IEEE Electrification Magazine - June 2017 - 18

The Greek nIIPSs
Main Characteristics of NIIPSs

Figure 1. Greek NIIPSs in the Aegean Sea. (Image courtesy of the Hellenic Electricity Distribution Network Operator.)

cases, depending on the size of the island, population, and
type of load, this potential could be sufficient to fully cover
the demand in terms of yearly energy balance, even though
the necessary market conditions, funding schemes, technology infrastructure, and regulatory framework are not
fully in place at the moment. During the last ten years, significant efforts have been made to further enhance RES
integration in the islands, although the legislative and
investment framework has been under continuous reform
mainly because of factors related to the general financial
environment in Europe and in Greece specifically. Currently,
power produced by RESs covers around 20% of the annual
electric energy demand of the NIIPSs.

800.0
700.0

NII

Crete

Rhodes

(GWh)

600.0
500.0
400.0
300.0
200.0
100.0

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Other NIIPS

Out of the 32 electrical systems in the Greek NIIPSs, 11
constitute groups of more than two islands interconnected to each other but not to the mainland grid (a total of 39
islands), and the remaining 21 are single-island insular
systems. Adopting the typology of the 2009/72/European
Union (EU) Directive, 31 of the 32 NIIPSs are isolated
microgrids, whereas one system (Crete) is a small isolated
system. Based on the classification of the NII Management
Code, NIIPSs are categorized by size depending on their
average peak demand over the last five years (APD 5) in
small (APD 5 ≤ 5 MW), medium-sized (APD 5 5-100 MW),
and large (APD 5 > 100 MW) systems, as shown in Table 1.
Island load demand presents high seasonal variability as
a result of the islands' high dependence on tourism. Peak
demand on all islands occurs during the summer, as shown
in Figure 2. This, in turn, impacts the annual load factor,
which is generally low, varying from 23% to 53% (Table 1).
Electrification of the islands primarily relies on conventional generating units, running on light fuel oil (LFO)
or heavy fuel oil (HFO), with a total installed capacity of
1,845 MW, comprising mostly internal combustion engines
with sizes varying from <100 kW to 50 MW. Steam turbines, gas turbines, and a combined cycle plant are also
used in the largest NIIPSs. Total capacities and number of
units per category are shown in Figure 3(a).
Installed capacity exceeds significantly peak demand
because of the necessary provisions for sufficient reserve
capacity, as dictated by the NII Management Code (at least
equal to the capacity of the largest conventional unit per system). Currently, installed capacities exceed annual peak
demand by 30-65%, which inevitably leads to low utilization
factors, especially for peaking units, also taking into account
the high seasonal variation of demand. As an example, the
cases of Mykonos and Astypalea are illustrated in Figures 4
and 5, where unit installed capacities and maximum available output power (at N and N−1 conditions) are shown,
along with the variation of peak
demand on a monthly basis. The case
of Astypalea, in particular, illustrates
a situation occurring in certain island
systems, where permanently installed capacity in the local power
stations trails peak demand at N−1
conditions, leading to ad-hoc solutions, either via rental capacity of
portable diesel units or transfer of
generating units from other systems
where surplus capacity is available.

2015

2016

Figure 2. The monthly load-demand variation in Greek NIIPSs (2015-2016).

I E E E E l e c t r i f i c ati o n M agaz ine / j un e 2017

Generation Cost
Because of the utilization of oil-fired
units, all NIIPSs are characterized by
high generation costs, leading to a

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2017