During the night hours, to match the lowest load demand by a power generation system, many different strategies can be employed: unit load following, unit shutdown and hydro storage. Obviously, the utilized strategy influences the power production (gas turbines, hydro turbines, etc.) during the peak load demand.

In this paper, the energy comparison among the above different strategies is carried out as a function of the load demand, the heat rate of the peaking units, the hydro storage total efficiency and the hydro stored energy.

In particular, two sets of intermediate load fossil fuel power units (conventional and advanced) are considered.

For the sets considered and relatively to the variable costs, the two-shift operation proved to be the most convenient strategy.

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