CONTENTS April 2004

ISSUE 2

a publication about NREL R&D highlights

Page i

2 New Horizons 

for Hydrogen

Aspects of a hydrogen future: The cover 

shows a photoelectrochemical cell that 

uses sunlight to produce hydrogen from 

water; a hydrogenase enzyme from the 

green alga Chlamydomonas rheinhardtii 

that catalyzes the release of hydrogen 

gas from water; and a single-wall carbon 

nanotube, which offers the promise of a 

safe and reliable way to store hydrogen.

The NREL Research Review. The National Renewable Energy Laboratory is operated by 

Midwest Research Institute and Battelle for the Department of Energy’s Office of Energy Efficiency 

and Renewable Energy. NREL is the nation’s premier laboratory for R&D on renewable energy and 

a leading laboratory for energy efficiency. The Research Review is published yearly and describes 

the Laboratory’s accomplishments in science and technology to a wide audience. The purpose is 

not simply to describe the progress being made, but also to show the promise and value of NREL’s 

R&D to people, industry, the nation, and the world. 

feature

articles

10 Unraveling the Structure 

of Plant Life Cellulase enzymes may be 

used to decompose the cellulosic 

fiber in plant material to sugars, 

which can then 

be used for making chemicals, 

fuels, materials, and other 

products.

16 Winds of Change By 2020, carbon dioxide emissions from power plants in the 

United States are expected to 

increase by nearly 50%. But 

much of this increase could be 

offset if the use of wind energy were to continue its rapid 

growth and gain a significant 

share of the electricity market 

by 2020.

departments

1 Perspective NREL’s R&D in hydrogen and other areas of renewable energy and 

energy efficiency will help our nation diversify 

its energy supply and power its economy, and 

will benefit its environment. 

20 Awards & 

Honors NREL wins 

four R&D 100 awards, 

two FLC technology transfer awards, and welcomes 

a new fellow of the American Association for the 

Advancement of Science.

22 NREL in Focus The Laboratory 

names a new research fellow, selects a director for the bioenergy center, assumes the role 

for integrating hydrogen systems, plans a new 

R&D facility, and builds computing capability.

25 Patents Nineteen new NREL technologies are patented, ranging from electrochromic and photoconductive materials to 

thin-film photovoltaics to ethanol production.
Page 1

Dr. Stanley R. Bull, Associate 

Director, Science & Technology

Pursuing the Goal

NREL’s focus on science 

and technology, from innovation to implementation, is to make abundant energy available to 

all people with minimal 

adverse effects on our environment. This 2003 edition of the NREL Research 

Review highlights some of 

the technology development advances we have 

made toward that goal, 

beginning with the production of hydrogen from 

renewable sources. NREL 

scientists made important strides in methods including the 

gasification and pyrolysis of biomass, 

electrolysis of water using electricity 

produced by wind and other renewable 

energy technologies, and direct watersplitting via photoelectrochemical and 

photobiological techniques. (See “New 

Horizons for Hydrogen,” page 2.)

In biomass research, NREL worked 

with industry to engineer enzymes 

that are more efficient at breaking 

down cellulose into sugars, culminating in a 12-fold reduction in the 

cost of enzymes. (See “Unraveling the 

Structure of Plant Life,” page 10.) Researchers also determined how to increase the amount of solids that could 

be tolerated in slurries while producing sugars from biomass, which will 

markedly reduce the cost of bio-based 

fuels, chemicals, and other products. 

NREL took another step forward in 

2003 toward the goal of cheaper, more 

reliable wind power by developing a 

capability to test industry’s wind turbine blades at their natural resonant 

frequency along two axes of the blade. 

This enables researchers to assess a 

wide range of larger blades for their 

tendency toward fatigue and delamination. As one of the most rapidly growing renewable electricity technologies, 

wind energy is a critical 

technology in offsetting 

carbon dioxide emissions 

that contribute to global 

warming. (See “Winds of 

Change,” page 16.)

Photovoltaics is also a vital technology 

that will reduce carbon dioxide emissions 

from conventional 

electricity production. 

NREL researchers and 

their industry partners recently set five 

conversion efficiency records, one involving the world’s 

most efficient cell design — a triple-junction GaInP2/GaAs/

Ge cell that converts 

36.9% of solar energy 

to electricity under a 

concentration of 309 suns. As another 

example, thin-film cells have reached 

efficiencies of 19.2%, a performance 

similar to standard multicrystalline 

 silicon cells. These lab-scale advances 

will ultimately help lower the cost of 

commercial-scale solar modules.

In the area of advanced vehicle and fuel technologies to reduce our dependence on foreign oil, NREL has licensed 

its simulation software — ADVISOR — 

to AVL Group, a company that develops power trains and advanced vehicle 

simulation technologies. ADVISOR is 

a modeling tool that helps automakers 

design fuel cell and hybrid power trains 

for optimum vehicle performance, 

economy, and emissions; and already 

has an established user community of 

several thousand users.

In buildings energy research, NREL 

scientists developed software — BEopt

— that enables engineers, architects, 

and others to choose the best materials and designs to minimize building energy use and costs for any given 

climate and location. The software also shows the most effective and least 

costly path toward designing buildings 

that could achieve zero net energy use.

