SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 11 - MAY 30, 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.
20060013271 National Renewable Energy Lab., Golden, CO USA
Tritiated Amorphous Silicon: Insights into the Staebler-Wronski Mechanism
Strandins, P.; Branz, H. M.; Whitaker, J.; Viner, J.; Johnson, E.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860694; NREL/CP-520-37023; No Copyright; Avail.: Department of Energy Information Bridge
Hydrogen, though essential for device-quality amorphous silicon, likely contributes to the light-induced degradation process (Staebler-Wronski effect) that reduces the solar cell efficiency by about 4 absolute percent. We are testing the role of hydrogen by using its isotope tritium. When tritium bonded to Si spontaneously decays into inert helium-3, it should leave behind the Si dangling bond defect. We have studied degradation due to tritium and note its resemblance to the Staebler-Wronski effect. Surprisingly, 100x fewer defects are created than expected from the tritium decay rate, suggesting a mechanism that heals most of the defects, even at temperatures down to 4 k. NTIS
Amorphous Materials; Amorphous Silicon; Solar Cells
20060013273 National Renewable Energy Lab., Golden, CO USA
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PV Manufacturing R&D Project--Trends in the U.S. PV Industry
Brown, K. E.; Mitchell, R. L.; Bower, R. I.; King, R.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860692; NREL/CP-520-37030; No Copyright; Avail.: Department of Energy Information Bridge
To foster continued growth in the U.S. Photovoltaic (PV) industry, the U.S. Department of Energy initiated the PV Manufacturing R&D (PVMR&D) Project-a partnership with U.S. PV industry participants to perform cost-shared manufacturing research and development. Throughout FY 2004, PVMR&D managed fourteen subcontracts across the industry. The impact of PVMR&D is quantified by reductions in direct module manufacturing costs, scale-up of existing PV production capacity, and accrual of cost savings to the public and industry. An analysis of public and industry investment shows that both recaptured funds by mid-1998 based on estimated manufacturing cost savings from PVMR&D participation. Since project inception, total PV manufacturing capacity has increased from 14 MW to 201 MW at the close of 2003, while direct manufacturing costs declined from $5.55/W to $2.49/W. NTIS
Industries; Manufacturing; Trends; United States
20060013275 National Renewable Energy Lab., Golden, CO USA
Quantum Dot Solar Cells: High Efficiency through Multiple Exciton Generation
Hanna, M. C.; Ellingson, R. J.; Beard, M.; Yu, P.; Micic, O. I.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860690; NREL/CP-590-37036; No Copyright; Avail.: Department of Energy Information Bridge
Impact ionization is a process in which absorbed photons in semiconductors that are at least twice the bandgap can produce multiple electron-hole pairs. For single-bandgap photovoltaic devices, this effect produces greatly enhanced theoretical thermodynamics conversion efficiencies that range from 45-85%, depending upon solar concentration, the cell temperature, and the number of electron-hole pairs produced per photon. For quantum dots (QDs), electron-hole pairs exist as excitons. NTIS
Excitons; Quantum Dots; Solar Cells
20060013277 National Renewable Energy Lab., Golden, CO USA
NREL PV System Performance and Standards Technical Progress
Osterwald, C. R.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860689; NREL/CP-520-37024; No Copyright; Avail.: National Technical Information Service (NTIS)
This paper presents a brief overview of the status and accomplishments during Fiscal Year (FY)2004 of the Photovoltaic (PV) System Performance & Standards Subtask, which is part of PV Systems Engineering Project (a joint NREL-Sandia project). NTIS
Photovoltaic Conversion; Renewable Energy; Thin Films
20060013279 National Renewable Energy Lab., Golden, CO USA
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Electron Microscopy Studies of GaP(N,As) Grown on Si
Norman, A. G.; Geisz, J.; Olson, J.; Jones, K.; Al-Jassim, M.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860687; NREL/CP-520-37035; No Copyright; Avail.: Department of Energy Information Bridge
The objective of this work is to perform transmission electron microscopy (TEM) studies of CaP(N,As) alloys grown by metal-organic chemical vapor deposition (MOCVD) on Si substrates. These alloys are of interest for the fabrication of high-efficiency tandem solar cells based on Si.
