Contents lists available at ScienceDirect Sustainable Energy Technologies and Assessments journal homepage: www.elsevier.com/locate/seta Transient simulation of a hybrid photovoltaic-thermoelectric system using a phase change material P. Motiei, M. Yaghoubi ⁎ , E. GoshtasbiRad School of Mechanical Engineering, Shiraz University, Shiraz, Iran ARTICLE INFO Keywords: Waste heat recovery system TEG PCM Photovoltaic-thermoelectric PV-TEG-PCM hybrid system Phase change material ABSTRACT In the present study, phase change material (PCM) was introduced as a heat sink attached to a PV-TEG (pho- tovoltaic- thermoelectric generator) to build a PV-TEG-PCM hybrid system. PCM is often used to save a great deal of latent heat during a phase change process with enhanced energy storage capacity. Such a combination controls the system temperature, reduces PV temperature, increases temperature difference across TEG, and improves efficiency. For analysis, a transient, two-dimensional modeling was conducted for two Klein days (the average day for each month) in summer and winter for the city of Shiraz, Iran. Solar radiation, average wind speed, ambient air temperature, as well as heat losses through convection and radiation are included in the model. The validity of the results was tested and approved against experimental studies. Computation was performed for a duration of 24 h. The results indicated that electrical performance of a PV-TEG-PCM is better than that of a PV-TEG and a sole PV systems. Also, the effect of the PCM thickness and melting point temperature was studied to find the optimum material and thickness, which depend on environmental conditions. The nu- merical two-dimensional unsteady state modeling was implemented by developing a computational code in FORTRAN 90. Introduction Solar power systems not only provide the world with clean energy but also reduce heavy fossil fuel dependency. Photovoltaic panels (PV) directly convert sunlight into electricity, with heating, cooling, and lighting supply using the electricity generated by PVs being of the most common applications of this kind of power. PVs have still a low effi- ciency to meet industrial requirements to compete with fossil fuels. PV devices cannot convert the whole solar radiation into electricity, and a share of that is absorbed through PV cells. The absorbed heat rises PV temperature which results in decrease of the band-gap of semi- conductors. The PV efficiency varies considerably by its temperature and decreases when the PV temperature increases [1,2]. The fast de- velopment of PVs reflects the need to use the wasted heat and further improve its efficiency. For cooling PV systems, a variety of active cooling approaches (air cooled or water cooled) have been presented. Cooling PVs by water is not suitable owing to the amount of water required especially for large areas. Moreover, for places with limited access to water such as remote areas or deserts, this type of cooling system will lead to higher costs [3]. Recently, passive cooling systems using thermoelectric generators (TEG) have been proposed to develop a PV-TEG hybrid system. Alternatively, phase change materials (PCM) have been propounded to make a PV-PCM hybrid system. Both systems have drawn worldwide attention due to their positive features. TEG is a technology through which thermal energy directly converts into elec- trical energy through the Seebeck effect. A TEG module can be in- tegrated with other heat generation systems to recover the thermal energy because of its different shapes and dimensions [4–7]. A so-called PV-TEG hybrid system enhances the overall efficiency of employing solar energy [8]. According to thermoelectric effects, the power gen- erated by a TEG depends on both temperature difference through semiconductors and the connected electrical load. Any nonlinearity such as unsteady state conduction, Joule effect or temperature dependent properties of the material that causes any re- duction in temperature difference, drops the TEG efficiency. So, the progress in using a TEG is limited by its low efficiency [9–11]. Wu et al. [12] studied the performance of a PV–TEG system applying nanofluids for cooling the system. Their results indicated that using nanofluids in comparison with forced air cooling highly improves the efficiency of a PV–TEG system. However, the efficiency and temperature of the system were suitable for practical applications [13]. Therefore, in a real si- tuation, to attenuate the fluctuations of solar radiation and force a PV- TEG system to operate under a fairly constant temperature, use of PCM is suggested. The PCM can absorb high latent heat through a phase https://doi.org/10.1016/j.seta.2019.05.004 Received 1 October 2018; Received in revised form 28 April 2019; Accepted 16 May 2019 ⁎ Corresponding author. E-mail addresses: yaghoubi@shirazu.ac.ir (M. Yaghoubi), goshtasb@shirazu.ac.ir (E. GoshtasbiRad). Sustainable Energy Technologies and Assessments 34 (2019) 200–213 2213-1388/ © 2019 Elsevier Ltd. All rights reserved. T