g., for grain or cellulosic ethanol, for algal or vegetable oils for biodiesel, or biomass gasification and Fischer–Tropsch reforming for

hydrocarbons. The photon energy densities and process productivities, plus the advantage of no arable land or freshwater displacement, create a scenario in which a minimal dedication of marginal land can serve to meet US renewable fuel standards. Comparisons are often made between the energy efficiencies of photosynthesis and those for solar electricity generation. It is important to make these comparisons in the proper context. Solar thermal or photovoltaic systems generate power requiring economical and efficient storage and transmission into the electrical grid, whereas the systems described here generate easily stored energy check details in liquid form. Moreover, values quoted for solar power systems are peak efficiencies that fall off precipitously under even momentary shading (Curtright and Apt 2008). Solar electricity efficiencies are also compounded by battery efficiencies and impedance losses that introduce system-specific variability. Manufacturing fuels to direct them into an existing refining, distribution,

and transportation infrastructure would be more fairly compared to other existing and developing technologies for energy conversion to reasonably storable forms and not to electricity. The aquatic species program report of 1998 (Sheehan et al. 1998) and the recently published National Algal Biofuels Technology Roadmap BIIB057 (2009) each conclude that photosynthesis could support

viable fuel processes given advances in organism and process productivities. Organism Thymidine kinase engineering, direct production, product secretion, and process optimization are areas for improvement to achieve viability. The direct photosynthetic platform is an alternative approach that addresses many of these ideas and offers efficiencies nearest to a thermodynamic maximum with more advantageous process economics. AZD9291 datasheet further application of systems and synthetic biology approaches could extend the range of efficiency for photosynthetic processes. For example, some photosynthetic microorganisms, particularly the nonoxygenic bacteria, have light capture systems allowing them to extend the PAR range into the near infrared (up to ~1,100 nm; Kiang et al. 2007). Incorporating these alternate photon-capturing and reaction center complexes into oxygenic production organisms to supplement endogenous systems and broaden the spectrum of light harvesting could further optimize efficiency relative to PAR. Other innovations that reduce culture reflection, enhance photon capture, and broaden temperature optima can also be envisioned using advanced organism-engineering tools.