Performance analysis of parabolic trough solar collector under varying optical errors

ABSTRACT

A typical parabolic trough solar field consists of a number of collectors that are made up of two main components: a parabola and a receiver. Various errors arise during the design/manufacturing, installation, and operation phases of the solar field. These errors influence the shape of the parabola as well as the alignment of the receiver. The present article aims to quantify the effect of these errors on the performance of a typical parabolic trough collector (PTC). To do so, a coupled optical-thermal model has been developed. The Monte Carlo Ray Tracing (MCRT) method is used to create and solve the optical model. The latter is then integrated with Computational Fluid Dynamics (CFD) to investigate the PTC’s thermal performance. The losses in performance induced by these errors are quantified. The analysis showed that small errors such as receiver dislocation or tracking error could induce a significant cut in the optical and overall performance. The loss in the optical efficiency due to tracking error of 16 mrad is about 50%. The error in the parabola profile can induce a reduction of 60% in the optical efficiency and up to 80% in the overall efficiency. A 0.05 m dislocation of the receiver can reduce the optical and overall efficiencies by about 37% and 49%, respectively. The results of the present study should support researchers and engineers in defining the optimum acceptable uncertainties through various phases of the design, manufacturing, and installation of the parabolic trough solar field.

KEYWORDS:

• Parabolic trough solar collector
• performance analysis
• optical study
• solar thermal modelling
• quantification

Nomenclature

A_a aperture area of collector parabola [m²]

A_e area of each element in tube [m²]

A_f geometric factor

D distance between intersection point on parabola and on absorber tube [m]

f focal length [m]

G_C geometric concentration ratios

h_p height of parabola [m]

L length of parabola [m]

N number of ray

Ne number of rays hits the element

q heat flux distribution [W/m²]

u_x,u_y,u_z directional cosines

W_a width aperture [m]

x,y,z Cartesian coordinate

x’,y’,z’ coordinate of intersection point on parabola

x₀,y₀,z₀ coordinate of initial position

Greek symbols

α tracking error angle [mrad]

α_aabsorptance of absorber tube

α Random number

α₀ Optical efficiency [%]

θ deflection angle [mrad]

θ_inc incidence angle [°]

θ_rim rim angle [°]

θ_sun sun finite size of the sun [mrad]

ρ reflectivity of reflector

τ_g transmittance of glass

Φ azimuthal angle [rad]

Φ_c circle angle [°]

Abbreviations

CFD Computational Fluid Dynamics

CSP Concentrating Solar Power

DNI Direct normal irradiance [W/m²]

EES Engineering Equation Solver

FVM Finite Volume Method

HTF Heat Transfer Fluid

LCR Local Concentration Ration

MCRT Monte Carlo Ray Trace

PTC Parabolic Trough Collector

SNL Sandia National Laboratory

Acknowledgments

The present study is supported by the Algerian Government under contract PRFU-A11N01ES160220190002 (Mechanical Engineering and Development Laboratory, National Polytechnic School, Algiers). Also, the support from the Directorate-General for Scientific Research and Technological Development (DG-RSDT) of the Algerian government in the form of a research grant is gratefully acknowledged.

Omar Behar gratefully acknowledges the Clean Combustion Research Center of the King Abdullah University of Science and Technology.

Disclosure statement

No potential conflict of interest was reported by the author(s).