1,720,973 research outputs found
Thermal energy storage for grid applications: Current status and emerging trends
Full text linkThermal energy systems (TES) contribute to the on-going process that leads to higher integration among different energy systems, with the aim of reaching a cleaner, more flexible and sustainable use of the energy resources. This paper reviews the current literature that refers to the development and exploitation of TES-based solutions in systems connected to the electrical grid. These solutions facilitate the energy system integration to get additional flexibility for energy management, enable better use of variable renewable energy sources (RES), and contribute to the modernisation of the energy system infrastructures, the enhancement of the grid operation practices that include energy shifting, and the provision of cost-effective grid services. This paper offers a complementary view with respect to other reviews that deal with energy storage technologies, materials for TES applications, TES for buildings, and contributions of electrical energy storage for grid applications. The main aspects addressed are the characteristics, parameters and models of the TES systems, the deployment of TES in systems with variable RES, microgrids, and multi-energy networks, and the emerging trends for TES applications
Long-Term Solar Irradiance Forecasting
Full text linkThe past decade has been characterized by considerable increase of the penetration level of solar photovoltaic systems in energy systems throughout the world. At the same time, solar irradiance has an intermittent nature. Thus, the efficient management of existing and new solar photovoltaic systems requires an accurate forecasting system of solar irradiance. The purpose of the paper is to develop and validate a long-term forecasting model for solar irradiance. This purpose is achieved by applying of clustering method and standard mathematical statistics. The modeling includes pre-processing of historical data used for forecasting and post-processing of the types of days resulted from the clustering analysis. Historical data include solar irradiance and sky coverage by clouds. Pre-processing supposes bi-normalization of the solar irradiance in time and amplitude, as well as clustering, and post-processing supposes denormalization to get the actual values. Error metrics and confusion matrix indices have been used to assess the accuracy of the proposed forecasting method. Four different model variants have been considered, which differ by pre-processing approach of initial data. The comparison of these model variants shows that for better accuracy it is required to use seasonality aspects of solar irradiance. The main result of paper is the created model, which can be used for the solar irradiance forecast with acceptable accuracy for this type of forecasting and for generating of the types of days for different annual scenarios. The importance of paper results consists in the possibility of using of these scenarios for feasibility assessment of the solar photovoltaic system and identifying of the best solutions for their integration in the energy system
Characterization of unbalanced and distorted distribution systems from experimental data
No full textKnowledge Discovery from the Statistical Analysis of On-Site Photovoltaic System Data
Full text linkThis paper presents some novel ideas and findings to assist data analysts and operators in discovering specific situations from the analysis of photovoltaic data collected in the field. The daily time series of solar irradiance and active power production are transformed into probability distribution functions (PDFs), then the skewness of the PDF is assessed as a potential indicator of orientation of the PV system in directions different from South. The relevant PDFs corresponding to bright days are identified by applying a clustering procedure. The combined calculation of skewness and correlation between solar irradiance and active power data is also used to discover specific cases in which high shadowing occurs in particular days of the year and at particular times. The analyses are carried out by using data collected on-site in PV systems installed at different locations
A tutorial time-frequency analysis application to the study of distribution system perturbations
No full textDynamic Thermal Rating of Electric Cables: A Conceptual Overview
Full text linkThis paper provides a tutorial overview of dynamic thermal rating concepts and methods applied to electric cables. Although most analytical developments and models have been proposed many years ago and are covered by IEC Standards, numerous recent developments suggest refinements to these models and enhanced applications. In particular, on the modelling side, the latest contributions refer to analytic models, variants of the equivalent circuit of the soil to be used in finite difference methods, applications of 2D and 3D finite element methods, and definitions of simplified models and equations validated with respect to the results obtained from FEM simulations and experimental measurements. On the methodological side, the overview also covers optimal cable sizing, reliability aspects, risk estimation, and forecasting of dynamic cable rating
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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