The world’s demand for electrical energy is increasing rapidly while the use of fossil fuels is getting limited more and more by energy policies and the need for reducing the impact of climate change. New sources of energy are required to fulfill the world’s demand for electricity and they are currently found in renewable sources of energy, especially in solar and wind power. Choosing the optimal PV nominal power minimizes the unnecessary surplus of electrical energy that is exported to the grid and thus is not making any impact on the grid more than necessary. Oversizing the PV system according to the Croatian net-metering model results in switching the calculation of the costs to the prosumer model which results in a decrease of the project’s net present value (NPV) and an increase in the payback period (PP). This paper focuses on formulating and solving the optimization problem for determining the optimal nominal power of a grid-connected PV system with a case study for Croatia using multiple scenarios in the variability of electricity production and consumption. In this paper, PV systems are simulated in the power range that corresponds to a typical annual high-tariff consumption in Croatian households. Choosing the optimal power of the PV system maximizes the investor’s NPV of the project as well as savings on the electricity costs. The PP is also minimized and is determined by the PV production, household consumption, discount rate, and geographic location. The optimization problem is classified as a quadratically constrained discrete optimization problem, where the value of the optimal PV power is not a continuous variable because the PV power changes with a step of one PV panel power. Modeling and simulations are implemented in Python using the Gurobi optimization solver.

https://www.mdpi.com/1996-1073/14/6/1746/pdf

A Quadratically Constrained Optimization Problem for Determining the Optimal Nominal Power of a PV System in Net-Metering Model: A Case Study for Croatia

The paper shows a method of optimizing local initiatives in the energy sector, such as energy cooperatives and energy clusters. The aim of optimization is to determine the structure of generation sources and energy storage in order to minimize energy costs. The analysis is carried out for the time horizon of one year, with an hourly increment, taking into account various RES (wind turbines (WT), photovoltaic installations (PV), and biogas power plant (BG)) and loads (residential, commercial, and industrial). Generation sources and loads are characterized by generation/demand profiles in order to take into account their variability. The optimization was carried out taking into account the technical aspects of the operation of distribution systems, such as power flows and losses, voltage levels in nodes, and power exchange with the transmission system, and economic aspects, such as capital and fixed and variable operating costs. The method was calculated by sixteen simulation scenarios using Mixed-Integer Linear Programming (MILP).

The Impact of Energy Storage along with the Allocation of RES on the Reduction of Energy Costs Using MILP

The European electrical power system is facing a number of challenges These challenges are determined by the currently observed and expected future directions of the development of European power systems Identification of these challenges was performed In the analysis, different perspectives of perception of power system as a reference point were assumed The analysis included not only technical aspects, but also formal and legal factors, social expectations, economic challenges, security requirements, energy independence, etc This allowed identifying the most important factors They may change the model of operation of power systems The publication focuses on the characterization of the most important factors identified as these which may cause the necessity to change the current approach to power system protection

Diagnosis of challenges for power system protection – selected aspects of transformation of power systems

the an integrated munities and municipalities depending on their urbanization and offers the use of conceptual analy tical model of generation-consumption. A number of normative and organizational-institutional proposals on the standardization of energy-efficiency improvement processes are provided. Analy sis of the energy efficiency of communities can be modeled at the conceptual level with the study using an analytical model: a) energy-efficiency factors of this model, financial instruments for its effective functioning as a mechanism of interest budget revenues and specialized funds functional dependence of the target function of the energy generation-consumption model, taking into account the generation methods and the main consumers at the appropriate levels; b) the risks and shortco-mings of this process, which propose a number of regulatory and institutional changes to improve the effectiveness of effective energy efficiency policies of communities and energy security of the state on the basis of energy cooperation and organization of the biofuel exchange. The model of organization and functioning of the cooperative for generation and consumption of solar energy, which is based on the regulatory framework, is represented as a model structural and functional solution. This allowed the development of scientific and applied recommendations for improving the legal provisions, which would allow the community to become an effective player in the wholesale energy market, selling it at a “green” tariff.

/pdf/a-conceptual-analytical-model-for-the-decentralized-energy-dstuc7d0.pdf

A conceptual analytical model for the decentralized energy-efficiency management of the national economy

1. The article presents the role that V2G technology could play in the energy community. Its potential for the energy community needs will be estimated on the basis of analytical and experimental analysis (case study results). Barriers limiting the possibility of widespread use of such solutions will also be indicated.

