Renewable and Sustainable Energy Reviews 79 (2017) 1314–1328 Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser Progress in concentrated solar power technology with parabolic trough MARK collector system: A comprehensive review ⁎ ⁎ Wang Fuqianga,b, Cheng Ziminga, Tan Jianyua, , Yuan Yuanc, , Shuai Yongc, Liu Linhuab,c a School of Automobile Engineering, Harbin Institute of Technology at Weihai, 2, West Wenhua Road, Weihai 264209, PR China b Department of Physics, Harbin Institute of Technology, 92, West Dazhi Street, Harbin 150001, PR China c School of Energy Science and Engineering, Harbin Institute of Technology, 92, West Dazhi Street, Harbin 150001, PR China ARTICLE INFO ABSTRACT Keywords: Advanced solar energy utilization technology requires high-grade energy to achieve the most efficient Concentrated solar power application with compact size and least capital investment recovery period. Concentrated solar power (CSP) Parabolic trough collector technology has the capability to meet thermal energy and electrical demands. Benefits of using CSP technology Tube receiver with parabolic trough collector (PTC) system include promising cost-effective investment, mature technology, Heat transfer fluid and ease of combining with fossil fuels or other renewable energy sources. This review first covered the CSP plant theoretical framework of CSP technology with PTC system. Next, the detailed derivation process of the maximum theoretical concentration ratio of the PTC was initially given. Multiple types of heat transfer fluids in tube receivers were reviewed to present the capability of application. Moreover, recent developments on heat transfer enhancement methods for CSP technology with PTC system were highlighted. As the rupture of glass covers was frequently observed during application, methods of thermal deformation restrain for tube receivers were reviewed as well. Commercial CSP plants worldwide with PTC system were presented, including those that are in operation, under construction, and announced. Finally, possible further developments of CSP plants with PTC system were outlined. Besides, suggestions for future research and application guidance were also illustrated. 1. Introduction The sun releases a tremendous amount of radiation energy to its surroundings: 1.74×1017 W at the upper atmosphere of the earth [28]. 1.1. Why solar energy When sunlight reaches the surface of the earth, it would be multi- attenuated due to the effects of reflection, absorption, and scatter by Energy resources can be divided into three main categories: fossil carbon dioxide, water vapor, and suspensoids in the atmosphere, as fuel, renewable energy, and nuclear energy [1–3]. Fossil fuel is the shown in Fig. 1 [29–31]. The total solar radiation falling on the earth preferred energy because of its competitive price and high-energy accounts approximately 51% of the total incoming solar radiation density [4,5]. Owing the global shortage of fossil fuel supply and which is still of huge amount after multi-attenuation [32–35]. environmental problems, there is an increasing demand of searching Therefore, solar energy is a much more abundant and environmental for renewable energy [6–10]. friendly resource compared to other energy sources and the linchpin of Renewable energy is defined as energy derived from resources sustainable energy development program [36–40]. which can be naturally replenished with close-to-zero emissions of both GHG and pollutions [11–14]. Ordinarily, renewable energy utilizes the 1.2. Why concentrated solar power technology direct forms of sun's energy and its indirect impacts on the earth (falling water, wind, biomass, etc.), tidal energy, and geothermal energy Advanced solar energy technology requires high-grade energy to as the resources from which useful formats of energy are generated produce the most efficient power with compact plant size and minimal [15–20]. These resources have huge energy potential with the char- capital investment recovery period [41,42]. Concentrated solar power acteristics of intermittence, dispersal, and distinct regional variability (CSP) technology has the capability to meet the thermal energy as well [21–25]. These characteristics lead to difficulties in usage, technical as electrical demands [43–45]. and economic challenges [26,27]. For CSP technologies, the incoming sunlight is concentrated on a ⁎ Corresponding authors. E-mail addresses: [email protected] (T. Jianyu), [email protected] (Y. Yuan). http://dx.doi.org/10.1016/j.rser.2017.05.174 Received 14 February 2017; Received in revised form 18 May 2017; Accepted 20 May 2017 1364-0321/ © 2017 Elsevier Ltd. All rights reserved. W. Fuqiang et al. Renewable and Sustainable Energy Reviews 79 (2017) 1314–1328 y Glass cover Receiver HTF PTC x Fig. 3. Schematic of PTC with tube receiver. 