The mains load resulting from the power requirements of the consumers must be covered by power plant operation adjusted in terms of time. Base load, intermediate load and peak load are distinguished in this context. The power plants are used in these ranges according to their operational and economic properties. Hydro-electric, lignite-fired and nuclear power plants run base load, coal-fired and gas-fired power plants run intermediate load, and storage and pumped storage power plants as well as gas turbine facilities cover peak loads. Optimum operation is ensured under today’s and future circumstances if the ratio of the power plant output in the base load on the one hand and in the intermediate and peak load on the other hand is 1:1.