Research Papers

Comparison of Different Strategies for Heliostats Aiming Point in Cavity and External Tower Receivers

[+] Author and Article Information
Marco Binotti

Group of Energy Conversion Systems (GECOS),
Dipartimento di Energia,
Politecnico di Milano,
Via Lambruschini 4,
Milano 20156, Italy

Paolo De Giorgi

Group of Energy Conversion Systems (GECOS),
Dipartimento di Energia,
Politecnico di Milano,
Via Lambruschini 4,
Milano 20156, Italy;
Thermal Power Group (GMTS),
University of Seville,
Camino de los descubrimientos s/n,
Seville 41092, Spain

David Sanchez

Thermal Power Group (GMTS),
University of Seville,
Camino de los descubrimientos s/n,
Seville 41092, Spain

Giampaolo Manzolini

Group of Energy Conversion Systems (GECOS),
Dipartimento di Energia,
Politecnico di Milano,
Via Lambruschini 4,
Milano 20156, Italy
e-mail: giampaolo.manzolini@polimi.it

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received July 14, 2014; final manuscript received December 14, 2015; published online February 5, 2016. Assoc. Editor: Dr. Akiba Segal.

J. Sol. Energy Eng 138(2), 021008 (Feb 05, 2016) (11 pages) Paper No: SOL-14-1204; doi: 10.1115/1.4032450 History: Received July 14, 2014; Revised December 14, 2015

This paper investigates different strategies for the reduction of peak heat fluxes on the receiver of a solar tower plant through the variation of the heliostats aiming points. The analysis is performed for two different solar tower receivers and heliostat field layouts. The innovative aspect of the work is in the methodology proposed: the effect of different aiming points is evaluated at different sun positions, and the yearly optical efficiency is calculated to determine drawbacks in terms of energy production. The optical simulation of the solar plant is performed with delsol through a matlab suite to easily manage the input and output. Preliminary assessments showed that the most important displacement is the vertical one, and the variation of the aiming point is important for the rows that are closer to the tower. With the appropriate strategy, the peak heat flux can be reduced by about 40% with limited spillage increase compared to the reference case. This result is similar for the two investigated plants, and it is confirmed also at different sun positions. The yearly optical efficiency with the optimal aiming strategy is reduced by less than 0.5% points. Future analysis will assess potential cost reductions and thermal efficiency increase brought about by the proposed strategies.

Copyright © 2016 by ASME
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Fig. 1

Overall heat input to the receiver (left side) and peak flux (right side) for the PS10 plant at 12.00 hr on March 21 and 16.00 hr on June 21. Reference values are taken from Refs. [31] and [32], options 1 and 2 refer to the abovementioned solar field modeling options in delsol. Both options 1 and 2 assume one single aiming point at the center of the receiver.

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Fig. 2

PS10 solar tower (left, http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=38) and Gemasolar (right, Copyright: Torresol Energy, Free Art License)

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Fig. 3

Aerial views of the PS10 (top left) and of the Gemasolar (top right) heliostat fields taken from Map Data 2014 Google, Inst. Geogr. Nacional and computation grid with 64 zones for the north (bottom left) and surrounded (bottom right) field

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Fig. 5

Flux map on the PS10 receiver panels on March 21 at noon, obtained with a central aiming on the receiver aperture for different solar field zones. Results show heat flux distributions corresponding to heliostats in zones 1–2 (left) and zones 61–62 (right), see Fig. 3.

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Fig. 6

Heat flux on PS10 receiver with the reference aiming strategy on March 21 at 12 p.m.

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Fig. 7

Flux map on the PS10 receiver panels obtained with aiming strategy 1 (a), strategy 5 (b), and strategy 6 (c)

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Fig. 8

Influence of the aiming strategy on spillage losses. Plots show the increase in spillage for the optimum strategy (strategy 6) with respect to the base aiming (strategy 1). Results correspond to the PS10 and two different sun positions.

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Fig. 9

Flux map on the Gemasolar receiver panels obtained with reference aiming strategy (a), strategy 1 (b), and strategy 6 (c). (Zero deg receiver angle coincides with the south direction.)

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Fig. 10

Comparison between the optimized (left) and reference (right) aiming in terms of spillage increase for Gemasolar at two different sun positions. The size of each heliostat is proportional to the cosine of the incidence angle.

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Fig. 11

Efficiency curves as a function of the zenith angle for different azimuth angles—PS10 (left) and Gemasolar (center) heliostat fields with reference aiming and efficiency gain/loss when aiming strategy 6 is used with respect to the reference aiming strategy (right)



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