EJEEE
https://doi.org/10.62909/ejeee.2024.002 Edison Journal for Electrical and Electronics Engineering
Article
Contrasting Energy Storage Systems for Small-Scale Isolated
Grids
Othman Waled Khalid 1, * and Nazar Adnan Hasan 2
1 School of Electrical and Electronic Engineering, Engineering campus, Universiti Sains Malaysia, Penang,
Malaysia; othmanalabbasi@student.usm.my
2 Communication system department, South Tehran Azad University, Iran; nazaradnan44@gmail.com
* Correspondence: Tel.: +60-193577627
Abstract: The goal of this article is to examine the best electricity storage methods, both in terms of
technology and economics, for tiny, independent electrical grids that are integrated with power
plants that generate renewable energy sources (RES). As case studies, three autonomous Greek is-
lands—Symi, Astypalaia, and Kastelorizo—with yearly and approximately for our work is peak
demand of 3.9 MW, 2.1 MW, and 0.889 MW, respectively, are examined. Every island under inves-
tigation has exceptional solar and wind potential, and their locations are perfect for the installation
of seawater PHS (pumped hydro storage). Regarding the energy storage facilities, two distinct strat-
egies are examined: PHS systems (for the two largest islands) and electrochemical storage, which is
another name for lead acid or lithium-ion batteries. Potential RES units include photovoltaic instal-
lations and wind farms. The analysed plants' dimensioning is optimised with a shared goal in mind:
achieving an annual percentage of RES penetration above 69.9% while keeping the selling price of
energy below the current specific production cost. The analysis is combined with the systems under
examination's economic assessment. It is demonstrated that wind-PHS is still a competitive alterna-
tive for Symi and Astypalaia given the proper land morphology for PHS installations, while a wind-
p/v-batteries features as the best choice for Kastelorizo. Only with PHS support can 99.9% annual
RES penetration be attained; with electrochemical batteries, annual RES penetration can range from
79.9 to 91.1%. Electricity selling prices between 199 and 349 €/kWh, which result in payback periods
between five and nine years, ensure the economic viability.
Keywords: photovoltaic facilities; pumped hydro storage systems; sustainable development in re-
mote and isolated areas.
1. Introduction
The European Commission has spearheaded a centrally coordinated initiative to en-
courage the adoption of Renewable Energy Sources (RES) in European independent is-
lands over the past two years [1]. Wind and photovoltaic (p/v) parks must be integrated
with energy storage technologies in order to be introduced more often and safely into
independent isolated grids. This results in the configuration of "hybrid power plants."
From a technical and financial standpoint, Pumped Hydro Storage (PHS) has been
shown to be the best electricity storage technology for medium- and large-sized systems
with power demands greater than 4.9 MW [2, 3], provided that suitable land morphology
is available for the sites. In these circumstances, the PHS system's setup-specific cost can
be as low as 29.9 €/kWh of storage capacity [4, 5], a figure that is unachievable with con-
ventional energy storage technologies. However, electrochemical storage or small-scale
compressed air energy storage systems (micro CAES) are the most practical choices for
systems with an annual peak demand of less than 0.99 MW [6]. However, there is a grey
area when it comes to choosing the best storage technology between 0.99 and 4.99 MW.
Citation: Khalid, O.W. and N.A.
Hasan, Contrasting Energy Storage
Systems for Small-Scale Isolated
Grids. Edison Journal for electrical
and electronics engineering, 2024. 2:
p. 6-11.
Academic Editor: Prof. Dr. Khairun
Nidzam Ramli
Received: 13/1/2024
Revised: 15/2/2024
Accepted: 23/2/2024
Published: 1/3/2024
Copyright: © 2024 by the authors.
Submitted for possible open access
publication under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
(https://creativecommons.org/license
s/by/4.0/).
EJEEE 2024, Vol.2 7 of 11
This is because it heavily depends on specific topographies and appearances happened in
the insular scheme (yearly energy request fluctuation, obtainable RES possible, obtaina-
bility of suitable terrestrial geomorphology for PHS connection, availability of inexpen-
sive petroleum obligatory for the process of a micro-CAES scheme) [7].
This object concentrations on independent narrow schemes with a yearly top request
between 0.99 and 4.99 MW, high solar radiation and wind potential, favourable land mor-
phology for photovoltaic systems, and a current specific cost of electricity production
greater than 0.249 €/kWh, which is determined via the price of introduced fossil fuels used
in nearby independent current energy stations. These kinds of islands are found mostly,
though not exclusively, in the Mediterranean and Aegean Seas. In order to secure a RES
yearly diffusion proportion advanced than 69.99% relative to the annual consumption, the
article for these isles goals to identify the best storing skill combined with a RES energy
station (wind square and/or photovoltaic plants). It also ensures the economic viability of
the necessary investments by putting the price at which electricity is sold below the cur-
rent specific cost of electricity production from the regional independent current energy
stations.
