PV guidelines – are the recommendations sufficiently evidence-based?
By: Nik Rus and Grunde Jomaas
FRISSBE, ZAG - Slovenian National Building and Civil Engineering Institute, Slovenia
Acknowledgement - The FRISSBE project has received funding from the European Union’s Horizon 2020 Research and Innovation under Grant Agreement No. 952395.”
Abstract
It is generally recognised that installing PV systems on buildings creates new fire hazards and fire safety challenges. To determine the present status of the scientific basis for the fire safety measures suggested for photovoltaic (PV) systems, recent installation guides, and guidelines for the fire safety of PV installations published by various stakeholder groups, were examined. There was very limited experimental or statistical evidence in the literature supporting the recommended preventive measures. This is worrisome, as proposing fire safety measures without any verified and scientifically sound basis might create a false sense of safety. The review's conclusions will hopefully urge future authors of these kinds of publications to elaborate more on the background for their suggestions or, better yet, include evidence to support their recommendations.
Introduction
Tackling climate change to mitigate the negative consequences for people and the environment has been one of the recurring focal points of international efforts in the last few decades, becoming more and more pressing in the last few years (United Nations Framework Convention on Climate Change (UNFCCC), 2018). Additionally, there are initiatives underway on different levels to move away from the generation of energy through carbon-based fuels (EU Solar Energy Strategy, 2022). The momentum behind Photovoltaic (PV) systems as a renewable energy source is rapidly increasing, with future trends predicting even faster acceleration (International Energy Agency (IEA), 2022). The EU alone plans to bring online over 300 GW of solar photovoltaic systems by the end of 2025 (EU Solar Energy Strategy, 2022) and rooftops are one of the primary locations for these installations, especially the flat roofs of warehouse-style, production facilities or large store structures.
There are two main categories into which PV systems in buildings can be divided – building integrated PV (BIPV), in which the PV installation acts as a part of the building's construction (i.e., it is a construction product and must be tested as such), and building applied PV (BAPV), in which the PV installation has no structural purpose. The distinction between BIPV and BAPV can seem clear enough, but as can be observed in Figures 1 and 2, the distinction, in reality, is not always very obvious. The current work focuses on BAPVs since the risks in BIPVs are, to some extent, addressed (at least in theory) by the regulations of the construction products, while the BAPVs are not deemed part of the construction and can currently be added to the building without much concern to fire risks.
A building's roof-mounted PV system increases a building's fire risk (Kristensen, 2022). First, it has been demonstrated that PV installations increase the probability of ignition if there is a failure in any of the system's electrical components – cables, connections, inverters, grounding problems, etc. (Zhao et al., 2013). Second, the PV system alters the fire dynamics of the roof fire and enables it to spread faster and farther than it would be the case without the PV installation (Kristensen et al., 2021). And third, by making it possible for a roof fire to spread more quickly and potentially even breach the building's compartmentation (“Brannen i Asko-bygget,” 2017). These last two points are equally pertinent when the fire starts outside the PV system, such as when it starts somewhere inside the building or is caused by arson or firebrands stemming from a nearby fire (wildfire or a neighbouring building).
Figure 1 A fire at the building-integrated PV (BIPV) installation at Farm Mis in early September 2023. Built in 2008, the installation was one of the first of its kind in Slovenia, and long before many guidelines for installation existed. Photo: Municipality of Medvode, Slovenia
Figure 2 Fire involving a building-applied PV (BAPV) system on a roof in Desinec, Slovenia at the end of October 2023. Photo: Studio Rakun, photographic and other services, Jani Pavlin s.p. for Firefighters’ association Črnomelj, Slovenia
Effective safety measures must be implemented to properly minimize the consequences of PV-related fires and lower their likelihood (Olsø et al., 2023). The effectiveness of the suggested safety precautions must first be verified using the scientific method —either statistically or experimentally— so that they can actually fulfil their intended purpose. Citing reliable sources for the proposed measures is one method of demonstrating that there is a scientific basis for them. The assessment identified three areas for each of which reference to reliable sources was examined to determine the basis for the proposed actions. The three areas consist of:
· Design of the array (size, spacing, geometry), which can affect how quickly and how far a fire spreads and how it affects the safety of firefighters.
· Employee qualifications (installers, maintenance personnel), which affect the likelihood of ignition.
