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RASEI Nozik Lecture

Reliable Decarbonized U.S. Electricity Systems

Nate Lewis | Caltech

Monday August 29th 2022, 1:30 PM

SEEC Auditorium C120

Using a data-driven approach based on 39 years of hourly weather data to derive the variability of the wind and solar resource across the contiguous U.S., we analyze the gaps between supply and historical demand that would be present in an electricity system in which generation was provided by variable wind and solar resources.  We then assess the dynamical relationships and in an idealized system assess the cost-effectiveness of various approaches to satisfy resource adequacy planning requirements, including overbuilding and extensive curtailment of variable renewable generation assets, short and long term storage embodied by batteries, flow batteries and power-to-gas-to-power, flexible nuclear generation, and flexible loads such as generation of hydrogen or electrofuels.  We additionally have assessed the implications of regionalization of generation assets and load-balancing regions such as California or the Western Interconnect on the needs for flexibility and storage in view of the increased variability and frequency and duration of resource droughts that occurs as the generation and load-balancing regions are confined geographically.  In California, we additionally show that addition of existing hydroelectric generation slightly increases the need for long-duration storage as opposed to decreasing it, due to the seasonal mismatch between hydroelectric generation and electricity demand.  The analyses moreover emphasize the need for multi-year planning to ensure resource adequacy in systems that have large contributions of generation from variable renewables.

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Department of Chemistry Lecture

Inorganic Phototropic Growth of Materials that See the Light

Nate Lewis | Caltech

Monday August 29th 2022, 4:00 PM

SEEC Auditorium C120

We have discovered a materials phenomenon, which we term inorganic phototropic growth, in which materials grow in real time, in 3-D space, towards a uniform intensity, uncorrelated beam of low intensity light, as occurs in for example palm trees, sunflowers, and corals.  The growth results in the rapid, light-directed formation of anisotropic complex, three-dimensional mesoscale morphologies of materials over macroscopic areas, providing access to nanostructures and morphologies that can not readily be made by any other method.  The phenomenon transcends traditional chemical and engineering disciplines: no lasers, no physical masks, no lithographic processing, no direct-write technology, no far-field modulation, no templates, and no chemical agents (ligands, surfactants) are used to direct the patterning, but full 3-D control is obtainable over the resulting morphology of the structure by manipulation the properties of the incident lightstimuli during growth. The nanostructures are created in a single-step synthesis and are determined both by the inherent response of the electronic processes within semiconductors to the presence of light, and by thetunable properties (e.g. wavelength, polarization, and direction) of light present during the electrodeposition. We have experimentally explored this emergent phenomenon by determining how specific optical inputs encode for specific morphologies, and have developed a model that accurately reproduces the experimentally observed nanostructures for the optical inputs and material systems explored thus far. Our work to date has been focused on the growth of Group II-VI materials (i.e. Se-Te alloys and PbSe); however, we expect that theemerging phenomenon underlying the growth process will prove general for the electrodeposition of semiconductors in the presence of light. We provide a brief overview of our work to date, and outline research directions designed to provide the further scientific insight into the processes behind this novel route to nanoscale and mesoscale materials design and synthesis that will be essential to the development of future technologies that exploit the phenomenon.