Reliability Evaluation of Micro-grids Containing PV System and Hydropower Plant

This paper presents the reliability evaluation for a microgrid composed of conventional generators (CGs), a photovoltaic (PV) system, and a small hydropower plant (HPP). The PV system has an intermittent output and the HPP output is limited depending on several constraints. Therefore, their reliability evaluation should be performed according to the CGs. This paper proposes a methodology to evaluate the reliability of the microgrid based on Monte Carlo simulations. To this end, a simple operational strategy for the HPP and reliability models for each component of the grid are introduced. By the operational strategy consisting of two stages, the HPP would be operated to generate power whenever water stored in the reservoir exceeds a certain threshold (called volume reference) or to discharge extra water when it is beyond the maximum volume of the reservoir. To demonstrate the proposed methodology, a case study is performed according to various volume references, and the results are obtained in terms of several reliability indices. Further, the appropriate volume reference is determined considering a trade-off relationship between the reliability and economics aspects.This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. NRF-2017R1A2B1007520)

Planning of a Hybrid Energy System Connected to a Distribution System

Global warming and excessive use of depletable energy resources are considered as some of the most serious problems that need to be solved. As a response, renewable energy sources (RES) have been gaining an increasing importance in recent years. The electrical power generated from RES tends to be fluctuating due to intermittency of wind speed and solar radiation which may result in frequency and voltage deviations in the grid as well as loss of the capacity to serve the load. Distributed generation of wind-photovoltaic hybrid systems connected to energy storage (ES) is proposed to overcome the variability of RES. However, the high cost of the equipment for such systems is also a challenge. In this dissertation, planning of a hybrid wind-photovoltaic energy system combined with ES connected to a distribution system is described. The planning procedure is done in two different configurations. In the first one, the objective is to find optimal ES size for a wind farm. The objective function measures the economic benefit gained from selling of the dispatched power to the grid against the cost of ES. The result of the optimization gives the optimal size of ES. A probability distribution function (pdf) is created to represent the optimal size of ES for the planning horizon and then a case study for one year is conducted to illustrate the proposed method. For the second configuration, optimization techniques which use linear programming, two stage stochastic programming and scenario aggregation are deployed in order to find the optimal plan for the hybrid energy system. The proposed procedure uses historical wind speed, solar radiation, energy market price, and load data to determine the system design. The objective function measures the total annual cost of the proposed system. The results of the optimization procedure give the optimal size for wind farm, solar farm, and ES needed to meet the load requirements, minimize the annual cost, and consider system uncertainties and system reliability

Control of Energy Storage

Energy storage can provide numerous beneficial services and cost savings within the electricity grid, especially when facing future challenges like renewable and electric vehicle (EV) integration. Public bodies, private companies and individuals are deploying storage facilities for several purposes, including arbitrage, grid support, renewable generation, and demand-side management. Storage deployment can therefore yield benefits like reduced frequency fluctuation, better asset utilisation and more predictable power profiles. Such uses of energy storage can reduce the cost of energy, reduce the strain on the grid, reduce the environmental impact of energy use, and prepare the network for future challenges. This Special Issue of Energies explore the latest developments in the control of energy storage in support of the wider energy network, and focus on the control of storage rather than the storage technology itself