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Security of supply

"No network", a message that occasionally appears on mobile phones, is not an option when it comes to supplying electricity. After all, electrical energy cannot be stored in large quantities. That is why it is necessary to produce the exact amount of power required. As a result, the grids have to be expanded as well, so that even the highest expected energy demand can be met safely and reliably.

The cornerstone of reliable electricity supply is the high voltage grid, which is used for cross-regional power transmission within the national and international interconnected system. The transmission system operators are not only obliged to provide sufficient transmission capacity, but are also responsible for system stability - this means that they have to keep generation and consumption well-balanced at all times. Furthermore, power generated from renewable energy sources is fed into the grid first, against a legally defined flat rate.

How is security of supply guaranteed?

Lightning on power line: is there a danger of a power outage? No: high voltage power lines are operated in such a way that when a failure occurs on a power line, the other line can take up the full transmission capacity (n-1 principle).

The 50Hertz extra high voltage grid consists of overhead lines with two electrical circuits. This means that the power connection is operated over two electrical circuits. In principle, the load on each circuit should not exceed 50 per cent. However, due to the high degree of meshing in the grid, local loads of about 70 per cent are also possible. This ensures that if one circuit fails, other circuits can absorb the load. Until the non-operational circuit can be used again, these may temporarily be operated at 100 per cent of their potential load.
This dangerous situation can only be avoided by expanding the grid on time and through the active cooperation of all interested parties.

Legal framework conditions

There are two main developments that give rise to the need for grid development: the substantial growth of renewable energy sources and the evolution towards a unified European electricity market. This causes a greater demand for transmission capacity. As also defined by law, it is our task to expand the high voltage grid as required.

Legal basis

For the expansion of the extra high voltage grid, transmission system operators are subject to legal conditions.

1. The European Internal Electricity Market Directive stipulates that transmission system operators must construct the grid such that unfettered trade in electricity, free grid access for all electricity producers and non-discriminatory grid use are guaranteed at all times. This means the transmission system operators must, as a matter of principle, provide sufficient transport capacity for all electricity producers.

2. In accordance with the German Energy Industry Act (EnWG), the transmission system operators are obliged to operate, maintain, and expand in accordance with demand, a safe, reliable, high-capacity power grid (section 11, subs. 1 EnWG.) The transmission of electricity must be as economical and environmentally friendly as possible (section 1, subs. 1 EnWG).

3. In addition, the Renewable Energies Act (EEG) stipulates that priority must be given to the feeding-in and transport of electricity from renewable energies. This means, on principle, every kilowatt-hour of electricity produced from renewable energies must be accepted into the grid - if necessary, at the expense of conventionally generated electricity. This promotes the generation of electricity from renewable sources such as wind, sun and biomass. The law accords priority to electricity generated from renewable energy sources over conventionally generated power, and guarantees the operators of EEG generation capacity a fixed revenue per kilowatt-hour. In order to meet their take-off and transmission obligations, the transmission system operators are, under the Renewable Energies Act, obliged to expand the grid as soon is this proves necessary to ensure the take-off and transport of electricity from renewable energies.

For several years already, 50Hertz has been proactively working to implement the grid expansion. The required planning and authorisation procedures are currently in progress for three line construction projects.
The continued development of RES and the progress towards a unified European energy market have created a growing demand for transmission capacity in Germany. 50Hertz Transmission GmbH is legally obliged to meet this demand - insofar as economically feasible - by expanding the extra high voltage grid accordingly.


Volker Kamm

Press Officer

Volker Kamm
Tel: +49 (0) 30-5150-3417
Fax: +49 (0) 30-5150-2199
E-Mail: volker.kamm@50hertz.com