2. Principle of PTC with tube receiver Fig. 1. Earth's energy budget (from NASA) [29]. 2.1. Introduction of PTC with tube receiver A PTC is a line focus solar collector that is straight in one dimension and curved as a parabolic shape in the other two dimensions, lined with high reflectivity mirrors [64–67]. The energy from solar radiation, which enters the PTC parallel to the plane of symmetry, is concentrated along the focal line, where a tube receiver is installed to receive the concentrated solar radiation [68,69]. The governing equation of a PTC shown in Fig. 3 is expressed as x2 =4fz (1) A single-axis tracker is employed to orient both the solar concen- trator and tube receiver toward the sun [70,71]. A metal tube coated with spectrum selective layers is placed inside an evacuated glass cover to compose a tube receiver (as shown in Fig. 3). A heat transfer fluid (HTF), such as synthetic thermal oil, molten salt, or water, flows into the tube receiver to absorb concentrated solar radiation [72]. Nickel–cadmium coatings with microstructure are commonly used as spectrum selective coating to achieve maximum solar energy absorption (short wave) and minimum infrared radiation (long wave) emittance [73]. Therefore, the heat losses of tube receiver can be significantly minimized by using spectrum selective coatings and evacuated glass covers [74]. Generally, PTC with tube receiver is arranged on a north-south direction to track the sun as it rotates from east to west to maximize the system optical efficiency. Alternatively, the PTC with tube receiver can also be arranged on an east–west direction, which lessens the system optical efficiency owing to cosine loss. However, this will only require Fig. 2. Typical solar concentrators: parabolic trough concentrator, parabolic dish adjustment of the PTC with tube receiver with variation in seasons, concentrator, linear Fresnel reflector, and heliostat field concentrator [57]. averting the requirement for tracking apparatus [68,69]. This type of tracking mode achieves the maximum efficiency in theory during the spring equinox and autumnal equinox with less precise concentration relatively small target area by mirrors or lens, and thus produces of sunlight at other times of the year. The regular sun tracking across medium to high temperature heat [46–51]. The increase in operating the sky also induces errors, maximum at sunrise and sunset, and temperature and amount of heat collected per unit area produce larger minimum at noon time. Owing to the sources of error, periodically thermodynamic efficiency and smaller absorbing surface area, which adjusted parabolic trough collectors are ordinarily planned with a lower results in significant decrease of convective and conductive heat losses concentration acceptance product [75]. [52–56]. According to the focus geometry and receiving technology, PTC with tube receiver has an unsophisticated structure; however, its solar concentrators can be divided into four classifications, namely concentration ratio is only one-thirdofthemaximumvalueintheoryfor parabolic trough concentrator (PTC), parabolic dish concentrator, the same acceptance angle (107.3), that is, for the same overall tolerances of linear Fresnel reflector, and heliostat field concentrator, as shown in the system to all types of errors, including tracking error, pointing error, Fig. 2 [57–60]. surface error, and alignment error. The maximum value in theory is better Benefits of using CSP technology with parabolic trough collector obtained with more sophisticated concentrators, based on primary–sec- system include promising cost-effective investment, mature technol- ondary designs using non-imaging optics, which could almost double the ogy, abundant operational experience, ease of coupling with fossil fuels concentration ratio of conventional PTCs and is adopted to enhance and other renewable energy sources [61–63]. applications, such as those with fixed receivers [73,76]. 1315 W. Fuqiang et al. Renewable and Sustainable Energy Reviews 79 (2017) 1314–1328 n =2a /f (8) The relationship between the maximum theoretical geometric W concentration ratio, CRmax, and the relative aperture n for a PTC can f be expressed as Ac nf W R α CR == =2 tan AfocW f (9) R In the equation above, the symbol A represents the aperture area of α c the PTC, and the symbol A denotes the area of the solar image on the b foc focal plane of the PTC. f ψ The expression of the parameter height (b)inFig. 4 is expressed in terms of the relative aperture (n) and focal length (f): a ⎛ ⎞ a2 (/2)nf 2 n2 bf=− =−f =1−f ⎜ ⎟ 4f 4f ⎝ 16 ⎠ (10) y Therefore, the relationship among the parameters R, ψ, f, and n follow