*3.3. The Electricity Demand*

The electricity demand appears to have both seasonal and daily variations. The seasonal variation of the electricity demand appears as two peaks, one during the winter and one during the summer. Loumakis et al. [31] considered the following three additive kinds of demand with different variation each: (a) A constant demand independently of the season, (b) a winter activities demand, and (c) a summer activities demand. A normal distribution was proposed to describe both the winter and summer activities with different characteristics. The resulting equation is [31]:

$$D\_i = \frac{D\_T(1 - d\_w - d\_s)}{365} + d\_w D\_T \cdot N(t\_{\text{two}}, \Delta t\_{\text{w}}, i) + d\_s D\_T \cdot N(t\_{\text{so}}, \Delta t\_{\text{s}}, i) \tag{2}$$

where the electricity demand *Di* (GWh/day) during the day *i* (1, 2, ... , 365) is calculated, when the following seven parameters are known:


The normal distribution is expressed by the following equation: *<sup>N</sup>*(μ, σ, *t*) = 1 √<sup>2</sup>πσ<sup>2</sup> *exp*−(*<sup>t</sup>*−μ)<sup>2</sup> 2σ<sup>2</sup> . The daily variation of the demand also appears to have two peaks, one at noon and another in the

evening. The above idea concerning the seasonal variation is also used to describe the daily variation:

$$D\_{\rm ij} = \frac{D\_{\rm i}(1 - d\_{\rm n} - d\_{\rm \varepsilon})}{24} + d\_{\rm n} D\_{\rm i} \mathcal{N}(t\_{\rm n0\prime} \Delta t\_{\rm n\prime}, j) + d\_{\rm \varepsilon} D\_{\rm i} \mathcal{N}(t\_{\rm 60\prime} \Delta t\_{\rm \varepsilon}, j) \tag{3}$$

where the electricity demand *Dij* (GWh/hour) during the hour *j* (= 1, 2, ... , 24) of the day *i* (1, 2, ... , 365) is calculated, when the total demand *Di* (GWh/day) of the day *i* is calculated from Equation (2) and the following six parameters are additionally known:

