Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Energy and exergy analysis of the PVT system: Eﬀect of nanoﬂuid ﬂow rate H. Fayaz a , R. Nasrin a,b, ⁎ , N.A. Rahim a,c , M. Hasanuzzaman a a UM Power Energy Dedicated Advanced Centre (UMPEDAC), Level 4, Wisma R&D, University of Malaya, 59990 Kuala Lumpur, Malaysia b Department of Mathematics, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh c Renewable Energy Research Group, King Abdulaziz University, Jeddah 21589, Saudi Arabia ARTICLE INFO Keywords: PVT system MWCNT-water nanoﬂuid Energy Exergy Eﬃciency ABSTRACT Solar energy is one of the promising resources to fulﬁl the energy demands to some level in place of fossil fuels to avoid environmental pollution. The eﬃciency of solar technology, e.g. photovoltaic panels, thermal systems or a combination of both technologies as photovoltaic thermal is a concern to increase at an optimum level. A three- dimensional numerical analysis of PVT systems using water and MWCNT-water nanoﬂuid has been completed with FEM based software COMSOL Multiphysics®. A numerical investigation has been validated by the indoor experimental research at diﬀerent mass ﬂow rates of 30 to 120 L/h while keeping solar irradiation ﬁxed at 1000 W/m 2 , inlet ﬂuid and ambient temperature at 32 and 25 °C, respectively. Percent improvement of electrical eﬃciency of PV with nanoﬂuid cooling at ﬂow rate 120 L/h is obtained about 10.72 and 12.25% of numerical and experimental cases respectively. Optimization of the nanoﬂuid for weight concentration is achieved at 0.75% MWCNT-water. Solar cell temperature reduces about 0.72 °C experimentally and 0.77 °C numerically per 10 L/h ﬂow rate increment. Approximately 7.74 and 6.89 W thermal energy is enhanced per 10 L/h ﬂow rate increment in numerical and experimental studies respectively. Percentage increment of thermal eﬃciency is found as 5.62% numerically and 5.13% experimentally for PVT system operated by water/MWCNT nanoﬂuid with compared to water. 1. Introduction Commercial photovoltaic panels convert lesser than 20% solar en- ergy into electrical energy while other part of energy is converted into heat energy. Due to the heat generated by a module, cell temperature rises resulting in an electrical eﬃciency drop signiﬁcantly. Along with reducing module electrical eﬃciency, higher produced temperatures in PV module can damage structures of the module creating thermal stresses (Nasrin et al., 2018a; Lamnatou and Chemisana, 2017; Maadi et al., 2017). Therefore, to counter such issues, combined PV and thermal collector systems are designed to extract extra generated heat into PV module and use it for other purposes. Thus, research on nano- ﬂuids has been carried out to investigate the eﬃcient heat transfer PV module to other thermal applications. To determine the eﬀectiveness of nano-ﬂuids in solar applications, solar system’s ability to convert light energy into thermal energy must be known (Nasrin and Alim, 2015b; Hassani et al., 2016; Zamzamian et al., 2014; An et al., 2016; Al-Waeli et al., 2017; Al-Shamani et al., 2016; Kalogirou et al., 2016). Reviews are conducted for the advancements and applications of nanotechnology in solar energy systems, for their improved eﬃciency (Al-Shamani et al., 2014). In the ﬁeld of economics, the authors showed that nanotech reduces manufacturing costs as a result of using a low- temperature process. Numerical investigation of the eﬀects of the water-based nanoﬂuid on the performance of the PVT system was presented by Xu and Kleinstreuer (2014). The authors presented a new model of thermal conductivity of nanoﬂuids to investigate the im- proved heat transfer. Also, thermal and electrical eﬃciencies, as well as the economic viability of the PVT systems of silicon and multi-junction solar cells, have been investigated by comparison. PVT collectors achieved the overall eﬃciency of 70% in simulation results with 11 and 59% of electrical and thermal energy respectively. Gangadevi et al. (2013) performance of water-Al 2 O 3 (0.5% volume fraction) nanoﬂuids was investigated applied in PVT. Use of that na- noﬂuid enhanced the electrical and thermal performance of the system considerably. The overall eﬃciency of a PVT was investigated with the eﬀects of ferroﬂuids used as a coolant by Ghadiri et al. (2015). These nanoﬂuids were mixed with distilled water at 1 and 3% by weight for the experiment, which was performed under indoor working conditions in 1100 and 600 W/m 2 with the solar emulator. Sardarabadi et al. (2014) studied the eﬀects of silica, SiO 2 -water nanoﬂuid on PVT elec- trical and thermal performance. Weight concentrations of nanoﬂuids of 1 and 3% were used. As compared to water the overall eﬃciency of the https://doi.org/10.1016/j.solener.2018.05.004 Received 6 November 2017; Received in revised form 6 April 2018; Accepted 1 May 2018 ⁎ Corresponding author at: Department of Mathematics, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh. E-mail address: rehena@math.buet.ac.bd (R. Nasrin). Solar Energy 169 (2018) 217–230 0038-092X/ © 2018 Elsevier Ltd. All rights reserved. T