ARPA-E's Direct Solar Fuel Technology workshop addressed the challenges and opportunities associated with Direct Solar Fuel Technologies. The goal of the workshop was to bring together thought leaders from distinct science communities to collectively develop new ideas and identify the most promising R&D pathways to capture and utilize solar energy for the production of infrastructure-compatible, organic high-energy transportable fuels. Specifically, ARPA-E explored the intersection of potential synergies that might bridge high efficiency energy capture and complex biosynthesis among the following: (1) high-efficiency organic and inorganic light harvesting; (2) synthetic biology for the creation of complex, high energy, infrastructure-compatible organic species; and (3) extremophile biology for the consideration of novel energy transduction modalities.

The workshop brought together experts in all three disciplines to discuss the challenges and opportunities at the interface of high-efficiency energy capture and the autonomous synthesis of complex fuels. Following a brief introduction and short presentations participants broke into working groups to consider the challenges and opportunities of solar fuels modality.

The primary objectives of the workshop were to:

• Identify the most challenging aspects of high-efficiency, deployable technologies for direct solar fuels, and promising R&D paths to meet such challenges;
• Develop a realistic set of quantifiable metrics for evaluating progress towards these goals and assessing R&D success;
• Foster a spirit of camaraderie between and among ARPA-E and the workshop participants

The one day workshop was scheduled on October 21, 2009, at the Booz Allen Hamilton Virginia Square Conference Center, Arlington, Virginia. Approximately 40 experts from academia and National/Federal labs participated. The meeting's output will help direct the actions of ARPA-E towards the most promising and appropriate high risk, high return R&D funding opportunities and management strategies. The meeting proceedings are summarized below.

Speakers and Presentations:

Dr. Eric Toone, Program Director, ARPA-E

“ARPA-E Background and Workshop Rationale” (pdf)

Dr. Robert Kelly, North Carolina State University and Dr. Michael Adams, University of Georgia

“H2-driven CO2 Fixation by Extremely Thermoacidophilic Archaea” (pdf)

Dr. Devens Gust, Arizona State University

“Bio-Inspired Solar Fuel Production” (pdf)

Dr. Pamela Silver, Harvard Medical School

“Designing Light Dependent Ecosystems and the Role of Synthetic Biology” (pdf)

Dr. Anna-Louise Reysenbach, Portland State University

“Hidden Microbial Diversity at High Temperatures” (pdf)

Dr. James Liao, University of California Los Angeles

“Photo-synthetic Biology for Fuels” (pdf)

Dr. John Golbeck, Pennsylvania State University

“Direct Solar CO2 to Formic Acid Conversion Using a Biological/Organic Photochemical Half-cell” (pdf)

Dr. Dan Nocera, Massachusetts Institute of Technology

“Personalized Energy for 1 (x 6 billion)” (pdf)

Breakout Sessions:

During the workshop, participants broke into 4 groups to discuss various energy related concepts. The first Breakout Session grouped participants in similar fields of expertise and the energy discussion questions were category specific (see below). Each group then made a short summary slide of what they discussed.

Metabolic Engineering/Synthetic Biology (pdf)

Discussion questions:

• What are the most promising biosynthetic routes to infrastructure compatible high-energy density liquid fuels? Especially interesting are C6-C10 branched chain alkanes, as well as longer (to dodecane) n-alkanes?
• What are the most promising approaches to the identification and/or development of novel biosynthetic routes to infrastructure compatible high-energy density liquid fuels?
• What are the fundamental biochemical precursors to these pathways? What are potential branch points into which novel biosynthetic pathways could be inserted?
• What are the most promising biochemical routes to secreting hydrocarbons from a living cell?

Biological Diversity (pdf)

Discussion questions:

• What fundamental energy inputs are utilized with high-efficiency (i.e. energy in to biomass out) for primary metabolism by organisms that does not use either light or the assimilation of other high-energy species (e.g. carbohydrates, lipids, etc) as energy inputs?
• Which (if any) of these energy input paradigms can be exported to other organisms?
• Which (if any) organisms that use novel energy inputs are genetically tractable? What are key metabolic convergence points; i.e. what are the key high energy intermediates in primary metabolism that might serve as junction points for the insertion of novel biosynthetic pathways?

Photon Capture Group A (pdf) and Photon Capture Group B (pdf)

Discussion questions:

• What are the most promising approaches to high-efficiency photon energy capture that use earth-abundant elements? Consider both efficiency (i.e. photon energy in to useable energy out) as well as deployability (resistant to photobleaching, oxygen degradation, water sensitivity, catalyst poisoning, etc.).
• What are the most promising energy outputs from artificial photon capturing systems? Here, “most promising” means both highest efficiency (i.e. fraction of photon energy in delivered as useable energy out) and most likely to be integrated with a biological system.

The second Breakout Session grouped different individuals of diverse scientific backgrounds to tackle what the most promising approach to the development of production of direct solar fuels given the discussions in the first Breakout Sessions. The four groups were asked the same question:

• • “Given the results of the first breakout sessions, what is the most promising approach to the development of an efficient, robust system capable of the production of direct solar fuels, i.e. of harvesting photons and producing infrastructure-compatible high-energy density liquid fuels in a single reactor?”

Discussion Results:

Group A (pdf)

Group B (pdf)

Group C (pdf)

Group D (pdf)