This paper presents the results of a numerical investigation of entropy generation of supercritical water in a vertical tube with concentrated incident solar heat flux on one side. The characteristics of heat transfer and pressure drop in the tube are analyzed first. The decrease in shear stresses near the pseudo critical region results in the decrease in turbulence production and the increase in friction factor. It is the common cause of heat transfer deterioration and an abrupt increase in pressure drop near the pseudo-critical region. Entropy generation mainly depends on the temperature gradient along the vertical tube's radial direction which is due to the thickness of the thermal boundary layer and the intensity of secondary flow. The results further show that entropy generation of supercritical water in a vertical tube with concentrated incident solar heat flux on one side decreases with increasing mass flux and decreasing incident heat flux. In addition, to balance the minimum irreversible losses and hydraulic resistance in the tube in a central receiver, the relationship between incident flux and mass flux is determined. (C) 2016 Elsevier Ltd. All rights reserved.