The results indicated that the nucleation and growth conditions used are critical for obtaining planar epitaxial layers with a low defect density.
In particular, antiphase domains are eliminated using a low growth temperature.
TEM studies of these alloy layers, which contain only a few percent N, revealed no phase separation. However, electron diffraction studies revealed the first evidence of CuPt-type atomic ordering in these P-rich, dilute nitride alloy layers. NTIS
Electron Microscopy; Metalorganic Chemical Vapor Deposition; Electron Diffraction; Nucleation
20060013284 National Renewable Energy Lab., Golden, CO USA
XPS and UPS Studies of Thin Film PV Materials Modified by Reactions in Liquids
Perkins, C. L.; Hasoon, F. S.; Al-Thani, H. A.; Asher, S. E.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860683; NREL/CP-520-57034; No Copyright; Avail.: Department of Energy Information Bridge
Water-based processing steps are ubiquitous in the semiconductor industry, and the field of photovoltaics (PV) is no exception. During chemical bath deposition (CBD) of CdS, complex chemical reactions occurring at surfaces and in solution are poorly understood, yet have been shown to have powerful effects on the performance in terms of reliability and efficiency of finished PV devices. In the past, electron spectroscopic studies of these reactions have been hampered by the conflicting requirements of ultra-high vacuum and exposure of samples to liquid water. In this paper we present initial results from a new tool at NREL that allows one to conduct atmospheric pressure, liquid phase chemical processes on thin film PV materials and subsequent examination via core and valence level electron spectroscopies without exposing samples to air contamination. NTIS
Atmospheric Pressure; Liquids; Photoelectron Spectroscopy; Photovoltaic Conversion; Thin Films; X Ray Spectroscopy
20060013286 National Renewable Energy Lab., Golden, CO USA, Georgia Inst. of Tech., Atlanta, GA USA
Hydrogenated Amorphous Silicon Emitter and Back-Surface-Field Contacts for Crystalline Silicon Solar Cells
Wang, T. H.; Iwaniczko, E.; Page, M. R.; Yelundur, V.; Wang, Q.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860682; NREL/CP-520-37033; No Copyright; Avail.: Department of Energy Information Bridge
Thin hydrogenated amorphous silicon (a-Si:H) layers deposited by hot-wire chemical vapor deposition (HWCVD) are investigated as emitters and back-surface-field (BSF) contacts to make silicon heterojunction solar cells on p-type crystalline silicon wafers. A common requirement for excellent emitter and BSF quality is minimization of interface recombination. Best results require immediate a-Si:H deposition and an abrupt and flat interface to the c-Si substrate. We obtain record 16.9% and 14.8% efficiencies on p-type planar float-zone (FZ) and Czochralski (CZ) silicon substrates, respectively, with HWCVD a-Si:H(n) emitters and Al-BSF contacts. Initial efforts with p-type HWCVD Si thin films as the BSF have yielded 12.5% efficiency on p-type CZ-Si. NTIS
Amorphous Silicon; Crystallinity; Emitters; Hydrogenation; Solar Cells
20060013288 National Renewable Energy Lab., Golden, CO USA
Raman Studies of Nanocrystalline CdS:O Film
Zhang, Y.; Wu, X.; Dhere, R.; Zhou, J.; Yan, Y.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860681; NREL/CP-590-37026; No Copyright; Avail.: Department of Energy Information Bridge
Oxygenated nanocrystalline Cds films show improved solar cell performance, but the physics and mechanism underlying this are not yet clearly understood. Raman study provides complementary information to the understanding obtained from other experimental investigations. A comprehensive analysis of the existing experimental data (including x-ray diffraction, transmission, transmission electron microscopy, and Raman) has led to the following conclusions: (1) The O-incorporation forms CdS1-xOx alloy nano-particles. (2) The observed evolution of the electronic structure is the result of the interplay between the alloy and quantum confinement effect. (3) The blue-shift of the LO phonon Raman peak is primarily due to the alloying effect. (4) Some oxygen atoms have taken the intersitital sites. NTIS
Solar Cells; Thin Films
20060013290 National Renewable Energy Lab., Golden, CO USA
XPS and AES Studies of Cu/CdTe(111)-B
Teeter, G.; Gessert, T. A.; Asher, S. E.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860680; NREL/CP-520-37038; No Copyright; Avail.: Department of Energy Information Bridge
