Institute on the Environment
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Browsing Institute on the Environment by Subject "College of Science and Engineering"
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Item Efficient charge transfer from excited state dye molecules into nanoparticles as a model for dye sensitized solar cells(2011-11) Hue, Ryan; Vatassery, Rajan; Hinke, Jon; Mann, Kent; Blank, David; Gladfelter, WayneWe deconstruct the DSSC and focus on the sensitization mechanism to extract a thorough understanding of the charge separation process. Our study of the dye's interactions with the nanoparticles provides details about the attachment, the surface environment and the ability for the dyes to inject electrons in competition with loss mechanisms.Item Heat Transfer in Liquid Piston Isothermal Air Compressor/Expander(2010) Rice, Andrew; Zhang, Chao; Saadat, Mohsen; Li, Perry; Simon, TerryAn "open accumulator" high pressure compressed air approach has been proposed for storing excess wind energy locally. This approach does not require special geological sites or additional fossil fuel as in conventional compressed air storage (CAES) approach. It relies on a combined hydraulics and pneumatic approach to attain both high energy density and power density. A critical element in the approach is an isothermal high pressure air compressor/expander. In this regard, research is underway to develop a liquid piston based compressor/expander with improved heat transfer and sealing properties.Item Hydrostatic Transmission for Wind Power Generation RS-0008-09(2010) Thul, Brenen; Dutta, Rahul; Stelson, Kim; Bohlmann, Brad; Gust, Mike; Kildegaard, ArneThe University of Minnesota is performing research on the application of continuously variable hydrostatic transmissions for wind turbines. By replacing the gearbox of traditional wind turbines with a continuously variable hydrostatic transmission (HST), the rotor speed could be controlled independent of the generator speed. This would allow the use of more conventional synchronous generators instead of higher cost variable speed permanent magnet generators, and eliminate the need for power electronics. The gearbox of traditional wind turbines is one of the primary sources of premature failure and maintenance. HSTs have been the dominant choice for propulsion in agricultural, construction, forestry, and mining vehicles for more than half a century. Thus, replacing the gearbox in a wind turbine with an HST should improve the reliability of the machine. The IREE seed funding will be used by the University of Minnesota to begin the process of building a lab scale (50 kW) test stand to perform research on applying HSTs to wind turbines. The research will initially focus on determining the best drivetrain hardware configuration as well as on optimizing the wind turbine’s control algorithm.Item Lossless Holographic Spectrum Splitter In Lateral Photovoltaic Devices(2011-11) Lin, Di; Torrey, Ethan R.; Leger, James R.; Cohen, Phil. I.Lateral photovoltaic structures require efficient partitioning of the solar spectrum and light delivery to the respective cells. Single-junction cells can be used, eliminating the need for current and lattice matching. We investigate the design issues associated with multiplexed volume holograms in fulfilling this role in a two-cell lateral PV system.Item New method to convert heat directly into electricity(2011-11) Song, Yintao; Srivastava, Vijay; Bhatti, Kanwal; Leighton, Chris; James, Richard D.Item Parasitic resistance effects of split-spectrum solar cell performance(2010) Krohn, Jennifer; Ruden, PaulSemiconductor solar cells absorb photons of energy greater than their band-gap and convert the photon energy to electrical energy less than the band-gap. Consequently, small gap solar cells can absorb a large part of the solar spectrum, but deliver little energy per photon absorbed. Large gap solar cells deliver more energy per photon, but can absorb only the high energy part of the spectrum. Splitting the solar spectrum into multiple segments with diffractive elements that separate the incident radiation spatially and focusing it on solar cells optimized for the narrower bands facilitates the energy conversion. Here, we explore limitations to this approach imposed by inevitable parasitic effects. Specifically, we introduce series and parallel resistances into an ideal solar cell model. Resistance of the cell material and the contacts, and current leakage through the junction, due to defects, can be captured by this model. Subsequently, current density characteristics, maximum power density, and efficiency are determined. Highly conductive, low band-gap cells show performance degradation due to series resistance, while highly resistive, large gap cells are sensitive to junction leakage. As a specific case, we consider a three-cell solar cell array fabricated from InxGa1-xN of varying composition.Item Solar Fuels from Nanostructured Ceria-based Oxides(2011-11) Petkovich, Nick; Rudisill, Stephen; Boman, Daniel; Stein, Andreas; Venstrom, Luke; Davidson, Jane H.The solar resource can be converted into liquid fuels to offset petroleum use in the transportation sector using a thermochemical process based on cerium oxide (CeO2). To increase the rate of fuel production in the process, three-dimensionally ordered macroporous (3DOM) CeO2-based oxides are employed.Item Thermochemical Seasonal Energy Storage using Calcium Chloride(2011-11) Quinnell, Josh; Davidson, JaneSpace heating accounts for 45 percent of all residential energy. The major challenge in using solar thermal systems for space heating is the inadequate winter solar resource. To address this challenge, we have developed long-term storage to save solar energy from the summer for use in the winter.Item Wide band gap CIGS based absorber for photovoltaic application(2010) Nagaich, Kush; Campbell, Stephen A.The sun is one of the clean and sustainable energy source of the known universe. A solar cell application is mainly based on converting the photon energy to electrical energy which can be used in many other areas. Copper ternary chalcogenide based solar cells became a recent solution to the high cost problem of solar cells. Copper Indium diselenide solar cells as it appears from the name has an architecture of several layers which are sorted by CIGS (copper indium gallium selenide) as absorber layer, CdS (cadmium sulfide) as buffer layer, ZnO (zinc oxide) and ITO (Indium Tin Oxide) layers as window layer and top contacts for the device. With the recent laboratory scale improvements, the efficiency of CIGS solar cells rose to 19.9 % by NREL. One of the current research areas is based on sustaining the same efficiency on a bigger scale. In this work, the CIGS layer is deposited on Mo sputtered four inch soda-lime glass substrates. CIGS deposition step is done by physical vapor deposition of elemental species in an ultra-high vacuum system. CdS is deposited using chemical bath deposition. Top window layers ZnO, ITO and Ni/Al are sputter deposited. In this work we are attempting to develop a wide band-gap absorber material based on CIGS with low trap density and good interface lattice matching. We have done some preliminary investigation on Al doped CIGS films to see the effect on the optical band gap. Al doped CIGS devices will be fabricated to investigate the effect of Al doping on trap density.