The long road to grid connection

Grid connection is a project in its own right when it comes to the construction of new generation plants. Even before the installation of the solar modules or the wind turbine tower, planning and approval are underway. Later, the technology in the transfer station must function reliably.

27.10.2023 – Every photovoltaic system and every wind farm has a grid connection. There, the electricity generated is fed into the public power grid. But the power grid is not an infinitely receptive sponge. It was originally designed to distribute electricity from large power plants to consumers in urban and rural areas.

But the energy world has changed. Millions of plants up and down the country now generate renewable electricity, thus presenting the grid with a task for which it is insufficiently prepared. To make matters worse, there is no such thing as a single network, but hundreds of small network areas, each with its own owners, its own structures and its own technical specifications. In these distribution grids, the majority of renewable generation plants are connected. Depending on the size of the systems, connections are made at different voltage levels – but the crux of the matter is the same in each case: If you want to put a system into operation, you need the grid operator to feed the generated energy into the power grid.

While grid connection for small plants is possible according to a simplified procedure – but not always quickly – grid connection is not an easy issue for plant project developers of larger plants. On the contrary: often a tough and lengthy process. Johannes Jörling explains which work steps are necessary for small and medium-sized solar and wind farms. At naturstrom, he is responsible for all questions relating to the grid connection of wind turbines and solar plants.

Johannes, how does the work on the grid connection begin?

It starts with the request to the network operator. Usually, a preliminary network information is issued, also known as non-binding network information. The network operator has eight weeks to provide this information. In some cases, the answer is actually received within the eight weeks, but in many cases the deadline is exceeded. We currently have a case where we have been waiting for the answer for eight months.

What happens next – can you then start with the concrete planning?

A reservation procedure follows. However, each network operator sets the rules of the game for itself. There is no legal requirement. In practice, there are simple, practicable procedures and very complex ones. According to the EEG, the grid operator must connect the system, but it defines the most economically advantageous grid connection point. However, if this is very far away from the plant – we have already had the specific case of 25 kilometres as the crow flies – the costs for the long cable route to the connection point burden the project.

However, there is not only the cable route to the connection point, transfer stations also have to be built. Is this a separate procedure?

Whether a substation or a transfer station is built depends on the output – but there is no fixed limit, but the specification also comes from the grid operator. Sometimes up to 20 megawatts of power can be fed into a medium-voltage grid without a substation. Over 20 megawatts, it almost always amounts to a substation. If a substation has to be built, this usually includes a building application. In some grid areas, however, a building application must also be submitted for transfer stations, which depends on the building authorities, sometimes in the districts of a federal state. In Brandenburg, there is also a special bureaucratic treat: a planning approval procedure for the construction of substations. Such methods are actually intended for the construction of overhead lines.

Let's move on to the components that are needed for the grid connection. Are there differences between solar parks and wind turbines?

The electricity from a system must be transformed up to the respective grid voltage. In wind turbines, transformers are usually already integrated. In the case of solar parks, we build the transformer stations in addition. This means that in the case of wind farms, we essentially only have the transfer station and the cable connection between this station and the wind turbines. Because wind turbines are used to a higher degree of time than solar systems, the components are also subject to significantly more stress, including in the transfer station.

And what components does a transfer station contain?

There are essentially four components: a medium-voltage switchgear, a parking control system, a protection and control cabinet and an uninterruptible power supply. In the medium-voltage switchgear, the transfer to the grid takes place. The connection is then also made by the grid operator. In total, the transfer station is about three by three meters in size.

Are the components readily available on the market?

There are delivery times, and they have been significantly extended in recent years. Ten years ago, there were delivery times for transformer stations of 12 to 16 weeks, two years ago they were 16 to 20 weeks, now we are at 45 to 60 weeks. The bottleneck is the concrete bodies, which are now in high demand. But copper and steel are also in short supply, so long delivery times are the order of the day.

In the transfer station, a lot is also measured and data is transmitted?

Yes, first of all, there are converters before the actual meters. But also monitoring devices that collect data from the components in the park and, last but not least, data about the electricity fed into the grid. These are also transferred to the direct marketer, for example. Data transmission works via the Internet, but a high transmission rate is not required either.

If everything goes well, will the transfer station last for the entire service life of the system?

The systems should last at least as long as the PV or wind power plant. However, the electronics in the stations will probably be outdated after 10, 20 years at the latest. Transformers can be reworked and sold again after 20 or 30 years.

What improvements would you like to see in the area of grid connection?

What slows us down the most is that the network operators have different reservation procedures and different specifications for the technology. In my opinion, standardizing this would be a great step forward. Grid expansion would also have to be accelerated, possibly via simplified approval procedures. At present, extensive research is required to determine where it can be fed into the grids.

Is there a region in Germany that serves as a role model?

Yes, the TEN, the Thuringian energy networks. There I have an easily accessible contact person. Most of the others are very difficult to reach. At this point, the shortage of skilled workers becomes clear. All network operators are urgently looking for new heads.

The interview was conducted by Petra Franke.

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