SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 9 - MAY 5, 2006
44 ENERGY PRODUCTION AND CONVERSION
Includes specific energy conversion systems, e.g., fuel cells; and solar, geothermal, windpower, and waterwave conversion systems; energy storage; and traditional power generators.
For technologies related to nuclear energy production see 73 Nuclear Physics.
For related information see also 07 Aircraft Propulsion and Power; 20 Spacecraft Propulsion and Power; and 28 Propellants and Fuels.
20060011314 National Renewable Energy Lab., Golden, CO USA
Improving Battery Design with Electro-Thermal Modeling. Preprint
Pesaran, A.; Bharathan, D.; Kim, G.; Vlahinos, A.; Duong, T.; Apr. 2005; 16 pp.; In English Report No.(s): DE2005-15016308; NREL/CP-40-37652; No Copyright; Avail.: National Technical Information Service (NTIS)
Temperature greatly affects the performance and life of batteries in electric and hybrid vehicles under real driving conditions, so increased attention is being paid to battery thermal management. Sophisticated electrochemical models and finite element analysis tools are available for predicting the thermal performance of batteries, but each has limitations. In this study we describe an electro-thermal finite element approach that predicts the thermal performance of a cell or module with realistic geometry, material properties, loads, and boundary conditions. To show the process, we simulated the thermal performance of two generations of Panasonic prismatic nickel-metal-hydride modules used in the Toyota Prius. The model showed why the new generation of Panasonic modules had better thermal performance. Thermal images from two battery modules under constant current discharge indicated that the model predicts the experimental trend reasonably well. These tools will greatly enhance the opportunity for lithium and other advanced batteries to perform better and become cost-effective alternatives in the future. The model has been used to improve the thermal performance of cylindrical lithium-ion batteries. NTIS
Electric Batteries; Electric Motor Vehicles
20060011317 Duke Univ., Durham, NC, USA
Modeling Metallic Precipitate Dissolution in Silicon Under Point Defect Injection. Final Subcontract Report, January 20, 2004-January 19, 2005
Tan, T. Y.; May 2005; 18 pp.; In English Report No.(s): DE2005-15016265; NREL/SR-520-37991; No Copyright; Avail.: Department of Energy Information Bridge
We have formulated the problem of gettering of metallic precipitates in Si for which there exists a volume misfit between the precipitate and the Si matrix material. The gettering process is modeled using an Al-Si liquid layer, and the volume misfit associated with dissolving the precipitates is assumed as accommodated by point defects, which may be dominated by vacancies (V), self-interstitials (I), or both contributing. Under the condition that V and I attained dynamical equilibrium, we found that for analytic purposes, the problem reduces to either the V or the I alone case, with the fast-diffusing case dominating. Our initial simulation results on gettering of FeSi2 (with a misfit of -0.15) showed that the process can be sped up by the injection of V. NTIS
Dissolving; Getters; Injection; Photovoltaic Conversion; Point Defects; Precipitates; Silicon
20060011611 National Renewable Energy Lab., Golden, CO USA
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Advanced in Solar Radiometry and Metrology
Myers, D.; Andreas, A.; Reda, I.; Gotseff, P.; Wilcox, S.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860501; NREL/CP-520-36989; No Copyright; Avail.: National Technical Information Service (NTIS)
The Solar Radiometry and Metrology task at the National Renewable Energy Laboratory (NREL) provides traceable optical radiometric calibrations and measurements to photovoltaic (PV) researchers and the PV industry. Traceability of NREL solar radiometer calibrations to the World Radiometric Reference (WRR) was accomplished during the NREL Pyrheliometer Comparison in October 2003. The task has calibrated 10 spectral and more than 180 broadband radiometers for solar measurements. Other accomplishments include characterization of pyranometer thermal offset errors with laboratory and spectral modeling tools; developing a simple scheme to correct pyranometer data for known responsivity variations; and measuring detailed spectral distributions of the NREL High Intensity Pulsed Solar Simulator (HIPSS) as a function of lamp voltage and time. The optical metrology functions support the NREL Measurement and Characterization Task effort for ISO 17025 accreditation of NREL Solar Reference Cell Calibrations. Optical metrology functions have been integrated into the NREL quality system and audited for ISO17025 compliance. NTIS
Metrology; Radiometers
20060011612 National Renewable Energy Lab., Golden, CO USA
CIGS Thin-Film Solar Cell Research at NREL: FY04 Results and Accomplishments
