A Conceptual Study of Implementing Composite Support Towers
for Offshore Wind Turbines. IAN TSE (Cornell University, Ithaca, NY, 14853) JASON COTRELL (National Renewable Energy Laboratory, Golden,
CO, 89401)
Offshore wind
turbine installations have the potential to supply a significant
portion of the nation’s electricity needs; however, the projected
cost of installing wind turbines offshore is significantly more
expensive than current land-based installations in part due to
the high cost of constructing structures to support the turbines
in the water. Support structures in deeper waters (greater than
30m) will likely use relatively expensive truss structures or floating
platforms to support the wind turbine and tower. The cost of these
underwater support structures depends mostly on the weight of wind
turbine and tower. Implementing lightweight towers made of composite
materials could be one way to minimize the estimated high costs
of the underwater support structure. The objective of this study
was to identify a composite design that had the best combination
of weight, stiffness, and cost. I designed a conventional steel
tower as an offshore baseline model with which to compare the cost
and weight of the composite towers. A set of composite towers of
similar geometry and strength as the baseline steel tower were
generated for comparison using a composite design program and simplified
analytical calculations. The results of the study indicate that
it is difficult to create a lightweight composite tower that is
as stiff as a steel tower without using expensive materials such
as carbon fiber. However, if the diameter of the composite tower
is increased, the results indicate that there is potential to create
a lighter tower of comparable cost. More analysis and optimization
of the composite tower design is required to quantify its potential.
In addition, alterative composite tower geometries and manufacturing
methods should be explored.
Analysis of Cell Wall Mutations in Maize using Pyrolysis Molecular Beam Mass
Spectrometry. BRIANNA HARP (Metropolitan State
College of Denver, Denver, CO, 0) MARK DAVIS (National Renewable
Energy Laboratory, Golden, CO, 89401)
This study applies
Pyrolysis Molecular Beam Mass Spectrometry (PyMBMS) as a high throughput
screen of cell wall substrates to characterize cell wall mutations.
We had 3 goals in our study: improve PyMBMS technique, confirm
cell wall mutations, and characterize differences between mutant
lines and controls. We tested two methods of extraction: the Accelerated
Solvent Extraction (ASE) and a simplified, rapid ethanol/acetone
extraction using PyMBMS and multivariate statistical analysis to
determine which method is most effective for removing extraneous
cell wall material. This investigation found the ASE extraction
to be most effective. A second study was performed using a combination
of ASE extracted and untreated whole mutant 33_’00FL-041-39 and
34_02S-1030-22 samples and controls to identify mutant lines and
characterize differences among the samples, while analyzing benefits
of the ASE extraction technique. The results of this study showed
no significant differences in cell wall chemistry or advantage
in using the ASE extraction technique. Our third investigation
sampled six different mutants using only whole samples. We found
that the mutant line 27_02s-1137-40 had a significant increase
in C5 and C6 sugars. The results of our analysis of mutant line
39_’00FL-042-20 (387, 388, 393, 395, 396, 399) is inconclusive.
Analysis of the Water-Splitting Capabilities of Gallium Indium Phosphide Nitride
(GaInPN). JEFF HEAD (University of Arizona, Tucson, AZ, 85705) JOHN TURNER (National Renewable Energy Laboratory, Golden,
CO, 89401)
With increasing
demand for oil, the fossil fuels used to power society’s vehicles
and homes are becoming harder to obtain, creating pollution problems,
and are posing hazard’s to people’s health. Hydrogen, a clean and
efficient energy carrier, is one alternative to fossil fuels. Certain
semiconductors are able to harness the energy of solar photons
and direct it into water electrolysis in a process known as photoelectrochemical
water splitting. P-type gallium indium phosphide (p-GaInP2) in
tandem with GaAs is a semiconductor system that exhibits water-splitting
capabilities with 12.4% solar-to-hydrogen efficiency. Although
this material is efficient at producing hydrogen through photoelectrolysis
it has been shown to be unstable in solution. By introducing nitrogen
into this material, there is great potential for enhanced stability.
In this study, gallium indium phosphide nitride Ga1-yInyP1-xNx
samples were grown using metal-organic chemical vapor deposition
in an atmospheric-pressure vertical reactor. Photocurrent spectroscopy
determined these materials to have a direct band gap around 2.0
eV. Mott-Schottky analysis indicated p-type behavior with variation
in flatband potentials with varied frequencies and pH’s of solutions.
Photocurrent onset and illuminated open circuit potential measurements
correlated to flatband potentials determined from previous studies.
Durability analysis suggested improved stability over the GaInP2
system.
Anemometer Standoff. NICHOLAS JOHNSON (University
of Colorado at Denver, Denver, Co, 80112)
HAL LINK (National Renewable Energy Laboratory, Golden, CO, 89401)
Accurate wind
speed measurements are critical in the analysis of wind turbine
power performance. Common industry practice is to measure wind
speed using a cup anemometer that is mounted in a position where
the supporting tower distorts the measurement. It is ideal to mount
the anemometer on top of the tower. Sometimes this is no practical
and must be mounted on a boom, that supports it away from the tower,
far enough to limit distortion errors to 1%. A theoretical model
has been used to quantify where a distortion will occur with respect
to the tower. However, some researchers have recently speculated
that the theoretical model inaccurately predicts the distance from
the tower where the 1% distortion error occurs. The objective of
this project was to experimentally measure and quantify this distortion
and thereby validate or disprove the model. To achieve this objective,
a test was configured where one anemometer was mounted above a
triangular lattice tower to measure the undistorted wind speed.
