Impact of correlation on reserve requirements of high wind-penetrated power systems Shahin Riahinia, Ali Abbaspour, Mahmud Fotuhi-Firuzabad ⇑ , Moein Moeini-Aghtaie Department of Electrical Engineering, Sharif University of Technology, Tehran, Iran article info Article history: Received 9 July 2014 Received in revised form 8 May 2015 Accepted 9 May 2015 Available online 6 June 2015 Keywords: Adequacy assessment Correlation Static reserve Wind farm Wind speed and load coincidence abstract This paper investigates the effects of two important factors, i.e., correlation of wind farms output with load and wind speed coincidence in determining the required static reserve in a high wind-penetrated power system. To this end, it suggests an analytical approach to involve the effects of these two factors in probabilistic analytical multi-state models of wind farms output generation. Based on an optimization framework with the objective of reaching the desirable level of correlation, the key idea is to calculate some joint probabilities for equivalent models of wind farms. As a result, these models become compat- ible with the ones for conventional generation units in adequacy studies of power systems. The proposed analytical approach, then, continues with evaluating the reliability level of power systems exactly and also practically employing these multi-state models once dealing with wind farms at multiple locations. The proposed analytical approach is applied to the modified IEEE-RTS and the obtained results and dis- cussions offered demonstrate the unavoidable effects of these important factors (load and wind speed coincidence) in real world applications. Ó 2015 Elsevier Ltd. All rights reserved. Introduction IND energy as a promising alternative for power generation is expected to make a significant contribution in future power sys- tems. Facing with environmental and energy security concerns, many countries around the world are employing supportive poli- cies aimed to increase the share of wind power in generation sector of power systems. Consequent upon these supportive policies, wind power installed capacity reached 282.5GW in 2012 [1]. In fact, 2012 was also a record-breaking year for worldwide wind power installations, with 44,000 MW installed and total capacity exceeding 280,000 MW. As a result, more than 80 countries now receive a portion of their electricity from wind power [1]. This environmentally-friendly source of energy, however, owns an unpredictable and intermittent nature which in turn results some impacts on technical and financial aspects of power systems. To properly investigate the pros and cons of wind energy utiliza- tion in power systems, there has been significant activities in the literature addressing these various issues [2–4]. Among them, reli- ability assessment of power systems including wind farms has widely been studied (see [4,5] as examples). Once the contribution of wind energy in generation sector of power system increases, many new factors needs to be considered in reliability evaluation of power systems including the wind power penetration level, the installed capacity of wind farms, the correlation between out- put generation of wind farms with the others and also load and wind farms output generation coincidence. This paper focuses on the impacts of wind farms output correlation with the other ones and also load and wind farms output coincidence in reliability studies of power systems. In this regard, at first, we need to develop an appropriate model for wind farms output generation. Employing this model, power system planners should be able to easily consider the effects of cor- relation in adequacy assessment of power systems. Sequential Monte Carlo simulation (SMCS) approach has been used to model wind farms output generation in adequacy analysis of wind-penetrated power systems [4,6]. This method is the most accurate one to evaluate adequacy studies of power systems incor- porating wind energy. The computational burden of this method and a long history of hourly wind speed data requirement, how- ever, threaten its practicality, specially, when applied to large-scale systems [7]. In response, some authors in [4,5] tried to preset an analytical model for wind farm output generation similar to the ones intro- duced for conventional units. These models can easily lend the http://dx.doi.org/10.1016/j.ijepes.2015.05.026 0142-0615/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Room 621 East, Electrical Engineering Department, Sharif University of Technology, Azadi Ave., Tehran, Iran. Tel.: +98 2166165921. E-mail addresses: shahinriahinia@gmail.com (S. Riahinia), abbaspour@sharif.edu (A. Abbaspour), fotuhi@sharif.edu (M. Fotuhi-Firuzabad), mmoeini@ee.sharif.edu (M. Moeini-Aghtaie). Electrical Power and Energy Systems 73 (2015) 576–583 Contents lists available at ScienceDirect Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes