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Open Access Publications from the University of California

Scholarly Works (9 results)

  • Article
LBL Publications (2013)
    Cover page: Exploring Light's Interactions with Bubbles and Light Absorbers in Photoelectrochemical Devices using Ray Tracing
    • Thesis
    • Peer Reviewed
    UC Berkeley Electronic Theses and Dissertations (2015)

    The use of optically concentrating lenses integrated with wireless photoelectrochemical cells provides a mechanism to potentially reduce the energy input required to manufacture solar fuels-producing devices. In this work, a modeling approach is used to assess the annual fuel production from such integrated devices. The model captures optical, heat transfer, photoelectrochemical and climactic phenomena. The variation of design parameters such as cell dimensions, lens type, photovoltaic cell type, optical reflection management coatings and deployment location is investigated for a system that uses an optical concentration ratio of 10. The model then predicts the system’s operating temperature, operating current density and solar fuel production efficiency for every hour of the year in any location for which sufficient weather data is available.

    It is found that the devices that perform most efficiently are sufficiently small to enable effective optical capture and minimize potential losses in the electrolyte. Small ion exchange membrane coverage fractions are sufficient to enable optimal light capture while exhibiting small ohmic drops in the photoelectrochemical cell. Careful management of antireflection coatings and protection layers is required to maximize optical transmission to the current-limiting junction in the device’s photovoltaic cell. Employing simple passive cooling to maintain sufficiently low cell temperatures during extreme, quiescent ambient conditions can be achieved in certain climates but not in others. Additional measures must be undertaken to prevent electrolyte freezing in colder climates. However, despite these challenges, annual weighted average solar to hydrogen efficiency of 11.2% can be realized in high insolation locations, and stably efficient operation is possible with proper cell design. Locations with very poor direct solar irradiation resources can still exhibit annual weighted average solar to hydrogen efficiencies in excess of 9%. Additionally, the model’s predictions of device temperature are found to be in agreement with results produced in COMSOL Multiphysics. These investigations therefore help to elucidate the potential research and development work needed for future development and deployment of this technology.

      Cover page: A Computational Assessment of Solar Fuels-Producing Devices from Thermal, Optical and Energy Yield Perspectives
      • Article
      • Peer Reviewed
      LBL Publications (2016)
      The commercial deployment of wireless photoelectrochemical cells (PECs) may provide a viable means to close the anthropogenic carbon cycle associated with the global transportation sector. The growing body of research on PECs has largely focused on developing and integrating the materials necessary for robust, efficient solar-fuel production on the laboratory benchtop. While these efforts are a prerequisite for the commercialization of PECs, deployed PECs will have to contend with extreme heat, cold, and insolation variations in the outdoor environment. They will also have to operate efficiently throughout their lifetime and in multiple locations. This paper reports a computational framework for estimating the hourly profiles of time-varying temperature and solar-to-hydrogen efficiency that optically concentrating, wireless PECs will attain over the course of a typical year. It is found that annual weighted average solar-to-hydrogen efficiencies in excess of 9 to 11% can be achieved in extremely cloudy and sunny locations, respectively. Additionally, typical PECs will likely incur damage due to overheating or freezing; measures to protect PECs from extreme heat and cold are outlined. The findings also help to bring into focus issues regarding real-world deployment of energy-generation technologies and methodologies towards tackling them.
        • Article
        • Peer Reviewed
        LBL Publications (2014)
        Membrane-encapsulated devices are attractive for solar-driven hydrogen production, as their design mitigates problems with concentration overpotentials, gas bubbles, and safety inherent in liquid electrolyte water-splitting devices. However, the competing processes such as heat, water, gas, and ion transport make it nontrivial to design such devices. Here, we show analytical expressions and associated design spaces for critical membrane dimensions and material properties required for stable and efficient gas, heat, proton, and water transport. The best condition for stable gas transport in thin film or gas channels is given by the critical Damköhler number. The maximum heating of the device is governed by the Heating and Nusselt numbers, which can be tuned to the desired level. The optimal dimensions of the device, to operate under tolerable ohmic losses, correspond to the maximum value of scaled Power-loss factor. An optimal device architecture is proposed for stable and efficient operation. © 2014 The Electrochemical Society.
          • Article
          Lawrence Berkeley National Laboratory (2006)

          The development of test plans to validate the CERTS Microgrid concept is discussed, including the status of a testbed. Increased application of Distributed Energy Resources on the Distribution system has the potential to improve performance, lower operational costs and create value. Microgrids have the potential to deliver these high value benefits. This presentation will focus on operational characteristics of the CERTS microgrid, the partners in the project and the status of the CEC/CERTS microgrid testbed. Index Terms Distributed Generation, Distributed Resource, Islanding, Microgrid, Microturbine

