Intelligent photovoltaic modular switch-off system

Photovoltaic (PV) systems have become an important and established source of power, with a current installed capacity of approximately 230 gigawatts worldwide. Around two-thirds of all PV systems are installed on rooftops.

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Maintaining and repairing PV installations should be just as easy and safe as it is to put them into operation. The Solarcheck RSD intelligent modular switch-off system allows PV systems to shut down automatically without requiring any technical knowledge from the operator.

Recent studies show that the feed-in capacity of PV systems will increase to approximately 600 gigawatts by 2020. This relatively small but significant share of the energy mix contributes towards slowing down climate change and helps us manage available energy resources in a sustainable way. PV is expanding in industrial and urban areas, highlighting its immense potential to improve the energy efficiency of buildings and businesses.

PV systems, which are often operated with string inverters, vary in terms of their yield from between 30 and 500 kilowatts. The PV modules in such systems are lined up in a row and connected to the inputs of inverters as a single unit.

This wiring method causes the system voltage to build up to a value between several hundred and a thousand volts, depending on the number of modules.

The concentration of direct current is very high in this part of the PV system. The current is only converted into alternating current—which can be used as a power source, for example—once it passes through the inverter.

Taking into account the physical conditions

Photovoltaic systems are being installed in industrial areas and public spaces more and more frequently because environmentally friendly power sources are perceived positively by the public. This trend is further fuelled by the fact that PV applications are easy to use: Unlike other energy sources, PV systems do not need to be supplied with fuel, have no moving parts, and are easy to install and wire.

The bulk of the work required to operate a PV system consists of annual maintenance, the odd repairs for damages caused by external factors, and cleaning the system to improve yield. Otherwise, PV systems generally produce power reliably and do not require further care.

We can generally assume that photovoltaic systems are reliable, since all system components are designed in such a way to function for many years when they leave the factor, even if exposed to the elements. This means that all components are insulated properly, making them safe for humans and animals alike. At the same time, every PV system produces power.

As safe as the systems are during normal operations, operators and engineers need to bear in mind the physical conditions involved when handling a photovoltaic system. Direct current, which is the standard type of current in a PV system, requires extra care since the voltage level of a direct current never drops to zero. If you have direct current running through your body, you cannot loosen your grip on the system component, unlike with alternating current.

Increasing risk of electricity-related accidents

Experience has shown that PV system operators and engineers need to carry out repairs more frequently than is prescribed for regular maintenance. This is because the cabling in photovoltaic systems is particularly susceptible to damage over the course of the year, according to relevant statistics. Insulation failures often arise in the cabling, which can be very dangerous when someone is handling the photovoltaic system.

The German Employer’s Liability Insurance Association regularly carries out targeted analyses to find out the causes of accidents. These analyses show that approximately ten percent of accidents recorded in 2012 were caused by electrical contact when working on a PV system. Although this figure seems rather low at first, we must bear in mind that the number of photovoltaic systems that are being installed has significantly increased since 2012.

As a result, the amount of repair work that is necessary and the potential for more accidents have increased as well. At the same time, this type of physical injury is completely avoidable if the DC voltage can be switched off at a modular level. This modular switch-off method prevents the build-up of high voltages, allowing engineers to work in completely safe conditions.

Automatic switch-off when system is running abnormally

A safety switch-off system needs to be affordable and capable of delivering real benefits in order to retain the appeal of PV systems as an energy source. To this end, Phoenix Contact has developed an intelligent modular switch-off device that can protect everyone who is involved with photovoltaic systems without them needing any specialised technical knowledge. Solarcheck RSD consists of two types of devices that fully and automatically shut down the PV system and switch it back on afterwards.

Each of the switching units, installed directly behind each module, functions independently and detects any abnormal behaviour exhibited by the module. Abnormal behaviour is regarded as an indication that operations are not safe and the module is subsequently shut down. If the invertor is switched off, this is assessed as irregular behaviour by Solar RSD, allowing the entire system to be shut down manually. This means that the operator or engineer can simply switch off the invertor in order to shut down the entire DC side of the PV system when cleaning, maintenance, or repair work is required.

Switching the system back on under controlled conditions

Solar RSD also ensures the safety of fire fighters on the scene whether or not there are technical specialists on site, putting to rest a concern that has been frequently discussed in the past. One of the first measures in this scenario is to shut down the entire building using the main fuse or to even deactivate an entire block using the main distribution board. These steps allow you to shut down the DC side of the invertor and all PV modules in accordance with applicable standards. The biggest challenge when a fire breaks out in a PV system is not in putting out the fire itself but in repairing and cleaning up the damaged parts. The cables are almost always damaged or have melted together, making it very difficult for the engineer to assess the situation. However, if the engineer has switched off all of the modules individually using Solarcheck RSD—an option that is not available in standard PV operations—he or she can work safely even in such an extreme situation. The photovoltaic system can then switch back on fully automatically under controlled conditions. Solarcheck RSD also ensures that the PV system does not restart until all repair work has been completed. The starting unit features intelligent checking programs specifically for this purpose, making sure that power only resumes flowing if the string is uninterrupted and the invertor is connected and released. This rules out the possibility of the system being switched back on accidentally.

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