D. Zafirakis

An Optimum Sizing Methodology for Combined Photovoltaic-Energy Storage Electricity Generation Configurations

The electrification of autonomous electrical networks is in most cases described by low quality of electricity available at very high production cost. Furthermore, autonomous electrical networks are subject to strict constraints posing serious limitations on the absorption of renewable energy sources (RES)-based electricity generation. To bypass these constraints and also to secure a more sustainable electricity supply status, the concept of combining photovoltaic (PV) power stations and energy storage systems comprises a promising solution for small scaled autonomous electrical networks, increasing the reliability of the local network as well. In this context, the present study is devoted in developing a complete methodology able to define the size of an autonomous electricity generation system, based on the maximum available solar potential exploitation at mini- mum electricity generation cost. In addition special emphasis is given in order to select the most cost-efficient energy storage confcguration available. According to the calculation results obtained, one may clearly state that an optimum sizing combination of a PV generator along with an appropriate energy storage system may significantly contribute on reducing the electricity generation cost in several island electrical systems, providing also abundant and high quality electricity without the environmental and macroeconomic impacts of the oil-based thermal power stations.

The Contribution of Renewables on Reducing the Electricity Generation Cost in Autonomous Island Networks

The Aegean Archipelago is a remote Hellenic area, including several hundreds of scattered islands of various sizes. The electricity demand in the Aegean Archipelago islands has up to now been covered by the existing autonomous power stations (APS) at very high electricity production cost. In order to face the continuous load demand increase an integrated solution based on the exploitation of the available renewable energy sources potential in collaboration with appropriate energy storage systems is investigated. According to the results obtained, the proposed solution is clearly more cost-effective than the operation of the existing thermal power stations, while remarkable environmental and macroeconomic benefits are also expected.

The role of hydrogen-based energy storage in the support of large-scale wind energy integration in island grids

To confront problems concerning large-scale integration of renewable energy sources, introduction of energy storage constantly gains ground. Benefits stemming from the adoption of energy storage include exploitation of otherwise rejected energy, increased reliability of energy supply and improved operation of a given power system overall. In this regard, contribution of such systems in achieving large-scale integration of wind energy into island grids is currently considered. More precisely, fuel cells and hydrogen storage (FC–HS) are investigated, in comparison with conventional batteries. For this purpose, a simulation algorithm is developed to study the energy performance of different FC–HS configurations used to recover wind energy curtailments. The developed algorithm is then applied to a representative Aegean island of medium–high quality wind potential. Results obtained indicate that FC–HS may become attractive in comparison with conventional batteries, only in the case that the use of hydrogen surplus to cover other energy flows is also put forward.

Combined photovoltaic and energy storage systems: an integrated electrification solution for small islands

The numerous small Aegean Sea islands present serious problems related to insufficient infrastructure, low quality of electricity available at very high production cost, as well as problematic connection with the mainland. On the other hand, the high solar potential of the area may encourage photovoltaic-based applications characterised by rather low maintenance support demands. In this context, an integrated electrification solution based on a photovoltaic generator along with an appropriate energy storage device is investigated. One of the main targets of the proposed solution is to maximise the solar energy exploitation of the area at minimum electricity generation cost, while special emphasis is given to the selection of the most cost-efficient energy storage configuration available. According to the results obtained, the solution under investigation is not only financially attractive but also improves the quality of electricity offered to the local communities, substituting for the expensive and heavily polluting operating thermal power stations.

An advanced microgrid simulator for stand-alone and market-dependent energy strategies

Aegean Sea islands, similar to other island regions around the globe, are determined by high quality wind and solar potential that stimulates the implementation of energy solutions based on renewable energy sources (RES). However, the current energy status suggests that RES penetration in the specific islands is limited in the order of 10%–15%, with oil-based power generation holding a dominant role. To this end, an advanced Microgrid Simulator has been developed in order to examine different energy strategies for island microgrids, considering both the option of stand-alone operation, as well as the option of interconnection to a host electricity system, which can be thought as equivalent of an electricity market.

Energy performance evaluation of a hybrid system in the Athos State

Based on the use of long-term energy measurements for an entire year, obtained from a hybrid station operating in the Monastery of “Simonos Petras” in Northern Greece, evaluation of the system energy management plan is presently carried out. The hybrid system under investigation comprises of a hydropower station, a photovoltaic (PV) generator and a diesel engine, while the entire installation is also supported by the employment of a battery bank. According to the analysis of results obtained, reassessment of the current energy management plan is as proved necessary in order to raise restrictions posed to the energy contribution of the PV generator. For this purpose, the theoretical maximum energy contribution of the PV generator is estimated and replacement of the diesel engine operation is explored, with results obtained being rather encouraging for the system future operation.