Boosting the optical and thermal efficiencies of parabolic trough concentrators is gaining renewal global interest for improving the overall concentrating solar power plant efficiency and reducing the specific costs of power generation. Using internal radiation heat shields in the annular space of the heat collection element is an attractive passive solution that is not well-addressed in the literature. This study is a first attempt to analyze and map both energetic and exergetic performances of parabolic trough concentrators in terms of the configuration of the radiation heat shield and the operating conditions of the concentrator. A 3D model based on Monte-Carlo ray tracing and computational fluid dynamics is developed, validated, and used to examine 420 combinations of design and operating parameters. The proposed design outperformed the conventional one in the whole spectrum of operating conditions, except for a narrow range of low operating temperatures and high flow rates. Floating radiation heat shields with small diameters and large shading angles enhanced the temperature uniformity of heat collection element and showed the highest enhancement ratios of both energy and exergy efficiencies, which were up to 15.4 and 14.4%, respectively. A radiation heat shield with a diameter of 75 mm and a shading angle of 150 degrees was found the best performing configuration for most operating conditions. Increasing the shield's emissivity (0.06) to that of the absorber tube (0.14) reduced the energy and exergy efficiencies by up to 33.75 and 29.06%, respectively. The effectiveness of the modified design was more pronounced at lower solar irradiance levels. The enhancements of energy and exergy efficiency decreased by 85.76 and 86.40% as the irradiance increased from 200 to 1000 W/m(2). However, the modified design was still more efficient at all considered values of emissivity and solar irradiance. (C) 2020 Elsevier Ltd. All rights reserved.