In this way, eight planning periods for the modelling of one day and 2 920 planning periods for the modelling of one year are required. The finally realised operation of the single power plants and storages results from the combination of unit commitment decisions from the day-ahead planning period with a forecasting horizon of 36 hours and the successive planning periods with the shorter planning horizon. Stochastic programming enables, in addition to a point forecast, the consideration of the possible distribution of the wind and load forecast error. The forecast error distribution is depicted by scenario trees with discrete error levels.