Reliability evaluation of generating systems

Wind energy sources are intermittent in nature. Even at a site with a high wind power potential, the wind can blow and stop frequently in a short period of time and can be totally absent when it is most needed. The amount of wind energy that can be absorbed by an electric power system at a particular time can be greatly limited as the available conventional units may not be able to respond quickly to the changes created by wind power fluctuations. In order to maintain the system stability, wind energy dispatch is usually restricted. Although wind power output at any time is not controllable, the power output from a wind park can be available when needed if energy storage is available. There has been significant work on large-scale integration of wind power into power systems [5, 6]. The value of bulk energy storage combined with standing reserve provided from conventional generation is investigated in [7]. Reference [8] presents an approximate technique for the reliability evaluation of power systems including wind energy conversion system (WECS) and energy storage. A probabilistic method for the calculation of reliability indices of a stand-alone wind energy system in parallel with a storage battery is presented in [9]. A general probabilistic model of a WECS containing wind turbine generator 783

Published in IET Generation, Transmission & Distribution Received on 8th September 2008 Revised on 17th March 2009 doi: 10.1049/iet-gtd.2008.0639
& The Institution of Engineering and Technology 2009

(WTG) units and battery storage is presented in [10]. Reference [11] presents a technique utilising Monte Carlo simulation (MCS) for the reliability evaluation of generating systems including wind and energy storage. This method incorporates an energy storage model appropriate for sequential simulation, and considers the chronological random nature of wind speed. This paper introduces a realistic energy storage model that can include the energy storage operating constraints for reliability evaluation using the MCS method. The model is developed for adequacy studies and not intended for security assessment. Various system operation and stability constraints important from an adequacy aspect are incorporated in the model. Possible strategies of wind farm operation and energy storage are presented and compared by evaluating the reliability benefit from energy storage and the amount of wind energy that can be stored. The studies are conducted by adding wind power to a small test system known as the Roy Billinton Test System (RBTS) [12]. The results from a wide range of studies considering variations in key factors, such as wind farm location, wind penetration level, energy storage capacity, energy storage operating constraints and wind energy dispatch restrictions, are also presented. An acceptable strategy for wind farm operation and energy storage for system operators and wind farm owners is illustrated, and valuable information is provided. the seasonal and diurnal distribution of the actual wind speed and therefore can be used in the reliability studies of power systems including WECS [15]. Wind speeds for a selected wind farm site are simulated using the site-specific ARMA model, which is mathematically expressed as yt ¼ f1 ytÀ1 þ f2 ytÀ2 þ Á Á Á þ fn ytÀn þ at À u1 atÀ1 À u2 atÀ2 À Á Á Á À um atÀm (1)
ISSN 1751-8687
Reliability evaluation of generating systems containing wind power and eneR. Billinton
Department of Electrical and Computer Engineering, University of Saskatchewan, Saskatoon, Canada E-mail: poh591@ask.ca
1
Introduction
Wind power generation in electric power systems will increase considerably throughout the world in the near future. Many countries have implemented or are in the process of implementing policies to promote renewable energy, such as a Renewable Portfolio Standard (RPS). Acceptance of the RPS is a commitment to produce a specified percentage of the total power generation from renewable sources within a certain date. Wind power is the fastest growing source to meet these renewable energy targets [1]. In Canada, Ontario, Nova Scotia and Prince Edward Island have committed to generate 10, 5 and 15%, respectively, of the total electricity production from renewable energy sources by the year 2010 [2]. Renewable energy policies, such as the Fixed Feed-in-Tariffs in Germany, Denmark and Spain [1] and Renewable Obligation in the UK [3], have driven the development of wind power in these countries. Large-scale integration of wind power in an electric grid can produce large power fluctuations, and result in a high risk in providing a continuous power supply [4]. This risk can be reduced by storing energy and using it during low wind or no wind periods. IET Gener. Transm. Distrib., 2009, Vol. 3, Iss. 8, pp. 783 – 791 doi: 10.1049/iet-gtd.2008.0639