Tailoring optical systems to optimized photobioreactors

Photobioreactor designs are commonly restricted by the ability of conventional optical systems to deliver prescribed solar intensities and flux distributions at high collection efficiency. We explore how non-imaging optical designs can be tailored to reactor conditions that maximize bioproductivity. We consider two distinct classes of photobioreactors: (I) stationary outdoor units; and (2) an indoor reactor that requires the total separation of the collection and delivery of solar radiation. For practical and economic reasons, the latter obliges solar collectors of immense optical concentration. The outdoor direct-illumination units comprise stationary mirrored troughs placed around standard reactor shapes, and replace expensive reactors with inexpensive reflectors, while enhancing bioproductivity. For the indoor reactors, we adopt the recent innovation of dual-axis tracking solar fiber-optic mini-dish concentrators to collect, concentrate and transport sunlight to a remote reactor. Contoured polymeric light extractors distribute the light uniformly and efficiently inside the reactor. In all cases, the principal demands are: (a) accommodating reactor shapes with high ratios of irradiated surface area to volume; (b) uniform flux on the irradiated surfaces; (c) high efficiency for collecting and delivering solar radiation; (d) being based on existing and affordable technologies; and (e) compactness. Flux levels of 2000 mumol m(-2) s(-1) of photosynthetically active radiation are realistically attainable over the entire transparent surface of the reactor. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.