Fire shutdown (photovoltaic system)
Under fire shut-off apparatus which is meant for photovoltaic systems of the photovoltaic modules generated DC voltage can switch off, which can be up to 1000 volts. It is an addition to the network monitoring device with associated switching devices (ENS).
Description and risks
As soon as light falls on them, photovoltaic modules generate an electrical voltage at their connection terminals . Several photovoltaic modules are connected in series, so-called strings, which increase the total voltages. Already four modules produce above the permissible protective low voltage lying DC (defined in VDE0100-712) of 120 V, more than loud Association for Electrical, Electronic and Information Technologies is to be considered (VDE) for the human body as harmless. If there is a fire in a building with a photovoltaic system, there is a high risk of electric shock for the helpers due to the voltage generated by the system. In recent years, however, it has also become apparent that there is an increased risk of electric shock not only in the event of a fire, but also during maintenance or cleaning work. A PV system, regardless of its size, generally always generates a very high DC voltage. A system with 15 modules already generates 600 V. There is also the risk of arcing, which can arise in the event of possible defects in cables, plug connections or other system parts. This can happen because a short circuit can occur under the cables or against system components . Animal bites or wind movements, chafing and open areas can very quickly lead to a short circuit that inevitably creates an electric arc. In contrast to alternating voltage (AC), an arc remains constant with direct voltage (DC). An arc can be interrupted by actuating the DC load break switch (mandatory in systems from June 2006). The best way to extinguish an arc is to switch off the energy source, i.e. the PV module.
Systems have been developed by various manufacturers that switch off the photovoltaic system in the event of a fire in order to keep the risk to the helpers deployed as low as possible (see: fire service switch ). Load switches in the inverter and generator junction box have been a legal requirement since June 1, 2006 .
Photovoltaic systems generate very high and dangerous voltages, which, however, can usually be controlled with the right means, which minimizes the dangers of a PV system. TÜV Rheinland, Fraunhofer ISE and the Federal Environment Ministry have researched previous fire incidents. It turned out that the dangers were sometimes exaggerated in forums and the press. For example, contrary to earlier information, a solar thermal system (for generating thermal energy) was not installed on a house in Rösrath, about the fire of which "Stern Online" reported.
In a position paper dated November 8, 2010, the German Fire Brigade Association (DFV) called on the photovoltaic industry to immediately develop a far-reaching technical solution for safe use in the area of photovoltaic systems.
In the case of fire alarm systems , the technical connection conditions in some federal states require automatic shutdown of the PV system.
functionality
Various systems are currently offered by different manufacturers (see: fire brigade switch ). There are electrical components that prevent the undesired formation of an island grid on the AC voltage side after the solar inverter .
Other components can interrupt the line between the roof and the inverter, but this is only a compromise solution and does not shut down the system. In this case, only the lines from the roof to the inverter are disconnected, the full voltage is still present on the roof itself, which in the event of a fire is usually no longer a problem for internal attacks.
The only way to switch off a PV system safely and completely is to switch off every single voltage source, i.e. every single PV module (see e.g. SolarEdge ). In order to achieve maximum safety for emergency and service personnel, each module must be short-circuited directly at its connections so that it can no longer emit voltage into the line system.
Web links
- Information portal for photovoltaic systems , German Fire Brigade Association
- Information portal for photovoltaics and fire prevention , Federal Association of the Solar Industry
- Pvsafety.de blog about safety in fire fighting operations, focus on electrical hazards and photovoltaics, private
Individual evidence
- ↑ DIN VDE 0105-100 / A1 "Operation of electrical systems"
- ↑ Research project on the safety of photovoltaic systems: prevention is better than extinguishing - fire protection in photovoltaic systems.
- ↑ Good to know ... The photovoltaic system ( Memento from May 20, 2014 in the Internet Archive )
- ↑ Research project on the safety of photovoltaic systems: fire incidents and damage in connection with photovoltaics.
- ^ Electricity hinders extinguishing work , Stern, March 16, 2010
- ↑ "Fire brigade calls for a shutdown mechanism for PV systems" (PDF; 24 kB), DFV - position paper, Nov. 8, 2010