On the same tower a boom-mounted anemometer was mounted below the
top of the tower to measure the distorted wind speed. Data were
collected by the boom-mounted anemometer at different "standoff" distances.
Standoff is the ratio of the separation of the anemometer and the
tower to the width of the tower. Data were sorted by wind direction
in order to plot where the critical distortion occurs - when the
anemometer is directly upwind of the tower. This value was reported.
A second tower was requisite to quantify the vertical spacing effects
between the top-mounted and the boom-mounted anemometers. This
test measured distortion effects for three configurations: at a
standoff of 2.31, the model predicts a distortion error of 1.6%,
the test indicated 3.2 %; at a standoff of 3.47, the model predicts
a distortion of 0.9%, the test indicated 2.6%; at a standoff of
4.62, the model predicts a distortion of 0.6%, the test indicated
1.6%. Based on these test results, NREL has concluded that the
model inaccurately predicts the distortion. To obtain accurate
wind speed measurements with boom-mounted anemometers a larger
than predicted standoff is required. Results to date are limited
to relatively small amount of standoff distance points, more research
is needed to create an acceptable model.
Bipolar Plate Design and Manufacturing for Proton Exchange Membrane Fuel Cells. RACHEL BACKES (Colorado School
of Mines, Golden, CO, 80401) JOHN TURNER (National Renewable Energy
Laboratory, Golden, CO, 89401)
The proton exchange
membrane fuel cell (PEMFC) is the preferred candidate for future
fuel cell automobiles. Metallic bipolar plates have the ability
to improve this type of fuel cell. This project focuses on how
stainless steel bipolar plates can be produced and designed for
use in PEMFCs. The plate material considered is type 446 stainless
steel. Flow patterns are designed to be stamped into the plate
through application of rubber pad forming techniques. Dies are
designed for the stamping process, and preliminary testing is done
with substitute materials. The results of preliminary testing were
successful, particularly with the softest backing material used.
Seals required for implementation in a fuel cell stack are also
designed. The result of this project is a set of preliminary designs
for the production and use of stainless steel bipolar plates in
a PEMFC.
Characterization of GaInPN:Si Tandem Cells for Hydrogen Production from Photoelectrochemical
Water Splitting. PAUL VALLETT
(University of Vermont, Burlington, VT,
5405) DR. JOHN TURNER (National Renewable Energy Laboratory,
Golden, CO, 89401)
In order for
hydrogen to be part of a renewable energy infrastructure, it must
be produced from a renewable energy resource. The direct photoeletrolysis
of water using certain types of semiconductors have been known
to split water using absorption of solar energy, but difficulties
concerning efficiencies and corrosion have limited this technology.
This research focused on the ability of GaInPN grown on a silicon
substrate to efficiently split water. Photocurrent spectroscopy
determined the band gap of the material to be 1.96 eV, which is
above the necessary 1.7 eV required for water splitting. Mott-Schottky
analysis, photocurrent onset, and open circuit potential were used
to determine potential of the Fermi level of the system in relation
to the redox potentials of hydrogen and oxygen formation. These
techniques showed that the Fermi level lied just below the oxygen
redox potential. The electrodes were platinized and short circuit
current density measurements under air mass (AM) 1.5 illumination
determined extent of water photolysis. Unbiased water splitting
was achieved, at a maximum of 0.65% solar to hydrogen conversion
efficiency (SHCE). Corrosion of the semiconductor in solution was
determined by applying a standard current to the electrode while
in solution and using profilometry to estimate the volume of semiconductor
removed. On average a 0.1 µm deep well was etched into the material
after 24 hours. Incident photon current efficiency (IPCE) measurements
of 30% revealed that the growing process for nitrogen addition
to the sample decreased the electronic properties of the material.
While this system is able to produce hydrogen from water using
solar power as the only energy input, and the addition of nitrogen
to the material appears to have increased its durability, the material
suffers a heavy loss in electronic efficiency, limiting its use
in potential solar water splitting devices.
Collection and Transmission Systems Cost and Performance Model for the Baseline
Offshore Wind Farm. AMY BOWEN (Baylor University, Waco, TX, 76798) JIM GREEN (National Renewable Energy Laboratory, Golden, CO,
89401)
The National
Wind Technology Center (NWTC) of the National Renewable Energy
Laboratory (NREL) has undertaken a series of concept studies to
evaluate the cost and performance of offshore wind farms. One of
these studies will evaluate the power losses experienced throughout
the electrical power collection and transmission systems as well
as the cost of the system components and their installation. A
hypothetical system was designed based loosely on the Horns Rev
offshore wind farm. This system was then sent out to manufacturers
with requests for electrical and cost data on the submarine cables
and transformers. Upon discovering that the electrical data available
for submarine cables is scarce, a very basic method of loss analysis
was developed using three parameters: conductor resistance, ampacity,
and power loss at capacity. The total losses are divided into two
groups: losses that are modeled as a quadratic term which varies
with current, and a base loss that is assumed to vary little with
current, and is thus modeled as constant. In the model, both costs
and losses are listed in per meter values to account for parameter
variability. Power losses varied between cables from different
manufacturers and also between different wind farm layouts. The
cost of cables varied widely between different manufacturers as
well, with one manufacturer’s cable more than two times higher
than another’s. The results obtained in this study will be applied
to the overall concept study.
