Thermal energy storage for grid applications: Current status and emerging trends

Thermal 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

Automated echocardiographic detection of heart failure with preserved ejection fraction using artificial intelligence

Background: Detection of heart failure with preserved ejection fraction (HFpEF) involves integration of multiple imaging and clinical features which are often discordant or indeterminate. Objectives: We applied artificial intelligence (AI) to analyze a single apical four-chamber (A4C) transthoracic echocardiogram videoclip to detect HFpEF. Methods: A three-dimensional convolutional neural network was developed and trained on A4C videoclips to classify patients with HFpEF (diagnosis of HF, EF≥50%, and echocardiographic evidence of increased filling pressure; cases) versus without HFpEF (EF≥50%, no diagnosis of HF, normal filling pressure; controls). Model outputs were classified as HFpEF, no HFpEF, or non-diagnostic (high uncertainty). Performance was assessed in an independent multi-site dataset and compared to previously validated clinical scores. Results: Training and validation included 2971 cases and 3785 controls (validation holdout, 16.8% patients), and demonstrated excellent discrimination (AUROC:0.97 [95%CI:0.96-0.97] and 0.95 [0.93-0.96] in training and validation, respectively). In independent testing (646 cases, 638 controls), 94 (7.3%) were non-diagnostic; sensitivity (87.8%; 84.5-90.9%) and specificity (81.9%; 78.2-85.6%) were maintained in clinically relevant subgroups, with high repeatability and reproducibility. Of 701 and 776 indeterminate outputs from the HFA-PEFF and H2FPEF scores, the AI HFpEF model correctly reclassified 73.5 and 73.6%, respectively. During follow-up (median [IQR]:2.3 [0.5-5.6] years), 444 (34.6%) patients died; mortality was higher in patients classified as HFpEF by AI (hazard ratio [95%CI]:1.9 [1.5-2.4]). Conclusion: An AI HFpEF model based on a single, routinely acquired echocardiographic video demonstrated excellent discrimination of patients with versus without HFpEF, more often than clinical scores, and identified patients with higher mortality

Orthodoxy and ecumenism: towards active metanoia

The questions that underlined and motivated this research project have been: Why do members of the Orthodox Church participate in the ecumenical movement, and how can they negotiate an involvement in ecumenical contexts, together with their non-Orthodox counterparts – considering that the Orthodox see their Church as the one and only true Church? The background of this exploration has been the context of hostility and prejudice, which some groups within the Orthodox Church have manifested towards ecumenical encounters, which has marred and obstructed a genuine dialogue between the Orthodox and the non-Orthodox Christian communities. This project is based on the analysis of sources from contemporary Orthodox and Western theological milieux. It has interpreted these sources with a view to determining how they interact and coalesce into visions that inform the relationship between Orthodoxy and ecumenism. The interpretative stage of the discussion reveals the necessity of delineating paradigms for Orthodoxy and ecumenism that will enable future ecumenical interactions of greater efficiency and integrity. Such paradigms outline a vision wherein central aspects of Orthodox theology would move away from a paradigm of ‘passive conservatism’ to one of ‘active metanoia’ (transformation), while ecumenism would come to be seen as a perennial process and intrinsic aspect of theology. These vantage points define a new Orthodox vision of ecumenism as an ever-enlarging catholicity, by bringing back to the fore the common theological core of both Orthodoxy and ecumenism

Experimental Indicators of Current Unbalance in Building Integrated Photovoltaic Systems

Unbalance of the three-phase currents in photovoltaic (PV) systems may depend on structural aspects of the installation, the effect of partial shading, or both. In this paper, a number of unbalance indicators are calculated starting from data measured during experimental analyses on a real building-integrated PV system representing different types of unbalance. Detailed information is obtained from indices identifying the balance and unbalance components also in the presence of waveform distortion. These indices extend the current definitions of unbalance given in the power quality standards. The results show that the unbalance cannot be considered negligible even without single-phase inverters and is more significant if non-linear loads add a contribution to both harmonic distortion and unbalance seen from the distribution transformer

Long-Term Solar Irradiance Forecasting

The 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

Dynamic Thermal Rating of Electric Cables: A Conceptual Overview

This 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