In the medium term UC optimization models are applied to define tentative scheduling of the power plants over typically one to three months horizon.  More specifically, there are 3 main objectives:

There are some differences from the long term UC (one-plus year horizon) approach. In the medium term the main goal is to assess the tentative reservoirs management for hydro in a more effective manner since some more accurate forecast are available, especially in the one month ahead horizon. The problem is still coupled with the producibility of a fossil fuel power plant and with the (non programmable) uncertain production of renewable power plants. While for short time horizons, typically of one day or of one week, the pure short term UC problem (but not max profit UC in market related) can also be considered deterministic, for medium management horizons, a special emphasis must be put on the uncertain nature of data. In particular, on a yearly or more scale, reservoir inflows, demand, as well as availability of the plants cannot be considered deterministic. For instance in winter time customer demand can vary up to one GW per degree Celsius for big countries such as Italy, UK, France or Germany. On the other hand a rainy season can fill reservoirs and let the hydro production plants produce much more w.r.t. a dry season. Another crucial factor is related to renewables (wind and solar) power plant whose productivity fluctuations can be high. In the following we give insight to the different goals and constraints of the long term UC:

In medium term UC, the strategies for the big Hydro reservoirs are defined. Hydro power is a renewable source of energy that plays a key role in electric power systems, especially due to its flexibility and to its ability to allow the integration of other intermittent renewable sources. The medium-term hydro-scheduling is a very complex task that involves a great variety of processes and variables,some of which are considered stochastic, because of their uncertainty in the medium term. Two combined methods are used by Iberdrola in medium-term hydro-scheduling: stochastic optimization and simulation. The objective is to schedule, on the short term, the hydoreservoir. Secondly, a risk analysis and decision about the start/stop of the powerplants are defined. For the hydro what is done is the strategy for using the water, mainly done by calculating Bellman values.

Contributors:

Prof. Antonio Frangioni, University of Pisa

Prof. Thorsten Koch, ZIB

Dr Fabrizio Lacalandra, QuanTek