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84 CHAPTER 3 Forecasting of Intermittent Solar Energy Resource

FIGURE 3.3
Prediction scale for energy management in an electrical network.
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A forecast error induces two negative effects: First, the network operator may
receive some high penalties because an inaccurate forecast would prevent him to
reach a predicted production profile and the use of back-up generators is more
important for compensating the gap between predicted and real production
[31,32]. A solution consists in using local storage in combination with ISRES to
compensate deviations between forecasted and produced electricity [18,23,31,32]
or in combining several ISRES spread over a large area in such a way that individual
prediction errors of each ISRES would be independent and the overall forecast error
reduced (aggregate effect).
The energy storage means appears at various time scales and their management
requires to know the power or energy produced by the ISRES and consumed at
various temporal horizons: from very short or short (power quality category) to hour-
ly or daily (bulk energy storages) [3]. For the storage management, the forecasting
allows to decrease the amount of flexible reserves and to optimize the management
of the energy storage by anticipating the charge and discharge phases.
Moreover, the electrical operator needs to know the future production (Fig. 3.3)
at various time horizons: from 1e3 days to prepare the production means (and to
schedule preventive maintenances), from some minutes to hours to plan the power
plants start-up in reserve (between 5 min and 40 h according to the energy produc-
tion means [5].