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.
Nomenclature
Aa aperture area of collector parabola [m2]
Ae area of each element in tube [m2]
Af geometric factor
D distance between intersection point on parabola and on absorber tube [m]
f focal length [m]
GC geometric concentration ratios
hp 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]
ux,uy,uz directional cosines
Wa 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]
αaabsorptance of absorber tube
α Random number
α0 Optical efficiency [%]
θ deflection angle [mrad]
θinc incidence angle [°]
θrim rim angle [°]
θsun sun finite size of the sun [mrad]
ρ reflectivity of reflector
τg transmittance of glass
Φ azimuthal angle [rad]
Φc 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).