Comparison of Surface Morphologies of Commercial Solar Cell Silicon Wafers
Measured by NREL-Reflectometer and Profilometer Technique. WILLIAM
JOHNSTON (Texas A&M University-Commerce, Commerce, TX, 75429) BHUSHAN SOPORI (National Renewable Energy Laboratory, Golden,
CO, 89401)
The production
of high quality silicon solar cells requires that good quality
control be in place at production facilities. The National Renewable
Energy Laboratory (NREL) has developed a reflectometer that can
quickly measure many solar cell parameters. To increase the applications
of the reflectometer in the solar cell industry research was conducted
to show that the reflectometer could characterize the roughness
present on the surface of a silicon wafer. For comparison silicon
wafers were characterized by the reflectometer and profilometer
technique. A silicon wafer was characterized in a rough sawn state
and after polishing to understand how the reflectometer measurements
and profilometry measurements change with decreasing surface roughness.
As the silicon wafer was polished the specular reflection off of
the surface increased while the roughness measured by profilometer
technique decreased. Also seen with increasing polishing time was
a decrease in diffuse reflection of short, <500 nm, wavelength
light. It was shown that the reflectometer and profilometer could
both measure the presence of roughness down to 10 micrometers in
width. The reflectometer is shown to also be capable of measuring
features of much smaller width. The reflectometer has been shown
to be able to rapidly characterize the entire surface of a silicon
wafer making it a valuable tool to the silicon solar cell industry.
COMPARISON OF THREE-PHASE AC/DC CONVERTERS IN A WIND TO HYDROGEN SYSTEM. JOSHUA PRICE (University of Colorado
at Boulder, Boulder, CO, 80303) CHRISTOPHER PINK (National Renewable
Energy Laboratory, Golden, CO, 89401)
Efficient production
of hydrogen from wind power can be achieved by direct coupling
of a variable-speed three-phase wind turbine to an electrolyzer
with a high quality three-phase ac/dc rectifier interface. This
paper compares three different topologies of three-phase high-quality
rectifiers for use in a wind to hydrogen system. A six-pulse phase-controlled
rectifier, a single-switch unidirectional ac/dc buck converter,
and a single-switch ac/dc single-ended primary inductance converter
(SEPIC) are developed and simulated using software-modeling techniques
to calculate power output and efficiencies determined by wind turbine
and electrolyzer operational characteristics. Software simulations
indicate that the single-switch ac/dc SEPIC exhibits an increase
in power production of 25% in the lower 25% of usable wind speeds
over the single-switch ac/dc buck converter, and an increase in
power production of 5% in the lower 10% of usable wind speeds over
a modified six-pulse phase-controlled rectifier, with less cost
and comparable efficiency. This work is part of a larger project
that investigates a methodology to maximize off-grid wind to hydrogen
production with a power electronics interface.
Design Assistance for Renovation and New Construction at Red Rock Canyon
National Conservation Area Using Building Energy Simulation. BENJAMIN
BARNES (University of Illinois
at Urbana Champaign, Urbana-Champaign, Illinois, 61801)
ROBI ROBICHAUD (National Renewable Energy Laboratory, Golden,
CO, 89401)
The Federal Energy
Management Program Technical Assistance team at NREL used eQUEST
software to help the Bureau of Land Management in their attempt
to reach and exceed the goals of the 2005 Energy Policy Act in
their new visitor center and renovated offices at Red Rock Canyon
National Conservation Area. EQUEST was chosen for its intelligent
defaults and its DOE-2 engine, which has been well validated against
real buildings. Weather data collected on site was used for simulating
external loads and visitation data from the current visitor center
was used to generate internal occupancy loads while other internal
loads were largely eQUEST defaults, except infiltration, which
was adjusted to account for the door use patterns of a visitor
center. The heating, ventilating and air conditioning (HVAC) equipment
in the design involves a dedicated outdoor air system (DOAS) serving
all zones and several recirculating, terminal units. The outdoor
air load was simulated by assigning the DOAS to a few central zones
and giving it the entire building outdoor air requirement while
the recirculating units served the zones they were specified to
with no OA load. Evaporative cooling (EC), on-off, two step and
continuous daylighting, moveable insulation, dual speed compressors
and a deeper Western overhang were all simulated. The EC and daylighting
achieved the majority of the savings (21% and 8% of total building
energy, respectively) while the results for the other measures
suggested that they can likely be ignored. It is recommended that
water conservation issues with EC be seriously investigated. Two
step daylighting controls should be implemented and, if it proves
feasible, combined with EC. The moveable insulation should be avoided
as it would introduce maintenance issues and actually has a net
detriment to energy use. The model, in the future, should be further
validated concerning its HVAC approximations and used to assist
in peak load management. Also, to be of greatest benefit, it must
be kept up to date with current design development.