Ramanthan, K.; Bhattacharya, R. N.; Contreras, M. A.; Hasoon, F. S.; Abushama, J.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860691; NREL/CR-520-37020; No Copyright; Avail.: Department of Energy Information Bridge
The Solar Radiometry and Metrology task at the National Renewable Energy Laboratory (NREL) provides traceable optical radiometric calibrations and measurements to photovoltaic (PV) researchers and the PV industry. Traceability of NREL solar radiometer calibrations to the World Radiometric Reference (WRR) was accomplished during the NREL Pyrheliometer Comparison in October 2003. The task has calibrated 10 spectral and more than 180 broadband radiometers for solar measurements. Other accomplishments include characterization of pyranometer thermal offset errors with laboratory and spectral modeling tools; developing a simple scheme to correct pyranometer data for known responsivity variations; and measuring detailed spectral distributions of the NREL High Intensity Pulsed Solar Simulator (HIPSS) as a function of lamp voltage and time. The optical metrology functions support the NREL Measurement and Characterization Task effort for ISO 17025 accreditation of NREL Solar Reference Cell Calibrations. Optical metrology functions have been integrated into the NREL quality system and audited for ISO17025 compliance. NTIS
Solar Cells; Thin Films
20060011615 National Renewable Energy Lab., Golden, CO USA
Local Built-in Potential on Grain Boundary of Cu(In,Ga)Se2 Thin Films
Jiang, C. S.; Noufi, R.; Ramanathan, K.; AbuShama, J.A.; Moutinho, H. R.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860499; NREL/CP-520-36981; No Copyright; Avail.: Department of Energy Information Bridge
We report on a direct measurement of two-dimensional potential distribution on the surface of Cu(In,Ga)Se2 (CIGS) thin films using a nanoscale electrical characterization of scanning Kelvin probe microscopy (SKPM). The potential measurement reveals a higher surface potential or a smaller work function on grain boundaries (GBs) of the film than on the grain surfaces. This demonstrates the existence of a local built-in potential on GBs and that the GB is positively charged. The role of the built-in potential in device performance was further examined by tuning Ga content or band gap of the film. With increasing Ga content, the GB potential drops sharply in a Ga range of 28%-38%. Comparing the change in the built-in potential to the theoretical and experimental photoconversion efficiencies, we conclude that the potential plays a significant role in the device conversion efficiency of NREL's three-stage CIGS device. NTIS
Grain Boundaries; Microscopy; Scanners; Thin Films
20060011616 National Renewable Energy Lab., Golden, CO USA
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Conductive Atomic Force Microscopy of CdTe/CdS Solar Cells
Moutinho, H. R.; Dhere, R. G.; Jiang, C.S.; Al-Jassim, M. M.; Kazmerski, L. L.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860498; NREL/CP-520-37014; No Copyright; Avail.: Department of Energy Information Bridge
Conductive atomic force microscopy (C-AFM) is a recently developed technique that applies an electric voltage between a very sharp tip and the sample, permitting the study of the electrical properties of the sample with very high spatial resolution. It also provides current-voltage measurements at well-defined spots. C-AFM is applied simultaneously with atomic force microscopy, providing topographic and current images of the same region. In this work, we analyze CdTe/CdS samples, before and after CdCl2 treatment, and after bromine/methanol and nitric/phosphoric etches. The as-deposited samples show grains with different contrasts, indicating that the material is not electrically uniform. The CdCl2 treatment resulted in less conductive grain boundaries, suggesting a relative decrease in the conductivity at these locations. After the bromine/methanol etch, the conductivity at grains boundaries was higher than inside the grains, whereas for the nitric/phosphoric etch the conductivity increased over the entire surface. NTIS
Atomic Force Microscopy; Cadmium Tellurides; Electric Potential; Solar Cells; Spatial Resolution
20060011617 National Renewable Energy Lab., Golden, CO USA
Integrating Deposition, Processing, and Characterization Equipment within the National Center for Photovoltaics
Nelson, B.; Robbins, S.; Sheldon, P.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860497; NREL/CP-520-37018; No Copyright; Avail.: Department of Energy Information Bridge
