This paper proposes a novel U-3PSS two-axis sun-tracking mechanism with parallel mechanism. The tracker is energy saving due to most of the gravity of mobile platform and solar mirror/panel supported by the passive U chain. Two most important performance indices of a solar tracker, workspace and energy consumption are studied and the optimum design is investigated utilizing a complex method. Based on workspace and energy consumption, optimal configurations of the U-3PSS solar tracker and its nonredudnant counterpart are analyzed, respectively. By taking Beijing as a sample city where the tracker is placed, the trajectory planning of the tracker is investigated and the direction of two orthogonal axes of the U joint is studied. The power of the U-3PSS solar tracker and its nonredudnant counterpart with their optimal configurations in spring equinox, summer solstice, autumn equinox and winter solstice are compared. Furthermore, the workspace and consumed energy of two solar trackers are compared. The results show that the U-3PSS solar tracker has a bigger workspace and smaller energy consumption in one year than its counterpart - U-2PSS solar tracker. (C) 2016 Elsevier Ltd. All rights reserved.