Vehicle to Grid as an Important Element of the Energy Community

Until now, electricity users are being connected to the LV networks by a physical electricity consumption point. In this point an electricity meter is assigned to each and every one user. A given user may use the flowing electricity only by the meter assigned to him at the consumer-specific point. This is a significant limitation in the non- restricted access to the power network. The Authors come with an idea to eliminate this restriction. The paper presents the concept of virtualization of a physical point of electric power consumption in a LV network. The proposed novel idea of using the power network will ensure the expected non-restricted access to any point of the power network for users. This seems particularly important nowadays and is dictated by the growing expectations of users’ mobility. The presented concept is dedicated especially to networks in the form of clusters (cooperatives) or energy clouds. Its application in LV networks will significantly simplify the users’ use of the power infrastructure, also in the aspect of financial settlements. This should also contribute to the rapid significant development of electro- mobility.

/pdf/the-idea-of-non-restricted-use-of-lv-networks-by-electricity-4ugbd5o9g5.pdf

The idea of non-restricted use of LV networks by electricity consumers, producers, and prosumers

The Network Code for HVDC systems introduces a requirement for such systems to remain in operation in an AC network during short-circuits. This requirement (among others) is determined by a time curve of a minimum voltage in HVDC connection point. The HVDC system is not allowed to be turned-off while the voltage value exceeds the values of the curve, however the HVDC system in LCC technology does not meet this requirement. The Network Code introduces the possibility of blocking the LCC systems. After the LCC system is blocked it stops transmitting the power, which prevents the LCC system from being turned off during a short-circuit in the network but results in a lack of power exchange between the network and the LCC system. Therefore, the authors developed a proposal to limit the power level being transmitted by the LCC system, thus there is no necessity to block the LCC system operation. The simulation research carried out clearly indicate the validity of this idea. In addition, the authors presented the concept of an automation system that adaptively adjusts the scale of the LCC system power level reduction to change the network operating conditions during a short-circuit in the network. The operation of this automation system is presented for the practical LCC system model installed in the Polish Power System.

/pdf/an-alternative-approach-to-provisions-of-the-network-code-on-56wmzulas4.pdf

An alternative approach to provisions of the Network Code on blocking HVDC LCC systems during short-circuits in AC network

The paper conducts a literature review of applications of autoregressive methods to short-term forecasting of power demand. This need is dictated by the advancement of modern forecasting methods and their achievement in good forecasting efficiency in particular. The annual effectiveness of forecasting power demand for the Polish National Power Grid for the next day is approx. 1%; therefore, the main objective of the review is to verify whether it is possible to improve efficiency while maintaining the minimum financial outlays and time-consuming efforts. The methods that fulfil these conditions are autoregressive methods; therefore, the paper focuses on autoregressive methods, which are less time-consuming and, as a result, cheaper in development and applications. The prepared review ranks the forecasting models in terms of the forecasting effectiveness achieved in the literature on the subject, which enables the selection of models that may improve the currently achieved effectiveness of the transmission system operator. Due to the applied approach, a transparent set of forecasting methods and models was obtained, in addition to knowledge about their potential in the context of the needs for short-term forecasting of electricity demand in the national power system. The articles in which the MAPE error was used to assess the quality of short-term forecasts were analyzed. The investigation included 47 articles, several dozen forecasting methods, and 264 forecasting models. The articles date from 1997 and, apart from the autoregressive methods, also include the methods and models that use explanatory variables (non-autoregressive ones). The input data used come from the period 1998–2014. The analysis included 25 power systems located on four continents (Asia, Europe, North America, and Australia) that were published by 44 different research teams. The results of the review show that in the autoregressive methods applied to forecasting short-term power demand, there is a potential to improve forecasting effectiveness in power systems. The most promising prognostic models using the autoregressive approach, based on the review, include Fuzzy Logic, Artificial Neural Networks, Wavelet Artificial Neural Networks, Adaptive Neurofuse Inference Systems, Genetic Algorithms, Fuzzy Regression, and Data Envelope Analysis. These methods make it possible to achieve the efficiency of short-term forecasting of electricity demand with hourly resolution at the level below 1%, which confirms the assumption made by the authors about the potential of autoregressive methods. Other forecasting models, the effectiveness of which is high, may also prove useful in forecasting by electricity system operators. The paper also discusses the classical methods of Artificial Intelligence, Data Mining, Big Data, and the state of research in short-term power demand forecasting in power systems using autoregressive and non-autoregressive methods and models.

/pdf/a-review-of-auto-regressive-methods-applications-to-short-3pcthppz.pdf

Rafał Czapaj

Papers

The idea of non-restricted use of LV networks by electricity consumers, producers, and prosumers

An alternative approach to provisions of the Network Code on blocking HVDC LCC systems during short-circuits in AC network

A Review of Auto-Regressive Methods Applications to Short-Term Demand Forecasting in Power Systems

Koncepcja procedury doboru zaczepu przesuwnika fazowego włączanego do sieci elektroenergetycznej