FIRE SAFETY OF PV SYSTEMS
INSIGHTS AND
RECOMMENDATIONS
Fire Safety of PV systems
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© Fronius International GmbH
Version 06/2020
Business Unit Solar Energy / System Technology
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TABLE OF CONTENTS
1 Introduction .....................................................................................................................................4
1.1 Objective ...........................................................................................................................................4
1.2 Risk of Fire vs. Risk for Firefighters ..................................................................................................4
2 PV Fires Statistics – Incidents and Causes .................................................................................6
2.1 Germany ...........................................................................................................................................6
2.2 United Kingdom ................................................................................................................................8
3 DC-Connectors – Necessity and Error Source ............................................................................9
3.1 Installation Errors ..............................................................................................................................9
3.2 DC-Connector Mismatching ........................................................................................................... 10
3.3 Power Optimizers – a Dangerous Safety Measure ....................................................................... 11
4 Safety for Firefighters and the NEC 2017 .................................................................................. 13
5 Fulfilling Rapid Shutdown in NEC 2017..................................................................................... 15
5.1 Selection Criteria for an Optimal Shutdown Solution ..................................................................... 15
5.2 Issues with Current MLPE Solutions ............................................................................................. 15
5.3 Rapid Shutdown Solutions with SunSpec Powerline Communication .......................................... 16
5.4 Comparison Example between MLPE and Module-Integrated SunSpec Solutions ...................... 18
6 Recommendations & Conclusion .............................................................................................. 20
7 Literature ...................................................................................................................................... 22
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1 INTRODUCTION
Recently, unsubstantiated safety concerns have been created by the media about the safety of PV systems,
despite photovoltaics being an extremely safe technology. Rumours about burning houses that can’t be
extinguished or firefighters who do not attack a fire if PV is involved put rooftop PV systems in a light they do
not deserve. In fact, PV systems are of a very high safety level concerning preventative fire protection as well
as operational safety and security in case of a fire. Many recent analyses of fire incidents related to PV, like
those from TÜV Rheinland and Fraunhofer ISE (Sepanski et al., 2015), BRE (2017b) and IEA PVPS (2017)
show that components of PV systems are tested according to very stringent safety and reliability test protocols
during the manufacturing process. This ensures they fulfil electrical safety requirements of various national
and international codes and standards. Additionally, aspects like the creation of fire compartments,
accessibility, functional integrity and mechanical safety have to be considered in planning, construction and
operation. Modules that act as a part of a roof (building integrated PV) have to fulfil the same fire resistance
tests as the roofing material.
According to the International Energy Agency Photovoltaic Power Systems Program (IEA PVPS), “PV systems
do not pose health, safety or environmental risks under normal operating conditions if properly installed and
maintained by trained personnel as required by electric codes.” (IEA PVPS 2017; p. 2).
1.1 Objective
The aim of this paper is to evaluate and display the actual situation concerning fire incidents including a PV
system in selected countries and to derive if there is a significant contribution of building related PV systems
to the risk of fire. Although PV is a very safe technology and incidents are rare, this analysis should highlight
the most common reasons for arc faults and therefore possible fire incidents. Based on the findings of this
failure analysis in selected countries, suitable measures for reducing the already small fire risk induced by PV
systems are derived.
Although low voltage electricity has been a part of almost every building for decades now, and fire fighters
know how to deal with it, a certain precariousness exists in the public when it comes to the topic of extinguishing
a PV-related fire. By analyzing different operation tactics and strategies as well as safety measures to reduce
the risk of electrocution for firefighters, this paper provides recommendations on how to act in the event of a
fire.
Furthermore, the new requirements for module-level shutdown (introduced by NEC 2017 to further increase
safety for emergency responders) as well as their unintended consequences are discussed, and an overview
of the options to safely fulfil such requirements is provided.
1.2 Risk of Fire vs. Risk for Firefighters
Before going into detail regarding the analysis of fire incidents related to PV, a distinct definition is necessary
regarding the risks related to a fire.
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When talking about the safety of PV systems, possible occurring risks related to a fire can be divided into two
categories:
/ Risk of fire: This risk describes the probability that a fire occurs. The
higher the probability, the higher the risk that a fire occurs.
/ Risk for emergency responders: This risk describes the probability that a firefighter or other
emergency personnel is injured during a rescue or fire fighting mission.
These two categories are both important when talking about increasing the safety of PV systems.
Taking appropriate measures which reduce the risk of fire directly reduces the risk for emergency responders,
as no fire means no risks for the emergency responders, and therefore this should be the top priority as far as
PV fire safety is concerned.
This conclusion is not always applicable the other way around. The new requirements for module-level
shutdown introduced by NEC 2017 are intended to increase the safety of emergency responders. However,
significant attention should be paid with regard to the type of measure used to comply with the standard. Some
measures currently available on the market, such as module-level power electronics (MLPE) devices, often do
not contribute to reducing the risk of fire, but could instead lead to an even increased risk of fire, as it will be
discussed in chapters 3 and 5.