The purpose of the process integration project of the National Center for Photovoltaics (NCPV) is to develop an infrastructure that will allow researchers to gain new knowledge that is difficult--if not impossible--to obtain with existing equipment. This difficulty is due, in part, to the state of our existing tool set, which lacks sufficient in-situ or real-time measurement capabilities, or lacks access to analytical tools where the sample remains in a controlled environment between deposition and processing or measurement. This new infrastructure will provide flexible and robust integration of deposition, processing (etching, annealing, etc.), and characterization tools via a standardized transfer interface such that samples move between tools in a controlled ambient. This concept will also require the cooperation of experts from various material technologies and characterization disciplines to work directly with each other to obtain answers to key scientific and technological questions. Ultimately, this synergistic effort between NREL staff, universities, and the photovoltaic (PV) industry--around an integrated tool base--will add to the PV knowledge base and help move many PV technologies forward. NTIS
Characterization; Deposition; Photovoltaic Conversion; Solar Energy
20060011618 National Renewable Energy Lab., Golden, CO USA
Electronic and Optical Properties of Spinel TCOs: SnZn2O4, SnCd2O4, and Cdln2O4
Wei, S. H.; Segev, D.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860496; NREL/CO-520-37008; No Copyright; Avail.: Department of Energy Information Bridge
Using the band-structure method, we have studied the electronic and optical properties of the transparent conducting oxides SnZn2O4, SnCd2O4, and CdIn2O4. We analyzed the atomic and orbital characters of the band edge states and explained the general trends observed in the fundamental band gap, the optical band gap, the energy difference between the first and the second conduction bands, and the electron effective mass. General rules for designing more efficient transparent conducting oxides are proposed. NTIS
Electrical Properties; Optical Properties; Oxides; Spinel; Transparence
20060011619 National Renewable Energy Lab., Golden, CO USA
High-Performance Photovoltaic Project Overview
Symko-Davies, M.; McConnell, R.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860495; NREL/CP-520-37013; No Copyright; Avail.: Department of Energy Information Bridge
The High-Performance Photovoltaic (HiPerf PV) Project was initiated by the U.S. Department of Energy to substantially increase the viability of photovoltaics (PV) for cost-competitive applications so that PV can contribute significantly to our energy supply and environment in the 21st century. To accomplish this, the National Center for Photovoltaics (NCPV) directs in-house and subcontracted research in high-performance polycrystalline thin-film and multijunction concentrator devices. In this paper, we describe the recent research accomplishments in the in-house directed efforts and the research efforts under way in the subcontracted area. NTIS
Photovoltaic Conversion; Cost Effectiveness
20060011620 National Renewable Energy Lab., Golden, CO USA
Module Design, Materials, and Packaging Research Team: Activities and Capabilities
McMahon, T. J.; delCueto, J.; Glick, S.; Jorgensen, G.; Kempe, M.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860494; NREL/CP-520-36988; No Copyright; Avail.: National Technical Information Service (NTIS)
Our team activities are directed at improving PV module reliability by incorporating new, more effective, and less expensive packaging materials and techniques. New and existing materials or designs are evaluated before and during accelerated environmental exposure for the following properties: (1) Adhesion and cohesion: peel strength and lap shear. (2) Electrical conductivity: surface, bulk, interface and transients. (3) Water vapor transmission: solubility and diffusivity. (4) Accelerated weathering: ultraviolet, temperature, and damp heat tests. (5) Module and cell failure diagnostics: infrared imaging, individual cell shunt characterization, coring. (6) Fabrication improvements: SiOxNy barrier coatings and enhanced wet adhesion. (7) Numerical modeling: Moisture ingress/egress, module and cell performance, and cell-to-frame leakage current. (8) Rheological properties of polymer encapsulant and sheeting materials. Specific examples will be described. NTIS
Modules; Packaging; Reliability
20060011621 National Renewable Energy Lab., Golden, CO USA
NREL PV Module Reliability and Performance R&D Status and Accomplishments
Osterwald, C. R.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860493; NREL/CP-520-36990; No Copyright; Avail.: Department of Energy Information Bridge
This paper presents a brief overview of the status and accomplishments during Fiscal Year (FY)2004 of the Photovoltaic (PV) Module Reliability and Performance R&D Subtask, which is part of the PV Module Reliability R&D Project (a joint NREL-Sandia project). NTIS
Photovoltaic Cells; Reliability; Solar Energy
20060011622 National Renewable Energy Lab., Golden, CO USA
Correlation of DLTS and Performance of GalnNAs Cells
Kurtz, S.; Johnston, S.; Friedman, D.; Ptak, A.; Geisz, J.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860492; NREL/CP-520-36972; No Copyright; Avail.: National Technical Information Service (NTIS)
