Research Papers

Development of the CellFlux Storage Concept for Sensible Heat

[+] Author and Article Information
Wolf-Dieter Steinmann

e-mail: wolf.steinmann@dlr.de

Christian Odenthal

German Aerospace Center,
Institute of Technical Thermodynamics,
Pfaffenwaldring 38-40,
Stuttgart 70568, Germany

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received March 6, 2012; final manuscript received April 17, 2013; published online July 22, 2013. Assoc. Editor: Werner Platzer.

J. Sol. Energy Eng 136(1), 011011 (Jul 22, 2013) (8 pages) Paper No: SOL-12-1066; doi: 10.1115/1.4024921 History: Received March 06, 2012; Revised April 17, 2013

Two tank storage systems using molten salt represent today's state of the art in energy storage for concentrating solar power (CSP) plants. This concept shows a limited potential for further cost reductions, since the capital costs are dominated by the expenses for the salt inventory. The application of solid storage materials represents a promising approach to reduce capital costs. While this approach avoids also the risk of freezing and lessens corrosion problems, the efficiency of the heat transfer between the heat transfer fluid (HTF) and the solid storage medium is crucial. This paper introduces the CellFlux concept, which uses an intermediate closed air loop to transfer energy between the HTF and the solid storage material. A modular concept is chosen to optimize the size of the air flow channels. An initial project will provide the fundamentals needed to design a CellFlux storage unit. The feasibility will be proven by a 100 kW/500 kWh pilot storage module.

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Kelly, B., and Kearney, D., 2006, “Thermal Storage Commercial Plant Design Study for 2-Tank Indirect Molten Salt System: Final Report May 13, 2002–December 31, 2004,” National Renewable Energy Laboratory, Golden, CO, Subcontract Report No. NREL/SR-550-40166.
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Fig. 1

Capital cost structure for two-tank molten salt storage concept according to Ref. [1]

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Fig. 2

Capital cost structure for concrete storage concept [6]

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Fig. 3

Schematic illustration of a single storage cell of the CellFlux concept; directions of flows are shown for charging process

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Fig. 4

Simplified scheme of the CellFlux storage concept integrated into a CSP plant; directions of flows are shown for charging process

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Fig. 5

Simplified schemes of storage volumes with nonhomogenous porosity for packed bed and regular shaped storage materials

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Fig. 6

Redirection of air flow inside the storage volume by integration of baffles

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Fig. 7

Exemplary values for pressure losses in a finned tube heat exchanger of a 10 MWthermal storage module dependent on mean temperature difference between HTF and closed air loop

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Fig. 8

Exemplary values for mass of a finned tube heat exchanger of a 10 MWthermal storage module dependent on mean temperature difference between HTF and closed air loop

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Fig. 9

Concept for using part of the storage material to extend heat transfer surface

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Fig. 10

Exemplary geometry for extended heat transfer structure made of storage material

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Fig. 11

Required specific air volume flow dependent on cyclic temperature difference for three different values of minimum air temperature. Minimum values of required volume flow are indicated for three different heat transfer fluids.

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Fig. 12

Allowed pressure losses for storage system requiring 5% of generated electricity for air circulation. Results shown for different inlet temperatures and different HTFs depending on cyclic temperature difference.

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Fig. 13

Simplified scheme of parabolic trough power plant with parallel configuration of CellFlux storage unit. Mean temperature difference air/HTF in the storage unit is 10 K.

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Fig. 14

Temperature profiles of air and thermal oil in the heat exchanger of the CellFlux storage unit according to Fig. 13, charging

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Fig. 15

Detail of scheme of parabolic trough power plant similar to Fig. 7 with sequential configuration of CellFlux storage unit (charging). Mean temperature difference air/HTF in the storage unit is 21 K.

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Fig. 16

Temperature profiles in the two heat exchangers of the CellFlux storage system according to Fig. 15, charging



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