In order to do mention matter, dual project reports for the Greek land mass of Symi
and Astypalaia—whose yearly top require is 2.1 MW and 3.9 MW, correspondingly—are
completed. Additionally, a last project education—for the eastmost Greek island of
Kastelorizo, with an annual top require of 0.89 MW—is implemented for integration and
comparison purposes.
2. Materials and Methods
2.1. Current energy use
Three small islands, Symi, Astypalaia, and Kastelorizo, are part of the Dodecanese
Complex in the eastern Aegean Sea. Their respective permanent populations are 2,589,
1,329, and 500 people. Based on official statistics from the grid operator [8], Table 1 pre-
sents the essential characteristics of the power consumption in 2012 [9].
Table 1 presents the essential characteristics of the current energy consumption in the
examined isolated routines [9].
Greatness
Symi
Astypalaia
Yearly energy utilization (MWh)
15564
7000
Yearly top requirement (MW)
3.99
2.23
Yearly common utilization per day (MWh)
41.999
19.24
Energy construction entire exact expense (€/MWh)
385.89
423.99
2.2. The potential of the available RES
Figure 1 shows the regular standard wind speed rate variation built in yearly wind
data from trio wind poles built in the islands of Kasos and Sifnos, as well as on Turkey's
west coast (9.49 n.m., directly across from Symi). The aforementioned data sets will be
used for the wind probable assessment of the isles of Symi, Astypalaia, and Kastelorizo,
respectively, due to the absence of wind observations on the islands under examination.
Based on data collected from the island of Samos, the yearly variability of the gross inci-
dent solar radiation on the level plane is also depicted in the same figure.
Figure 1 shows the average monthly values of the solar potential and wind used ob-
servations for the islands under investigation.
EJEEE 2024, Vol.2 8 of 11
Figure 1. Relations between wind velocity and period
Figure 1 shows the high-RES possible potential, with average monthly wind veloci-
ties above 10 m/s. During summer, when days with low wind speeds are common, the
case entire solar energy on the level surpasses 999.9 W/m2, providing another energy ob-
tain. This, in performance, leads to the maximisation of power utilization because indoor
air conditioning systems are used more frequently.
2.3 The hybrid power plants under investigation
We look at two different designs for hybrid power plants for the islands of Astypalaia
and Symi. In a previous article [10], both of them were presented in detail with respect to
their design and algorithm of functioning. The storage technology they use is where they
diverge most. A PHS arrangement has been established in the first layout under examina-
tion, while lead-acid and lithium-ion strings have investigated in the second layout. This
is because lead-acid batteries continue to have the minimal purchasing costs, while lith-
ium-ion batteries are the highest favorable battery equipment. Potential RES units include
photovoltaic stations and/or wind parks.
For dynamic security considerations, the direct RES energy access fraction in the case
of PHS systems is maintained at a maximum of 30.9% compared to the present power
consumption. In order to permit permanent energy creation from the hydro turbines, the
system should be dimensioned to guarantee that there will always be adequate water
stored in the PHS reservoirs. Due to the electrochemical batteries' direct reaction through
their bidirectional inverters to a possible loss in power output, this percentage can reach
99.9% in the case of electrochemical storage technologies.
In order to maximise the flexibility of the hybrid power plant, the PHS systems
should be built with double penstocks. Additionally, an appropriate number of independ-
ent battery strings should be developed, as indicated by the dimensioning process. This
will allow the storage technology to be charged and discharged simultaneously.
The two PHS systems were precisely located in digitally rendered terrain, and all
necessary volumetric computations were carried out by computer means. Perfect loca-
tions were identified for each island, with absolute heights of 439.9 metres for Symi and
329.9 metres for Astypalaia, respectively. These locations were near the coast, with gentle
mountain slopes leading towards the coast, allowing the penstocks to be installed on the
ground and obviating the need for costly tunnel construction and underground installa-
tions. Pumped straight from the ocean, seawater will power both PHS systems. In both
scenarios, the solar panels or wind turbines are positioned in a nearby mountain range
(Symi) or along the upper reservoir shore (Astypalaia), thereby removing the need to es-
tablish new access roads and connection grids.
In conclusion, a wind, PV, and electrochemical storing station are going to examine
for the Kastelorizo island approach. The adoption of a PHS system just for energy storage
is not justified by the tiny size of this system.
