1,721,117 research outputs found
Losses Allocated to the Nodes of a Radial Distribution System with Distributed Energy Resources-A Simple and Effective Indicator
Full text linkThis paper presents the effectiveness of exploiting the losses allocated to the nodes of a radial distribution system as an indicator of the impact of the diffusion of distributed energy resources in the network. The calculation of the losses allocated to the nodes is not included in the commercial power flow solvers, even though the implementation of this calculation is simple and the results provide meaningful information. The interpretation of the allocated losses is illustrated in this paper, on the basis of the results obtained on a typical test network under different case studies
Heuristic optimization of electrical energy systems: Refined metrics to compare the solutions
Full text linkMany optimization problems admit a number of local optima, among which there is the global optimum. For these problems, various heuristic optimization methods have been proposed. Comparing the results of these solvers requires the definition of suitable metrics. In the electrical energy systems literature, simple metrics such as best value obtained, the mean value, the median or the standard deviation of the solutions are still used. However, the comparisons carried out with these metrics are rather weak, and on these bases a somehow uncontrolled proliferation of heuristic solvers is taking place. This paper addresses the overall issue of understanding the reasons of this proliferation, showing a conceptual scheme that indicates how the assessment of the best solver may result in the unlimited formulation of new solvers. Moreover, this paper shows how the use of more refined metrics defined to compare the optimization result, associated with the definition of appropriate benchmarks, may make the comparisons among the solvers more robust. The proposed metrics are based on the concept of first-order stochastic dominance and are defined for the cases in which: (i) the globally optimal solution can be found (for testing purposes); and (ii) the number of possible solutions is so large that practically it cannot be guaranteed that the global optimum has been found. Illustrative examples are provided for a typical problem in the electrical energy systems area – distribution network reconfiguration. The conceptual results obtained are generally valid to compare the results of other optimization problem
Impact of the time resolution for data gathering on loss calculation and demand side flexibility
Full text linkAccurate data metering is needed for enabling demand side flexibility and the related services. Sufficient resolution in time of the data gathered is essential to obtain detailed information on how consumers and prosumers use electricity. This paper addresses two specific points concerning the effects of the time resolution on (i) the estimation of the network losses, and (ii) the assessment of the average power peak magnitude and duration. Specific indicators are introduced to estimate the losses and assess the peak power based on the load pattern shape. These effects are analysed based on examples taken from real measurements. The results clearly show that the time resolutions used today (from 15 min to 1 hour) are insufficient to perform effective assessments oriented to enhance demand side flexibility. Interval metering with better resolutions (1 min or less) or innovative technologies such as event-driven energy metering should be used to provide significantly better solutions
Understanding the value of net metering outcomes for different averaging time steps
Full text linkThe installation of distributed energy resources (DER) heavily impacts on the power patterns of the prosumers. In fact, the variability of the generation, together with the technical characteristics of the storage systems, may introduce a huge variety in the shape of the net power curves seen from the point of common coupling (PCC). This leads to completely rethink the definition of the time series required to create homogeneous group of prosumers, for providing useful tools to manage the emerging paradigms in the electricity system, such as energy communities and local energy markets. Moreover, the differences between the local energy production and consumption at the PCC could become hidden, if the local energy management has to be considered as a private decision of the local user. In this case, only net metering (that implies a unique measurement of the net electricity taken from the grid) will be used to evaluate the impact on the network of the net power curves. Hence, new approaches are required to properly measure the electricity exchange at the PCC. This paper addresses how the net metering outcomes depend on the time resolution of the measured data, and how the information taken from net metering can be valued by giving different price rates to positive and negative values. Specific examples are provided to remark the importance of the time resolution to properly characterise the prosumers
High-Quality Load Pattern Reconstruction from Smart Meter Data to Enhance the Assessment of Peak Power and Network Losses
No full textThe solutions recommended by international roadmaps and technical reports on smart metering refer to interval metering with time resolutions higher than 15 min to 1 hour as traditionally used. Based on the characteristics of the users power patterns in distribution networks, this paper shows that in practical cases the resolutions of the traditional metering are not sufficient to assess peak power and network losses effectively. Effective interval metering solutions should have resolutions of one minute or less. Moreover, this paper shows the advantages of assessing the average power peak (amplitude and duration) and estimating the network losses through innovative solutions beyond interval metering, based on event-driven energy metering (EDM). The use of EDM significantly enhances the quality of pattern representation and reduces the amount of data required with respect to high-resolution interval metering. Based on the Pareto analysis of conflicting objectives, a novel procedure to set up the EDM thresholds is presented. The applications shown use real data and refer to a single user, some users connected to a distribution network feeder, and many users connected to a large distribution system. The EDM benefits are quantified using specific indicators that consider energy losses and peak power
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
An Improved Model for AC Power from Grid Connected Photovoltaic Systems and Comparison with Large-Scale Hourly Measured Data
Full text linkThe diffusion of renewable energy sources (RES) can lead to cost reductions for the ancillary services provided to the transmission system operator, in particular, when the RES production can be estimated with appropriate accuracy. This article presents significant improvements to photovoltaic (PV) power conversion models found in the literature for grid-connected PV systems. The refinement of the conversion model is based on public hourly data of irradiance and ambient temperature, referred to the sites of three groups of PV plants, to calculate the hourly average power injected into the grid. The values obtained are compared with the hourly average power measured by the distribution system operator meters on the PV systems. A double-step optimization procedure, based on seasonal analysis, sets up the various parameters in the PV conversion model. The key result is that the deviation between the simulated and measured annual energy is reduced to less than 2%. Moreover, with the proposed model the monthly energy deviations are limited to a few percentage points. This allows for significant improvements in the estimation of the production of grid-connected PV systems
Optimisation of Generation Models for Clusters of Photovoltaic Plants
Full text linkThe present work analyses the actual production profiles of a group of tens of thousands of PV plants. Actual PV generation profiles are represented as hourly average powers gathered from the energy meters measured at the point of common coupling with the grid. After filtering, data cleaning and statistical analysis, reference PV plants are selected for the improvements of the PV generation models. Production profiles are calculated by using literature generation models, with weather data as inputs. An optimisation is performed on the parameters of the literature models to minimise the differences between the cumulative distribution functions of calculated profiles and measured data. The study compares the performance of the different models and shows how the optimisation increases the quality of the calculated profiles
Benefits of on-load tap changers coordinated operation for voltage control in low voltage grids with high photovoltaic penetration
Full text linkThe transformers that connect the Medium Voltage (MV) grid with the Low Voltage (LV) system are classically equipped with tap changers with tap positions variable only at no load. The evolution of the technologies and the increasing needs of controlling the voltage profile in the LV networks require better control capabilities. The use of MV/LV transformers with On Load Tap Changers (OLTCs) is increasing, to provide further control capabilities in LV grids with high penetration of distributed generation. In this paper, centralised voltage control is evaluated by simulating the operation of an OLTC installed inside the MV/LV transformer substation. The goal is to stabilise the voltage at the LV bus of the transformer. It is supposed that the OLTC does not communicate with other devices in the grid; thus, it does not know the voltage levels at the other nodes. At the same time, the distributed PV inverters control the voltage in their grid connection points without any information about the other nodes. The expected benefits of exploiting OLTCs in LV grids with high photovoltaic (PV) penetration are determined through indicators that assess the voltage deviations with energy flows, the global overvoltage or undervoltage persistence, and the overvoltage or undervoltage duration. The results show that the use of an OLTC can help the mitigation of voltage fluctuations, especially limiting the undervoltages. The effectiveness strongly depends on the control parameters, especially the maximum number of daily taps
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