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Research Papers

Generation of a Parabolic Trough Collector Efficiency Curve From Separate Measurements of Outdoor Optical Efficiency and Indoor Receiver Heat Loss

[+] Author and Article Information
Charles Kutscher, Frank Burkholder

Engineer III National Renewable Energy Laboratory, MS 5202, 1617 Cole Boulevard, Golden, CO 80401chuck.kutscher@nrel.gov

J. Kathleen Stynes

Department of Mechanical Engineering,  University of Colorado, Boulder, CO 80301

J. Sol. Energy Eng 134(1), 011012 (Nov 29, 2011) (6 pages) doi:10.1115/1.4005247 History: Received March 15, 2011; Revised August 01, 2011; Published November 29, 2011; Online November 29, 2011

The thermal efficiency of a parabolic trough collector is a function of both the fraction of direct normal radiation absorbed by the receiver (the optical efficiency) and the heat lost to the environment when the receiver is at operating temperature. The thermal efficiency can be determined by testing the collector under actual operating conditions or by separately measuring these two components. This paper describes how outdoor measurement of the optical efficiency is combined with laboratory measurements of receiver heat loss to obtain the thermal efficiency curve. This paper describes this approach and also makes the case that there are advantages to plotting collector efficiency versus the difference between the operating temperature and the ambient temperature at which the receiver heat loss was measured divided by radiation to a fractional power (on the order of 1/3 but obtained via data regression)—as opposed to the difference between operating and ambient temperatures divided by the radiation. The results are shown to be robust over wide ranges of ambient temperature, sky temperature, and wind speed.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 2

Collector efficiency plotted versus the difference between the heat transfer fluid temperature and ambient temperature

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Figure 3

SkyTrough normal incidence efficiency from combining collector optical efficiency and receiver heat loss results, for three radiation values

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Figure 4

SkyTrough normal incidence thermal efficiency with three radiation values collapsed onto a single curve

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Figure 5

Impact of ambient temperature on receiver heat loss

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Figure 6

Impact of sky temperature on receiver heat loss

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Figure 7

Impact of wind speed on receiver heat loss

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Figure 1

Collector efficiency plotted versus the heat transfer fluid temperature

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