Fronius sets the focus on decreasing the risk of fire as a required first step for increasing the already high level
of security concerning fire protection, which directly influences the risk for emergency responders and therefore
is a sustainable and more beneficial approach. When implementing an additional layer of safety for firefighters,
proper measures have to be developed that are able to achieve such a higher protection without compromising
the first layer of safety, which is aimed at reducing the risk of fire.
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2 PV FIRES STATISTICS – INCIDENTS AND CAUSES
Figure 2: Type of error; allocation for Germany (data from
Sepanski et al. 2015)
Figure 1: Error source; allocation for Germany (data from
Sepanski et al. 2015)
As mentioned in the introduction, this chapter should give an overview about fire incidents involving building
related PV systems in selected countries.
2.1 Germany
Germany is one of the oldest PV markets worldwide, and the biggest in Europe. Its installed PV capacity is
comparable with that of the United States, and represents therefore a good source of reference. In 2015, TÜV
Rheinland in cooperation with Fraunhofer Institute for Solar Energy Systems (ISE) published a report about
fire incidents involving building related PV systems until 2013 and their causes. This detailed analysis showed
that 430 Fire/Heat damages were officially reported, whereof 210 were triggered by the PV system itself.
Compared to a total number of installed PV systems of about 1.3 Mio. as of 2013, this equals 0.016 % of all
PV systems installed in Germany (Sepanski et al. 2015). The following figures show an allocation of the fire
incidents to various types of error and error sources.
The analysis showed that more than 70 % of the errors are based on external influences or installation failures
(see figure 2). Only about 17 % of the errors resulting in fire are based on product failure (see figure 2), and
only 10 % of the errors occur in the inverter (see figure 1).
A detailed fault analysis pointed out the most common reasons for serial arc faults, which are the main causes
of fire incidents involving PV systems. These reasons are listed in Table 1, and sorted according to component
and likelihood of occurrence.
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Table 1 Possible reasons for arc faults, sorted according to component and likelihood of occurrence (Sepanski et al. 2015)
Component
Possible reason for arc fault
DC-connector
connector poorly crimped on site
mismatch of DC-connector
connector not fully inserted
connector mechanically damaged or corroded
due to improper installation, weathering, animal
bites or production failure
connector poorly crimped in production
Screw terminals in field distributor, inverter (DC-
side)
screwing contact tightened inadequately,
inadequate insertion of cable
undersized, arranged too close to each other
clamped cable-insulation
Solder connection (in module)
bad solder connection, aging due to
mechanical/thermal stress
Bypass diode
overvoltage due to lightning storm or switching
operation in system
long-term failure due to thermal overload
Module
cell damages (micro cracks, …)
torn-off cell connectors
cell breakage/glass breakage
DC-fuses
unsuitable fuses
incorrect installation
DC-cable
long-term failure due to weathering (UV-
radiation, humidity, temperature change, …)
damage due to improper installation (kink, …)
animal bites
DC-circuit breaker
not suitable for DC
Junction box
bad solder connection
aging due to mechanical/thermal stress
General installation
improper protection class (humidity, dust)
top down cable insertion in PG-gland
The analysis showed that, next to external error sources, most of the errors that lead to a fire incident are due
to installation failure on the DC-side of the PV system. Especially the DC-connectors, which connect the PV
modules of an array, are a common error source.
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2.2 United Kingdom
Figure 3: Error source; allocation for the UK (data from BRE
2017a)
Figure 4: Type of error; allocation the UK (data from BRE
2017a)
In 2017, a detailed report about fire incidents involving building related PV systems was published by the BRE
National Solar Centre.
According to this report (BRE 2017a), compared to a total number of about 1 million PV systems installed in
the UK, 58 fire incidents involving building related PV systems were reported since 2010. This is equivalent to
a percentage of 0.0058 % of all installed PV systems in the UK. The following figures show an allocation of the
fire incidents to various types of error and error sources.
Excluding the category “Unknown type of error”, most of the fire incidents are based on external influences
and installation failures. Only about 9 % of all fire incidents were demonstrated to be caused by product failure
(see figure 4).
The following list shows the main causes of arcing identified in the report (BRE 2017a), many of which are
related to issues with DC connectors. Contrary to the list in table 1, this list is not sorted by likelihood of
occurrence.
/ Moisture ingress causing a degradation of connections in DC connectors, junction boxes & switches
/ Incorrectly crimped connector contacts
/ Mating of incompatible connectors & sockets
/ Connectors & sockets are not fully engaged
/ Not fully tightened screws or loose screw terminals within junction boxes or isolator switches
/ Poorly soldered joints within a PV module junction box or other junction box defects
/ Damage to a component (e.g. broken busbars within a PV module)
Similar to the results of Germany (see chapter 2.1), the analysis of the fire incidents involving building related
PV systems for the UK showed that, next to external error sources, most of the errors that lead to a fire incident
are due to installation failure on the DC-side of the PV system. DC-connectors were found to be a highly
vulnerable component subject to installation faults, and the related issues will be highlighted in the next
chapter.
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