Direct current (DC) microgrids (MG) constitute a research field that has gained great attention over the past few years, challenging the well-established dominance of their alternating current (AC) counterparts in Low Voltage (LV) (up to 1.5 kV) as well as Medium Voltage (MV) applications (up to 50 kV). The main reasons behind this change are: (i) the ascending amalgamation of Renewable Energy Sources (RES) and Battery Energy Storage Systems (BESS), which predominantly supply DC power to the energy mix that meets electrical power demand and (ii) the ascending use of electronic loads and other DC-powered devices by the end-users. In this sense, DC distribution provides a more efficient interface between the majority of Distributed Energy Resources (DER) and part of the total load of a MG. The early adopters of DC MGs include mostly buildings with high RES production, ships, data centers, electric vehicle (EV) charging stations and traction systems. However, the lack of expertise and the insufficient standards’ framework inhibit their wider spread. This review paper presents the state of the art of LV and MV DC MGs in terms of advantages/disadvantages over their AC counterparts, their interface with the AC main grid, topologies, control, applications, ancillary services and standardization issues. Overall, the aim of this review is to highlight the possibilities provided by DC MG architectures as well as the necessity for a solid/inclusive regulatory framework, which is their main weakness.

The modern energy requirements and the orientation towards Renewable Energy Sources (RES) integration promote the transition of distribution grids from passive, unidirectional, fossil fuel-based into active, bidirectional, environmental-friendly architectures. For this purpose, advanced control algorithms and optimization processes are implemented, the performance of which relies on the Distribution System State Estimation (DSSE). DSSE algorithms provide the Distribution System Operator (DSO) with detailed information regarding the network’s state in order to derive the optimal decisions. However, this task is quite complex as the distribution system has inherent unbalance issues, often faces lack of adequate measurements, etc. The purpose of this paper is to review the DSSE algorithms that a system can incorporate with emphasis on their particular requirements, the mathematical formulation of the problem, the analysis of the existing model-based and data-driven approaches and the recommended solutions regarding observability issues, bad data detection, and meter placement strategies. Furthermore, special attention is paid to DSSE applications, including the use cases where they can be deployed, the approaches that are usually followed, the integrated distributed power supply units, as well as their future trends and challenges, thus highlighting their business-related aspects.

The ongoing energy transition has caused a paradigm shift in the architecture of power systems, increasing their sustainability with the installation of renewable energy sources (RES). In most cases, the efficient utilization of renewable energy requires the employment of energy storage systems (ESSs), such as batteries and hydro-pumped storage systems. The need for ESS becomes more apparent when it comes to non-interconnected power systems, where the incorporation of stochastic renewables, such as photovoltaics (PV) systems, may more frequently reduce certain power quality indicators or lead to curtailments. The purpose of this review paper is to present the predominant core technologies related to ESSs, along with their technical and life cycle analysis and the range of ancillary services that they can provide to non-interconnected power systems. Also, it aims to provide a detailed description of existing installations, or combinations of installations, in non-interconnected European islands. Therefore, it provides an overview and maps the current status of storage solutions that enhance the sustainable environmentally friendly operation of autonomous systems.

The ongoing energy transition has changed the architecture of electricity networks in ways that conventional power transformers are not able to cope with the new required functionalities. For this purpose, the solid state transformer (SST), which comprises state of the art power electronics with galvanic isolation to interconnect two separate alternating current (AC) or direct current (DC) power grids, is considered to be the dominant solution. The purpose of this paper is to provide a practical, application-oriented review of the SST. In this context, the main functionalities and possible applications of the SST are presented, including smart grids (SGs), data centres, railways, offshore wind farms, etc. Furthermore, the main developed SST prototypes are analysed with special focus on the related projects, demonstrators, stakeholders and rated values, e.g., voltage, switching frequency and power. The analysis is concluded with the future trends and challenges regarding the wider implementation of SST technology in the electrical grid.

This paper presents a day ahead optimal dispatch method for smart grids including two-axis tracking photovoltaic (PV) panels, wind turbines (WT), a battery energy storage system (BESS) and electric vehicles (EV), which serve as additional storage systems in vehicle to grid (V2G) mode. The aim of the day ahead schedule is the minimization of fuel-based energy, imported from the main grid. The feasibility of the proposed method lies on the extensive communication network of the smart grids, including sensors and metering devices, that provide valuable information regarding the production of the distributed energy resources (DER), the energy consumption and the behavior of EV users. The day ahead optimal dispatch method is applied on a smart grid in order to showcase its effectiveness in terms of sustainability, full exploitation of DER production and ability of EVs to act as prosumers.

The design of adaptive façades as complex systems that dynamically respond to weather conditions and occupants’ demands is rapidly increasing in modern constructions since they are highly energy efficient. Adaptive Dynamic Building Envelopes (ADBEs) exploit the benefits of technologies that manage the energy and mass transfer between building and outdoor environments actively and selectively. There is a wide range of technologies used in the design of ADBEs that differ from one another in terms of user controllability and the level of how active or passive their technologies are. This paper provides a systematic search in literature on the technologies devised in the ADBEs, specifying the most prevalent practices, and highlights the most cutting-edge research approximations. The analysis shows more than half of the studies use photovoltaics (PVs) in their design. Using mechanical ventilation and heat pumps were the next popular choices. Moreover, approximately half of the studies were carried out using simulation methods alone, whereas only 13% of studies couple simulations with experimental work. This highlights a clear gap in coupling digital modeling and simulation software with practical field testing and successful mass production.