Copper is frequently used as a p-type dopant to improve the performance of back contacts in CdTe thin-film solar cells. In this study, surface-analysis techniques are used to probe fundamental interactions between Cu and the CdTe(11)-B surface. The results presented here were facilitated by the newly constructed surface-analysis cluster tool in the Measurement and Characterization Division at NREL; they reveal a host of fundamental phenomena that occur in the Cu/CdTe system. NTIS
Copper; Photoelectron Spectroscopy; Solar Cells; X Ray Spectroscopy
20060013311 National Renewable Energy Lab., Golden, CO USA
Workshop on Crystalline Silicon Solar Cells and Modules (15th): Materials and Processes. Extended Abstracts and Papers
Al-Jassim, M.; Kalejs, J.; Rand, J.; Saitoh, T.; Nov. 2005; 242 pp.; In English Report No.(s): DE2006-861051; NREL/BK-520-38573; No Copyright; Avail.: National Technical Information Service (NTIS)
The silicon photovoltaic (PV-Si) industry has undergone rapid growth in the last few years, leading to new production capabilities that will exceed GW/yr and take us to multi-GW production in the near future. This rapid growth was fostered by many technical achievements and breakthroughs in the science and technology of photovoltaics. Some of these technologies were developed by the industry itself while others were adopted from R&D performed at various universities and academic institutions. These technical and scientific advances have occurred around the globe and, in many cases, were prompted by strong government assistance. In the USA, NREL/DOE offers many programs that support Si research and development. One of them is the Silicon Workshop, which is geared to help the PV-Si industry by (1) bringing together the industry, research, and academic communities, (2) disseminating scientific and technical information by nurturing collective views on critical research areas, and (3) providing feedback to NREL/DOE on important research tasks, as seen by the community. NTIS
Abstracts; Crystallinity; Modules; Solar Cells
20060013349 National Renewable Energy Lab., Golden, CO USA
Improved Performance in CulnSe2 and Surface-Modified CuGaSe2 Solar Cells
AbuShama, J.; Noufi, R.; Johnston, S.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860989; NREL/CP-520-37614; No Copyright; Avail.: Department of Energy Information Bridge
In this paper, we present an update and review on the progress made in the development of low-bandgap CuInSe(sub 2) (CIS) and wide-bandgap CuGaSe(sub 2) (CGS) solar cells. Our research project is primarily concerned with the optimization of the bottom and top cells of the tandem solar cell. This past year, we achieved new world record total-area efficiencies of 15.0% and 10.2% for CIS and surface-modified CGS solar cells, respectively. These achievements were possible by modifying the growth process for CIS and CGS absorbers.We attempt to modify the surface region of the CGS absorber to be CIGS-like in composition. In the mean time, we are designing a mechanical-stacked tandem solar cell where the CIS cell serves as the bottom cell. NTIS
Solar Cells; Energy Gaps (Solid State); Efficiency
20060013351 National Renewable Energy Lab., Golden, CO USA
Direct-Write Contacts for Solar Cells
Kaydanova, T.; van Hest, M.; Miedaner, A.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860930; NREL/CP-520-37080; No Copyright; Avail.: National Technical Information Service (NTIS)
We report on our project to develop inkjet printable contacts for solar cells. Ag, Cu, and Ni metallizations were inkjet printed with near vacuum deposition quality. Thick, highly conducting lines of Ag and Cu demonstrating good adhesion to glass, Si, and PCB have been printed at 100-200 deg C in air and N(sub 2), respectively. Ag grids were inkjet-printed on Si solar cells and fired through silicon nitride AR layer at 850 deg C resulting in 8% cells. Next-generation multicomponent inks (including etching agents) have also been developed with improved fire-through contacts leading to higher cell efficiencies. The approach developed can be easily extended to other conductors such as Pt, Pd, and Au, etc. In addition, PEDOT-PSS polymer-based conductors were inkjet-printed with the conductivity as good or better than those of spin-coated films. NTIS
Deposition; Solar Cells
20060013354 National Renewable Energy Lab., Golden, CO USA
Solar Decathlon 2005
