2010 E3 Conference Posters

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Parasitic resistance effects of split-spectrum solar cell performance
(2010) Krohn, Jennifer; Ruden, Paul
Semiconductor 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.
Path Creation and Learning in the Clean Tech Industry
(2010) Marcus, Alfred
Clean tech – the production of electricity and fuels with a smaller environmental impact –saw a mini-investment boom occurred in the first decade of the 21st century. This study investigates the degree to which the strategies of clean tech investors varied over time in response to learning from investment successes and failures and from changes in public policy. The literature on path dependence predicts, all else equal, that initial patterns persist into the future. The past character of the investments will continue into the future without much alteration. Our model suggests that this pattern can be broken based on the feedback that investors receive from successful or unsuccessful rounds of venture capital funding and from the changes in the global economy, energy prices, and the clean tech polices of global governments. Thus, there is another perspective that should be applied to the strategic choices that investors in this domain make, that is learning theory. Its predictions would be that adjustments in strategic choices will take place based on factors included in our model.
Efficient Inorganic-Bonded Wood Panels for Construction Applications
(2010) Aro, Matthew
We have combined the unique properties of chemically-bonded inorganic binders with wood feedstock to develop fire-, moisture-, decay-, and mildew-resistant prototype composite panels for construction applications. The inorganic binders are magnesium-based and require significantly less energy to produce than the traditional petroleum-based resins found in most wood-based construction panels. The manufacture of the composite panels requires no heat, and the wood feedstock does not need to be dried. Thus, the manufacturing process requires much less energy and releases minimal VOCs when compared to traditional wood-based panels. Further, the inorganic binders do not contain formaldehyde, unlike most traditional resins. We envision this product as an improved and energy-efficient replacement for plywood, particleboard, and high- and medium-density fiberboard in several applications, including laminating platforms and substrates for laminate flooring and/or engineered wood flooring; laminating platforms for kitchen and bathroom countertops; and bottom panels for sink bases. We are gauging industry interest in these and other applications and are continuing with further development.
Adding Value to Ethanol Production Byproducts Through Production of Biochar and Bio-oil
(2010) Spokas, K.; Ruan, R.; Morrison, B.
The goal of this project is to increase the value of distillers grain by sequestering carbon and producing additional renewable energy resources (bio-oil and syngas) through microwave assisted pyrolysis. More specifically, we will have an optimized process for capturing additional bio-energy, and at the same time producing a potential soil improvement agent from an existing byproduct. We will examine the potential increase in soil fertility and carbon storage of this produced biochar. The potential long-term outcomes of this research are the development and promotion of on-farm energy production using microwave assisted pyrolysis and distillers grain as a feedstock as well as improving the sustainability of corn production through returning carbon to the field.
Development of a Solar Smoleniec/Stirling Hybrid Thermo-Mechanical Generator
(2010) Goldberg, Louise F.
The Thermo-Mechanical Generator was invented in 1967 and is an ingeniously simple and elegant heat engine operating on a Stirling thermodynamic cycle that can yield cogenerated electrical and thermal energy from moderately hot heat sources (200-500°C). A new version of this heat engine has been invented that is capable of operating off concentrated solar energy provided by inexpensive, acrylic Fresnel lenses. A key innovation in the technology is the use of a digital thermodynamic Smoleniec/Stirling cycle to optimize the performance of the heat engine in real time. A state space analysis of the engine has been completed that demonstrates that the invention can operate successfully. So far, the analysis has predicted an output electrical power of 1.9 kW when operating between hot and cold temperature limits of 500 C and 20 C respectively. Under these conditions the engine operates at a frequency of 87 Hz.
Hydrostatic Transmission for Wind Power Generation RS-0008-09
(2010) Thul, Brenen; Dutta, Rahul; Stelson, Kim; Bohlmann, Brad; Gust, Mike; Kildegaard, Arne
The 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.
Lactic acid fermentation using dairy manure as the sole carbon and nitrogen source
(2010) Sun, Jianping; Yao, Wanying; Miller, Curtis; Zhu, Jun
L-Lactic acid is one of the most important organic acids utilized in food, pharmaceutical, and chemical industries. A major and unique contribution that lactic acid can make to a renewable environment is its use in the production of biodegradable plastics that can replace the fossil-fuel-based non-biodegradable plastic materials widely used in many aspects of life today, leading to the reduction of global consumption of the diminishing petroleum resources. This project is aimed at exploring a novel idea of producing lactic acid from dairy manure, a vast renewable resource, via batch fermentation by microorganisms such as fungi, with emphasis on the feasibility and possibility of microbial use of the nutrients in the manure (carbon and nitrogen source) for lactic acid production. The specific objectives of this project can be summarized as follows: 1) develop effective processes for dairy manure hydrolysis by fungi by determining the most effective microbial culture or flora and the optimal operating parameter values for hydrolysis and 2) investigate the feasibility and techniques of converting the hydrolysates from dairy manure into lactic acid through fermentation without external nutrients and optimize the fermentation conditions to enhance lactic acid production.
Biobased Pressure-Sensitive Adhesives
(2010) Roerdink Lander, Monique; Zhang, Jiguang; Houtman, Carl J.; Severtson, Steven J.
