Diluted cheese whey (CW) solution was used for hydrogen gas production by electro-hydrolysis using photo-voltaic cells (PVC) as source of electricity. Effects of initial chemical oxygen demand (COD) concentration on the rate and yield of hydrogen gas production were investigated using a completely mixed and sealed reactor with aluminum electrodes. Cumulative hydrogen gas formation (CHF) increased with increasing initial COD concentration. The highest cumulative hydrogen gas volume (26472 mL), hydrogen gas production rate (4553 mL d(-1)), hydrogen yield (7004 mL H-2 g(-1) COD), and percent COD removal (21.5%) were obtained with initial COD of 35172 mg L-1. H-2 gas formation from water control was only 5365 mL. pH of the CW solution increased with decreasing conductivities during the course of experiments. Gas phase contained more than 99% H-2 at the end of experiments. The highest energy efficiency (20.4%) was also obtained with the highest COD content. Nearly pure hydrogen gas formation by electro-hydrolysis of cheese whey using PVC panels was proven to be an effective method. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.