Reliability and Operational Performance of Electric Power Systems Incorporating an Increased Penetration of Renewable Energy Sources and Storage Facilities

National Technical Univ. of Athens
School of Electrical and Computer Engineering, Greece
E-mail:dialynas@power.ece.ntua.gr

The operational procedures that are being applied in the electric power systems have shown significant changes during the last years due to the increased penetration of Renewable Energy Sources (RES), such as wind parks and photovoltaic systems. The main achievement of these facilities is the low emission performance of power systems being obtained but certain concerns exist about the impact on their reliability and operational performance. This fact together with certain generation issues that concern the commissioning of new and the decommissioning of old power plants, have resulted in certain aspects that need to be considered thoroughly for assuring the reliable supply of electric energy to the customers and the ability of the systems to respond to any disturbances that may occur.

The power systems are designed to handle significant variability in load demand requirements and, for this purpose, appropriate control and protection devices may be used that enable the transmission systems to accommodate bigger variations in load and voltage, such as Flexible AC Transmission Systems (FACTS), bulk storage systems and “virtual power plants”. However, additional operational procedures need to be performed by the System Operator in order to manage the variability of RES generation (mainly wind power generation).

The most common one concerns the spinning reserve capacity that must be available in appropriate generating units when a sudden decrease of power generation occurs while a reverse (or negative) reserve capacity needs also to be available when an increase occurs. The required reserve capacities are usually determined by applying various deterministic criteria that take into account certain operating features of the power systems, such as the wind penetration level and the installed capacity of the conventional generating units. One of the most commonly used criteria (Criterion 1) defines reserve capacity levels that are equal to the output of the largest unit in operation, while, in certain power systems, an alternative criterion may be applied (Criterion 2) that considers a spinning reserve capacity being equal to either a certain percentage of the system load demand (i.e. 10%) or a constant capacity value. An additional amount of spinning reserve capacity may be required in power systems with a relatively high level of wind power penetration that covers the sudden reduction events of wind power generation. For this purpose, an additional security criterion (Criterion 3) is applied, concerning the respective hourly variations, that is combined with the previously mentioned criteria while various methods can be used for deducing an appropriate capacity level incorporating this criterion into the system operation. All these system features and the respective operational procedures being applied may affect significantly the system operational performance and the effective use of the RES generation facilities (mainly wind parks). Therefore, in order to maximise the absorption of the RES generation in the systems, it is required to determine all the possible reduction events of wind power generation being occurred so that all the necessary actions will be applied.

The purpose of this presentation is to describe computational probabilistic techniques that have been developed for assessing the reliability and operational performance of power systems that incorporate increased penetration levels of RES generation and storage facilities. These techniques are based on the Monte – Carlo sequential simulation approach and simulate realistically the stochastic nature of the RES facilities. An appropriate set of indices is calculated for quantifying the system performance. A number of alternative case studies are described representing various operational schemes of a typical power system based on the Greek interconnected power system. These schemes include different planning features and operating conditions, such as different criteria for spinning reserve requirements and various wind penetration levels. The obtained results of the indices are presented and compared in order to examine their impact on the system operation.

Biography: Evangelos N. Dialynas received the Diploma in electrical engineering from National Technical Univ. of Athens (NTUA), Athens, Greece, in 1975 and the M.Sc. and Ph.D. degrees from the Univ. of Manchester Institute of Science and Technology, Manchester, United Kingdom, in 1977 and 1979 respectively.
He is presently a Professor in electric power systems at the School of Electrical and Computer Engineering at NTUA and the Director of the Postgraduate Programme “Production and Management of Energy Systems”. His teaching and research interests include various subjects such as reliability modeling and evaluation, power system probabilistic assessment, power system operation in the framework of the competitive electric energy market, regulatory issues, impact of high penetration of renewable energy sources on the reliability and operational performance of interconnected and isolated power systems, modeling of storage facilities, modeling of smart grids, power quality indices and computer applications of power systems. As a result of his research activities, he has written more than 70 papers published in international technical journals after review and more than 120 papers presented in various international conferences and published in their proceedings.
Prof. E. Dialynas is a member of the Technical Chamber of Greece, a senior member of IEEE and a member of IET. He is also a distinguished member of CIGRE and a member of the Administrative Council of CIGRE.