Population and societal growth coupled with technological progress, have all lead to a rapid increase in energy usage and consequent depletion of fossil fuel reserves. Although one could question the credibility of these estimations as supported by the recent revision in the case of natural gas reserves, the fact that the worldwide demand will keep on growing unabated leaves no doubt that the solution is not to procrastinate but to look for alternative sources of energy. At the same time, there is a growing belief that the use of fossil fuel and the consequent release of greenhouse gases are mainly responsible for the observed global warming trend. Hence there is a big push for developing new sources of clean, alternative energy for replacing the fossil fuels. In addition, if the source is renewable, that will further help provide a long term solution. However, one should note that the Sun is the main source of energy; the energy received from the Sun is transformed into various sources like solar, wind, ocean, geothermal, nuclear, biomass, fossil fuel, etc., over widely differing space and time scales by mainly ecological and artificial processes. The term renewable has a spatial and temporal connotation. Hence what is “renewable” for one nation or part of the world may not be renewable and in fact even be available for another part of the world. Thus energy source has become an important commodity for survival and progress and has to be evaluated on thermoeconomic and socioeconomic bases. It requires 21st century cutting edge science, technology and systems for harvesting energy from the available sources and transforming it efficiently and economically into electricity, heat or power required for human consumption with minimal perturbation to the ecology. It is also important to note that the present energy crisis has occurred mainly because of dependence on only a few sources. Hence this needs to be addressed not only by exploring and evaluating all possible sources but also by developing systems for efficient transformation, storage and distribution of energy. All this involves development of technology in all areas and their cross transplantation for reaching the goal and sustaining the progress.

The continuing public concern and the engineering interest prompted the Advanced Energy Systems Division (AESD) of ASME in collaboration with the Solar Energy Division (SED) to start a Conference on Energy Sustainability in 2007. The success of that conference in meeting the goals of providing a forum for researchers in universities and research laboratories, and engineers in industries to present, discuss and disseminate knowledge relating to energy science and technology prompted organizing the 2008 ASME 2nd International Energy Sustainability Conference at Jacksonville, FL between Aug. 10–14. The papers published in this issue are amongst a few selected from that Conference and invited for consideration for publication. They underwent a 2nd round of peer review for meeting the journal standards.

A large number of papers were presented in the area of energy efficiency relating to systems, processes and operation, which covers a large part of this issue also. The paper by Ryu et al. demonstrates energy savings and storage by using waste heat from a turbine to drive a vapor absorption refrigeration system supplying two loads including an off peak ice making system to store energy during off peak hours for utilizing it during peak demand, thus enabling load balancing of the distributed energy system. Cohen et al. have proposed a technique for optimizing the operation of coal based electric power plants by turning the emission reduction system on and off depending on load, thus reducing the cost of electricity while keeping the cost of operation and the total plant emission also under control. The paper by Mahmoud et al. describes techniques for detailed modeling of leakage and friction in rotary expanders for estimating the inefficiency caused by those mechanisms. Luckow et al. demonstrate the potential of polymers as efficient and economical material for application in seawater–methane heat exchangers that could be used in the liquefaction of natural gas on offshore platforms by considering the energy required for manufacturing also. Similarly, the paper by Shah et al. suggests a method of assessing exergy consumed during the complete life cycle for designing heat exchangers starting from scratch rather than accounting for energy wasted during operation or functioning of the component only.

There are three papers dealing with thermoeconomic analysis of hydrogen as well as coal to liquid (CTL) production technologies. Zhu et al. have applied detailed exergy analysis to evaluate and optimize various CTL technologies for system performance improvement. Harwego et al. not only present useful information for selection of the type of infrastructure required for realizing the green dreams of hydrogen economy but also provide baseline data for the cost of producing hydrogen using high temperature electrolysis, which appears to compete reasonably well with other methods like steam-methane reforming, which results in production of the unwanted CO2 also. Lubis et al. have reported a detailed life cycle including environmental impact analysis of hydrogen production by thermochemical water splitting using the copper–chlorine cycle. They have concluded that the main environmental impact occurs during the construction phase of the nuclear and thermochemical plants and improvement in construction processes/techniques are required for mitigation of such impact.

Finally, Fonk et al., in their paper have made use of the present estimates of population, renewable and nonrenewable energy consumption, expected growth rates of population as well as per capita energy consumption to estimate the required growth rates of the renewable energy resources like biomass, solar, wind and geothermal for maintaining a sustainable energy future. Such assessments are essential for future planning of energy sustainability.

I would like to thank all authors for submitting their research work to the special issue of this journal. In addition, I am grateful to the members of the panel listed below, who readily agreed to contribute their time and expertise for reviewing the papers. Finally my thanks are due to Dr. Sriram Somasundaram, a General Chair for the Conference who supported the publication of this issue and to Dr. Andrew Wojtanowicz, Editor of this journal, without whose help, along with that of his Editorial Assistant, Ms. Janet Dugas', it would not have been possible to bring out this special issue.

Review Panel

Professor Abel Hernandez Guerrero, Universidad de Guanajuato, Salamanca, Mexico

Professor Antonio Bula,Universidad del Norte, Barranquilla, Colombia

Professor George Tsatsaronis, Technische Universität Berlin, Germany

Professor James Menart, Wright State University, Dayton, OH

Professor Reinhard Radermacher, University of Maryland, College Park, MD

Professor Yogi Goswami, University of South Florida, Tampa, FL