Design of Blade Rotation System for a Large Wind Turbine Blade Test Stand. MICHAEL SMITH (Portland State University, Portland, OR, 97201) JASON COTRELL (National Renewable Energy Laboratory, Golden,
CO, 89401)
Wind turbine
blade testing is a key element in the development and success of
the blade manufacturing industry. Testing is necessary to achieve
higher reliability and meet international certification requirements.
NREL (National Renewable Energy Laborotories) tests blades on both
faces by mounting the blade on a test stand and applying static
loads. The blades must be rotated between tests to apply loads
to a second face. The objective of this study is to create and
evaluate design options for a blade rotation system. Project deliverables
include design specifications, graphic models, and cost estimates.
The primary components of the rotational system include large adaptor
plates, a rotational guide, and a drive. The focus of the study
is on the design and selection of the rotational guide. Two main
concepts were developed for comparison; one in which the blade
is mounted to a heavy duty slewing bearing and one that uses calipers
with rollers to support and guide blade during rotation. The results
of this study indicate that the caliper design is likely to be
a more expensive and complicated choice. However, the caliper design
offers options for scalability and modularity that may make it
more cost effective in the long term.
Development and Application of
the Small Blade Fatigue Life Equivalency Test (SB-FLET) on the
Southwest Windpower Skystream 3.7 Wind Turbine. WILLIAM RIDDLE (Montana State University, Bozeman, MT, 59717) JASON COTRELL (National Renewable Energy Laboratory, Golden,
CO, 89401)
Development and
Application of the Small Blade Ftigue Life Equivalancy Test on
the Southwest Winpower Skystream 3.7 Wind Turbine. WILLIAM RIDDLE
(Montana State University, Bozeman, MT 59715) SCOTT HUGHES (National
Wind Technology Center, Boulder, CO 80303). The Small Blade Fatigue
Life Equivalency Test (SB-FLET) system is implemented by the structural
testing group of the National Wind Technology Center (NWTC). The
SB-FLET incorporates a test-loading fixture, designed to test wind
turbine blade and rotor packages under fatigue loading. The system
allows for testing multiple specimens at one time. The SB-FLET
is used with industry partners as a tool to validate analytical
design models of wind turbine blades and rotors for fatigue durability.
A description of the SB-FLET method and application to the downwind,
1.8kW, 3.72m rotor diameter Southwest Windpower (SWWP) Skystream
3.7 turbine is presented in this paper. A lifetime of operational
loading in the filed is transformed into an accelerated bending
moment range that, when applied over 106 test cycles, represents
20 years of in-field service. Using representative blade data,
a detailed dynamic (fatigue) model is created and subsequently
used to specify SB-FLET parameters. The test is performed by mounting
three blades to the rotor package and adding ballast weights to
two spanwise locations on each blade. A hydraulic actuator applies
a sinusoidal forcing function to the hub assembly, simulating out-of-plane
test bending moments. Data from a static failure pre-test ensures
that the range is within the ultimate strength of the blade and
helps quantify potential structural sensitive areas of the blade.
The test runs at the natural frequency of the system (blade, ballast
weights, and hub). Typically the test is run for one million cycles
with regular inspections intervals to monitor the behavior of the
test articles. Strain gages are used as the primary health monitoring
system. A total of 22 strain gages were implemented fro the SWWP
test. Once the one-million cycle count is completed, testing is
continued until failure to determine at what percentage of life
the blade fails; i.e. failure at an additional 200,000 cycles would
correspond to a120% damage equivalent design life.
Enhancement of Airside Heat Transfer in Air-Cooled Condensers for Binary Cycle
Geothermal Power Production. CHRISTOPHER
HANNEMANN (University of California, Berkeley, Berkeley, CA, 94720) CHUCK KUTSCHER (National Renewable Energy Laboratory, Golden,
CO, 89401)
Binary cycle
geothermal power production requires a majority of the thermal
energy in the working fluid to be rejected after exiting the turbine.
Because abundant sources of cool water are not available near many
of these geothermal wells, air-cooled condensers must be used instead
of the preferred water-cooled systems. The capital cost for these
condenser arrays, as well as the parasitic power consumed to run
the required fans, contributes significantly to the total cost
of geothermal power. To improve the airside heat transfer in these
condensers, enhanced fins are being tested at the National Renewable
Energy Laboratory; slit and bent annular fins are examined in the
present study. Transient testing is performed on small tube sections
to determine performance improvements based on heat transfer coefficients
and pressure drops as well as to select an optimum bending angle.
Using the results from the transient tests, a steady-state test
using a 17 tube, single pass cross flow heat exchanger is performed.
The slit fins are tested unbent and bent at 12° in two different
configurations, using water as the working fluid and testing each
sample at four different air flow rates. The “staggered” arrangement
is shown to perform the best, and the 12° bent fins are shown to
outperform the unbent fins by 3 – 5% heat transfer per unit hydraulic
power. Both the unbent and bent fins underperform model predictions,
possibly due to corrosion within the tubes. Further work will focus
on retesting the bent slit fins with the corrosion removed as well
as examining the effects of twisting the slit fins.
