INDUSTRY I GRID
standards and directives in particular often fail to provide the required documentation and simulation model. Consequences include delays and unscheduled retrofitting measures which may jeopardise timely project completion and the profitability of the plant later on. Given this, the most sensible approach is to obtain impartial expertise as early as possible to counter possible risks in the planning stage before they turn into problems.
Certification of a power generating plant The plant certificate builds on completed PGU certification and checks the interoperability of the entire plant and its performance in the grid. Similarly to unit certification, the experts develop a data model which also includes the operating equipment and the utility network at the point of common coupling. The model is based on the project-specific PGU certificates and the calculation model, a single-line diagram of the solar farm and a diagram of its control system (“decoupling control”). Also reviewed within the scope of this process are the wiring diagrams of the medium-voltage systems, the data sheets (owners of solar farms / owners of distribution grids) and the technical data of the cables, transformers and operating equipment used, such as switchgear, controllers or dynamic reactive power compensation.
Plants may not be connected to the grid without the PGP certificates. The grid owners require the certificate to ensure that the plant as a system is compatible to the grid. Given this, the certification experts consider all power generating units and components up to the point of common coupling. After the parties have clarified detailed questions, the entire power generating plant, its components and a simplified model of the utility grid at the point of common coupling are simulated on the computer. Using special grid software, the experts carry out the required calculations in accordance with FGW-TR8. These simulations are aimed at verifying that plant behaviour is in conformity with the rules and regulations and form the basis of a detailed conformity report in which the experts summarise the test results. For the certificate to be issued, all documents (see info box 2)
Criteria for power generating plant (PGP)
certification The data sheets of the solar farm owners and the grid operators
The project-specific unit certificates and simulation models A single line diagram of the power generation plant Wiring diagrams of the medium-voltage systems; Documentation of the control system and decoupling control
A diagram of the control system of the power generating plant
The control concept of the reactive and active power supply Certificates and declarations of conformity for operating equipment
Technical data of cables, transformers, controllers, control panels and other components
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must have been submitted to the accredited certification body and reviewed for completeness and plausibility there, and all technical requirements must have been fulfilled in simulation.
After the plant has been installed and taken into service the certification body carries out final approval, which is a prerequisite for the feed-in tariff under Germany’s Renewable Energy Sources Act. Have all components been installed in accordance with the requirements and as set forth in the certificates? For the certification experts to issue the final declaration of conformity, all documents required for placing the plant into service, other records and wiring diagrams as well as the ongoing operation of the plant must be in compliance with the rules.
Electrical characteristics and grid stability The electrical characteristics of the photovoltaic plants must impact positively on grid stability. In concrete terms this means that photovoltaic plants must have suitable systems, enabling them to react to changes in the grid. Another critical factor involves the system support services that must be provided by the power generating units.
These services include reduction of the feed-in of active power as specified by the grid owner and the generation or consumption of reactive power depending on the voltage in the grid. The plants must further satisfy low-voltage ride-through requirements. This means that plants must remain connected to the grid even in case of faults and short circuits unless these faults occur in their cable branch. In addition to the above, the plant must supply additional reactive power during the fault. Short circuits resulting in voltage drop also may not render the plant unstable or result in its disconnection from the grid.
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