As the efforts for achieving energy neutrality within the EU by 2050 are increased, member states are facing multiple challenges. While the targets for 2020 have been met at a European level, there is still a long way ahead for the 2030 target for the more ambitious targets arising by the “Fit for 55” EU package.
Following the publication of the Renewable Energy Directive (RED)  in 2008, where member states agreed upon specific targets at both national and European level, the revision of RED (2018)  came to propose new, more ambitious targets. Specifically, a share of at least 32% of renewable energy by 2030 at a European level has been agreed. This came as a result of cumulative efforts made by member states during the past decade that led to encouraging results regarding renewable targets. According to Eurostat , the share of renewables in gross final energy consumption stood at 19.7% in the EU-27 in 2019, compared with 9.6% in 2004. The revision of the Renewable Energy Directive (2018) introduces new targets in the electricity sector to be met, with a strong emphasis on new investments in the electricity sector that also include a significant amount of capital investments in the energy infrastructure components.
Following the above, member states align their policy towards sustainability to meet the agreed targets. As such, Cyprus has published the targets and actions for the decade to come in the National Energy and Climate Plan. The target of 13% in Renewable Energy Sources for 2020 has been achieved, while the target of 23% in RES for 2030 is achievable or exceeded under certain conditions. However, to achieve this target, multiple studies [4–7] prepared by the Cyprus Government suggest that actions are required in both policy formulation, support schemes improvement, and regulated efforts to overcome the lack of non-operational electricity market in Cyprus.
The Cyprus energy system presents several unique challenges since it’s still isolated from the rest of the European Union grid. At the same time, the economies of scale that can be applied in the other EU Member States can not be used at the same level in Cyprus.
In  the authors presented a classification of the so-called “off-grid” systems and their challenges, including a limited amount of energy available for a restricted period reduces the acceptability of the solution and sufficient power reserve to face unexpected generation failures or load demand change. In addition,  are raising the fact that the reliance of RES in weather conditions (RES intermittency) is an important issue, especially in cases where the portion of Renewable power injected into the grid is relatively high, leading to a significant percentage of curtailments. The challenges of isolated systems are also presented in , where the authors discussed the challenges and presented a hybrid Renewable energy system paradigm.
Energy storage systems are classified into two categories. Those that are behind the meter and those that are located after the meter. Both Energy Storage systems come to address various challenges, enabling multiple services and components of the market such as Bulk Energy Services, Ancillary Services, Transmission and Distribution Infrastructure services (i.e. Voltage support, congestion etc), and customer energy management services.
Such solutions have been a subject of study for researchers to identify feasible solutions in both economical and practical terms in different conditions.
In , the authors performed a thorough review of the, at the time, available storage solutions. More specifically, they identified technologies such as flywheel, battery, supercapacitor, hydrogen pneumatic and pumped storage solutions (or new techniques that are taking advantage of gravitational energy). They classified them in terms of their specific energy and specific power. An important conclusion was that batteries are the most suitable solution for continuous energy supply.
Similarly, in , the authors presented an analysis of the role of storage systems in the development of smart grids. Various technologies were examined, and the importance of energy storage was outlined through two case studies. Electrical and electrochemical energy storage technologies are the first choices when considering smart grids.
An attempt to identify suitable energy storage technologies in small isolated systems has been performed in , with the results suggesting that BESS technology may be financially feasible while considerably decreasing the levels of RES curtailment. In other works, [10, 13–14] energy storage technologies are investigating their applicability in different scenarios. However, it is acceptable that no study was identified to explore all the available commercial storage technologies for Cyprus. Thus the purpose of this work is to compare previous results and provide recommendations using the deliverables of this study
It is worth mentioning that Gravity storage solutions also seem to be a promising solution and have received significant attention in recent years. In  the authors presented an approach to optimally configuring a wind-photovoltaic-storage hybrid power system based on a gravity energy storage system showing that such systems could be economically viable. Energy Vault  is an example of how gravity storage systems can be applied in the real world. The project first introduces the managed mechanical storage using cranes and cement blocks. This technology is one of the up-and-coming technologies. Based on a recent presentation in the IRENA Assembly meeting (online meeting Jan. 2021), this technology can have an LCOE as low as 3 $cents/kWh.
The understanding of energy systems challenges and the prediction of their behavior was enhanced through simulation and analysis tools. In , the authors developed a global electricity system model and evaluated the operation of power plants under various scenarios. In , the authors performed a link between different models to investigate the contributions to the system flexibility for cross-sectoral interactions on the future European system. The energy production of a hybrid photovoltaic system associated with a storage system in an isolated site has been modeled in .
A methodological review of some of the existing energy system models for assessing Variable RES is presented in . The authors identified clear advantages and disadvantages of the proposed approaches, arguing that each methodology is highly dependent on the modeling situation, modeler skills, and data availability.
Simulation tools are employed for assessing operational developments (RES penetration, storage integration, interconnection etc) within the energy grid. Such tool is the Dispa-SET , mainly developed within the Joint Research Centre of the EU Commission, in close collaboration with the University of Liège and the KU Leuven (Belgium) and is focused on the balancing and flexibility problems in European grids. Other tools used in previous work for the Cyprus model were the PLEXOS, DigSILENT, OSeMOSYS, custom-made tools in Matlab, and MESSAGE while currently, IRENA FlexTool is under evaluation
This work utilizes the Dispa-SET tool and investigates various scenarios for integrating energy storage solutions in the Cyprus energy network while achieving a high degree of RES penetration. All scenarios are aligned to the existing NECP of Cyprus (Jan. 2020), providing further insight on the potential of RES penetration to Cyprus’ grid and on the benefits associated with coupled RES/storage deployment.
The remainder of this paper is structured as follows: In the following paragraphs, the methodology is first presented along with a brief introduction of the Dispa-SET model, followed by the description of Cyprus’ generation system building blocks and the presentation of the scenarios. Based on the preliminary data attained, different scenarios have been investigated, presenting the mid-term RES/storage deployment needed for achieving the NECP goals in terms of electricity energy mix.