2008; Rosenberg et al. 2008; Schenk et al. 2008; Angermayr et al. 2009; Stephens et al. 2010; Weyer et al. 2009; Wijffels and Barbosa 2010; Zemke et al. 2010; Zijffers et al. 2010) and for photosynthetic efficiency associated with production of plant biomass (Zhu et al. 2008, 2010) and we have incorporated the relevant aspects of these published reports to bound the current analysis. Our analysis of the algal process closely follows the assumptions of Weyer et al. (2009) with the exception that we use the more common open-pond scenario. Note that we also make a clear distinction between biodiesel esters

derived from algal biomass and fungible alkane diesel synthesized directly. Fig. 1 Schematic comparison between algal biomass and direct photosynthetic processes. The direct process, developed by Joule

and called Helioculture™, combines an engineered cyanobacterial organism NVP-BGJ398 datasheet supplemented with a product pathway and secretion system to produce and secrete a fungible alkane diesel product continuously in a SolarConverter™ designed to efficiently and economically collect and convert photonic energy. The process is closed and uses industrial waste CO2 at concentrations 50–100× higher than atmospheric. The organism is further engineered to provide a switchable control between carbon partitioning for biomass or product. The algal process is based on growth of an oil-producing culture in an industrial pond on atmospheric CO2, biomass harvesting, oil extraction, and chemical esterification to produce a biodiesel ester buy ACY-1215 Photosynthetic efficiency The cumulative energy input and the derived energy output are critical factors in comparing processes for fuel production. In discussing

energy input, photosynthesis has an additional consideration. Unlike most chemical processes that scale three-dimensionally with volume, photosynthetic processes scale with the two-dimensional area of solar capture. Light energy scales with the number of photons striking an area per unit time, e.g., μE/m2/s, where E (Einstein) is equal to one mole of photons. In a photosynthetic industrial process, areal productivity is most sensitive to the amount of light energy captured over the area of insolation and its conversion to product. Typically, either open algal ponds or all closed photobioreactors have been used. For efficient areal capture, a reactor design is required that optimizes solar insolation, culture density, gas mass transfer, mixing, and thermal management. Different fields of photonic research use different boundary conditions when discussing cumulative energy demand and it is important to distinguish them: specifically, efficiencies may be stated based either on (1) total solar radiation directed to the earth, (2) total radiation penetrating the atmosphere and striking the earth, or (3) total useful radiation that drives a process or phenomenon, e.g., weather, solar PV generation, photosynthesis, etc.