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The future power system must provide electricity that is reliable and affordable. To meet this goal, both the electricity grid and the existing control system must become smarter. In this paper, some of the major issues and challenges of smart grid’s development are discussed, and ongoing and future trends are presented with the aim to provide a reader with an insight on the relevant research topics, challenges and actual engineering tasks in smart grids. The focus areas of this review study are distributed generation, microgrids, smart meters’ deployment, energy storage technologies, and the role of smart loads in primary frequency response provision. The exploration of smart grid technologies and distributed generation systems has been accomplished, and a general comparison of the conventional grid and a future smart model is included. The issue of increasing penetration of renewable energy sources to the power system and posers related to the integration of distributed generation are also presented.

To reduce emissions worldwide, decarbonization has also affected for power engineering and its conventional methods of power generation, distribution, and transmission. This fact affects not only the production of power and supply itself, but also other parts related to it, namely systems for the protection of electricity generation facilities and the location of faults in distribution networks and transmission systems. Is this new technology of renewable energy sources (RES) mastered enough to be able to replace traditional methods of energy generation reliably and safely? If we can answer the previous question, we could proceed to the next phase of putting these technologies into practice, considering the actual state of distribution networks and transmission systems. The aim of the article will be to evaluate the current state of systems and production sources of electricity in the Slovak Republic and to provide a better insight and suggestions for rebuilding current networks on a smart grid. The proposals will also include models of some RES in the Matlab/Simulink software.

The effect of slurry mixing in an anaerobic digester on biogas production was intensively studied in the last few years. This subject is still debatable due to fact that this process involves three phases, solid-gas-liquid, along with the involvement of microbes during biochemical reactions, which are highly vulnerable to changes in hydrodynamic shear stresses and mixing conditions. Moreover, the complexity in the direction of optimization of mixing magnifies due to the implication of both fluid mechanics and biochemical engineering to study the effect of mixing in anaerobic digestion (AD). The effect of mixing on AD is explored using recent literature and theoretical analysis, concentrating on the multi-phase and multi-scale aspects of AD. The tools and methods available to experimentally quantify the function of mixing on both the global and local scales are summarized in this study. The major challenge for mixing in an anaerobic digester is to minimize dead zones and maintain uniform distribution of viscosity and shear at low mixing intensities without disrupting the microbial flocs and syntrophic relationships between the bacteria during the AD process. This study is a critical analysis of various techniques and approaches adopted by researchers to evaluate the effectiveness of mixing regimes and mixing equipment. Most studies describe biogas production performance and hydrodynamic characteristics of the digesters separately, but the evaluation of mixing requires interdisciplinary experts, which include mechanical engineers, microbiologists and hydrodynamic experts. Through this review, the readers will be guided through intensive literature regarding agitation, the best possible way to scrutinize the agitation problems and the approach to answering the question “why is the optimization of mixing in an anaerobic digester still a debatable subject?”.

This article aims to present some opportunities for improved solar energy utilization by raising the share of renewables in energy generation in the Visegrád Countries (Poland, Czech Republic, Slovakia, and Hungary). The analysis is based on the status of the renewable energy targets in the member countries and their future possibilities. This paper derives input through a thorough investigation of independent data, government policies, European Commission reports, and other data available online with free access. The analysis is processed by focusing on Hungary, as a country with various possible facets of solar energy demand and supply in the region. The assessment methodology is in the context of a geographical map, technical regression analysis, temperature distribution profiles, and the relative trends of solar potential in Hungary. The country currently has ten solar power plants with more than 10 MWp, and five remarkable plants under 10 MWp capacity spread over Hungary. The analysis on geographical aspects clubbed with technical and solar affecting parameters was carried out to harvest the sustainable potential of solar energy in the region. This study attempts to establish a relationship between the current and future prospects of solar energy in Hungary as a nation, and as part of the Visegrád countries, based on assessment for a sustainable future.

This paper discusses the problem of reliability of the Polish medium voltage power lines. It presents the benchmarking of power lines and values of SAIDI. The probability density distribution of the medium voltage lines length as well as selected indicators of the MV power lines reliability, being operated by the distribution companies under test, are also introduced. The analysis is based on the actual MV lines and uses the nonparametric method of kernel density estimation.

