Parametrical analysis of the design and performance of a solar heat pipe thermoelectric generator unit Wei He a,⇑ , Yuehong Su b , S.B. Riffat b , JinXin Hou a , Jie Ji a a Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei 230026, China b Institute of Sustainable Energy Technology, Department of Architecture and Built Environment, University of Nottingham, University Park, Nottingham NG7 2RD, UK article info Article history: Received 11 January 2011 Received in revised form 7 July 2011 Accepted 9 July 2011 Available online 6 August 2011 Keywords: Constant solar irradiation Heat pipe (HP) Thermoelectric generator (TEG) Parametrical analysis abstract This paper describes a solar heat pipe thermoelectric generator (SHP-TEG) unit comprising an evacuated double-skin glass tube, a ﬁnned heat pipe and a TEG module. The system takes the advantage of heat pipe to convert the absorbed solar irradiation to a high heat ﬂux to meet the TEG operating requirement. An analytical model of the SHP-TEG unit is presented for the condition of constant solar irradiation, which may lead to different performance characteristics and optimal design parameters compared with the con- dition of constant temperature difference usually dealt with in other studies. The analytical model pre- sents the complex inﬂuence of basic parameters such as solar irradiation, cooling water temperature, thermoelement length and cross-section area and number of thermoelements, etc. on the maximum power output and conversion efﬁciency of the SHP-TEG. Simulation based on the analytical model has been carried out to study the performance and design optimization of the SHP-TEG. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction With the diminishing reserve of fossil fuels and the pressing is- sues of environmental pollution caused by combustion of fossil fuels, research to ﬁnd new energy sources and affordable new power generation methods has been become more and more important. Compared to conventional electrical power generator systems, thermoelectric generators (TEG) theoretically offer many advantages such as being simple and highly reliable, having no moving parts, and being environmentally friendly. However, they have relatively low conversion efﬁciencies, so their applications have been usually limited to the speciﬁc situations where reliabil- ity is a major consideration such as in aerospace and military appli- cations. More recently, there has been a growing interest to use TEG for electricity generation from waste heat of various sources such as combustion of solid waste, power plants, biomass cooking, and other heat-generating processes when the cost of the thermal input do not need to be considered [1–5], and many researches on system optimization and performance improvement of thermo- electric generators for waste heat recovery have been reported in numerous publications [1–10]. In a study, the cost of electricity produced by TEG from waste warm water is predicted to be £0.08/kW h and even to be £0.04/kW h, which can challenge the cost of electricity produced by conventional methods from oil or coal fuels [8]. On the other hand, solar heat driven TEG is emerging as a com- peting alternative technology to the dominating solar photovoltaic (PV) systems. Though its low conversion efﬁciency compared to PV, solar-driven TEG technology still attracts increasing attention as other simple and competitive way to produce electricity from solar energy [11–15]. In fact, the low conversion efﬁciency may be not a serious barrier for use of the free and friendly solar energy. With the decreasing price of thermoelement materials, the TEG technology is attracting more research interest to develop it for so- lar energy applications and a number of studies on design and opti- mization of systems and analysis of their performance have been reported in the recent literature. The performance of the TEG in a hybrid PV-TEG system, where the TEG operates independently as a secondary generator to improve the overall efﬁciency of the sys- tem, has been studied [10,11,14]. The analytical method used in these studies are not much different from that used in the study of TEG for waste heat recovery, and calculation of the TEG was based on the temperature difference between the hot side and cool side of a TEG, which was usually chosen at 60 K, 80 K or 100 K. Typ- ically, the thermal conductivity of a TEG is about 1.5 W m 1 K 1 and the depth of commercial TEG is about 4 mm (including the ceramic electric insulation), so the heat ﬂux through a TEG could be higher than 20000 W m 2 for a temperature difference of 60– 100 K. However, the solar irradiation is usually less than 1000 W m 2 , which is obviously too low to match the required heat ﬂux of a TEG to obtain a large temperature difference for a considerable efﬁciency. Solar heat could be accumulated or solar radiation could be concentrated to match the required heat ﬂux of a TEG. A study has used a liquid such as water circulation system 0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.07.017 ⇑ Corresponding author. Tel.: +86 5513601641; fax: +86 5513606459. E-mail address: hwei@ustc.edu.cn (W. He). Applied Energy 88 (2011) 5083–5089 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy