Energy and Buildings 151 (2017) 320–331 Contents lists available at ScienceDirect Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild A simplified estimation model for determining the optimal rooftop photovoltaic system for gable roofs Cheolwoo Ban a , Taehoon Hong b,∗ , Kwangbok Jeong b , Choongwan Koo c , Jaewook Jeong d a Republic of Korea Marine Corps., P.O. Box # 202-8, Yeonpyeong, Ongjin, Incheon, 23108, Republic of Korea b Department of Architecture & Architectural Engineering, Yonsei University, Seoul, 03722, Republic of Korea c Department of Building Services Engineering, Hong Kong Polytechnic University, Kowloon, Hong Kong d Kolon Global Corporation, Incheon, 22001, Republic of Korea a r t i c l e i n f o Article history: Received 21 February 2017 Received in revised form 27 May 2017 Accepted 28 June 2017 Available online 29 June 2017 Keywords: Photovoltaic system Gable roof Life cycle cost Life cycle CO2 Net present value Saving-to-investment ratio a b s t r a c t This study aimed to develop a simplified estimation model for determining the optimal rooftop PV system for gable roofs that can evaluate life cycle economic and environmental assessment, by considering the type of installation to be used for such rooftop PV system. The military facilities located in three regions (i.e., Gimpo (northern part), Deajeon (middle part), and Pohang (southern part)) in South Korea were selected for the case studies. The results of this study are as follows. First, in terms of NPV 25 (net present value in 25 years), for the roofs with a lower orientation, ToI-2 opt. was selected as the optimal rooftop PV system, and for the roofs with a higher orientation, ToI-2 ext. or ToI-3 opt. was selected as the optimal rooftop PV system. Second, in terms of SIR 25 (savings-to-investment ratio in 25 years), for the roofs with a lower orientation, ToI-1 ext. was selected as the optimal rooftop PV system, and for the roofs with a higher orientation, ToI-3 opt. was selected as the optimal rooftop PV system. The simplified estimation model may be useful for decision makers, including experts and non-experts (i.e., architects, owners, construction managers, etc.), or policymakers in determining the optimal rooftop PV system for a gable roof. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Greenhouse gas (GHG) emissions are the main cause of global warming, and to reduce its GHG emissions by 37% below its business-as-usual level until 2030, South Korea established a national carbon emission reduction target (CERT) [1–3]. To achieve this target, the South Korean government has been implementing the Renewable Portfolio Standard since 2012, and has established the policy of obtaining 11% of the country’s primary energy needs from new and renewable energy (NRE) by 2035 [4,5]. Specially, the photovoltaic (PV) system, among the various NREs, has been evaluated as the largest potential resource that can reduce GHG emissions by replacing fossil fuel [6–8]. Accordingly, the South Korean government is promoting the use of the rooftop PV sys- tem, but due to the uncertainty of the economic profitability of the said system, there is a limit to the success of such efforts. The rea- son for the uncertainty of the economic profitability of the rooftop PV system is that the annual electricity generation (AEG) of such ∗ Corresponding author at: Yonsei University 50 Yonsei-ro, Seodaemun-gu, Seoul, 03722, Republic of Korea. E-mail address: hong7@yonsei.ac.kr (T. Hong). system is determined according to various factors (i.e., region, PV system design, etc.) pertaining to the rooftop PV systems [7,9–11]. To improve the city landscape, it is recommended that gable roofs be installed in several cities in South Korea (i.e., Anyang, Jecheon, Incheon, etc.) based on the country’s district unit plan [12,13]. The slope and orientation of a gable roof can be variously designed by region and topography. Therefore, it is necessary to develop a model for evaluating the economic profitability of the rooftop PV systems considering various factors (i.e., region and design). To address this challenge, this study aimed to develop a simplified estimation model for determining the optimal rooftop PV system for gable roofs that considers the type of installation (ToI), which can be used for life cycle economic and environmental assessment. According to Hachem et al. [14], Hachema et al. [15], and Chiras et al. [16], the rooftop shape has a significant effect on the AEG of the rooftop PV system because various design parameters (i.e., the installation area of the rooftop PV system, the slope of the installed panel (SoP), the azimuth of the installed panel (AoP), etc.) are deter- mined by the rooftop shape (i.e., flat roof, gable roof, etc.). The rooftop shapes of the rooftop PV system are generally categorized into (i) flat roof and (ii) gable roof. http://dx.doi.org/10.1016/j.enbuild.2017.06.069 0378-7788/© 2017 Elsevier B.V. All rights reserved.