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Research Papers

# Economic Potential of Solar Thermal Power Plants With Direct Steam Generation Compared With HTF Plants

[+] Author and Article Information
Jan Fabian Feldhoff

Institute of Technical Thermodynamics, German Aerospace Centre (DLR), Pfaffenwaldring 38-40, 70569 Stuttgart, Germanyjan.feldhoff@dlr.de

Daniel Benitez

Flagsol GmbH, Aggripinawerft 22, 50678 Cologne, Germanydaniel.benitez@flagsol.de

Markus Eck

Institute of Technical Thermodynamics, German Aerospace Centre (DLR), Pfaffenwaldring 38-40, 70569 Stuttgart, Germanymarkus.eck@dlr.de

Klaus-Jürgen Riffelmann

Flagsol GmbH, Aggripinawerft 22, 50678 Cologne, Germanyklaus-juergen.riffelmann@flagsol.de

J. Sol. Energy Eng 132(4), 041001 (Aug 19, 2010) (9 pages) doi:10.1115/1.4001672 History: Received July 29, 2009; Revised April 06, 2010; Published August 19, 2010; Online August 19, 2010

## Abstract

The direct steam generation (DSG) in parabolic trough collectors is a promising option to improve the mature parabolic trough solar thermal power plant technology of the solar energy generating systems (SEGS) in California. According to previous studies [Langenkamp, 1998, “Revised LEC Projections and Discussion of Different DSG Benefits,” Technical Report No. DISS-SC-QA-02, Almeria, Spain; Price, , 2002, “Advances in Parabolic Trough Solar Power Technology,” ASME J. Sol. Energy Eng., 124(2), pp. 109–125; Zarza, E., 2002, “DISS Phase II Final Report,” Technical Report EU Contract No. JOR3-CT98-0277, Almeria, Spain], the cost reduction in the DSG process compared with the SEGS technology is expected to be 8–25%. All these studies were more or less preliminary since they lacked detailed information on the design of collector fields, absorber tubes required for steam temperatures higher than $400°C$, and power blocks adapted to the specific needs of the direct steam generation. Power blocks and collector fields were designed for four different capacities ($5 MWel$, $10 MWel$, $50 MWel$, and $100 MWel$) and different live steam parameters. The live steam temperature was varied between saturation temperature and $500°C$ and live steam pressures of 40 bars, 64 bars, and 100 bars were investigated. To assess the different cases, detailed yield analyses of the overall system were performed using hourly data for the direct normal irradiation and the ambient temperature for typical years. Based on these results, the levelized costs of electricity were determined for all cases and compared with a reference system using synthetic oil as heat transfer fluid. This paper focuses on two main project findings. First, the $50 MWel$ DSG system parameter comparisons are presented. Second, the detailed comparison between a DSG and a SEGS-like $100 MWel$ system is given. The main result of the investigation is that the benefit of the DSG process depends on the project site and can reach an 11% reduction in the levelized electricity cost.

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## Figures

Figure 1

Annual load curves of the DNI for the investigated sites

Figure 2

Calculated thermal collector efficiency excluding optical efficiency for SCHOTT’s new high temperature absorber tube coating (HTC) compared with its state-of-the-art absorber tube (PTR-70)

Figure 8

Mean yearly solar field efficiency depending on temperature and pressure with new high temperature coating for a 50 MW DSG collector field

Figure 9

Thermodynamic efficiency potential of the increased temperature or pressure level compared with the corresponding basic variant (x-axis label) for Seville

Figure 10

LEC of the three most promising 50 MW DSG options up to 100 bars

Figure 11

Sensitivity analysis of a 50 MW system for the main influencing parameters

Figure 12

LEC comparison of the HTF reference plant with the detailed 400°C/120 bars DSG system and further improved DSG options

Figure 5

Schematic diagram of the applied 50 MW power block with steam reheat and preheaters

Figure 3

Schematic diagram of a solar field layout

Figure 4

Schematic diagram of a DSG subfield with central steam separator

Figure 6

Gross efficiencies of the 50 MW power blocks for DSG and the 100 MW reference HTF plant

Figure 7

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