A four-junction GaInP/GaAs/GaInAsN/Ge solar cell should be able to reach 40% efficiency if each of the junctions can be made with a quality similar to that demonstrated for GaAs. However, the GaInAsN subcell has shown poor performance. Deep-level transient spectroscopy (DLTS) can elucidate recombination centers in a material and could help identify the problem with the GaInAsN. So far, DLTS studies of GaInAsN have shown many peaks. In this paper we compare the performance of the GaInAsN solar cells with the DLTS spectra to identify which DLTS peak is correlated with the device performance. NTIS
Correlation; Solar Cells; Spectroscopic Analysis; Spectroscopy; Indium Phosphides; Gallium Phosphides; Gallium Arsenides
20060011623 National Renewable Energy Lab., Golden, CO USA
Packaging Materials and Design for Improved PV Module Reliability
Jorgensen, G.; Terwilliger, K.; Kempe, M.; Perm, J.; Glick, S.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860491; NREL/CP-520-36835; No Copyright; Avail.: Department of Energy Information Bridge
A number of candidate alternative encapsulant and soft backsheet materials have been evaluated in terms of their suitability for photovoltaic (PV) module packaging applications. Relevant properties, including peel strength as a function of damp heat exposure and permeability, have been measured. Based on these tests, promising new encapsulants with adhesion-promoting primers have been identified that result in improved properties. Test results for backsheets provided by industry and prepared at the National Renewable Energy Laboratory (NREL) have suggested strategies to achieve significantly improved products. The ability of glass/glass and glass/breathable backsheet constructions laminated with various encapsulant and/or edge seal materials to protect thin-film aluminum coatings deposited onto glass substrates was assessed. Glass/glass laminate constructions can trap harmful compounds that catalyze moisture-driven corrosion of the aluminum. Constructions with breathable backsheets allow higher rates of moisture ingress, but also allow egress of deleterious substances that can result in decreased corrosion. NTIS
Encapsulating; Packaging; Photovoltaic Conversion; Reliability
20060011625 National Renewable Energy Lab., Golden, CO USA
Advanced Indoor Module Light-Soaking Facility
del Cueto, J. A.; Osterwald, C.; Pruett, J.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860490; NREL/CP-520-39686; No Copyright; Avail.: Department of Energy Information Bridge
An overview of the accelerated, indoor light-soaking test station is presented in this paper, along with data obtained for six modules that underwent exposure. The station comprises a climate-controlled chamber equipped with a solar simulator that allows 1-sun light intensity exposure. Concurrently, we monitor the electrical characteristics of multiple PV modules and exercise active control over their electrical bias using programmable electronic loads, interfaced to a data acquisition system that acquires power-tracking and current-voltage data. This capability allows us to the test different bias conditions and to cyclically alternate between them. Additionally, we can vary the light intensity and module temperatures to garner realistic temperature coefficients of module performance. Data obtained on cadmium telluride (CdTe) and amorphous silicon (a-Si) modules are presented. NTIS
Solar Simulators; Modules; Electric Potential; Active Control
20060011626 National Renewable Energy Lab., Golden, CO USA
Scanning Tunneling Luminescence of Grain Boundaries in CU(In,Ga)Se2
Romero, M. J.; Jiang, C. S.; Al-Jassim, M. M.; Noufi, R.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860489; NREL/CP-520-36975; No Copyright; Avail.: Department of Energy Information Bridge
At the Laboratory, photon emission in semiconductors has been mapped in the nanoscale using scanning tunneling microscopy (STM). In this Solar Program Review Meeting, we report on the latest results obtained in Cu(In,Ga)Se2 (CIGS) thin films by this adapted STM. Scanning tunneling luminescence (STL) spectroscopy suggests that photons are emitted near the surface of CIGS. STL is excited either by (1) diffusion of tunneling electrons and subsequent recombination with available holes in CIGS or (2) impact ionization by hot electrons. Which process becomes predominant depends on the voltage applied to the STM tip. Photon mapping shows electronically active, extended defects near the surface of CIGS thin films. NTIS
Grain Boundaries; Luminescence; Scanning Tunneling Microscopy
20060011627 National Renewable Energy Lab., Golden, CO USA
Development and Testing of Solar Reflectors
Kennedy, C.; Terwillinger, K.; Milbourne, M.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860488; NREL/CR-520-36582; No Copyright; Avail.: Department of Energy Information Bridge
