Simulation of the daily sunlight illumination pattern for bacterial photo-hydrogen production

Methods of illumination to simulate the daily sunlight irradiation pattern were studied in relation to photohydrogen production using the photosynthetic bacterium Rhodobacter sphaeroides RV. Three illumination patterns were compared, in which the light intensity was changed in 1, 3, or 6 steps. As a control, outdoor experiments were also carried out over a 3-d period in Tsukuba, August 1996. Outdoors, hydrogen production by Rba. sphaeroides RV was dependent on the sunlight intensity: the total volume of hydrogen produced per day varied from 14 to 28 l.m(-2), while the total light energy ranged from 5.5 to 6.4 kWh.m(-2). d(-1). The maximum hydrogen production rate was 2.8 l.m(-2).h(-1) under a 4.5-cm light path and the average light energy conversion efficiency was 1.1%. Indoors, the hydrogen production rate was found to be independent of the mode of illumination among the three patterns employed. The maximum hydrogen production rate was 3.3 l.m(-2).h(-1) with a light energy conversion efficiency of 1.0%, and it was concluded that the single-step illumination method provides an appropriate simulation of sunlight. Saturation of hydrogen production occurs during high light intensity around noon and this plays a key role in the simulation.