Research Papers

Comparison of Two Linear Collectors in Solar Thermal Plants: Parabolic Trough Versus Fresnel

[+] Author and Article Information
G. Manzolini

e-mail: giampaolo.manzolini@polimi.it
Politecnico di Milano,
Dipartimento di Energia,
Via Lambruschini 4,
20156 Milano, Italy

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received September 2, 2011; final manuscript received March 20, 2012; published online June 22, 2012. Assoc. Editor: Manuel Romero Alvarez.

J. Sol. Energy Eng 135(1), 011001 (Jun 22, 2012) (9 pages) Paper No: SOL-11-1188; doi: 10.1115/1.4006792 History: Received September 02, 2011; Revised March 20, 2012

Parabolic trough (PT) technology can be considered the state of the art for solar thermal power plants thanks to the almost 30 yr of experience gained in SEGS and, recently, Nevada Solar One plants in the United States and Andasol plant in Spain. One of the major issues that limits the wide diffusion of this technology is the high investment cost of the solar field and, particularly, of the solar collector. For this reason, research has focused on developing new solutions that aim to reduce costs. This paper compares, at nominal conditions, commercial Fresnel technology for direct steam generation with conventional parabolic trough technology based on synthetic oil as heat-transfer. The comparison addresses nominal conditions as well as annual average performance. In both technologies, no thermal storage system is considered. Performance is calculated by Thermoflex®, a commercial code, with a dedicated component to evaluate solar plant. Results will show that, at nominal conditions, Fresnel technology has an optical efficiency of 67%, which is lower than the 75% efficiency of the parabolic trough. Calculated net electric efficiency is about 19.25%, whereas PT technology achieves 23.6% efficiency. In off-design conditions, the performance gap between Fresnel and parabolic trough increases because the former is significantly affected by high incident angles of solar radiation. The calculated sun-to-electric annual average efficiency for a Fresnel plant is 10.2%, which is a consequence of the average optical efficiency of 38.8%; a parabolic trough achieves an overall efficiency of 16%, with an optical efficiency of 52.7%. An additional case with a Fresnel collector and synthetic-oil outlines the differences among the cases investigated. Since part of the performance difference between Fresnel and PT technologies is simply due to different definitions, we introduce additional indexes to make a consistent comparison. Finally, a simplified economic assessment shows that Fresnel collectors must reduce investment costs of at least 45% than parabolic trough to achieve the same levelized cost of electricity.

Copyright © 2012 by ASME
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Fig. 1

Layouts of indirect-cycle plants (a) and DSG plant (b). These figures are screenshots from Thermoflex® 20.

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Fig. 2

Angles definition of a linear Fresnel reflector with horizontal N-S orientation tracking axis [26]

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Fig. 3

Longitudinal and transversal IAM trend as a function of incidence angle

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Fig. 4

Annual maps of OR for PT (top) and LFR (bottom) technology

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Fig. 5

Monthly net electricity production for the technologies investigated

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Fig. 6

February 5 (top) and July 2 (bottom), DNI and net power output for the three plant layouts studied




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