· Product and Material Requirements, influencing both the probability of ignition and consequent fire spread.
PV systems consist of many components that perform various tasks in diverse aspects with each introducing different risks to the overall functioning of the installation. Be it electrical, fire or any other type of risk, they should be recognised and mitigated to acceptable levels to prevent unintended consequences. Electrical risks have already been addressed to a fair extent in the guidelines, but recognising, understanding, and adequately addressing the fire risks remains a significant challenge.
The present status of referencing the supporting scientific facts for the safety measures suggested in the recommendations by various PV field stakeholders is evaluated in the review that follows.
Methodology
Three groups of stakeholders in the PV field were identified to be the most actively involved in the act of producing and publishing their guidelines regarding the fire safety of PV systems: manufacturers of PV panels, insurance companies and various safety consultancies.
A few examples of the most recent publicly available guidelines were gathered from different stakeholder groups, with an emphasis on the most recent ones (not older than 2019). The only outlier in the assessed group is the Slovene guideline by SZPV from 2016 but was included because of its relevance to Slovenia, the country of the author’s origin. The list of stakeholders and the dates of their publishing dates are available in Figure 3. (Allianz Risk Consulting, 2019) (AXA XL Risk Consulting, 2021) (RSA Insurance Group, 2020) (SZPV, 2016) (BVS - Brandverhütungsstelle, 2022) (VdS, 2023) (LONGi Solar Technology Co., Ltd., 2023) (Canadian Solar Inc., 2020) (Shanghai JA Solar Technology Co., Ltd., 2019) (LG Electronics Deutschland GmbH, 2019)
Figure 3 Overview of industry segments and organisations whose guidelines were selected for the assessment.
To ensure that the documents selected for the evaluation are representative of the current state of the art in this field, care has also been taken to ensure that the documents originate from different parts of the world. This is also shown in Figure 3 inside the parentheses after the names of the organisations.
As mentioned in the introduction, the documents were reviewed for referencing concerning fire risk reduction in three areas: Design of the array, Employee qualifications, and Product and Material Requirements. The proposed measures and the reasons for them were assessed to determine which risks are mitigated and how the proposed measures address them.
Results and discussion
Design of the array
The risks inherent in PV systems are not solely determined by the properties of the individual materials and products used in the installation (Kristensen et al., 2022). Rather, it is the combination of the roofing material, PV panels and especially the geometry between the two (height and inclination) – i.e., the system – that can have synergistic and significant impacts on how fast and far the fire spreads and how for how long time it burns (Kristensen et al., 2021).
Two measures were noticed in most of the documents – the area of the array and the spacing between them (in more than 80 % of the documents coming from the insurance companies and the safety consultancies). The area of the array is prescribed ranging from 40 m x 40 m to 45 m x 45 m and the spacing between the arrays ranging from 1 m to 2 m, depending on some additional requirements specified in individual guidelines.
Table 1 shows data from the documents by the insurance companies and safety consultancies. It is also worthwhile to point out that none of the manufacturer guideline documents mention the importance of the design of the entire installation.
Table 1 Array size and distancing around arrays
|
Publisher
|
Size of the array
|
Distancing between arrays and other elements on the roof
|
|
Allianz
|
45 m x 45 m
|
1.2 m
|
|
AXA XL
|
45 m x 45 m
|
1.2 m or 1.8 m 1
|
|
RSA Insurance
|
46 m x 46 m
|
1.2 m
|
|
SZPV
|
40 m x 40 m
|
1.0 m or 2.0 m 2
|
|
BVS3
|
up to 1,800 m2 (approx. 42 m x 42 m)
|
1.0 m or 2.0 m 4
|
|
VdS
|
Not given
|
Not given
|
1.0 m for cases with non-combustible roof surface (e.g. 5 cm thick gravel surface) and if the roof cladding is combustible (also classification Broof(t1) without protection by a 5 cm thick gravel surface), a horizontal distance of 2 m must be maintained.
Considering the lack of any referencing regarding the proposed fire safety measures for the design of the arrays in the assessed documents, further revision of some older documents was undertaken to discover the origin of the used numbers.