Pressure sensitive adhesive (PSA) products have become ubiquitous in our homes and offices through address labels, stamps, sticky notes, and tapes. The majority of these PSAs are based on petroleum-derived acrylates. In 2006, more than 300 million dry pounds of acrylic adhesive was sold in the United States. Incorporation of biomass-derived resources as a substitute for acrylates will make a significant contribution in the development of sustainable products. We developed PSAs with high biomass-content using biomass-based macromonomers, which can copolymerize with standard adhesive acrylates and replace 40-60% of petroleum-based raw materials. The work described here is an example of a novel, yet pragmatic approach to develop sustainable PSA formulations by simple modifications of successful commercial products, while maintaining performance.
Sustainable Forest Feedstock for Bioenergy Production: Environmental, Economic, and Social Availability
(2010) Becker, Dennis R.; Klapperich, Jon; Domke, Grant; Kilgore, Michael A.; D'Amato, Anthony W.; Current, Dean; Ek, Alan R.
Despite the potential for significant utilization in the production of bioenergy and biofuels, little is known of the economic, environmental, and social availability of forest biomass or the cumulative effects of increased demand. Past studies have estimated total physical biomass available without taking into account the range of constraints imposed by transportation distances, harvest costs, environmental laws, or site access. Supply estimates are further complicated by uncertainties about the willingness of private landowners to sell timber or thin forests for biomass. The result is a potential overestimation of supply that threatens the viability of new and existing businesses, and the sustainability of the forest resource. Study results are presented on the long-term physical availability of forest biomass across northern Minnesota and Wisconsin to compare to measures of environmental, economic, and social availability. Variations in management intensity are modeled to illustrate changes in volume under different sustainability thresholds and implications for increasing the use of biomass for bioenergy production in the Lake States.
The Unintended Climate Consequences of Carbon Sequestration in North American Forests
(2010) Snyder, Peter K.
Planting forests is one of few readily available and proven approaches to mitigating climate change through the sequestering of atmospheric carbon dioxide (CO2). In order to avoid a doubling in the concentration of atmospheric CO2 from preindustrial values by mid-century will require a multitude of technologies and approaches - carbon sequestration through forest planting being one of the more practical ones. However there is considerable uncertainty over whether afforestation/reforestation will actually do more harm than good. Planting a forest may decrease the surface reflectivity resulting in greater net radiation being absorbed at the surface and thus, surface warming. In some cases this warming can more than offset the climate benefit derived from carbon sequestration. Using a dynamic global vegetation model, the competing effects of fraction cover of forest, stand age, and local climate on the total benefit to the climate system is evaluated. Model results indicate that regionally there are large variations in the climate benefit of forest placement. This study offers new insight on the feasibility of large-scale forest planting as a climate mitigation strategy.
PBC-DFT : An Efficient Method to Calculate Energy Band Gaps of Conducting Polymers used in Solar Cells
(2010) Schmidt, Jennifer A.; Koehn, Ryan E.; Pappenfus, Ted M.; Alia, Joseph D.
In recent years, conducting polymers have gained attention for their promising application in solar cells due to their potential low cost, lightweight, and flexibility. Desirable polymers have a small band gap and a low HOMO energy level. Methods of finding this band gap exist using density functional theory (DFT) by calculating the energy gaps of increasing oligomer lengths (n), and plotting the HOMO-LUMO gap (in eV) as a function of the reciprocal polymer length (1/n). This method, however, proves time consuming and computationally costly. An alternative, less time-consuming method using periodic boundary conditions (PBC) exists. In our research, we studied existing donor-acceptor polymers from the literature and used PBC to calculate their band gaps for comparison with experimental data. To perform these calculations we used DFT at the B3LYP/3-21G(d) level of theory on optimized dimers. The PBC method yields results consistent with experimental values and can be useful in determining theoretical band gaps prior to synthesis which can aid in saving valuable lab time.
Renewable Energy and Sustainable Chemistry Across the Undergraduate Chemistry Curriculum
(2010) Pappenfus, Ted M.; Carpenter, Nancy E.; Soderberg, Timothy J.; Power, Caleb; Koehn, Ryan E.; Schmidt, Jennifer
Issues of energy and sustainability are having a direct impact on the public and are capturing the interests of many. As result, it is no surprise that science, including the field of chemistry, will become more connected with society in the future. To address this connection, we are in the process of integrating important elements of renewable energy and sustainable chemistry across the undergraduate chemistry curriculum at the University of Minnesota, Morris. This project strives to create a curriculum which is more interdisciplinary with respect to both teaching and research and which introduces topics that are timely, yet essential in preparing undergraduate students. Our initial efforts are focused on three key areas: (i) developing new courses in renewable energy and sustainability; (ii) integrating photovoltaics across the undergraduate curriculum; and (iii) illustrating the role of biochemistry in renewable energy and sustainability. Our goal is to develop a far-reaching energy and sustainable chemistry curriculum that complements the traditional curriculum and better prepares our future graduates for success in addressing global problems. An overview of the project will be presented along with our preliminary results.
Heat Transfer in Liquid Piston Isothermal Air Compressor/Expander
(2010) Rice, Andrew; Zhang, Chao; Saadat, Mohsen; Li, Perry; Simon, Terry
An "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.
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.