2.4 Techniques
EJEEE 2024, Vol.2 9 of 11
In conclusion, this work investigates two alternate layouts for the two largest islands,
one of which uses two different battery technologies; as a result, a total of three potential
systems are investigated:
• Wind, PV, and PHS systems
• Photovoltaic, wind, and electrochemical packing tools, like lead acid or lithium-ion
strings.
Furthermore, the latter of the aforementioned layouts is also investigated for
Kastelorizo, the smallest island, using the two different battery technologies. Two times
three times two, or eight, various cross energy stations are analysed and optimised. Uti-
lising yearly period sequences of normal hourly estimates for the energy necessity and the
prospective energy output from the required RES machineries, the yearly process of en-
tirely the studied methods has been modeled. The authors have constructed software ap-
plications to realise the procedure process of the approaches under examination, which
are used to run the simulation [11].
For every architecture that was analysed, different dimensioning scenarios were set
up with respect to the connected energy of the relevant RES energy stations and the stor-
ing volume of the storage capacities. The goal was to determine the best way to dimension
each system under examination for each isolated grid under high annual RES penetration
(above 69.9%, with a goal of 99.9%). At the same time, the goal was to maximise the finan-
cial viability of the investments, which was verified using particular economic indices.
The real purchase costs for the majority of the necessary equipment and the outcomes
of comparable work completed by the authors for review research [12] constitute the basis
of the profitable valuation of the procedures under examination. An replacement mone-
tary evaluation has been conducted for the comparable approaches, specifically for lith-
ium-ion batteries, given the predictions of a significant decline in their procurement cost
over the next ten years. This analysis adopted a procurement cost of 49.9 €/kWh for the
specific technology, whereas the current range for this feature is 499.9 €/kWh. The limita-
tion on the electricity vending charge, which must be significantly less than the current
electricity production total specific cost in the under consideration isolated systems, is the
final essential and fundamental prerequisite adopted in the economic evaluation of the
examined systems (see Table 1).
In summary, the optimisation method seeks to optimise the financial keys of the nec-
essary savings, subject to two primary limitations:
• a yearly percentage of RES penetration more than 69.9%, with the goal of reaching
99.9% in comparison to annual consumption
• A selling price for electricity that is less than the local thermal power plant's current
production costs.
The authors' software programmes, created in the LabVIEW environment, are used
to carry out the optimisation procedure.
5. Results
Table 2 summarises the outcomes of the simulations that were run with reference to
the dimensioning optimisation and the attained RES insight.
Table 2 An overview of the dimensions optimisation computations' results.
Island
Storage station
Wind Park
energy(MW)
P/V con-
trol (MW)
Storage minor
size (MWh)
Autonomy control
interval (times)
RES yearly ac-
cess (%)
RES yearly
excess (%)
Symi
PHS
7.0
2.49
646.9
15.31
0.99
25.9
Lead acid
4.49
1.99
17.99
0.5
79.29
31.0
Lithium-ion
4.49
1.99
12.149
0.30
79.1
32.0
Astypalaia
PHS
4.49
0.0
366.9
19.32
0.99
24.0
EJEEE 2024, Vol.2 10 of 11
Lead acid
3.59
0.99
14.51
0.80
88.1
52.2
Lithium-ion
3.59
0.99
10.9
0.60
86.1
52.9
Kastelorizo
Lead acid
0.89
0.899
7.3
0.90
86.1
27.1
Lithium-ion
0.89
0.899
6.1
0.70
90
39.1
It is observed that yearly RES diffusion ratios greater than 77.9% have been attained
with the resulting dimensioning, whereas 99.9% RES diffusion has been completed for the
PHS-supported systems. One other significant aspect of the achieved findings is the ex-
tremely large storage capacity provided by the PHS systems. Lastly, it is also important
to note the large RES production surplus that is computed annually for the systems that
are stayed by electrochemical storing strategy. This is because, in relation to the overall
size of the hybrid energy station, these systems have a relatively little storage capacity.
Table 2 presents the respective outcomes of the ensuing economic examination. The
following presumptions guided the execution of the economic analysis:
The finance plan comprised 49.9% loans and 49.9% equity from the European Invest-
ment Bank, with a 1.499% interest rate and a 15-year repayment period. The economic
analysis was conducted using a 20-year life expectancy for all systems.
The related investment's stocks are referenced by the economic indexes that are being
given.
