Abstract
Nowadays, with the large-scale penetration of distributed and renewable energy resources, ES (energy storage) stands out for its ability of adding flexibility, controlling intermittence and providing back-up generation to electrical networks. It represents the critical link between the energy supply and demand chains, being a key element for increasing the role and attractiveness of renewable generation into the power grid, providing also numerous technical and economic benefits to the power system stake-holders. On islanded systems and micro-grids, being updated about the state-of-the-art of ES systems and their benefits becomes even more relevant. Hence, in the present paper a comprehensive study and analysis of ES leading technologies' main assets, research issues, global market figures, economic benefits and technical applications is provided. Special emphasis is given to ES on islands, as a new contribution to earlier studies, addressing their particular requirements, the most appropriate technologies and existing operating projects throughout the world.

Abstract
This chapter aims to provide an overview of renewable energy systems (RESs) and the underlying issues related to the RES theme such as climate change and its mitigation. The types of RESs are also briefly discussed focusing on their characteristics and technological aspects. This is followed by the most important economic aspects as well as the challenges and opportunities of integrating RESs in power systems. This chapter also discusses the need for optimization tools adequately equipped to effectively capture the intrinsic characteristics of RESs and facilitate their optimal integration in power systems. All this leads to an efficient exploitation of their wide-range benefits while sufficiently minimizing their negative impacts. Finally, the chapter is summarized with some concluding remarks.

Abstract
The share of renewable energy sources (RESs) in the overall power production is on the upward trend in many power systems. Especially in recent years, considerable amounts of RES type distributed generations (DGs) are being integrated in distribution systems, albeit several challenges mainly induced by the intermittent nature of power productions using such resources. Optimal planning and efficient management of such resources is therefore highly necessary to alleviate their negative impacts, which increase with the penetration level. This paper deals with the optimal allocation (i.e. size and placement) of RES type DGs in coordination with reconfiguration of distribution systems (RDS). Moreover, the paper presents quantitative analysis with regards to the impacts of RDS on the integration level of such DGs in distribution systems. To this end, a tailor-made genetic algorithm (GA) based optimization model is developed. The proposed model is tested on a 16-node network system. Numerical results show the positive contributions of network reconfiguration on increasing the level of renewable DG penetration, and improving the overall performance of the system in terms of reduced costs and losses as well as a more stabilized voltage profile.

Abstract
The integration of renewable energy sources (RESs) cannot be postponed given the several techno-economic and environmental factors. However, the intermittent nature of RESs brings several challenges because such sources introduce significant operational variability and uncertainty in the system. Framed in this context a new stochastic mathematical planning model is proposed considering the placement and sizing of energy storage systems and reactive power sources that altogether enable high penetration of RESs. The model employs a linearized AC model, balancing well accuracy with computational burden. The model is tested on a standard distribution network system. Numerical results show that the simultaneous integration of energy storage systems and reactive power sources largely leads to a substantially increased penetration of RESs in distribution systems. Furthermore, dramatic reductions in losses, system costs and emissions are observed. Results analysis also reveal the positive contribution of such a planning on the overall voltage stability in the system.

Abstract
Although wind power generation has extended a maturity in technology, there are still many concerns regarding the optimal support of regulatory bodies for renewable resources. In this context, the regulatory body should form a market structure or consider market rules and regulations to not only attract investors to renewable power plants, but also provide an efficient market that reflects a safe and clear competition environment. In this paper, an agent-based game-theoretic model is developed to investigate the electricity market behavior under oligopoly circumstances. The proposed model reveals the potential of collusive and strategic behavior of market participants. By employing the proposed model, impacts of different supportive schemes on the behavior of the wind power producer and conventional thermal units are investigated. According to the results obtained, if the regulatory bodies do not consider strategic collusion of market participants, adverse consequences for wind power producers might happen in the long-term horizon. © 2016 IEEE.

Abstract
Because of the development of enabling technologies such as appropriate metering infrastructures and communication possibilities, the smart-grid vision has started to be implemented. Smart appliances and Plug-in Electric Vehicles (PEV) at the residential end-user premises constitute a typical example. Nevertheless, a distribution system (DS) that has been designed and operated by a distribution system operator (DSO) for decades considering only inflexible consumers has to be equipped with appropriate operating strategies and technological upgrades in order to adapt to the new conditions. This study examines the case in which PEV have penetrated in the DS without any supportive operational strategy. Next, a coordination strategy employed from the DSO for EV charging together with the scheduling of smart-appliances is proposed. In both cases, the selection of the daily optimal radial configuration of the DS is considered in order to facilitate the operational goals of the DSO. The optimality criterion is the minimization of the active power losses and both cases are compared by means of operational performance.