ECS Lecture | Nathan S. Lewis

208th ECS Meeting | Los Angeles, CA | Oct. 17, 2005

Nathan S. Lewis

Scientific Challenges in Sustainable Energy Technology

Nathan S. Lewis, the 2002 George L. Argyros Professor of Chemistry at the California Institute of Technology, delivered the plenary address on Monday morning.

Prof. Lewis has been on the Caltech faculty since 1988 and is also a principal investigator at the Beckman Institute Molecular Materials Resource Center on campus. His research interests include light-induced and “dark” electron transfer reactions at semiconductor/electrolyte interfaces, photoelectrochemistry and solar energy conversion, solar energy processes involving transition-metal complexes and dye-sensitized solar cells, and novel uses of conducting polymers and polymer/conductor composites including the development of sensor arrays.

Prof. Lewis began his highly entertaining and informative lecture by calibrating the audience on power units ranging from a watt (consumed by a laptop computer) to a kW (typical of a bread toaster device) all the way to a terawatt (1 TW=1012 W) typical of global power consumption. His talk was organized into the present primary power mix, future constraints imposed by sustainability, theoretical and practical energy potential of various renewables, and the challenges to exploit renewables economically on the needed scale to meet environmental constraints. He referred to his campus website (; see the “Global Energy Perspective” link) where the talk is available and can be downloaded. He showed figures on the available fossil fuel resource base, illustrating that there is plenty of coal for the next hundred odd years—enough to meet projected demands. Thus, renewables will not play a role in primary power generation unless or until technological/cost breakthroughs are achieved or externalities are introduced (e.g., environmentally driven carbon taxes).

The talk then switched to a discussion on energy and sustainability, and specifically the analysis of Marty Hoffert et al. (“Energy Implications of Future Atmospheric Stabilization of CO2 Content,” Nature, 395, 881, 1998). These authors underscore the pitfalls of a “wait-and-see” policy. They point out that stabilization of greenhouse gases (specifically CO2) in the atmosphere, to levels that are considered safe in terms of catastrophic climate changes, will not occur unless and until policy incentives are made on renewable energy R&D to overcome socioeconomic inertia. Capitalization of carbon-free power is needed on a 10-30 TW scale by 2050. This, in the authors’ crystal ball, could require efforts, perhaps international, pursued with the urgency of the Manhattan Project or the Apollo space program. Lewis then displayed graphic examples of observations of global climate change including the systematic and gradual retreating of glaciers (Glacier National Park, 1910-1997), melting of the Greenland ice sheet, coral bleaching, and the rising of sea levels.

The talk then turned to examining the energy potential of various forms of renewable energy (hydro, geothermal, ocean/tides, wind, biomass, and solar) and also the nuclear (fission and fusion) option. Carbon sequestration technology was reviewed. The final part of the talk centered on solar energy conversion. It was noted that solar electricity is currently capacity-limited (100 MW mean power output manufactured in 2001) and also subsidized in countries like Japan and Germany. The industry shows high growth; but starts from a small base. The cost is favorable, and technology competitive, in off-grid installations. The rudiments of solar photovoltaic technology were then presented, the author noting the need to produce fuel to offset the down-time (at nightfall) of a solar energy system. A fuel cell was compared and contrasted with a photoelectrolysis system that produces hydrogen from water.

The speaker concluded his fastmoving talk by noting that “disruptive” technologies were needed (e.g., solar paint) to make the solar option practically viable in a renewable energy mix. Policy changes will also be needed to gradually wean ourselves away from carbon-centric energy, because failure is not an option in terms of the environmental consequences.