Research Papers

Economic Optimization of a Concentrating Solar Power Plant With Molten-Salt Thermocline Storage

[+] Author and Article Information
Scott M. Flueckiger

School of Mechanical Engineering,
Purdue University,
585 Purdue Mall,
West Lafayette, IN 47907-2088

Brian D. Iverson

Department of Mechanical Engineering,
435 Crabtree Building,
Brigham Young University,
Provo, UT 84602

Suresh V. Garimella

School of Mechanical Engineering,
Purdue University,
585 Purdue Mall,
West Lafayette, IN 47907-2088
e-mail: sureshg@purdue.edu

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received May 28, 2013; final manuscript received August 14, 2013; published online October 25, 2013. Assoc. Editor: Nathan Siegel.

J. Sol. Energy Eng 136(1), 011015 (Oct 25, 2013) (8 pages) Paper No: SOL-13-1153; doi: 10.1115/1.4025516 History: Received May 28, 2013; Revised August 14, 2013

System-level simulation of a molten-salt thermocline tank is undertaken in response to year-long historical weather data and corresponding plant control. Such a simulation is enabled by combining a finite-volume model of the tank that includes a sufficiently faithful representation at low computation cost with a system-level power tower plant model. Annual plant performance of a 100 MWe molten-salt power tower plant is optimized as a function of the thermocline tank size and the plant solar multiple (SM). The effectiveness of the thermocline tank in storing and supplying hot molten salt to the power plant is found to exceed 99% over a year of operation, independent of tank size. The electrical output of the plant is characterized by its capacity factor (CF) over the year, which increases with solar multiple and thermocline tank size albeit with diminishing returns. The economic performance of the plant is characterized with a levelized cost of electricity (LCOE) metric. A previous study conducted by the authors applied a simplified cost metric for plant performance. The current study applies a more comprehensive financial approach and observes a minimum cost of 12.2 ¢/kWhe with a solar multiple of 3 and a thermocline tank storage capacity of 16 h. While the thermocline tank concept is viable and economically feasible, additional plant improvements beyond those pertaining to storage are necessary to achieve grid parity with fossil fuels.

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Fig. 1

Schematic illustration of a molten-salt thermocline tank, including the porous quartzite rock bed and the liquid heel. Hot salt is supplied at the liquid heel through the top manifold and is extracted via the hot pump. Cold salt enters the porous bed through the bottom manifold but is also extracted through the manifold via the cold pump.

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Fig. 2

Steam generators and steam Rankine cycle layout. LP is the low pressure pump and HP is the high pressure pump.

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Fig. 3

Annual solar thermal energy discarded due to thermocline tank energy saturation. Values are normalized with respect to the total amount of sunlight available for collection. Plant performance corresponds to weather data recorded near Barstow, CA, for the year 1977.

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Fig. 4

Annual power tower plant capacity factor. Plant output increases with both solar multiple and thermocline tank energy capacity.

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Fig. 5

Annual capacity factor normalized with respect to the theoretical maximum for each solar multiple

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Fig. 6

Annual thermocline tank storage effectiveness. All cases exhibit effectiveness above 99%, validating the thermocline storage concept for implementation in long-term CSP applications.

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Fig. 7

Levelized cost of electricity for a 100 MWe power tower plant with thermocline energy storage. Minimum LCOE is observed at a solar multiple of 3 and thermocline energy capacity of 16 hours.

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Fig. 8

Individual power tower plant costs at the minimum LCOE of 12.2 ¢/kWhe. Heliostats incur the largest plant capital cost and require improvement to achieve grid parity with fossil fuel.




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