Pumped-storage unit commitment with considerations for energy demand, economics, and environmental constraints M.E. Nazari a , M.M. Ardehali a, * , S. Jafari b a Energy Research Center, Department of Electrical Engineering, Amirkabir University of Technology, Tehran, Iran b Department of Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran article info Article history: Received 2 January 2010 Received in revised form 15 June 2010 Accepted 19 June 2010 Available online 21 July 2010 Keywords: Unit commitment Pumped-storage Environmental constraints abstract Aside from their zero fuel costs, the pumped-storage units can reduce emissions of thermal generating units. The objective of this study is to investigate (a) thermal unit commitment with considerations for environmental constraints (ECUC), and (b) pumped-storage and thermal unit commitment with considerations for environmental constraints (PSECUC) based on a new optimization methodology. The PSECUC determines the start-up and shut-down schedules of pumped-storage and thermal generating units that meet the required demand so that the costs for fuel, start-up, and emissions (TC) are mini- mized. For the ECUC (thermal generating units only), the results show improvements of 0.03 and 0.50% in TC and excess emissions (EXEM), respectively. For the PSECUC, it is determined that 2-pumped-storage units can simultaneously decrease the TC and EXEM by 1.20 and 60%, respectively. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction World energy systems today are highly dependent on fossil fuels. Fossil fuels share in world energy production is more than 85% [1] and in electricity generation more than 60% [1]. Unfortu- nately, fossil fuels harm the global ecosystem by emitting noxious gases and toxic substances, causing greenhouse effect. Hydro pumped-storage (PS) can be utilized to reduce the undesirable effects of fuel price fluctuations and environmental emissions of greenhouse gases such as SO 2 , CO 2 , and NO 2 . The utilization of a PS unit results in saving fuel, start-up and emissions costs (TC) by decreasing the dependency on thermal generating units (TGU) during the peak load periods with hydro energy and benefits from pumping the water back up into the reservoir at lower demand periods. A PS unit is a special kind of a hydroelectric generating plant, which has many advantages as peaking unit: quick response and relatively low capital cost [2]. PS units are utilized in three opera- tional modes, namely, pumping, idle, and generating. One mode can change over to any other rapidly. In general, approximately 5 min is needed to transfer from the full pumping to the full generating mode [2]. Also, a PS unit can provide ancillary services such as spinning reserve [2e5]. Several methodologies are applied to solve TGU unit commit- ment [6] with considerations for environmental constraints (ECUC) [7e12]. Those studies have focused on economiceenvironmental scheduling of TGUs. Based on literature review and emission reduction ability of PS units, a study on unit commitment of PS and TGUs with considerations for environmental constraints (PSECUC) is lacking. The PSECUC determines the start-up and shut-down schedules of PS units and TGUs that meet the required demand so that the TC is minimized. The committed PS units and TGUs must meet the power system demand and reserve requirements at the minimum TC subject to several system and operational constraints. The system constraints are concerned with the power system demand, emission, and spinning reserve, whereas the operational constraints are related to the constraints of TGU and PS units such as generating capacity, minimum up/down time, and water flow constraints [13]. The objective of this study is to investigate (a) ECUC, and (b) PSECUC based on a new optimization methodology (NOM). The organizational flowchart of activities in this study is shown in Fig. 1 . The ECUC problem is formulated and solved with the NOM. To verify the efficiency of NOM, a 26-TGUs power system [11,12] is used and the results are compared with Ref. [12]. The PSECUC includes PS unit commitment (PSUC) to determine the output power of PS units causing a change in total power system demand and spinning reserve met by TGUs [14] and, ECUC to determine the output power of TGUs, when total power system demand and spinning reserve are changed after implementing PSUC. The NOM * Corresponding author. Tel.: þ98 21 6357874169; fax: þ98 21 64543323. E-mail address: ardehali@aut.ac.ir (M.M. Ardehali). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.06.022 Energy 35 (2010) 4092e4101