            Cover page: Validation of the CERTS Microgrid Concept The CEC/CERTS Microgrid Testbed
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2013)
            Salmonella is an important cause of bacterial food-borne gastroenteritis. Salmonella encounters multiple abiotic stresses during pathogen elimination methods used in food processing, and these stresses may influence its subsequent survivability within the host or in the environment. Upon ingestion, Salmonella is exposed to gastrointestinal acidity, a first line of the host innate defense system. This study tested the hypothesis that abiotic stresses encountered during food processing alter the metabolic mechanisms in Salmonella that enable survival and persistence during subsequent exposure to the host gastrointestinal acidic environment. Out of the four different abiotic stresses tested, viz., cold, peroxide, osmotic, and acid, preadaptation of the log-phase culture to cold stress (5°C for 5 h) significantly enhanced survival during subsequent acid stress (pH 4.0 for 90 min). The gene expression profile of Salmonella preadapted to cold stress revealed induction of multiple genes associated with amino acid metabolism, oxidative stress, and DNA repair, while only a few of the genes in the above-mentioned stress response and repair pathways were induced upon exposure to acid stress alone. Preadaptation to cold stress decreased the NAD+/NADH ratio and hydroxyl (OH·) radical formation compared with those achieved with the exposure to acid stress alone, indicating alteration of aerobic respiration and the oxidative state of the bacteria. The results from this study suggest that preadaptation to cold stress rescues Salmonella from the deleterious effect of subsequent acid stress exposure by induction of genes involved in stress response and repair pathways, by modification of aerobic respiration, and by redox modulation.
              Cover page: Preadaptation to Cold Stress in Salmonella enterica Serovar Typhimurium Increases Survival during Subsequent Acid Stress Exposure
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2017)
              Microbial community analysis experiments to assess the effect of a treatment intervention (or environmental change) on the relative abundance levels of multiple related microbial species (or operational taxonomic units) simultaneously using high throughput genomics are becoming increasingly common. Within the framework of the evolutionary phylogeny of all species considered in the experiment, this translates to a statistical need to identify the phylogenetic branches that exhibit a significant consensus response (in terms of operational taxonomic unit abundance) to the intervention. We present the R software package SigTree, a collection of flexible tools that make use of meta-analysis methods and regular expressions to identify and visualize significantly responsive branches in a phylogenetic tree, while appropriately adjusting for multiple comparisons.
                Cover page: SigTree: A Microbial Community Analysis Tool to Identify and Visualize Significantly Responsive Branches in a Phylogenetic Tree
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2016)
                The hydrogen energy provided by solar-driven photoelectrochemical (PEC) water splitting must be greater than the energy used to produce and operate the technology, as a fundamental system requirement to enable energetic benefits to society. PEC H2 production will require significant advances from both basic scientific research and applied technology development, prior to manufacturing and field deployment. To identify opportunities and priorities, here we use prospective life cycle system modeling to investigate the net-energy significance of six characteristics describing the PEC life cycle: (1) embodied energy of active cell materials, (2) embodied energy of inactive module materials, (3) energy intensity of active cell fabrication, (4) energy intensity of PEC module assembly, (5) initial energy use for production of balance-of-system (BOS), and (6) ongoing energy use for operation and end-of-life of BOS. We develop and apply a system model describing material and energy flows during the full life cycle of louvered thin-film PEC cells and their associated modules and BOS components. We find that fabrication processes for the PEC cells, especially the thin-film deposition of active cell materials, are important drivers of net energy performance. Nevertheless, high solar-to-hydrogen (STH) conversion efficiency and long cell life span are primary design requirements for PEC systems, even if such performance requires additional energy and material inputs for production and operation. We discuss these and other system dynamics, and highlight pathways to improve net energy performance.
                  Cover page: Opportunities to improve the net energy performance of photoelectrochemical water-splitting technology
                  • Article
                  • Peer Reviewed
                  UC Irvine Previously Published Works (2016)
                  An integrated cell for the solar-driven splitting of water consists of multiple functional components and couples various photoelectrochemical (PEC) processes at different length and time scales. The overall solar-to-hydrogen (STH) conversion efficiency of such a system depends on the performance and materials properties of the individual components as well as on the component integration, overall device architecture, and system operating conditions. This Review focuses on the modeling- and simulation-guided development and implementation of solar-driven water-splitting prototypes from a holistic viewpoint that explores the various interplays between the components. The underlying physics and interactions at the cell level is are reviewed and discussed, followed by an overview of the use of the cell model to provide target properties of materials and guide the design of a range of traditional and unique device architectures.
                    Cover page: Modeling, Simulation, and Implementation of Solar‐Driven Water‐Splitting Devices
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