INDUSTRY I GRID
types of certificates: the power generating unit (PGU) certificate that is issued for the individual inverters as confirmation that they are compatible to the grid, and the power generating plant (PGP) certificate that confirms that the performance of the entire plant is in conformity with the standards.
Certification of the inverter
Before the start of the certification process, the plant owner compiles all relevant documents and submits them to an accredited certification body such as TÜV SÜD. The certification body now reviews the documentation for completeness and plausibility. Based on this review, the certification experts will assess whether the power generating unit (PGU, in the case of photovoltaic systems, the inverter, is in conformity with the requirements. Conformity assessment is carried out in accordance with the technical guidelines of the FGW, the German public association of the renewable energy sector, and includes analysis of the active power output, control systems and decoupling control as well as grid impact (FGW-TR8).
Subsequently, the certification professionals validate the simulation model of the PGU in accordance with FGW-TR4. This grid calculation model enables steady-state load flow analysis and the simulation of symmetrical and asymmetrical faults. A summary report then informs the owner of the plant whether all relevant standards, directives and requirements have been fulfilled. The certification body only issues a PGU certificate if there are no concerns that the generating unit has the characteristics required for grid connection.
A critical factor for ensuring rapid certification is the availability of the required documents and simulation model. In the case of inverters – the power generating units of photovoltaic systems – this is not always ensured. Manufacturers who are insufficiently familiar with the certification process and the applicable
cable system is over 2 km long, even if the apparent power at the medium-voltage grid is below 1 MVA. This provision also applies if the plant and its cable system up to the PCC are located on the same premises, such as a large industrial company or an airport.
Criteria for connection to the low-voltage grid At present the regulations do not require power generating units or plants connected to the low voltage grid to be certified. Connection to the low-voltage grid is governed by various standards and a specific application code. Following revision of the “Generators connected to the low-voltage distribution grid” guideline, issued as an application guideline by the FNN (the forum network technology/network operation in the VDE), additional demands are now made with regard to aspects including the behaviour of these plants in the case of frequency fluctuations in the grid. Given this, these power generating plants no longer act as passive power distributors but are required to play an active role in the electricity grid. However, retrofitting of existing plants will not be necessary for the time being.
Certification by TÜV SÜD – what does it involve?
Grid-compatibility certification is a further criterion governing eligibility for the feed-in tariff guaranteed under Germany’s Renewable Energy Sources Act (EEG). There are two different
Criteria for power generating unit (PGU)
certification A manufacturer’s certificate of the specific data of the PGU in accordance with FGW-TR3
A detailed technical description of the PGU The complete documentation, including reports of measurements and type approval in accordance with EN 17025 by an accredited testing laboratory
A simulation model of the PGU including a description of the model in accordance with FGW TR4
The measured data underlying the test report in accordance with FGW TR3
Component certificates in as far as relevant for PGU certification
Declarations of conformity and technical descriptions by the manufacturers of other relevant operating equipment (e.g. control systems, protection devices)
A minimum of a single-line diagram of the PGU Evidence of a certified quality management system in accordance with EN ISO 9001 for the manufacture of PGU
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