Examination of Dislocations in Lattice Mismatched GaInAs/GaAs for III-V Photovoltaics. ALEJANDRO LEVANDER (Pennsylvania State University, State College, PA, 16802) JOHN GEISZ (National Renewable Energy Laboratory, Golden, CO,
89401)
Dislocations
act as sites for nonradiative electron/hole pair recombination,
which reduces the efficiency of photovoltaics. Lattice-matched
materials can be grown on top of one another without forming a
high density of dislocations. However, when the growth of lattice-mismatched
(LMM) materials is attempted, many dislocations result from the
relaxation of strain in the crystal structure. In an attempt to
reduce the number of dislocations that propagate into a solar device
when using LMM materials, a compositionally step-graded buffer
is placed between the two LMM materials. In order to confine the
dislocations in buffer layer, and therefore increase material quality
and device efficiency, the growth temperature and thickness of
the buffer layer were varied. A GaInP compositionally graded buffer
and GaInAs p-n junction were grown on a GaAs substrate in a metal-organic
chemical vapor deposition system. A multi-beam optical stress sensor
(MOSS) and X-ray diffraction (XRD) were used to characterize the
strain in the epilayers. Electrical and optoelectronic properties
were measured using a probe station and multimeter setup, solar
simulator, and a quantum efficiency instrument. It was determined
that device functionality was highly dependent on the growth temperature
of the graded buffer. As growth temperature increased, so did the
dislocation density in the device despite an increase in the dislocation
velocity, which should have increased the dislocation annihilation
rate and the diffusion of dislocations to the edge of the crystal.
The thickness of the graded buffer also affected device efficiency
with thinner samples performing poorly. The thinner graded buffer
layers had high internal resistances from reduced carrier concentrations.
The empirically derived recipe developed at the National Renewable
Energy Laboratory (NREL) produced the highest quality cells. Future
work will concentrate on further determining the scientific theory
explaining dislocation propagation in LMM buffer layers, possibly
by examining the effect of dopant type.
Indium Zinc Oxide Active Channel Layer in Transparent Thin Film Transistors. ANDREW CAVENDOR (Colorado School
of Mines, Golden, CO, 80401) DAVID GINLEY (National Renewable Energy
Laboratory, Golden, CO, 89401)
Amorphous indium
zinc oxide (IZO) shows promise for being the active channel layer
in a transparent thin film transistor (TTFT). In the last 2 years,
oxide based transistors have begun to be investigated showing the
promise to replace amorphous silicon (a-Si) and microcrystalline
silicon TFTs to lead to transparent electronics. IZO is a lead
candidate because it can be deposited at room temperature and is
amorphous, making it suitable for flexible substrates. Also, IZO
has higher Hall mobility (µh) > 30
cm2V-1s-1 than
conventional materials (< 1 cm2V-1s-1), which makes faster TFT switching times possible. We used DC
magnetron sputtering with O2/Ar gas from 0-10% to optimize the active channel layer, for
transistors. Addition of O2 to the sputter gas reduces the carrier concentration () while
preserving high mobility µh. Amorphous IZO films were produced at 70/30 atomic percent In/Zn
with µh as
high as ~55 cm2V-1s-1 and as low as ~1016 cm-3. TFT devices were made in the gate down method through photolithography.
The source and drain were produced at 84/16 atomic percent In/Zn,
to achieve good conductivity ~2000 S cm-1. Films were incorporated into functional transistors which showed
on-to-off current ratios ~106.
Linking Conductivity Measurements of Composite Heteropoly Acid Proton Exchange
Membranes with Membrane Compositions and Fabrication Methods. DANA LIPFERT (Colorado School of
Mines, Golden, CO, 80401) JOHN TURNER (National Renewable Energy
Laboratory, Golden, CO, 89401)
Fuel cells have
been proven as an efficient energy conversion device and are employed
in several applications at which they have performed well. In high
temperature applications (ł100°C) fuel cells require a cooling
and humidification system to function properly. This increases
weight, size, and cost of these applications, making fuel cells
impractical for them. A proton exchange membrane that functions
at high temperatures will alleviate these complications and allow
for mass production of fuel cells for high temperature use. Composite
heteropoly acid proton exchange membranes have shown promise for
high temperature use, but a chemically and mechanically stable
composite membrane with sufficient conductivity has yet to be obtained.
The wide variety of heteropoly acids, membrane compositions and
fabrication methods allows for a plethora of composite membranes,
most of which do not satisfy all requirements. The objective of
this work was to associate conductivity trends with fabrication
methods, conditioning methods, and weight ratios of heteropoly
acids and silanes (a fixing agent for heteropoly acids). For this
work 12-silicotungstic acid (12STA) and tetraethyloxosilane (TEOS)
at varied weight percents were used in composite membranes fabricated
by either a sol-gel solution cast method or a doctor blade film
forming method. Most membranes were cured, though uncured membranes
were also tested. Conductivity tests were performed at a constant
cell temp of 80°C with relative humidity (RH) ranging from 50-100%.
