Spatial Light Dilution as a Technique for Conversion of Solar Energy to Algal Biomass

• Main Author: Dye, Daniel J.
• Format: Others
• Published: DigitalCommons@USU 2010
• Subjects: algae; biodiesel; efficiency; photobioreactor; renewable; solar; agricultural engineering; Mechanical Engineering; Optics; Physics
• Online Access: https://digitalcommons.usu.edu/etd/751; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1747&context=etd

A photobioreactor has been designed and developed to efficiently utilize solar irradiance through spatial dilution of sunlight. The concept of spatial light dilution is simple: incident sunlight is spread over a large surface area, thus reducing the photon flux density of the light. The implementation of this technique, however, is difficult. The reactor described within uses a new approach to spatial light dilution, utilizing recently-developed optical components to diffuse concentrated sunlight inside an algae culture. Preliminary productivity tests indicate a 2-3 fold increase in productivity per unit aperture (sunlight collection area) over a control reactor with direct-sunlight. Aperture productivity of up to 15 gm m-2 day-1 and total solar efficiency of 2% were achieved. A new parameter and yield coefficient are introduced. The parameter total light delivered is defined as the quantity of photons delivered per unit volume per day. The coefficient for yield of biomass on photons is also introduced. For the organism studied in this research, Neochloris oleoabundans, the yield of biomass on photons is approximately 1.09 gm mass per mol photons. The total light delivered to a culture over 24 hours, multiplied by the yield coefficient, provides an estimate of the volumetric productivity of the reactor in sequential-batch operation. In a series of laboratory studies, the total light delivered ranged from 0.097 to 0.945 mol photons L-1 day-1, and the volumetric productivity ranged from 0.11 to 0.945 gm L-1 day-1. A reactor productivity model, integrating reactor geometry and optics with the biomass yield coefficient and volumetric productivity model, predicts that the model organism in the proposed reactor can produce an annual average of 40 gm biomass per square meter of collector area. The model predicts an annual aperture yield of 14.6 kg m-2, at 3% efficiency. This predictive model can be applied to any location that solar data exists, and the techniques can be applied to other types of organisms and reactors to provide productivity estimates.