Our grid’s power circuit length covers a distance of 10,490 kilometres across the entire eastern part of Germany as well as Berlin and Hamburg. We transport a constantly increasing share of renewable energy over large distances at the extra high-voltage levels of 150, 220 and 380 kilovolts (kV). In substations, we exchange electricity with the distribution system operators; here, transformers convert electrical energy from one voltage level to another. Large producing units such as power plants or wind farms (onshore and offshore) as well as large industrial companies such as steel mills are directly connected to our extra high-voltage grid. We constantly maintain our lines and substations and repair damage resulting from old age or storms, for example.
We guarantee a secure electrical system; 24 hours a day, 365 days a year. Background: due to the laws of physics, production and consumption have to be in balance at all times. Our colleagues at system management ensure this balance: when more energy is required, they request the additional production, or have the output of installations reduced when more electricity is fed into the grid than can be consumed and transported. This balancing is a particularly challenging task in our grid area as more fluctuating energy is generated from renewable sources than by conventional power plants. This mainly concerns wind turbines and solar panels. Their feed-in quantity constantly changes at short intervals, depending on the time of day and the weather conditions.
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Due to the enormous growth in renewable energy, the demands on our grid have changed, too. Large quantities of electricity have to be transported to the consumption centres in the south and south-west of Germany. We have to adjust our lines and substations in order to fulfil this task. This is done in application of the NOVA principle: grid optimisation before grid reinforcement before grid expansion. First of all, we try to meet an increasing demand for transmission by better managing existing line connections.
One instrument to this end is the so-called overhead line monitoring, also referred to as weather-dependent overhead line operation. The background is that the transmission capacity of overhead lines is limited by the maximum operating temperature of the conductor. If more electricity flows through the line, the transmission lines heat up. Wind and cold can cool off the lines. During overhead line monitoring, we permanently survey the operating temperature of lines and can transport more electricity in case of cold weather or strong wind.Another way to optimise existing lines is to install high-temperature transmission lines. These can be subjected to a higher operating temperature and therefore transport more electricity. This does not require the construction of a new line, but only the replacement of the transmission lines on the towers of an existing overhead line. 50Hertz for example installed high-temperature transmission lines on the important north-to-south line from Remptendorf in Thuringia to Redwitz in Bavaria without having to replace the towers on this section. Since early 2018, so-called phase shifting transformers (Download in German) have been installed that also enable more effective exploitation of the existing grid. Phase shifters can be compared to a valve that controls the flow of electricity. Because of this redirection of the energy to other lines, the stress on certain line sections is relieved. So far, 50Hertz has put phase shifting transformers in substations Vierraden (Brandenburg) and Röhrsdorf (Saxony) into operation, with the primary objective to reduce unplanned load flows via cross-border connections to Poland and the Czech Republic. After the completion of the conversion works in Vierraden and Röhrsdorf, it will also be possible to use these phase shifting transformers to improve the distribution of electricity within the 50Hertz grid as well.
A newly developed concept for better load distribution on the existing grid, which is currently only theoretical, consists of the so-called grid boosters. The idea: large batteries or additional consumers such as Power-to-Heat installations are available on the grid to accept energy surpluses, e.g. when a lot of wind power is generated in case of strong wind and the grid would not be able to handle this electricity volume. Instead of reducing output by production units as a precautionary measure, which we do today, the system operators could put a greater load on their lines than before and only rely on these new installations in case of an imminent overload on the lines. Together with the other German transmission system operators, 50Hertz is testing whether such a concept can be realised.
If a grid optimisation measure is not sufficient, 50Hertz plans reinforcing that particular grid structure. This, for instance, involves the replacement of 220 kilovolt (kV) lines with 380 kV lines which can transport much more electricity. This requires the construction of a completely new route as the existing towers cannot carry the weight of the heavier transmission lines.
When the construction of such a new replacement line is planned, 50Hertz enters into dialogue with residents, municipalities and authorities at an early stage. We present our plans locally and gather information to ensure that the route of the new lines can be realised with as little impact on man and nature as possible.
We only consider the construction of a completely new line after we have exhausted all other possibilities. In 2017, for instance, we put the South-West Interconnector into full operation. This interconnector runs from Bad Lauchstädt near Halle in Saxony-Anhalt over Vieselbach near Erfurt in Thuringia to Bavaria. The section on the Bavarian side was realised by system operator TenneT. This fully new north-to-south line makes a significant contribution to the integration of renewable energy from the north-east of Germany into the grid and to its transmission to where it is required. Furthermore, the costs for consumers are reduced (Redispatch Rechner): production by conventional power plants has to be increased or decreased less often (redispatch) and the output of RES installations has to be lowered less frequently (feed-in management); the legally stipulated compensation for the operators of the plants and installations are therefore also lower. Find more information here.
In order to transport future volumes of renewable energy, we are planning our first onshore direct current project together with TenneT: the SuedOstLink, a north-to-south direct current connection from Wolmirstedt near Magdeburg to the power plant site in Isar near Landshut in Bavaria. Ordinarily, this line should be realised as an underground cable. Overhead line sections will only be possible in highly limited exceptions. 50Hertz and TenneT are currently planning the exact course of the section, in dialogue with the affected municipalities and residents.
Overview of grid expansion projects at land
Overview of grid expansion projects at sea