Research Papers

Conceptual Design of a 2× Trough for Use Within Salt and Oil-Based Parabolic Trough Power Plants

[+] Author and Article Information
Gregory J. Kolb, Richard B. Diver

 Sandia National Laboratories, MS 1127, Albuquerque, NM 87185-5800gjkolb@sandia.gov

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A reviewer of this paper performed an independent analysis using the methodology described in Ref. 17 and found the approaches to agree within 1% for most cases presented in this paper.

The 5.4 mrad total collector error we assess needs to be verified with field test data. However, the spillage we calculate with this error is similar to values used by trough designers and defaulted within EXCELERGY .

A few errors were found in this paper: (1) all cases in Fig. 1 were based on a 5 m aperture, not the stated values of 5.76–8 m; (2) the maximum plant size studied was 250 MW, not the stated value of 200 MW.

Kelly stated that the 150 MW oil plant in Fig. 1 was near the maximum size. The field size was 1.3×106m2.

The total cost of the mirrors plus mirror-support structure is assumed to be the same ($/m2) for the conventional and 2× trough. As discussed in Sec. 2, mirrors are expected to cost more for the 2× trough but this may be compensated by a lower-cost mirror-support structure.

J. Sol. Energy Eng 132(4), 041003 (Aug 19, 2010) (6 pages) doi:10.1115/1.4002080 History: Received September 16, 2008; Revised April 21, 2010; Published August 19, 2010; Online August 19, 2010

Recent studies in the United States suggest that parabolic trough levelized energy costs (LECs) can be reduced 10–15% through integration of a large salt energy storage system coupled with the direct heating of molten salt in the solar field. While noteworthy, this relatively small predicted improvement may not justify the increased technical risks. Examples of potential issues include increased design complexity, higher maintenance costs, and salt freezing in the solar field. To make a compelling argument for development of this new system, we believe that additional technical advances beyond that previously reported will be required to achieve significant LEC reduction, greater than 25%. The new technical advances described include the development of a high-concentration trough that has double aperture and optical concentration of current technology. This trough is predicted to be more cost-effective than current technology because its cost ($/m2) and thermal losses (W/m2) are significantly lower. Recent trough optical performance improvements, such as more accurate facets and better alignment techniques, suggest a 2× trough is possible. Combining this new trough with a new low-melting point salt now under development suggests that a LEC cost reduction of 25% is possible for a 50 MW, 2× salt plant relative to a conventional (1×) 50 MW oil plant. However, the 2× trough will also benefit plants that use synthetic oil in the field. A LEC comparison of 2× plants at sizes 200MW shows only a 6% advantage of salt over oil.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

EC comparison of current and future trough technology (2)

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Figure 2

Trough-HELIOS prediction of incident flux upon a 0.07 m diameter HCE for a current 5 m aperture trough and a future 10 m trough. System errors are 5.4 mrad for the 5 m trough and 2.5 mrad for the 10 m trough. Trough-HELIOS requires surface pointing-type errors. Beam error=2∗ pointing error. The King sunshape (9) and 1000 W/m2 insolation were assumed.

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Figure 3

Photograph showing the impact of mirror mount distortion on curvature of an LS-2 mirror (a). (b) is the same mirror with the mirror mount loosened.

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Figure 4

Sandia 10 kWe dish/string system dish system. The structural honeycomb facets have slope errors in the range of 8–1.4 mrad.

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Figure 5

The TOP alignment system can potentially reduce facet alignment errors to 0.5 mrad

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Figure 6

Solar flux tracker for parabolic trough collectors




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