King, R.; Jan. 2005; 10 pp.; In English Report No.(s): DE2006-860841; NREL/CP-520-37076; No Copyright; Avail.: Department of Energy Information Bridge
Solar Decathlon 2005 is a U.S. Department of Energy and National Renewable Energy Laboratory competition involving 19 colleges and universities from the USA, Canada, and Spain. These teams will compete to design, build, and demonstrate solar homes. In fall 2005, teams will transport their competition solar houses to Washington, D.C., where they will construct a solar village on the National Mall. When the houses are assembled, the teams will compete against each other in 10 contests (hence, a decathlon) for about a week. The contests range from design to comfort to energy performance. Each team must provide an aesthetically pleasing entry that produces sufficient solar energy for space conditioning, hot water, lighting, appliances, and an electric car. The Solar Decathlon is co-sponsored by BP, The Home Depot, the American Institute of Architects, the National Association of Home Builders, and the DIY Network. NTIS
Competition; Solar Energy
20060013527 Ishikawajima-Harima Heavy Industries Co. Ltd., Tokyo, Japan
Development of Micromachine Gas Turbines at Tohoku University
Isomura, Kousuke; Tanaka, Shuji; Togo, Shin-ichi; Micro Gas Turbines; December 2005, pp. 10-1 - 10-34; In English; See also 20060013522; Original contains color and black and white illustrations; Copyright; Avail.: CASI: A03, Hardcopy; Available from CASI on CD-ROM only as part of the entire parent document
Development of micromachine gas turbines is underway at a group lead by Tohoku University in Japan. The goal is to develop a light-weight power source to replace the heavy batteries that may limit the progress of humanoid robots. Internal combustion engines have advantages of both high power density and high energy density, so it can be the best choice for the power source for mobile machines. The project is currently challenging to develop the smallest possible gas turbine of three-dimensional geometry to be fabricated by machining. The micro-combustor has already been completed the validation test, and experimental validation of the turbo-unit and the generator of the diameter 10mm is underway. Current major technical challenges are the development of the bearings to sustain the high-speed rotation of the rotors and the technologies to fabricate the bearings within the required tolerance. Author
Microelectromechanical Systems; Gas Turbines; Fabrication; Robots; Machining; Combustion Chambers; Internal Combustion Engines
20060013528 Technische Hochschule, Aachen, Germany
Micro Gas Turbine and Fuel Cell - A Hybrid Energy Conversion System with High Potential
Bohn, Dieter; Micro Gas Turbines; December 2005, pp. 13-1 - 13-46; In English; See also 20060013522; Original contains color and black and white illustrations; Copyright; Avail.: CASI: A03, Hardcopy; Available from CASI on CD-ROM only as part of the entire parent document
This paper reports an assessment of coupling micro gas turbine and high temperature fuel cell (SOFC) as a possibility to realize power plant with an efficiency of 75%. The application of such a technology will be in the decentralized feed-in of housing estates and buildings with electricity, heat and cooling energy. Nowadays the first implemented prototypes reach efficiencies among 57- 58% /1/. The paper shows the necessity of further developments to be able to reach an efficiency of 75%. The developments include improvements in all components of the system like compressor, turbine, bearing and the increasing of the operating temperature. Author
Gas Turbines; Fuel Cells; Efficiency; Energy Conversion; Compressors; Electricity; Cooling
20060013531 Royal Military Academy, Brussels, Belgium
Micro Turbines from the Standpoint of Potential Users
Decuypere, Roland; Verstraete, Dries; Micro Gas Turbines; December 2005, pp. 15-1 - 15-14; In English; See also 20060013522; Original contains color and black and white illustrations; Copyright; Avail.: CASI: A03, Hardcopy; Available from CASI on CD-ROM only as part of the entire parent document
