Control power is the power required to compensate for unexpected power imbalances between energy supply and energy demand in order to ensure grid stability. This can include both the provision of additional power (positive control power) in the event of an increase in demand and the reduction of the power provided or increase in load (negative control power) in the event of a fall in demand or increased feed-in. The importance of balancing power is increasing as part of the transition to renewable energies, as the fluctuating feed-in from photovoltaic and wind power plants is increasing grid instability. The demand for control power is put out to tender by the transmission system operators Tennet, Amprion, 50Hertz and TransnetBW. A distinction is made between primary control power, secondary control power and minute reserve power.