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Research Papers

Design Point for Predicting Year-Round Performance of Solar Parabolic Trough Concentrator Systems

[+] Author and Article Information
Men Wirz, Matthew Roesle

Department of Mechanical and
Process Engineering,
ETH Zurich,
Zurich 8092, Switzerland

Aldo Steinfeld

Department of Mechanical and
Process Engineering,
ETH Zurich,
Zurich 8092, Switzerland;

Solar Technology Laboratory,
Paul Scherrer Institute,
Villigen CH-5232, Switzerland
e-mail: aldo.steinfeld@ethz.ch

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received April 5, 2013; final manuscript received September 24, 2013; published online November 26, 2013. Assoc. Editor: Markus Eck.

J. Sol. Energy Eng 136(2), 021019 (Nov 26, 2013) (7 pages) Paper No: SOL-13-1112; doi: 10.1115/1.4025709 History: Received April 05, 2013; Revised September 24, 2013

Thermal efficiencies of the solar field of two different parabolic trough concentrator (PTC) systems are evaluated for a variety of operating conditions and geographical locations, using a detailed 3D heat transfer model. Results calculated at specific design points are compared to yearly average efficiencies determined using measured direct normal solar irradiance (DNI) data as well as an empirical correlation for DNI. It is shown that the most common choices of operating conditions at which solar field performance is evaluated, such as the equinox or the summer solstice, are inadequate for predicting the yearly average efficiency of the solar field. For a specific system and location, the different design point efficiencies vary significantly and differ by as much as 11.5% from the actual yearly average values. An alternative simple method is presented of determining a representative operating condition for solar fields through weighted averages of the incident solar radiation. For all tested PTC systems and locations, the efficiency of the solar field at the representative operating condition lies within 0.3% of the yearly average efficiency. Thus, with this procedure, it is possible to accurately predict year-round performance of PTC systems using a single design point, while saving computational effort. The importance of the design point is illustrated by an optimization study of the absorber tube diameter, where different choices of operating conditions result in different predicted optimum absorber diameters.

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Figures

Grahic Jump Location
Fig. 1

DNI versus incidence angle over a full year for Seville, using (a) the empirical correlation and (b) TMY data

Grahic Jump Location
Fig. 2

Thermal efficiency as a function of DNI and incidence angle for Seville, Spain

Grahic Jump Location
Fig. 3

Thermal efficiency as a function of the absorber diameter for different IDNI and θ values for Golden, CO

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