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Research Papers

# Assessment of Solar Power Tower Driven Ultrasupercritical Steam Cycles Applying Tubular Central Receivers With Varied Heat Transfer Media

[+] Author and Article Information
Csaba Singer, Reiner Buck, Robert Pitz-Paal, Hans Müller-Steinhagen

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

J. Sol. Energy Eng 132(4), 041010 (Oct 04, 2010) (12 pages) doi:10.1115/1.4002137 History: Received August 21, 2009; Revised June 28, 2010; Published October 04, 2010; Online October 04, 2010

## Abstract

For clean and efficient electric power generation, the combination of solar power towers (SPTs) with ultrasupercritical steam cycle power plants could be the next development step. The methodology of the European concentrated solar thermal roadmap study was used to predict the annual performance and the cost reduction potential of this option applying tubular receivers with various appropriate high temperature heat transfer media (HTM). For the assessment, an analytical model of the heat transfer in a parametric 360 deg cylindrical and tubular central receiver was developed to examine the receiver’s efficiency characteristics. The receiver’s efficiency characteristics, which are based on different irradiation levels relative to the receiver’s design point, are, then, used to interpolate the receiver’s thermal efficiency in an hourly based annual calculation of one typical year that is defined by hourly based real measurements of the direct normal irradiance and the ambient temperature. Applying appropriate cost assumptions from literature, the levelized electricity costs (LEC) were estimated for each considered SPT concept and compared with the reference case, which is a scale-up of the state of the art molten salt concept. The power level of all compared concepts and the reference case is $50 MWel$. The sensitivity of the specific cost assumptions for the LEC was evaluated for each concept variation. No detailed evaluation was done for the thermal storage but comparable costs were assumed for all cases. The results indicate a significant cost reduction potential of up to 15% LEC reduction in the liquid metal HTM processes. Due to annual performance based parametric studies of the number of receiver panels and storage capacity, the results also indicate the optimal values of these parameters concerning minimal LEC.

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## Figures

Figure 1

Power tower system schematic with modified temperatures and USC process parameters (4)

Figure 2

Assessment tools and data workflow

Figure 3

Efficiency matrix of the solar field used for assessment

Figure 4

Example of the receiver efficiency characteristic depending on ambient temperature and levelized irradiation/solar salt, 335 MWth incident power at DP, and six serial panels

Figure 5

Schematic heliostat efficiency of the preliminarily designed heliostat field with 335 MW thermal input onto the receiver at DP/37°23′N, Seville, Spain

Figure 6

Flux distribution onto the tubular central receiver at DP

Figure 7

Schematic of the tubular receiver model (side view). Note: if the total number of panels is odd, the symmetry axis for the calculations is prior to the last panel, which will, then, be a flow-through from both sides with twice as high a mass flow as the panels before it. If the total number of panels is even, the symmetry axis for the calculations is after the last panel of each half.

Figure 8

Height averaged flux distribution over the receiver’s perimeter for different irradiation levels with exemplified panel specific average flux (horizontal lines) for the DP with six serial panels

Figure 9

Draft of the area specific heat balance of one tube

Figure 10

Thermal receiver efficiency at DP over number of applied panels using different HTM

Figure 11

Thermal receiver efficiency at DP including thermal loss due to parasitics over number of applied panels using different HTM

Figure 12

Efficiency matrices of applied Na and solar salt, respectively, using two or 12 serially arranged panels estimated with and without parasitic losses of the receiver

Figure 13

LEC and the influence of the receiver parasitics over the number of panels with NaNO3–KNO3 as HTM

Figure 14

LEC and the influence of the receiver parasitics over the number of panels with LiCl–KCl as HTM

Figure 15

LEC and the influence of the receiver parasitics over the number of panels with Sn as HTM

Figure 16

Cost reduction potential with optimal and equal storage size and optimal number of panels

Figure 17

Cost assumption sensitivity on the LEC

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