More and more homeowners are installing photovoltaic systems on their roofs. However, most are unaware that these photovoltaic systems pose particular risks for firefighters in the event of a fire. General Solar energy can be harnessed in two types of systems. The first option is solar thermal systems. In solar collectors, the sun's energy is transferred to a medium (e.g. thermal oil or water). This type of solar energy is mainly used in Germany to heat domestic water. The second type is so-called photovoltaic systems, in which the sun's energy is converted directly into electrical voltage. Since solar collectors do not pose any particular risks for firefighters - apart from falling parts (e.g. broken glass) and respiratory toxins - the following section focuses on photovoltaic systems, which also pose the additional dangers of electrical voltage. Photovoltaic systems generate direct current (DC). This can either be stored in batteries or fed directly into the energy provider's power grid. For this purpose, the direct current is converted into alternating current (AC) with the help of inverters. How a photovoltaic system works The solar energy is converted in the photovoltaic modules, which are usually made of silicon, which has the property of generating electrical voltage when exposed to light. Voltage is produced even with relatively weak light sources, such as halogen spotlights used by fire departments to illuminate emergency scenes. This means that voltage is immediately present in the photovoltaic modules as soon as light hits them. The generation of electrical voltage can only be stopped if the light is prevented from hitting the modules. Depending on the manufacturer, a single photovoltaic module can generate up to 50 volts direct current. Since several modules (sometimes up to 20) are connected in series in photovoltaic systems, voltages of over 700 volts can easily be generated. Direct current can cause life-threatening electric shocks to the body even at a voltage of just 120 volts. The higher the voltage, the greater the risk of electric shocks to the body. Furthermore, the dangerous arcs last particularly long with direct current. Dangers of photovoltaic systems In the event of damage, there is a risk of electric shock if the DC voltage cables are touched as long as light (even comparatively weak light on cloudy days) falls on the photovoltaic modules. When the DC isolation point is activated, the voltage is maintained from the modules to the isolation point. Currently, there is no requirement for additional switching points or a DC emergency stop switch to de-energize the photovoltaic modules. The only way to de-energize the modules is to completely darken them. Two options have been tested so far, but neither has been successful. The first attempt was to cover the modules with an opaque film. However, under operational conditions, it is not feasible to completely cover areas that can sometimes be several hundred square meters in size. In the other – equally unsuccessful – attempt, the photovoltaic modules were completely covered with fire-fighting foam. Despite the closed foam blanket, the voltage could only be reduced to a maximum of 50% of the output voltage. Since photovoltaic modules have a self-cleaning surface, the output voltage is reached again after five minutes at the latest. Safe work on photovoltaic systems in operation is therefore currently not possible. Another source of danger is the fastenings used to attach photovoltaic modules to roofs. These are usually made of aluminum, which begins to melt at temperatures of around 600°C. The static load on aluminum is exceeded at around 300°C. This temperature is easily reached in the event of a fire. As soon as the fastenings burst, the entire module slides off the roof like an avalanche. The enormous heat generated during fires can also shatter the glass covering of the modules, causing a shower of glass shards to rain down on the heads of emergency personnel. Firefighters are exposed not only to fires but also to floods. Since DC isolation points are usually located in basements (and thus in flooded areas), there is a risk of electric shock if emergency personnel come near the isolation point. For their own safety, emergency services will not enter flooded areas where cables and components of photovoltaic systems are present. The fire brigade will provide assistance Despite the risks described above, the fire brigade will of course still fulfill its legal duty and extinguish fires - regardless of whether there are photovoltaic systems on the roof or not. However, the presence of photovoltaic systems can hamper firefighting efforts, as the fire brigade must observe special safety regulations due to the high voltage or because existing photovoltaic modules prevent the roof membrane from being opened. To minimize the risks for emergency services, it is advisable for homeowners who have installed a photovoltaic system to inform the local fire brigade. The fire brigade should be provided with a plan showing the location of the DC isolation point and the route of the power lines. In addition, a sign indicating the presence of a photovoltaic system should be displayed in a clearly visible place.