Biobutanol: science,engineering, and economics

Among several liquid alternative fuels, biobutanol has shown great promise because of its very similar properties to gasoline. This review provides an overview of research activities in acetone–butanol–ethanol (ABE) fermentation over the past two and a half decades. We have addressed seven important facets of ABE fermentation, viz. biochemistry, microbial cultures, alternative substrates, solvent recovery, fermentation mode and reactor designs, mathematical modeling, and economics. Development of mutant strains having higher yield, selectivity and tolerance to inhibition, and search for cheap alternative substrates for fermentation are most important thrust areas in biobutanol production. New and efficient processes have been developed for in situ removal and recovery of the ABE solvents. Several rigorous kinetic and physiological models for fermentation have been formulated, which form useful tool for optimization of the process. These research activities have been reviewed in this paper. Finally, we have summarized studies on the economic viability of large‐scale ABE fermentation processes employing various process designs, substrates, and microbial cultures. With the use of new strains, inexpensive substrates, and superior reactor designs, economic potential of ABE fermentation has been found to be highly attractive. Research efforts in science, engineering, and economics of ABE fermentation have brought biobutanol close to commercialization as liquid alternate fuel. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrogen carriers: Production,transmission, decomposition,and storage

Recognizing the potential role of liquid hydrogen carriers in overcoming the inherent limitations in transporting and storing gaseous and liquid hydrogen, a complete production and use scenario is postulated and analyzed for perspective one-way and two-way carriers. The carriers, methanol, ammonia and toluene/MCH (methylcyclohexane), are produced at commercially viable scales in a central location, transmitted by rail or pipelines for 2000 miles, and decomposed near city gates to generate fuel-cell quality hydrogen for distribution to refueling stations. In terms of the levelized cost of H₂ distributed to the stations, methanol is less expensive to produce ($1.22/kg-H₂) than MCH ($1.35/kg-H₂) or ammonia ($2.20/kg-H₂). Levelized train transmission cost is smaller for methanol ($0.63/kg-H₂) than ammonia ($1.29/kg-H₂) or toluene/MCH system ($2.07/kg-H₂). Levelized decomposition cost is smaller for ammonia ($0.30–1.06/kg-H₂) than MCH ($0.54–1.22/kg-H₂) or methanol ($0.43–1.12/kg-H₂). Over the complete range of demand investigated, 10–350 tpd-H₂, the levelized cost of H₂ distributed to stations is aligned as methanol « ammonia ~ MCH. With pipelines at much larger scale, 6000 tpd-H₂, the levelized cost decreases by ~1 $/kg-H₂ for ammonia and MCH and much less for methanol. Methanol is a particularly attractive low-risk carrier in the transition phase with lower than 50-tpd H₂ demand.     

Emerging evaluation issues: persistence, behavior, rebound, and policy

In this paper, we focus on a select group of technical and policy issues, which are currently important and/or are expected to become more critical in the coming years. The first set of technical issues deals with the evaluation of (1) persistence, (2) behavior and behavior change, and (3) rebound. We provide an overview of the importance of these issues, discuss key data collection and analytical challenges involved in evaluating them, and identify some recent methodological advances that have been made in these areas. These technical issues are becoming more important as energy efficiency and demand side management are increasingly being relied upon as a means of achieving long-term energy resource and environmental objectives. The second set of policy issues deals with (1) the evaluation of energy efficiency at the “policy” rather than the “program” level, (2) the use of “top-down” rather than “bottom-up” evaluation of energy efficiency programs and policies, and (3) closing the loop between evaluators and implementers. We provide an overview of the importance of these issues, particularly as seen by policymakers at the state, federal, and international levels.     

Oxide electrochromics: Why, how, and whither

Electrochromic oxides form the basis of “smart windows” which are able to provide energy efficiency and indoor comfort simultaneously. This paper attempts to give an introduction to “smart windows” technology, which finally seems to be ready for large-scale applications. The “whys” and “hows” are discussed from the viewpoints of materials, device technology, low-cost manufacturing aspects, and applications to buildings as well as niche products. Furthermore, there are some speculations as to the “whithers” of oxide electrochromics for applications to buildings of the future.     

LiMoNAED: a limited motion, non-shading, asymmetric, ecliptic-tracking dish

The conventional design of a parabolic dish for a small solar conversion system places the receiver along the line between the center of the dish and the sun. This forces the receiver to move in a large arc during tracking, and produces some shading of the dish. In some applications, such large movement of the receiver is not acceptable. A new concentrator design is proposed for small systems with a constraint of limited mobility of the receiver. This is accomplished by using a first polar axis and a second axis that is aligned with the normal to the ecliptic plane. The new design features limited motion of the receiver, with inclination changing only within ±23.45°; off-axis reflector to eliminate shading; constant rotation speed in both axes; and constant flux distribution on the receiver.