As can be observed, with the dimensioning completed, the needed selling price of
the generated electricity should be between 249 and 349 €/MWh for the storage technolo-
gies that are currently in use, but it is significantly lower in the event that the cost of pur-
chasing lithium-ion batteries drops in the future. Contempt the small scope of the isles
under investigation, PHS systems are still very competitive because they offer a number
of benefits like high storage capacity, low setup costs per unit of storage capacity, long
autonomy times, long lifespans, and the one scheme that container ensure 99.9% RES sat-
uration. It is also emphasised that all battery replacements necessary over the course of
the hybrid power plants' lifespan are taken into account when determining the setup-spe-
cific costs of the storage plants.
On the other hand, the expensive setup costs and, typically, the drawn-out licencing pro-
cess are the main disadvantages of hybrid energy stations with PHS systems.
Lastly, it should be mentioned that the economic evaluations were carried out over 19-
year lifespans. Longer life spans (such as 49 years) would make the systems with PHS
assistance much more economically feasible because they would require more electro-
chemical battery replacements, which would raise the related plants' life cycle costs.
6. Conclusions
The paper looks into three small-scale Greek island autonomous systems' require-
ments for having a high-RES penetration rate. In order to guarantee great-RES access and
financial viability with power having fees less than the current production specific fee of
the independent routines, alternative storage technologies are investigated. In principle,
all of the substitute plants can be used to meet the aforementioned goals. Beside evaluat-
ing another researched equipment amongst them, we determine that:
Firstly, the yearly RES access ratios scale from 77.9 to 89.9% with the use of electrochemical
technology. Secondly, it is only possible to obtain 99.9% yearly RES penetration percent-
age using PHS systems. Thirdly, PHS systems have extremely long independent operating
times, which is a critical component for autonomous grids. Fourthly, PHS systems have
the highest setup costs, but over time, these costs are offset because they are built only
once and don't need to be replaced, unlike batteries. Fifthly, PHS systems have the lowest
particular cost of setup per storage capacity unit. then, the primary alluring aspects of
power plants utilising battery technologies are their minimal setup expenses and their
expedited and less complicated licencing procedure. Also, if procurement costs for
EJEEE 2024, Vol.2 11 of 11
lithium-ion batteries drop by 89.9% over the course of the next ten years, they may become
a very appealing choice. Finally, Payback periods of five to nine years are reached for the
investments' equity under a finance strategy of 49.9% equities and 49.9% bank loan
(1.499% rate, 15 years payback term), retaining the energy selling price below the present
current energy creation price.
The aforementioned is predicated on the notion that good terrain topography would
be advantageous for PHS installations.
Conflicts of Interest: Declare conflicts of interest or state “The authors declare no conflict of inter-
est.”
References
1. Blackford, M.G., Fragile paradise: the impact of tourism on Maui, 1959-2000. 2001: Development of Western Resourc.
2. Dincer, I. and M.A. Ezan, Heat storage: a unique solution for energy systems. 2018: Springer.
3. Stoddard, I., et al., Three decades of climate mitigation: why haven't we bent the global emissions curve? Annual Review of
Environment and Resources, 2021. 46: p. 653-689.
4. Muellner, N., et al., Nuclear energy-The solution to climate change? Energy Policy, 2021. 155: p. 112363.
5. Magazzino, C., et al., The relationship between nuclear energy consumption and economic growth: evidence from Switzerland.
Environmental Research Letters, 2020. 15(9): p. 0940a5.
6. Datas, A., A. Ramos, and C. del Cañizo, Techno-economic analysis of solar PV power-to-heat-to-power storage and trigeneration in
the residential sector. Applied energy, 2019. 256: p. 113935.
7. Spelling, J., B. Laumert, and T. Fransson, A comparative thermoeconomic study of hybrid solar gas-turbine power plants. Journal
of engineering for gas turbines and power, 2014. 136(1): p. 011801.
8. Avvisati, G., et al., Perception of risk for natural hazards in Campania Region (Southern Italy). International Journal of Disaster
Risk Reduction, 2019. 40: p. 101164.
9. Singh, A.K., et al. Load forecasting techniques and methodologies: A review. in 2012 2nd International Conference on Power, Control
and Embedded Systems. 2012. IEEE.
10. Katsaprakakis, D.A., et al., Comparing electricity storage technologies for small insular grids. Applied Energy, 2019. 251: p. 113332.
11. Mourtzis, D., Simulation in the design and operation of manufacturing systems: state of the art and new trends. International Journal
of Production Research, 2020. 58(7): p. 1927-1949.
12. Hanga, K.M. and Y. Kovalchuk, Machine learning and multi-agent systems in oil and gas industry applications: A survey.
Computer Science Review, 2019. 34: p. 100191.