Research Papers

Performance of a 100 kWth Concentrated Solar Beam-Down Optical Experiment

[+] Author and Article Information
Marwan Mokhtar

Research Engineer
Laboratory for Energy and Nano Science (LENS),
Department of Mechanical Engineering,
Masdar Institute of Science and Technology,
Abu Dhabi 54224, UAE
e-mail: marwan.mukhtar@gmail.com

Steven A. Meyers

Research Engineer
Laboratory for Energy and Nano Science (LENS),
Department of Mechanical Engineering,
Masdar Institute of Science and Technology,
Abu Dhabi 54224, UAE

Peter R. Armstrong

Associate Professor
Laboratory for Energy and Nano Science (LENS),
Department of Mechanical Engineering,
Masdar Institute of Science and Technology,
Abu Dhabi 54224, UAE
e-mail: parmstrong@masdar.ac.ae

Matteo Chiesa

Associate Professor
Laboratory for Energy and Nano Science (LENS),
Department of Mechanical Engineering,
Masdar Institute of Science and Technology,
Abu Dhabi 54224, UAE
e-mail: mchiesa@masdar.ac.ae

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 April 7, 2014; final manuscript received April 10, 2014; published online May 15, 2014. Editor: Gilles Flamant.

J. Sol. Energy Eng 136(4), 041007 (May 15, 2014) (8 pages) Paper No: SOL-14-1113; doi: 10.1115/1.4027576 History: Received April 07, 2014; Revised April 10, 2014

An analysis of the beam down optical experiment (BDOE) performance with full concentration is presented. The analysis is based on radiation flux distribution data taken on Mar. 21st, 2011 using an optical-thermal flux measurement system. A hypothetical thermal receiver design is used in conjunction with the experimental data to determine the optimal receiver aperture size as a function of receiver losses and flux distribution. The overall output of the plant is calculated for various operating temperatures and three different control strategies namely, constant mass flow of the heat transfer fluid (HTF), constant outlet fluid temperature and real-time optimal outlet fluid temperature. It was found that the optimal receiver aperture size (radius) of the receiver ranged between (1.06 and 1.71 m) depending on temperature. The optical efficiency of the BDOE ranged from 32% to 37% as a daily average (average over the ten sunshine hours). The daily average mean flux density ranged between 9.422 kW/m2 for the 1.71 m-receiver and 20.9 kW/m2 for the 1.06 m-receiver. Depending on the control parameters and assuming an open receiver with solar absorptivity of 0.95 and longwave emissivity of 0.10. The average receiver efficiency varied from 71% at 300 °C down to 68% at 600 °C. The overall daily average thermal efficiency of the plant was between 28% and 24%, respectively for the aforementioned temperatures. The peak of useful power collected in the HTF was around 105 kWth at 300 °C mean fluid temperature and 89 kWth at 600 °C.

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Grahic Jump Location
Fig. 1

BDOE overview. (a) Ganged-Type heliostat field and CR mirrors. CCD camera aperture is in the center of the CR taking images of the target below it. (b) Embedded within the target are water-cooled HFS at eight locations to calibrate the CCD camera images. (c) A typical luminance map taken by the CCD camera.

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Fig. 2

BDOE heliostat field

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Fig. 3

Day-average intercept factor (γ) as a function of receiver aperture radius (R)

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Fig. 4

DNI during the test day

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Fig. 5

Optical efficiency with optimal aperture

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Fig. 6

Intercept factor variation during the test day for different receiver aperture sizes

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Fig. 7

Luminance maps at different times of the day (local time UTC+4) shown in cd/m2. x and y axes are in pixels. Aberration is evident in early and late parts of the day which correspond to reduced intercept factor.

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Fig. 8

Net power collected as a function of receiver radius. Convection and radiation losses are also shown as a function of receiver size, Tfo = 400 °C. Daily average is calculated over the ten sunshine hours of the test day.

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Fig. 9

Receiver thermal efficiency. Average efficiency at 300 °C is 71%, at 400 °C is 73%, at 500 °C is 71% and at 600 °C is 68%.

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Fig. 10

Overall efficiency of the BDOE. Overall efficiency at 300 °C is 28%, at 400 °C is 26%, at 500 °C is 25%, and at 600 °C is 24%.

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Fig. 11

Thermal output of the receiver as function of time and outlet temperature

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Fig. 12

Maximum mechanical power, which is indicative of the solar-to-electricity efficiency of the BDOE

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Fig. 13

Comparison of control strategies. (a) Daily variation of maximum mechanical power, (b) mean fluid output temperature, (c) mass flow rate.




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