Foundation for growth and prosperity
Whilst the availability of electricity within our daily lives might seem like a matter of course, our electricity supply is only guaranteed thanks to a stable energy infrastructure that has grown over decades – a complex interplay of power stations, transformers, energy storage facilities and power lines. As one of the world’s leading industrial nations, it is absolutely essential for Germany to have a stable supply of energy as a foundation for growth and prosperity.
The basis of the energy infrastructure is the electricity grid, which is divided into a number of different voltage levels. The electricity transmission grid managed by the transmission system operators form the backbone of Germany’s energy infrastructure. Different network operators are responsible for different sectors – from ultra-high voltage to low voltage grid. Within the ultra-high voltage grid, the ‘energy highways’ transport large amounts of electricity at up to 380 kilovolts throughout Germany, covering vast distances from the power stations to the regional distribution grids. In addition to this, the transmission grids connect the German electricity grid to those of its neighbouring countries, thus enabling cross-border energy exchanges throughout Europe. The transmission grid has a total length of over 35,000 km; it ensures that each of Germany’s 82 million inhabitants and all of its corporate consumers are provided with the energy that they need, twenty-four hours a day, seven days a week.
Once it has reached its regional destination, the electricity is reduced step by step to a lower voltage until it finally arrives at a household plug socket measuring just 230 or 400 volts. At this low and medium voltage level, so-called distribution network operators connect local electricity consumers such as individual households to the grid. At a regional level, electricity is likewise distributed by distribution network operators using medium-high voltage grids; larger consumers, such as energy-intensive businesses, are among the recipients here.
n-1 security – stricter criteria for high degree of supply security
The transmission grid – and the other networks operating at different voltages – has been specially designed and constructed to ensure that the electricity supply in Germany and Europe is as secure as possible. It continues to work reliably even if individual power lines fail unexpectedly, for example if lightning strikes a mast. The principle behind this safety reserve is called (n-1) security.
The basic principle of (n-1) security in network planning states that if a component – e.g. a transformer or circuit – should fail or be shut down in a network operating at the maximum forecast levels of transmission and supply, the network security must still be guaranteed. This means that, in this case, undue interruptions in supply or the spreading of a failure must not occur. Voltage levels must remain within the permitted limits and the remaining resources must not be overloaded.
The (n-1) principle also serves as a criterion in the network calculations made to prepare the Grid Development Plan.
“New grids for new energy forms” – no energy transition without grid expansion
Our energy grids face challenges that are growing continuously. Expanding the supply from renewable energy sources brings about fluctuations in electricity generation and extra loads in the grids, which must be successfully managed by the network operators.
It is only by constructing new power lines that it will be possible to bridge the vast distances between core generation areas and centres of consumption in future. For example, electricity that is produced in the wind farms in the North Sea and the Baltic Sea will need to be transported to consumption hubs in the South. This results in new levels of demand for capacity in the electricity grid. In addition to this, additional capacity demands on the grid can be traced back to three other developments – as a result of weather-induced fluctuations, electricity generation in national and regional networks is to become more inconsistent, which will have an impact on grid stability. Electricity generation is also becoming more diverse and more decentralised, because more and more small generation facilities such as wind farms need to be connected to the grid. Electricity currents are also considerably more complex these days because, for example, electricity now flows in multiple directions, on its way from the transmission grid to the distribution grid and on to consumers. Finally, as a transit country in the heart of Europe, it is likely that Germany will have to handle considerably more cross-border electricity trade and transport than other countries in the future. One of the most important goals within the EU’s current energy policy is the increased merging of national energy markets in Europe to create a single European market for electricity. The German transmission system operators play a decisive role in this with the energy networks that they manage.
Delayed grid expansion – the transmission system operators and congestion management
You can find more information about injection management and redispatching on the websites of the four TSOs:
The proportion of renewable energy sources used in electricity generation in Germany is currently increasing much faster than the necessary grid expansion to transport it. Consequently, this may result in temporary bottlenecks in transmission. If the electricity generated by a producer cannot reach the consumers due to a lack of transmission capacity, this is known as ‘grid congestion’. This phenomenon can have a variety of different causes. The transmission system operators can use a range of different measures during ongoing network operation to avoid or rectify congestion. Two such measures are injection management and redispatch management.
Both processes serve to bypass temporary cases of congestion. However, they are no substitute for the fundamental rectification of permanent congestion by means of expanding the grid.
Injection management – protecting the grid from capacity overload
Due to the above-mentioned fluctuations in the amount of electricity that can be fed in to the grid, current grid capacities are not sufficient to transport all the electricity that is being generated. At these times, the grid operators turn to injection management to avoid congestion and ensure security of supply.
In these situations, the network operators inject less energy from renewable power sources into the grid, although these sources are usually given priority over others. In specific terms, this means that wind turbines are temporarily restricted or the inverters in solar plants are switched off. As a basic principle, the TSOs only use injection management as the final option in order to avoid congestion. This process is different from peak capping which is already used in network planning.
Redispatch – balancing current flows in different directions
Redispatch management is a measure used to control current flows. It involves using physical laws to relieve certain parts of the electricity network. In redispatching, the power station output is systematically reduced on one end of the line and increased on the other end. This reduces the total current in the line. The necessary arrangements for this process are agreed upon between the respective network operators and the appropriate power station operators.