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Research Papers

A Numerical Model for Off-Design Performance Prediction of Parabolic Trough Based Solar Power Plants

[+] Author and Article Information
Giampaolo Manzolini1

Andrea Giostri, Claudio Saccilotto, Paolo Silva, Ennio Macchi

 Politecnico di Milano – Dipartimento di Energia, Via Lambruschini 4, 20156 Milano, Italy

For sake of simplicity, the variations in viscosity and density are neglected because of their limited impact on results;

Under design conditions, heat losses are considered equal to 170 W/m for hot headers and 120 W/m for cold one;

When phase transition occurs, the heat exchanger area is divided into sections each corresponding to a constant phase and the sum of each area must match design conditions.

The hourly step is limited because of the weather data resolution. A higher resolution can be used by patto ;

results are not symmetric to midday, because of TMY3 input;

1

Corresponding author.

J. Sol. Energy Eng 134(1), 011003 (Nov 01, 2011) (10 pages) doi:10.1115/1.4005105 History: Received July 12, 2010; Accepted September 06, 2011; Published November 01, 2011; Online November 01, 2011

This paper deals with the development and testing of an innovative code for the performance prediction of solar trough based concentrated solar power (CSP) plants in off-design conditions. Off-design calculation starts from data obtained through the on-design algorithm and considers steady-state situations. The model is implemented in flexible software, named patto (parabolic trough thermodynamic optimization): the optical-thermal collector model can simulate different types of parabolic trough systems in commerce, including a combination of various mirrors, receivers and supports. The code is also flexible in terms of working fluid, temperature and pressure range, and can also simulate direct steam generation (DSG) plants. Solar plant heat and mass balances and performance at off-design conditions are estimated by accounting for the constraints imposed by the available heat transfer areas in heat exchangers, as well as by the characteristic curve of the steam turbine. The numerical model can be used either for single calculation in a specific off-design condition or for complete year simulation, by generating energy balances with an hourly resolution. The model is tested with a view to real applications and reference values found in literature: results show an overall yearly efficiency of 14.8% versus the 15% encountered in the Nevada Solar One. Moreover, the capacity factor is 25%, i.e., equal to the value predicted by sam ® . Code potential in the design process reveals two different aspects: it can be used not only to optimize plant components and layout in feasibility studies but also to select the best control strategy during individual operating conditions.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 7

Gross power output as a function of HTF mass flow for various HTF maximum temperature (Tamb = 30°C)

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Figure 8

Gross power output as a function of HTF mass flow with variable ambient temperature

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Figure 9

Daily energy balances (21 June)

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Figure 10

Daily energy balances (21 December)

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Figure 11

Optimization of the minimum HTF mass flow rate for North–South (N–S) and East–West (E–W) orientations

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Figure 12

HTF temperature and mass flow variations on 21 June. Dotted lines refer to start-up and shut-down conditions

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Figure 13

Monthly electricity output for N–S and E–W orientations

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Figure 14

Comparison between monthly electricity outputs calculated according to sam Physical model [25] and patto codes

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Figure 15

Sankey diagram of yearly solar field energy production and losses

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Figure 1

K(θ) for two commercial solar collectors

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Figure 2

Incidence angle (solid lines) and incidence angle cosine (dotted line) on 21 June and 21 December for Daggett (CA) with a N–S orientation

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Figure 3

Mass flow coefficient variation at part load

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Figure 4

Turbine kinetic losses as a function of axial velocity

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Figure 5

Solar field efficiency as a function of HTF and ambient temperature (SCA = ET-100, Receiver = Solel Uvac, DNI = 800 W/m2 )

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Figure 6

Turbine inlet pressure (P_in_tur), steam mass flow (m_steam) and condensing pressure (P_cond) at part load

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