The document Photovoltaics and Firefighters’ Operations: Best Practices in Selected Countries (International Energy Agency (IEA) et al., 2017) reports that a Japanese directive, developed between 2012 and 2014, “limits the distance between any passage and the centre of a PV array to within 24 m, so that water being directed from the passageway can reach the fire”. This shows that the size limits for the PV arrays proposed in various guideline documents do not necessarily address any characteristic of the fire risks, but rather consider the limits of the firefighters’ equipment.
Similarly, for the distancing between the arrays the same document (International Energy Agency (IEA) et al., 2017) points to a guideline released by the German Firefighters association in 2010, which states in a part related to electrical hazards of the PV installation that one should “ be sure to keep at least 1 m away from components that may be live (energized).” This shows that the separation distances used in the reviewed guideline documents probably do not propose the distancing between the arrays for the sake of limiting the fire spread on the roof, but rather address the electrical hazards that the live components of the PV system might present.
Employee qualifications
The quality of the installation process (Mohd Nizam Ong, Sadiq, et al., 2022) and the importance of maintenance during operation of PV system have been recognised as risk factors for PV-related fires (Mohd Nizam Ong, Mohd Tohir, et al., 2022; Pester et al., 2017). Therefore, requirements regarding personnel performing the installation and the maintenance were assessed in the guideline documents.
It was found that there was a significant difference in how the documents address the tasks related to installation and inspection/maintenance. Most of them just has a general requirement for the personnel doing any of the jobs to be certified, qualified, or trained. But what is lacking is a more in-depth definition of what any of these terms actually mean. Only one of the documents (VdS, 2023) referenced to a document in accordance with which the personnel is supposed to be qualified.
Some of the documents ((Allianz Risk Consulting, 2019; AXA XL Risk Consulting, 2021; LONGi Solar Technology Co., Ltd., 2023; RSA Insurance Group, 2020; Shanghai JA Solar Technology Co., Ltd., 2019; SZPV, 2016) also explicitly describe the tasks and the period in which they should be carried out, but in three cases no requirements were set for the personnel carrying out the installation, inspection and maintenance (in one document for both the inspection/maintenance and the installation and in another only for the installation part).
Product and Materials Requirements
The requirements for the products (panels) and the materials (roofing materials) are addressed differently in the consulted documents, but it should be noted that the assessed documents come from different parts of the world, so legislative requirements regarding the products being put on the market can vary greatly.
For the panels, the compliance was addressed in a way that a standard is usually specified (or a few of them) in accordance with which the products should be tested.
In the documents prepared by the manufacturers, there was usually data for which standard each of their products is compliant with and in what class it is ranked if the standard foresees it.
Figure 3 List of standards related to PV fire safety that were mentioned in the assessed documents
The standards mentioned in the different documents are shown in Figure 3, noting that some of the guideline document authors explicitly state which version (year) of the standard they are referring to while others do not.
On the other side, there is also a case of a guideline document by an insurance company that states that the modules can also have approval from internationally recognised testing laboratories (TÜV Rhineland, Underwriters Laboratories (UL), FM Approvals or CSTB) to be acceptable for the installation without explicitly mentioning any standard.
As for the roofing materials, there is no reference in any of the documents, except one (Shanghai JA Solar Technology Co., Ltd., 2019), and all resort to different descriptive statements. Some suggest separate measures for combustible and non-combustible roofing materials, and one (VdS, 2023) applies a risk matrix for the likelihood of fire spread on different types of roofs.
This type of descriptive suggestion leaves too much room for various interpretations by different readers and more detailed or sharply defined boundaries should be used to eliminate opportunities for misinterpretation. Perhaps this could be improved by defining a characteristic (e.g. heat of combustion for the roofing material) which then indicates which group a material falls into. Some of the groups are conducting extensive testing to develop appropriate testing standards (Cancelliere et al., 2021), intending to predict the associated risks.
Conclusions
A review of the latest safety guidelines and guidance documents for PV systems was carried out to assess whether they used scientifically sound data as the basis for the proposed fire safety measures. The review of the documents focussed on three areas: Design of the array (size, spacing, geometry), Employee qualifications, and Product and Material Requirements. The current state of the art in the guidance documents shows a worrying lack (or in the best cases limited scope) of references to the comprehensive data supporting the proposed measures regarding fire safety. To better communicate why and how a particular measure contributes to the reduction of the fire risk, future guide authors should ensure that they reference credible sources that support their proposed measures.
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