Conductivities ranged from 0.36 mS/cm to 18.7 mS/cm, the highest
conductivity produced at 100% RH by a membrane with 174 weight
percent (wt%) 12-STA and 56 wt% TEOS fabricated by the solution
casting method. Membranes fabricated by the doctor blade method
were more flexible and produced higher conductivities than membranes
of the same composition fabricated with the solution casting method,
which tended to be brittle. Membranes conditioned in DI water produced
lower conductivities than membranes of the same composition conditioned
ambiently. UV-visible absorption analysis performed on water extracts
for membranes after five day soaking showed that approximately
25 wt% 12-STA were leached out of the membranes. Uncured membranes
were shown to have lower conductivities than cured membranes of
the same composition.
New Liquid Precursors for the Deposition of Molybdenum. ROBERT
PASQUARELLI (Rochester Institute of Technology, Rochester, NY, 14623) CALVIN CURTIS (National Renewable Energy Laboratory, Golden,
CO, 89401)
Copper indium
diselenide (CIS) solar cells have demonstrated record high efficiencies,
but the technology required and number of deposition systems necessary
for processing CIS solar cells makes them expensive and difficult
to scale up for manufacturing. A new means of depositing molybdenum
(Mo), which serves as the back contact for these devices, from
liquid precursors can help lower costs and make CIS a more viable
energy alternative. Deposition was studied using the organometallic
precursors bis(ethylbenzene)molybdenum and tetraallyldimolybdenum
dissolved in organic solvents. These solutions were deposited on
glass microscope slides at temperatures between 100 and 340°C under
nitrogen atmosphere. Commercial bis(ethylbenzene)molybdenum dissolved
in both tetrahydrofuran and toluene was deposited on glass substrates
at 200 and 340°C via spraying to produce films metallic in appearance.
X-ray diffraction (XRD) showed broad peaks that could be assigned
to Mo and carbonaceous contaminants (cubic Mo2C and hexagonal ß-Mo2C), but most of the material present appeared to be amorphous.
Elemental composition should be studied in future analysis to quantify
the amount of carbide and metallic Mo present. The resistivity
of a sprayed film was determined using a four-point probe to be
(3.23 ± 0.76) x10-4 O-cm,
a value about two orders of magnitude greater than that of pure
Mo and one order of magnitude greater than the sputtered films
currently used. Tetraallyldimolybdenum was synthesized under Schlenk
line conditions and deposited from solution via drop coating to
produce powdery films with poor adhesion. The composition of these
films could not be determined using XRD given their amorphous nature.
Future work will focus on removing carbide contaminants by depositing
in the presence of hydrogen and producing more crystalline material.
Opportunities for Direct Current Power Distribution in Commercial Buildings. PEARL DONOHOO (Franklin W Olin College of Engineering, Needham, MA, 29492)
MICHAEL DERU (National Renewable Energy Laboratory, Golden, CO,
89401)
Direct current
(DC) systems in commercial buildings have the potential for energy
savings through increased motor efficiency, elimination of rectifiers,
and use of distributed generation of renewable energy. These potential
savings are documented through past studies on power supply efficiency,
motor efficiency, and new concepts in DC distribution. Despite
alternating current (AC) distribution, components of heating, ventilation,
and air conditioning (HVAC) systems, fluorescent ballasts, and
plug loads all use DC power. To quantify energy savings, a DC system
model of the Pennsylvania Department of Environmental Protection
Cambria Office building was completed. The three major building
systems, HVAC, interior lighting, and plug-load were modeled, which
covered 96% of building energy use. The buildings systems were
modeled twice using data from a previous study of the building,
first assuming one large rectifier and secondly assuming supplied
DC power. The model predicted an annual average savings of $2,700
with a rectifier and $3,200 without.
Power Performance Analysis of Wind Turbine Generation Systems. LAUREN
COOPER (Colorado School of Mines, Golden, CO, 80401)
ARLINDA HUSKEY (National Renewable Energy Laboratory, Golden, CO,
89401)
Modern wind technology
is among the most effective and profitable ways to simultaneously
address global warming and meet America’s growing energy needs.
Nevertheless, further advancements, including the optimization
of offshore wind turbines, will be necessary for continued success
in the United States. This paper describes a MATLAB-based rotor
design optimization program called Rotor Optimization for Offshore
Turbines (ROOT) that includes both land-based and offshore cost
models. The program uses MATLAB’s Genetic Algorithm Tool to find
the rotor radius, number of blades, chord distribution, and twist
distribution that result in a minimum cost of energy (COE) for
a given wind regime. To predict aerodynamic performance, ROOT uses
a program developed at the National Wind Technology Center called
WT_Perf, which relies on blade element momentum theory. ROOT includes
a basic structural analysis as well as losses due to soiling, wind
farm array effects, availability, and power conversion. Although
ROOT requires further development, such as improvements in the
structural and cost models, the version discussed in this paper
proved to be an effective rotor design tool. ROOT consistently
generates blade shapes that closely resemble existing designs,
even when the program begins with a random set of geometrically
unusual designs. For a wind regime near the Nantucket Sound, ROOT
generated a rotor design that would improve COE by 4.6% over the
baseline design.