To make concentrating solar power technologies more cost competitive, it is necessary to develop advanced reflector materials that are low in cost and maintain high reflectance for extended lifetimes under severe outdoor environments. The Advanced Materials Team performs durability testing of candidate solar reflectors at outdoor test sites and in accelerated weathering chambers. Several materials being developed by industry have been submitted for evaluation. These include silvered glass mirrors, aluminized reflectors, and front-surface mirrors. In addition to industry-supplied materials, NREL is funding the development of new, innovative reflectors, including a new commercial laminate reflector and an advanced solar reflective mirror (ASRM). To help commercialize the ASRM, a cost analysis was performed; it shows the total production cost could meet the goal. The development, performance, and durability of these candidate solar reflectors and cost analysis results will be described. NTIS
Advanced Solid Rocket Motor (STS); Solar Reflectors
20060011638 National Renewable Energy Lab., Golden, CO USA
Thin Films and the Systems-Driven Approach
Zweibel, K.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860486; NREL/CP-520-36968; No Copyright; Avail.: National Technical Information Service (NTIS)
A systems-driven approach is used to discern tradeoffs between cost and efficiency improvements for various thin-film module technologies and designs. Prospects for reduced system cost via such strategies are enhanced as balance-of-systems costs decline, and some strategies are identified for greater research focus. NTIS
Solar Energy; Thin Films
20060011639 National Renewable Energy Lab., Golden, CO USA
Recent and Planned Enhancements for PVWATTS
Marion, B.; Anderberg, M.; Gray-Hann, P.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860485; NREL/CP-520-37016; No Copyright; Avail.: National Technical Information Service (NTIS)
PVWATTS is an Internet-accessible software program that allows the user to easily calculate the energy production and cost savings for grid-connected photovoltaic (PV) systems located throughout the USA. Recent enhancements have been made to allow the user to define the system location by the use of zip code or latitude and longitude coordinates, and to receive more detailed performance information by providing a.c. energy production for each hour of the year. Future enhancements under consideration are also discussed. They include more flexibility for the user in defining system losses from soiling and in the conversion from d.c. to a.c. power, an option for international locations, and accounting for PV module shading. NTIS
Augmentation; Photovoltaic Cells; Simulation; Spatial Resolution
20060011640 National Renewable Energy Lab., Golden, CO USA
Outreach is Serious Fun
Larsen, W.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860484; NREL/CP-520-36977; No Copyright; Avail.: Department of Energy Information Bridge
This paper outlines the planning and effort that goes into a successful, inexpensive outreach project. Since 1996, the National Renewable Energy Laboratory has had an educational exhibit booth and has also presented workshops on renewable energy at the two-week-long National Western Stock Show held each January in Denver, Colorado. In our exhibit booth and workshops, farmers, ranchers, and homeowners learn how solar, wind, and biomass energy systems can provide economical electricity for the agricultural community. We show how this outreach has grown to include the presentation of renewable energy exhibits at events in South Dakota and Illinois at the request of the Deputy Secretary for Energy of the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, and our support of the U.S. Department of Agriculture in Kansas and Nebraska on the issuance of the 2004 Farm Bill. NTIS
Electricity; Renewable Energy
20060011647 National Renewable Energy Lab., Golden, CO USA
Small Hybrid Systems and Applications Testing at NREL's Outdoor Test Facility
Roybal, L.; Jan. 2005; 10 pp.; In English Report No.(s): DE2005-860830; NREL/CP-520-37078; No Copyright; Avail.: National Technical Information Service (NTIS)
The PV International Program at the National Renewable Energy Laboratory recently installed a small hybrid solar and wind energy system that could produce enough electricity to power a cabin or provide electricity in a remote village, without being connected to a utility grid. The solar system can provide 1,400 watts of power, and the wind turbine is rated at 900 watts when the wind is blowing at 28 miles per hour. The 48-volt system has eight batteries for storage. When the batteries are fully charged, the control system slows down the wind turbine so as not to overcharge the batteries. The turbine is mounted on a tilt-down, guyless, 30-foot tower that allows one person to easily lower and raise the machine for maintenance. A data acquisition system is being designed to monitor the individual outputs from the solar system and the wind system. The small hybrid system is housed in an insulated shed, the PV International Program's Test Building (ITB). The ITB contains electrical loads found in the average home, including a refrigerator, lights, heaters, air coolers, computers, and a radio. NTIS
Energy Conservation; Renewable Energy; Solar Energy; Test Facilities; Windpower Utilization
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