Paper deals dynamic calculations. It presents two cases for real black start tests and shows their dynamic simulation.

This paper deals with the analysis of the transient phenomena caused by the operation of the electric arc furnace in the 22 kV network, describes the causes of their origin and proposes the possibilities of their reduction with regard to the fulfillment of the quality of electric energy. In particular, it focuses on assessing the short-term flicker rate and the use of the STATCOM device to reduce it. The analysis and subsequent reducing of transient phenomena impact was realized by simulations using the Matlab / Simscape Power Systems tool. The obtained results were evaluated in accordance with the valid European standards and legislation of the Slovak Republic.

This paper deals with the impact of a low voltage smart grid on the distribution system. The last European directives 2014/94 / EU, 2009/28/EC and 2010/31 / EU, bring new problems to solve for distribution system operators. The existing networks of distribution systems are not prepared to fulfill these criterions. Paper shows results related with application of this new directives on existing distribution systems.

The world demands a smart and green future in every sector, which directly corresponds to increases in electrical energy demand one way or another. It is unfeasible to attain future energy demand with the present electrical infrastructure. That means more research and development is required. Future energy sources should be intermittent, and, in addition, the energy sector should be more inwards for distributed energy generation with demand side control. In such cases, the smartest and most autonomous system would be essential to deliver an adequate power supply with all electrical properties. A real-time monitoring and control system with a self-healing infrastructure is a forthcoming desideratum. By accepting these challenges, we have designed a smart street. The basic idea of the smart street is presented in this paper as a landing page, the paper is more focused on emphasizing information regarding the electrical energy flow algorithm for the household, street, and street battery storages. This algorithm is helpful for two-way energy flow and the automatic detection of islanding and the grid connection mode. It will be not only helpful for the users but to the utility as well.

One way of handling short-time short-circuits without causing equipment failure is the management of the reclose function integrated into smart switchboard which is described in this article. Due to the cost of the application, the optimal placement of such equipment must be well-planned. During the planning of the placement optimization of a low-voltage electricity network quality, the increase of the consumer supply security must be considered along with the best economic utilization. The research presented in this article aims to introduce a new special decision support methodology calculated with these variables. The management of smart switchboard (SSB) tool installation into low voltage (LV) network was investigated. The selection of the placement nodes is based on the complex investigation of the network characteristics. Investigation is performed by empiric analysis. This method can support the power companies to make the optimal decision. The presented new device can have outstanding importance for the electric industry and for further research as no testing results of such investigations have been published yet.

Paper deals with short circuit calculations. It compares results of three different tools for short circuit currents calculation.

The increased demand for power transfer in combination with environmental and economic issues which set constraints to building new lines, force the implementation of new technologies into the existing system in order to improve its power capability. This paper investigates the use of specific FACTS devices and WAMS systems to maximize total transfer capability generally defined as the maximum power transfer transaction in Central-East-Europe power system. Optimal allocation and control of these devices will be very important for TSO or other power market regulators. Effectiveness, optimal allocation and utilization of phasor measurement units (PMUs) for different types of FACTS devices designed for power flow control and increasing transfer capacity were investigated. Paper also compares the economic aspects of these devices.

This paper deals with the solution of transient phenomena during the connection of the photovoltaic power plants. There was investigated the impact of the failure of current protection for renewable energy sources during the network disconnection. There was verified the possibility of network operation during the islanding operation. Failure of network protection represents the significant hazard for employees of distribution system operator so it is necessary to solve the accurate current and voltage values during the connection of particular renewable energy sources.

This article deals with the analysis of a day-ahead generation diagram in specific part of a power network with renewable energy sources. As a renewable energy source a photovoltaic power plant was chosen. Input data for a day-ahead analysis was obtained from the database of previous measurement that was realised on the existing configuration in off-grid network at the department of authors. The simulation network was created in Matlab/Simscape Power System environment that consisted of rotating generators (for regulation of generated power due to fluctuated power generation from photovoltaic sources) and photovoltaic power plant of variable energy generation and loads. The results refer to a necessity to consider the previous measured data of the weather for prediction of future expectation of a day-ahead load diagram.