In this presentation we will talk about how asymmetrical nonimaging optics can use flexible materials to accommodate different range of acceptance angles, resulting in tracking the seasonal changes of the sun, while integrate to the roof with a none-shading configuration.
The authors discuss the application potential of desalination for a novel low-cost solar thermal technology called the integrated compound parabolic concentrator (ICPC). This collector is designed using nonimaging optic principles, previously introduced in last year’s SPIE conference, 2019. Optical and thermal models are demonstrated, with preliminary experimental results. When coupled with a latent heat thermal storage system, the combined effort supplies sufficient heat demand for thermal desalination processes.
In this research work, the performance of a novel secondary concentrator in the vacuum receiver of the parabolic trough collector was investigated. The secondary concentrator was designed, the optical and thermal performance analysis is conducted analytically and validated numerically by using Finite Element Analysis based computational software. From the initial optical and thermal modeling, it was found that the use of secondary reflector gives a concentration of 53X versus a concentration in 20’s X of conventional trough collectors to provide an optical efficiency of 75% and a thermal efficiency of 55% at 650oC. The receiver with the novel secondary reflector was designed, assembled and tested indoors using resistance heaters. Heat loss measurement at 650oC at the absorber demonstrated emissivity of less than 0.2.
KEYWORDS: Vacuum tubes, Solar thermal energy, Compound parabolic concentrators, Solar energy, Reflectors, Absorption, Solar processes, Nonimaging optics, Thermal energy technology
The external compound parabolic concentrator (XCPC) is an emerging solar thermal technology which combines nonimaging optics and metal-glass vacuum tube technology to provide high operating temperatures from a stationary collector. In this paper we describe the technology and detail the latest performance of a 50 m2 solar field operating the following loads: space heating (70 °C), wastewater evaporation (150 °C), and double-effect absorption cooling (180 °C).
KEYWORDS: Solar energy, Solar thermal energy, Carbon monoxide, Manufacturing, Thermal efficiency, Compound parabolic concentrators, Solar cells, Agriculture, Solar processes, Renewable energy
U.S. energy consumption is reviewed from a top-down approach with special emphasis on thermal energy consumption in the residential, commercial, and industrial sectors. The solar thermal R&D efforts of the past 10 years at UC Merced are then presented which detail (i) a low cost combined heat and power collector (PV/T) for space heating, hot water, and electricity (ii) a nonimaging integrated compound parabolic concentrator (ICPC) with phase change thermal energy storage (TES) for low cost (< $0.015 / kWhth) dispatchable (24/7) solar for 120 °C process heating (iii) a mediumtemperature external compound parabolic concentrator (XCPC) for 100-250 °C process heat which has been used to demonstrate efficient solar cooling and solar driven wastewater evaporation for brine management, and (iv) a two-stage high concentration parabolic trough collector with a nonimaging secondary to achieve < 650 °C operation.
In this research work, the performance of novel secondary concentrator in the vacuum receiver of the parabolic trough collector is investigated. The secondary concentrator is designed, the optical and thermal performance analysis is done analytically and validated numerically by using Finite Element Analysis based computational software. From the initial optical and thermal modeling, it is found that the use of secondary reflector gives the concentration of 53X against the concentration in 20’s X of conventional trough collectors, the optical efficiency of 75% and the thermal efficiency of 60% at 650oC. After the design and analysis, the secondary concentrator is formed to the shape and photogrammetry technique is adopted to validate the optical simulations. In future work, the secondary concentrator and selective coated absorber will be produced and will be packaged inside the vacuum receiver. The installation, testing and commissioning of the full system two-stage concentration parabolic trough collector with novel secondary concentrator will be performed at University of California Merced in 2020.
The Compound parabolic concentrator used in the solar collector discussed in this paper is of the novel design, glass encased with 23% truncated reflectors and all glass receiver. Optical modeling was done in Light tools illumination design software to determine the optimum optical efficiency within a range of half acceptance angle and the heat transfer modeling and simulation was done in COMSOL Multiphysics simulation software. The Collector was built, tested and performance characterization was done. The experimental tests performed are stagnation test, water test for optical efficiency at low temperatures and closed loop oil test for thermal efficiency at high temperatures as high as 200°C. For the water and oil test, Flow rate method and Calorimetry method were used. The light tools optical modeling gave the optical efficiency of 64%. The stagnation temperature recorded at the absorber at 0% efficiency was 350°C. The water test at the temperature of 30-40°C gave the efficiency of 59%.
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