50Hertz Transmission GmbH

Control energy

As electrical energy cannot be stored in large volumes, the production of electrical energy has to exactly match consumption at any given time. This requires accurate consumption forecasts to ensure that generation, control of which is based on a generating schedule, is in line with actual consumption. Broadly speaking, the responsibility for planning and forecasting rests with the electricity generators and users connected to the 50Hertz system.

50Hertz offsets any discrepancies between generation and consumption by procuring so-called control power, without which frequency stability could not be ensured, and energy would be pulled from neighbouring systems. Control energy is mainly procured from power plants maintaining reserve capacity specifically for this purpose, including de-ratable steam, hydroelectric, pumped-storage and gas turbine power plants.


Pumped-storage power plant

Pumped-storage power plants are useful for permanent balancing of energy production and consumption: They allow for interim storage of electrical energy with the help of water. This is needed each time much energy is generated while little is being used. At times of low energy demand, "surplus" electricity is used to pump water up into a storage basin at a higher altitude. Later on, when the temporarily stored energy is needed, the water from the reservoir is raced back through turbines, generating electricity.

50Hertz restores the balance

A need for control energy will, for example, arise when, at half-time of a televised football match, refrigerators and electric ranges start working simultaneously, or a large coal-fired generation unit is suddenly on outage. In such a case, control energy must be made available within a matter of seconds. This is where primary balancing comes in, with the corresponding power plants of all interconnected AC networks participating. Then balance must be restored in the system or control area where the variation in the schedule occurred. To do this, secondary control energy is procured - an operation that is automatically controlled. To maintain the secondary balancing capability of the 50Hertz control area, additional minute reserve may have to be mobilised in certain situations. This reserve, however, rather than having to be delivered immediately, may be supplied 15 minutes after the call is received.

To be able to call on control energy, its providers must keep the corresponding capacity in place. The required scope of secondary control power and minute reserve to be held on stand-by is determined on the basis of probabilistic calculations. The provision of such stand-by capacity is separately charged.

The required control energy is calculated based on the total of all variations occurring in each of the balancing groups. Certain electricity feeding quantities and take-off quantities are assigned to each balancing group, and it is the responsibility of the balancing group operator to ensure their equilibrium. In the event of an imbalance, which is determined by 50Hertz for every balancing group, the expenses for control energy procurement are charged to the party causing the respective need.