Rotor Design Optimization for Offshore Wind Turbines. PAUL KREINER
(Stanford University, Stanford, CA, 94305) PATRICK MORIARTY (National Renewable Energy Laboratory, Golden,
CO, 89401)
Modern wind technology
is among the most effective and profitable ways to simultaneously
address global warming and meet America’s growing energy needs.
Nevertheless, further advancements, including the optimization
of offshore wind turbines, will be necessary for continued success
in the United States. This paper describes a MATLAB-based rotor
design optimization program called Rotor Optimization for Offshore
Turbines (ROOT) that includes both land-based and offshore cost
models. The program uses MATLAB’s Genetic Algorithm Tool to find
the rotor radius, number of blades, chord distribution, and twist
distribution that result in a minimum cost of energy (COE) for
a given wind regime. To predict aerodynamic performance, ROOT uses
a program developed at the National Wind Technology Center called
WT_Perf, which relies on blade element momentum theory. ROOT includes
a basic structural analysis as well as losses due to soiling, wind
farm array effects, availability, and power conversion. Although
ROOT requires further development, such as improvements in the
structural and cost models, the version discussed in this paper
proved to be an effective rotor design tool. ROOT consistently
generates blade shapes that closely resemble existing designs,
even when the program begins with a random set of geometrically
unusual designs. For a wind regime near the Nantucket Sound, ROOT
generated a rotor design that would improve COE by 4.6% over the
baseline design.
Solvent-induced Bandgap Effects in Poly(3-hexylthiophene). RENEE
GREEN (University of Pittsburgh, Pittsburgh, PA, 15213) GARRY RUMBLES (National Renewable Energy Laboratory, Golden,
CO, 89401)
Poly(3-hexylthiophene)
is a well-studied semiconducting polymer whose absorbance, and
thus, optical bandgap, can be altered via formation of thin films
or addition of poor solvent. These methods are known to change
the color of the polymer from yellow (“Y-form”) to red (“R-form”).
The change in absorbance of the two forms of polymer results in
the widening of its optical bandgap, but the resulting alteration
of the electrical bandgap is poorly understood. Absorbance spectra
were taken on dilute solutions of poly(3-hexylthiophene) dissolved
in THF as methanol was added to bring about the absorbance transition.
The resulting absorbance wavelengths were then converted into electron-volts
to determine the polymers’ optical bandgaps. Cyclic voltammetry
was then performed on the solutions containing varying methanol
volume fractions to evaluate the polymers’ electrical bandgaps.
Y-form polythiophene was found to have an approximate optical bandgap
of 2.3eV, while that of the R-form was found to be 1.9eV. The electrical
bandgap of only the Y-form of the poly was able to be determined,
at approximately 1.8eV. Solvent oxidation interference is suspected
to be the cause of poor R-form electrochemical data, thus other
solvents will be tested. Furthermore, while it is assumed that
both phases of R-form polythiophene are energetically analogous,
we aim to eventually demonstrate this concept by comparing the
electrical and optical bandgap data of the polymer in solution
and in thin-film.
Sugar Yields and Rheological
Changes during Enzymatic Saccharification of High Solid Biomass
Slurries . EVAN MITCHELL (State University
of New York College
of Environmental Science and Forestry, Syracuse, NY, 13210) CHRIS SCARLATA (National Renewable Energy Laboratory, Golden,
CO, 89401)
Cellulosic ethanol
production involves several steps of biomass slurry processing
that include extraction of sugars using chemical and/or enzymatic
reactions, fermentation of sugars to ethanol, as well as transport
of slurries between unit operations. It is desirable that the amount
of water in these slurries be minimized to reduce equipment size
and energy input required for processing. A lower water content,
however, results in "high solid slurries" which are rheologically
challenging. In this investigation, we have studied the effects
of solid concentrations on enzymatic conversion and have quantified
the rheological property changes in high solid slurries during
enzymatic saccharification. Results from digestibility studies
showed that cellulose conversion decreased from 72% to 39% when
initial solid concentrations were increased from 15% to 40%. It
was also interesting to note that final glucose concentrations
increased from 83.6 g/L at 15% solids to 159.0 g/L at 30% solids,
but stayed at nearly the same level at higher solids concentrations.
Further, results from rheological measurements also showed that
viscosity changes were more pronounced during digestions with the
lower initial solid concentrations of 25 and 30%, when compared
to digestions at higher initial concentrations of 35 and 40%. The
preliminary rheological characterization also showed that the material
stays pseudoplastic, or shear thinning, throughout digestion .
However, a more complete rheological characterization of the material
was not possible due to limited capabilities of available instrumentation,
and warrants further investigation. These results indicate that
lower conversions at high solid concentrations are likely due to
sugar inhibition of enzymes. Overall, our studies indicate that
the break point in sugar release at 30% initial solid concentration
correlates with rheological property measurements. At higher solid
concentrations, it is likely that enzymes are inhibited either
due to lack of sufficient free water or due to build up of sugars
in the liquid phase. Further kinetic and rheological studies are
required to better elucidate this decrease in digestibility.