This paper describes some micro turbine aspects from the standpoint of potential users. First, some of the pros and the cons of small gas turbines compared to other competing technologies are given. The discussed aspects are mainly focussed on technical advantages and disadvantages as it is hard to predict how fast and to what extent the different technologies (including that of mini gas turbines) will mature. Even though the final applications will obviously strongly depend upon the economical benefits that the technology would offer, an economical comparison is not made here. Therefore the comparison made throughout this contribution remains relatively general. Once the pros and the cons are discussed, some potential applications are described. The possible applications are divided into two different categories: power generation for portable devices and vehicle propulsion. For each class of applications some examples are given. Finally, then, some conclusions are drawn. Author
Gas Turbines; Propulsion; Turbines
20060013532 Rochester Inst. of Tech., NY, USA
Compact Heat Exchangers for Microturbines
Shah, R. K.; Micro Gas Turbines; December 2005, pp. 2-1 - 2-18; In English; See also 20060013522; Original contains color and black and white illustrations; Copyright; Avail.: CASI: A03, Hardcopy; Available from CASI on CD-ROM only as part of the entire parent document
With distributed power generation market, the most economical solution today is to generate power through small gas turbine systems, arbitrarily categorized as microturbines (5 200 kW) and miniturbines (200 500 kW). The thermal efficiency of such microturbines is about 20% or less if no recuperator is used in the system. Using a recuperator (regenerator can also be considered but has a number of problems) operating at 87% effectiveness, the efficiency of the gas turbine system increases to about 30%, a substantial performance improvement. However, cost of the recuperator is about 25 30% of the total power plant. This means that the heat exchanger (recuperator) must be designed to get high performance with minimum cost. While the offset strip fin geometry is one of the highest performing surface it is also quite expensive to manufacture. This necessitates the use of all prime surface heat exchangers with no brazing. In this paper, after providing the necessary concise information on microturbines, the discussion is presented on various types of heat exchanger surfaces and novel designs considered for the cost effective heat exchangers and packaging in the system. For hot fluid inlet temperature of less than about 675 C, stainless steel material can be used for the heat exchanger, which has reasonable cost. However, for higher inlet temperatures in heat exchangers associated with higher turbine inlet temperatures, superalloys are essential which increases the material cost of the exchanger alone by a factor of 4 to 5. The design, material/finished heat exchanger cost, performance, durability, and other related issues of compact heat exchangers for microturbines are covered in this paper. The discussion and coverage is primarily for metal heat exchangers since the ceramic heat exchangers are in infant stage after last 50 years of development associated with the gas turbine applications. Author
Inlet Temperature; Heat Exchangers; Thermodynamic Efficiency; Regenerators; Heat Resistant Alloys; Gas Turbines
20060013536 Naples Univ., Italy Performance and Transient Behaviour of MGT Based Energy Systems
Tuccillo, R.; Micro Gas Turbines; December 2005, pp. 6-1 - 6-56; In English; See also 20060013522; Original contains color and black and white illustrations; Copyright; Avail.: CASI: A04, Hardcopy; Available from CASI on CD-ROM only as part of the entire parent document
After a preliminary overview of the multiplicity of solutions for the set up and operation of energy conversion systems based on micro-gas turbines, this paper outlines the method for performance evaluation under both steady state and transient conditions. The cycle analysis aims at the evaluation of thermal efficiency and energy saving indices under different fueling conditions and with variably recuperated cycle. The subsequent component matching simulation extends the MGT analysis to the off-design conditions and it leads to the definition of methods for an efficient fulfillment of variable external loads. Finally, the study of some typical transient developments, of both the full-to-part and the part-to-full load type, introduces to the problem of defining proper fuel control laws as to prevent excesses in both energy consumption and component stresses and instabilities. Author
Energy Conversion; Fuel Control; Thermodynamic Efficiency; Control Theory; Gas Turbines
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