The provision of what is known as balancing energy serves to secure the power supply. It is used when there is either excess demand or excess supply on the power market. To be able to compensate variations in the power market, the large Transmission System Operators must provide between 5,000 and 6,000 MW of balancing energy (in total) at all times. And this applies to both positive and negative balancing power, so that both excess demand and excess supply can be compensated. With the aid of this reserve, variations can be equalised within seconds (primary reserve), five minutes (secondary reserve), fifteen minutes (minute reserve) or hours (hour reserve).
The operators of small plants are now gaining importance, particularly in the minute reserve area. Since the 1st January 2012, there has been the possibility of compensating network variations caused by the feed-in of renewable energy with likewise renewable energy.
For example, an excess in photovoltaic power can be compensated by a simultaneous reduction in the operation of a biogas plant (negative balancing energy).