Temperature Measurements of Lage-Area TCOs under Vacuum. JENNIFER
GADDIS (University of Illinois
at Urbana Champaign, Urbana, IL, 61801) BRENT NELSON (National Renewable Energy Laboratory, Golden,
CO, 89401)
The National
Center for Photovoltaics (NCPV) has developed new standards for
deposition and characterization tools in order to facilitate process
development and integration. The first tool designed to these specifications
is a sputtering tool for transparent conducting oxides. One such
specification dictates that all systems must hold 6”x 6” substrates.
Concerns were raised internally at the NCPV about temperature uniformity
across the substrates and the performance of large-area heaters.
In this study, large area heater characteristics were studied using
Type-K thermocouples and an Infrared camera; preliminary work on
verifying temperature uniformity and creating intentional non-uniformity
was also conducted. Both optical and direct contact measurement
techniques were used to create a heater calibration curve for Corning
1737F glass substrates. However, the temperature measured optically
was significantly higher due to radiation from the back-plate of
the substrate holder. Using the thermocouple measurement, the temperature
of the glass was found to achieve only about one half of the heater
temperature (°C). For combinatorial deposition, the ability to
produce both uniform and intentionally non-uniform heating is desired.
An infrared camera was used to create temperature maps of glass
substrates. The uniformity of the substrates from 100-400 °C was
verified to within a standard deviation of 2.6% of the substrate
temperature. Intentional temperature reduction of 15% over a specified
area of the substrate was produced using a Tantalum radiation shield.
Future work will focus on creating a standard temperature measurement
method for 6”x 6” substrates, exploration of other materials and
thicknesses for the substrate platen, and manipulations of temperature
for combinatorial deposition.
The Effect of Phthalocyanines on Solution-Processed Organic Photovoltaic Devices. TALIA GERSHON (Massachusetts Institute of Technology, Cambridge, MA, 2139) DR. SEAN
SHAHEEN (National Renewable Energy Laboratory, Golden, CO, 89401)
Organic photovoltaics
(OPVs) are one mode of renewable energy utilization that promises
to provide a cleaner energy alternative to fossil fuels. Initial
devices called bulk heterojunctions are commonly made using an
active layer composed of a blend of a p-conjugated polymer and
a fullerene, in our case poly(3-hexylthiophene) (P3HT) or Poly[2-methyl,5-(3*,7**
dimethyl-octyloxy)]-p-phenylene vinylene (MDMO-PPV) and [6,6]-phenyl
C61 butyric acid methyl ester (PCBM). These devices have optical
band gaps approximately equal to 1.9 eV where an optimal device
would have a band gap closer to 1.4 eV, thus adding a third component
to red-shift absorption should increase the amount of light absorbed
as well as improve the efficiencies of these devices. Liquid crystalline
zinc-phthalocyanine (Zn LC PC) and liquid crystalline copper phthalocyanine
(Cu LC PC) are materials that have peak absorbances around 650
nm, which would enhance absorption in the active layer in this
way; because of their liquid crystalline morphologies, these materials
may also improve ordering and, thus, improve transport and efficiency
in OPV devices. Other non-liquid crystalline materials that have
similar optical densities have also been considered, including
a Titanyl Phthalocyanine (TiO PC) and a Free Base Phthalocyanine
(Free Base PC). Our research explored the effects of adding such
materials to the P3HT:PCBM or MDMO-PPV:PCBM active layers in the
bulk heterojunction. Though there is some evidence indicating an
improvement in absorption and transport with these materials, no
increases in cell efficiency have been observed to date.
Verification and Application of a Thermosiphon Solar Water Heater Model. JAY JOHNSON (University of Missouri - Rolla, Rolla, MO, 65409)
JAY BURCH (National Renewable Energy Laboratory, Golden, CO, 89401)
Rising energy
prices and global warming have sparked added interest in wind,
biomass and solar technologies. Solar water heating can reduce
domestic water heating costs by more than half and currently new
Solar Domestic Hot Water (SDHW) systems are in development and
production. Thermosiphon systems are a relatively mature technology,
but there are still a number of uncertainties their behavior. Thermosiphon
systems use the natural buoyancy of hot water to drive flow during
the day, but at night cooler ambient conditions cause reverse thermosiphoning.
The National Renewable Energy Laboratory (NREL) has developed a
new model using TRNSYS software, which can smoothly transition
between forward and reverse flows. Two of the new NREL components
in this model were verified by comparing analytical results to
the TRNSYS solution. Then using this model, reverse thermosiphoning
was studied and quantified in different climates and loop geometries
to understand the energy penalty of the typically ignored reverse
thermosiphoning phenomenon. New passive solar thermal systems have
the tank nearly coincident with the collector, so the penalty from
reverse thermosiphoning was of particular interest. All modeling
showed some level of reverse thermosiphoning regardless of climate
or tank position. Although these systems are highly dependant on
hot water draws, the reverse thermosiphon mass was nine times larger
in low tank configurations, forward thermosiphon mass was 80% larger
with the high tank configuration and hence the high tank configuration
was capable of delivering 25% more energy annually than the low
tank configuration. This points to using systems with high tank
configurations, but attic limitations and the inconvenience of
tank mounting may not always make such geometry feasible. This
work quantifies the penalty and shows that such configurations,
though not optimal, produce reasonable savings.
