Pilot tests of sequential dark and photo fermentation H2 production were for the first time conducted in a 11 m3 reactor (3 m3 for dark and 8 m3 for photo compartments). A combined solar and light-emitting diode illumination system and a thermal controlling system was installed and tested. With dark fermentation unit maintained at pH 4.5 and 35 °C and photo fermentation unit at pH 7.0 and 30 °C, the overall biogas production rate using hydrolyzed corn stover as substrate reached 87.8 ± 3.8 m3/d with 68% H2 content, contributed by dark unit at 7.5 m3-H2/m3-d and by photo unit at 4.7 m3/m3-d. Large variation was noted for H2 production rate in different compartments of the tested units, revealing the adverse effects of poor mixing, washout, and other inhomogeneity associated with large reactor operations.