Solar-driven photoelectrochemical water splitting technology is a promising avenue for a sustainable hydrogen production. In this work, a comprehensive 2-dimensional model is developed and numerically simulated with hematite (alpha-Fe2O3) as the principal photo electrode. The model evaluates light absorption, charge transport and electrochemical reactions to elucidate the effects of light transmitting materials, electrolyte height and electrolyte velocity on hydrogen and oxygen gas production. Results indicated that major losses in photocurrents are attributed to the transparent conducting oxide while losses due to the electrolyte increase with its height. Gas concentrations increase with increasing photocurrent densities and also in the direction of the flow. Gas bubbles however decrease with increasing electrolyte velocity. From these results, light reception in the reactor is uneven and poses a bigger challenge due to the bias in gas bubble distribution. Prospects of upscaling tandem schemes hence not only lie in the semiconductor material combinations but rather in the proper integration of system components and operating conditions. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.