View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Hertfordshire Research Archive A Review of Solar Collectors and Thermal Energy Storage in Solar Thermal Applications Y. Tian a, C.Y. Zhao b a School of Engineering, University of Warwick, CV4 7AL Coventry, United Kingdom Email: [email protected] b School of Mechanical Engineering, Shanghai Jiaotong University, 200240 Shanghai, China Email: [email protected] Article history: Received 24 July 2012 Revised 18 November 2012 Accepted 20 November 2012 Available online 22 December 2012 Doi: http://dx.doi.org/10.1016/j.apenergy.2012.11.051 Cited as: Y Tian, CY Zhao. A review of solar collectors and thermal energy storage in solar thermal applications. Applied Energy 104 (2013): 538–553. ABSTRACT Thermal applications are drawing increasing attention in the solar energy research field, due to their high performance in energy storage density and energy conversion efficiency. In these applications, solar collectors and thermal energy storage systems are the two core components. This paper focuses on the latest developments and advances in solar thermal applications, providing a review of solar collectors and thermal energy storage systems. Various types of solar collectors are reviewed and discussed, including both non-concentrating collectors (low temperature applications) and concentrating collectors (high temperature applications). These are studied in terms of optical optimisation, heat loss reduction, heat recuperation enhancement and different sun- tracking mechanisms. Various types of thermal energy storage systems are also reviewed and discussed, including sensible heat storage, latent heat storage, chemical storage and cascaded storage. They are studied in terms of design criteria, material selection and different heat transfer enhancement technologies. Last but not least, existing and future solar power stations are overviewed. 1 Keywords: Solar collectors; Thermal energy storage; Heat transfer enhancement; Metal foam; PCM; Solar power stations. Highlights ► The latest developments and advances in solar thermal applications are reviewed. ► Various types of solar collectors are studied, in terms of optical optimisation, heat loss reduction, heat recuperation enhancement and sun-tracking mechanisms. ► Various types of thermal energy storage systems are studied, in terms of design criteria, material selection and heat transfer enhancement technologies involved. ► Existing and future solar power stations are reviewed. Table of Contents 1. Introduction................................................................................................................... 4 2. Solar collectors .............................................................................................................. 5 2.1. Non-concentrating collectors................................................................................... 5 2.1.1. Flat-plate collectors.......................................................................................... 5 2.1.2. Hybrid PVT collectors ...................................................................................... 7 2.1.3. Enhanced hybrid PVT collectors –Bifacial PVT ............................................. 8 2.2. Concentrating collectors.......................................................................................... 9 2.2.1. Heliostat field collectors................................................................................... 9 2.2.2. Parabolic dish collectors................................................................................ 10 2.2.3. Parabolic trough collectors............................................................................ 11 3. Solar thermal energy storage ..................................................................................... 12 3.1. Criteria for design.................................................................................................. 12 3.2 Materials................................................................................................................. 13 3.2.1. Sensible heat storage materials ...................................................................... 13 3.2.2. Latent heat storage materials ......................................................................... 14 3.2.3. Chemical heat storage materials.................................................................... 14 3.3. Heat transfer enhancement technologies............................................................... 15 3.3.1. Incorporation of high-thermal conductivity enhancers .................................. 15 3.3.2. Cascaded storage............................................................................................ 17 4. An overview of existing and future solar power stations ........................................ 18 4.1. Existing solar power stations................................................................................. 18 4.2. Solar power stations under construction ............................................................... 19 5. Conclusions.................................................................................................................. 20 Acknowledgements ......................................................................................................... 21 2 References ........................................................................................................................ 21 Table Captions ................................................................................................................ 32 Table 1.............................................................................................................................. 33 Table 2.............................................................................................................................. 34 Table 3.............................................................................................................................. 35 Table 4.............................................................................................................................. 36 Table 5.............................................................................................................................. 37 Table 6.............................................................................................................................. 38 Table 7.............................................................................................................................. 39 Table 8.............................................................................................................................. 44 Figure Captions............................................................................................................... 46 Fig. 1................................................................................................................................. 47 Fig. 2................................................................................................................................. 47 Fig. 3................................................................................................................................. 48 Fig. 4................................................................................................................................. 49 Fig. 5................................................................................................................................. 49 Fig. 6................................................................................................................................. 50 Fig. 7................................................................................................................................. 51 Fig. 8................................................................................................................................. 51 Fig. 9................................................................................................................................. 52 Fig. 10............................................................................................................................... 53 Fig. 11............................................................................................................................... 53 Fig. 12............................................................................................................................... 54 Fig. 13............................................................................................................................... 55 3 1. Introduction CO2-induced global warming has become a pressing issue, and needs to be tackled. Efficient utilisation of renewable energy resources, especially solar energy, is increasingly being considered as a promising solution to global warming and a means of achieving a sustainable development for human beings. The Sun releases an enormous amount of radiation energy to its surroundings: 174 PW (1 PW = 1015 W) at the upper atmosphere of the Earth [1]. When the energy arrives at the surface of the Earth, it has been attenuated twice by both the atmosphere (6% by reflection and 16% by absorption [1]) and the clouds (20% by reflection and 3% by absorption [1]), as shown in Fig. 1 [2]. Another 51% (89 PW) of the total incoming solar radiation reaches the land and the oceans [1]. It is evident that, despite the attenuation, the total amount of solar energy available on