Pilot tests of sequential dark and photo fermentation H-2 production were for the first time conducted in a 11 m(3) reactor (3 m(3) for dark and 8 m(3) 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 degrees C and photo fermentation unit at pH 7.0 and 30 degrees C, the overall biogas production rate using hydrolyzed corn stover as substrate reached 87.8 +/- 3.8 m(3)/d with 68% H-2 content, contributed by dark unit at 7.5 m(3)-H-2/m(3)-d and by photo unit at 4.7 m(3)/m(3)-d. Large variation was noted for H-2 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.