Life cycle economic and environmental assessment for establishing the optimal implementation strategy of rooftop photovoltaic system in military facility Kwangbok Jeong, Taehoon Hong * , Cheolwoo Ban, Choongwan Koo, Hyo Seon Park Department of Architectural Engineering, Yonsei University, Seoul, 120-749, Republic of Korea article info Article history: Received 29 December 2014 Received in revised form 19 March 2015 Accepted 16 May 2015 Available online 27 May 2015 Keywords: Photovoltaic (PV) system Life cycle cost Life cycle CO 2 Military facility Gable roof abstract The Ministry of National Defense (South Korea) promotes its Defense Green Growth policy to reduce greenhouse gas emissions. Based on this background, this study aimed to conduct the life cycle economic and environmental assessment for establishing the optimal implementation strategy for rooftop photovoltaic system in military facility. Considering three factors (i.e., the orientation of the gable roof, the installation area of the PV system, and the slope of the installed panel), 12 implementation scenarios of PV system were established. The detailed results by prototype are summarized in terms of the two perspectives (i.e., the absolute and relative investment values): (i) Prototype 1 (south-north): P1-S/N (opt.) in terms of the NPV 25 (net present value at year 25) and P1-S (opt.) in terms of the SIR 25 (savings- to-investment ratio at year 25); (ii) Prototype 2 (southeast-northwest): P2-SE/NW (opt.) in terms of the NPV 25 and P2-SE (ext.) in terms of the SIR 25 ; and (iii) Prototype 3 (east-west): P3-E/W (ext.) in terms of the NPV 25 and P3-E (opt.) in terms of the SIR 25 . The results of this study can help decision-makers to determine the optimal strategy for implementing rooftop PV systems on the gable roof of military fa- cilities through life cycle economic and environmental assessment. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction The global increase in greenhouse gas (GHG) emissions has resulted in the rise of the global warming potential (IPCC, 2013). According to the United Nations Office for Disaster Risk Reduction, the economic loss due to the abnormal climate change caused by global warming has reached 25 trillion dollars (UNISDR, 2014). Thus, the world has been making continuous efforts to reduce GHG emissions. For example, the United States has established its na- tional carbon emissions reduction target (CERT) as 17% below its 2005 level by 2020 (Ji et al., 2014; Jeong et al., 2014), and the South Korean government has established its national CERT as 30% below business-as-usual by 2020 (KEI, 2012). The military is also making efforts to reduce its GHG emissions. First, the U.S. Department of Defense aims to reduce its GHG emissions from buildings by 30% under its 2008 level by 2020, and to replace 18.3% of the energy consumed by buildings to new and renewable energy (NRE) system by 2020 (CRS, 2012; NREL, 2011). In addition, the U.S. Air Force aims to replace 25% of the energy consumed by the buildings to NRE system by 2025, and toward this end, it installed a 14 MW photovoltaic (PV) system at Nellis Air Force Base in 2007 (NREL, 2011). Second, in 2009, the Ministry of National Defense of South Korea established its Defense Green Growth policy, under which it promotes energy savings and GHG emissions reduction activities (MND, 2012a). For example, in 2010, the country's Air Force established a 130 kW PV system, and the Service Support Group of the country's Ministry of National De- fense installed nine solar streetlights. The Air Force Academy has also installed a 354RT geothermal heat pump system (MND, 2011). Previous studies on the implementation of NRE systems in military facilities had the following limitations.  First, while there were several studies on implementing the PV system on a flat roof, no studies have been conducted on implementing it on a gable roof. Hong et al. (2013, 2014a,b,c) conducted the economic and environmental assessment for the implementation of the PV system on a flat roof (Hong et al., * Corresponding author. Tel.: þ82 2 2123 5788; fax: þ82 2 365 4668. E-mail addresses: kbjeong7@yonsei.ac.kr (K. Jeong), hong7@yonsei.ac.kr (T. Hong), qkscjfdn@naver.com (C. Ban), cwkoo@yonsei.ac.kr (C. Koo), hspark@ yonsei.ac.kr (H.S. Park). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro http://dx.doi.org/10.1016/j.jclepro.2015.05.066 0959-6526/© 2015 Elsevier Ltd. All rights reserved. Journal of Cleaner Production 104 (2015) 315e327