3.2. Fluctuating Power Plants
Fluctuating power plants, on the other hand, do not provide
a permanent and guaranteed energy supply, since their energy
sources are not steadily available, due to the unsettled weather
conditions. Consequently, the amount of energy generation
cannot be controlled and the amount can only be projected to
a limited extent. In contrast to the continuous power plants,
the fluctuating power plants do not offer constant
characteristic values in terms of their energy generation. Thus,
the planning is based on long-term and short-term forecasts of
the energy yield, typically covering the future 12 months to 4
days, respectively [9]. However, the forecast values measured
in kWh are not reliable; instead they represent the average in a
range of calculable variations of the energy amount [10]. The
shorter the forecast horizon gets, the higher the reliability, and
thus the narrower the range of variation [11]. Figure 1
illustrates this development.