  Volatile electrical energy prices are a challenge and an opportunity for
small and medium-size companies in energy-intensive industries. By using
electrical energy storage and/or an adaptation of production processes,
companies can significantly profit from time-depending energy prices and reduce
their energy costs.
  We consider a time-discrete optimal control problem to reach a desired final
state of the energy storage at a certain time step. Thereby, the energy input
is discrete since only multiples of 100 kWh can be purchased at the EPEX SPOT
market. We use available price estimations to minimize the total energy cost by
a rounding based dynamic programming approach. With our model non-linear energy
loss functions of the storage can be considered and we obtain a significant
speed-up compared to the integer (linear) programming formulation.
