a Government green subsidy payment.
These are not the first rooftop fires to be linked with solar PV installations in the UK and elsewhere similar incidents have also been highlighted in the USA, France, Germany and Australia in recent years.
At present there is no reason to believe that the fire risks associated with PVs are greater than those associated with any other electrical equipment, but all these situations highlight the importance of ensuring the safety and quality of all PV installations.
As well as requiring fire and rescue services to formulate appropriate operational guidance for dealing with fires involving PV systems, these incidents also continue to emphasise the need for PV systems to be correctly designed, consist of properly tested components that are competently installed, and which are regularly tested and maintained.
PV systems are unusual in that the energy source cannot be switched off. If there is daylight falling on a PV panel it will produce electricity and it is possible for a relatively small array of only a few panels to deliver a lethal shock.
Another important point is that PV panels generate DC voltage, which is not always commonly used by electricians in their normal work. In addition‚ because of the current limiting properties of PV cells‚ they may not be capable of producing sufficient fault currents to operate over-current protection devices such as fuses.
Once established a fault may remain undetected, not only posing a hazard for an extended period, but also wasting valuable energy generated by the PV system.
In many cases simple electrical faults or wiring failures can therefore cause a serious inefficiency in the ability of the system to produce power. This is particularly important for installers working on ‘roof rental’ schemes where installation has been provided free of charge in return for receipt of the FiT payments.
In this way undetected faults may also develop into a fire hazard over time. Without fuse protection against such faults, elimination of a fire risk can only be achieved by both good system design and careful installation alongside appropriate electrical inspection and testing.
In the main, proper electrical commissioning procedures are among the best defences against latent fire or electrocution hazards – although once installed, ongoing and effective electrical testing is also vital both to prove the continuing safe installation of a PV system but also to verify ongoing functional performance over extended periods.
Setting the standards for safety
The international standard, ‘IEC 62446: 2009 Grid connected PV systems – minimum requirements for system documentation, commissioning tests, and inspection’, specifies the minimum requirements for PV system documentation‚ commissioning tests and inspections.
After the installation of a solar electrical system̦, subsequent building or electrical works in the vicinity of the PV array are likely and the ownership of a building with a system may also change. As a result‚ this standard recognises that only by providing adequate documentation at the outset can the long term performance and safety of the PV system be ensured.
Although standards are not regulatory or government imposed, they can be used to help support national regulations. They are created as a result of experts, professionals and consumers working together to establish guidance and advice for mutual benefit and to ensure high quality.
In the case of solar PV systems, compliance with IEC 62446 means PV system owners should be assured that the installation they are investing in is safe and adheres to an internationally recognised level of expected quality.
IEC 62446 does this by setting out the information and documentation that should be provided to the customer following the installation of a solar PV panel system and also the initial (and periodic) electrical inspection and testing required.
In short the standard sets out measures to ensure that:
- The PV panels and electrical supply connections have been wired up correctly
- That the electrical insulation is good
- The protective earth connection is as it should be
- There has been no damage to cables during installation
In Europe, the standard has been adopted as a European EN in many member states and is generally regarded as making a significant contribution to improving the quality and safety of PV systems.
In the UK, for example, the British Microgeneration Certification Scheme (MCS) has adopted the principles of IEC 62446 as the basis for its testing and documentation regime. As a result, the fundamentals of the standard are effectively enforced because no feed-in-tariff will be paid unless the installation has been installed by an MCS accredited installer.
It is interesting to note that the emphasis is on documentation, and this is in effect the evidence used to demonstrate that appropriate precautions and tests were undertaken prior to the handing over of a PV system to the property owner. Such information not only provides evidence to the consumer that work has been performed correctly, but it also acts as a check list to an installer and ensures that best practice is followed with the work that is being undertaken.
There are many instruments available that are sold under the title of ‘solar testers’ so it is vital to ensure that the instruments selected are capable of performing all of the tests required by the various compliance requirements.
The absolute minimum testing that needs to be undertaken involves earth continuity measurements (where applicable), open circuit voltage, polarity, short circuit current, insulation and irradiance.
To meet the electrical test needs some contractors have used multiple instruments that typically include an earth continuity and insulation resistance tester‚ a multimeter, DC clamp meter along with various associated connectors and leads to apply a short circuit to the system under test.
However, the danger with such ‘homemade kits’ is that they may pose a risk of harm to the user, not all of the tests required by IEC 62446 will be covered and, with different PV system electrical tests potentially requiring the use of different testers, using such an array of instruments can be cumbersome and time consuming.
When it comes to solar PV electrical test instrumentation, the choice for the installer is therefore between using general purpose individual items of equipment against all in one combination PV testers and dedicated electrical test kits that enable measurements to be taken in a fast, safe and efficient fashion.
In this respect, given the recent reductions to solar feed in tariffs, the ability of multi-function testers to help installers to work faster and more efficiently without reducing the integrity of testing is set to become even more important in terms of remaining competitive. In addition, all in one testers only require a single calibration service, which also reduces the ongoing cost of PV system testing when compared to using multiple instruments.
In terms of working more efficiently dedicated solar PV testers can also record and provide results in a format that is compatible with data recording programs that assist greatly in the creation of comprehensive system information folders for use in customer test certificates and system commissioning packs.
A better understanding and acceptance of the importance of effective installation, commissioning and testing is therefore a fundamental requirement to safeguard the fires safety and integrity of solar PV installations.