NREL is in the forefront of the developments needed to bring distributed generation of electricity into the 

 marketplace, which will benefit not only 

individual buildings but also industrial plants, communities, and other localized electrical loads. Working with 

industry and utilities, NREL researchers led the effort to develop and win 

approval for new uniform national 

standards for the interconnection of 

distributed generation technologies. 

These standards will enable the interconnection of distributed generation 

systems of various types to the electrical grid, other distributed systems, and 

individual loads, helping to improve 

power reliability and quality while 

 improving the environment.

The foundation of all this work is our 

basic understanding of the materials and fundamental mechanisms related to these technologies. In 2003, 

nanosciences made important advances at NREL. Scientists are using 

self-assembling proteins — bacterial 

cellulosomes — to organize III-V semiconductor quantum dots into arrays, 

with eventual applications in high-efficiency solar cells, solid-state lighting, 

and lasers. NREL also made significant 

progress in understanding and developing carbon nanotube structures that 

can store effective amounts of hydrogen in a lightweight device for future 

use in fuel-cell vehicles.

Computational science is becoming 

an equal partner with experimental 

and theoretical science (see page 24). 

NREL scientists are simulating the diffusion of oxygen and hydrogen in algal hydrogenase, which will guide genetic modification of the algae and 

optimize production of hydrogen. Researchers are also simulating the fluid 

and thermal dynamics of spray cooling 

to study the application of this technique to automotive electronics, condensers at geothermal power plants, 

and other areas. With research applications multiplying rapidly, we will continue to build our capability in this 

critical methodology.

As exciting as these advances have 

been in 2003, much remains to be 

done. We look forward to both steady 

progress and important breakthroughs 

as we keep pursuing the goal in 2004.

PPeerrssppeeccttivivee
Producing Hydrogen from

Renewable Resources

New

Horizons

For

Hydrogen

Producing Hydrogen from

Renewable Resources

Page 2 

These days, you’ll likely notice the buzz about 

hydrogen and fuel cells — in conversations at 

local coffee shops, in newsstand headlines, and 

on the nightly news report. The president’s Hydrogen Fuel Initiative, unveiled in his January 

2003 State of the Union address, has captured 

the nation’s attention by highlighting the possibility of a clean and sustainable energy future 

based on hydrogen. This vision of a new hydrogen economy “will mean a world where our pollution problems are solved and where our need 

for abundant and affordable energy is secure...

and where concerns about dwindling resources are a thing of the past.”-- Spencer Abraham, 

Hydrogen Energy Roadmap, November 2003.

Renewable Hydrogen

Hydrogen is the most abundant element in the 

universe. And while it doesn’t exist by itself on 

Earth, it can be produced from a wide variety of 

resources — coal, oil, natural gas, biomass, and 

water. This versatility contributes to the promise 

of hydrogen, allowing it to be produced where 

and when we need it.

About 95% of the hydrogen we use today comes 

from reforming natural gas. The remainder, 

high-purity hydrogen from water electrolysis, 

is primarily produced using electricity generated by burning fossil fuels. But to realize the 

full benefits of a hydrogen economy — sustainability, increased energy security, diverse energy supply, reduced air pollution and greenhouse 

gas emissions — hydrogen must be produced 

cleanly, efficiently, and affordably from domestically available renewable resources.
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The hydrogen cycle: 

When generated from 

renewable sources, such 

as via photoelectrolysis, 

hydrogen production 

and use are part of a 

clean, cyclic process.

Page 3

hydrogen (H2), and water vapor (H2O), with 

by-products of char and ash. In the second step, 

the char is gasified at 800°–850°C through reactions with oxygen (O2), steam, and H2. This 

yields a mixture of gases that primarily consists 

of CO, CO2, and H2. Some of the unburned 

char is combusted to provide the heat needed 

for the gasification. The overall reaction is:

Biomass + O2 ➞ CO + H2 + CO2

The gas product of this process requires conditioning to remove tars and inorganic impurities. 

Carbon monoxide is converted to additional 

 hydrogen by the water-gas-shift reaction:

CO + H2O ➞ CO2 + H2

Pyrolysis is a process that thermally degrades 

biomass to a mixture of gases, char, and an 

 oxygen-rich liquid called bio-oil. Pyrolysis 

takes place at 500°–800°C in the absence of 

 oxygen. The overall reaction is:

Biomass + Energy ➞ Gases + Char + Bio-Oil

The relative proportions of the three products 

depend on the pyrolysis method, the characteristics of the biomass, and the reaction conditions — heating rate, temperature, and residence time. For example, pyrolysis has been 

used to produce charcoal for centuries. This requires relatively slow reaction rates at very low 

temperatures to maximize solid yield. Fast 

 pyrolysis is used to maximize either the gas or 

liquid products, depending on the temperature 

employed. 

The bio-oil and gases are converted 

to hydrogen using catalytic steam 

reforming, followed by the 

water-gas-shift reaction. The 

 catalytic steam reforming reaction takes place at 750°–850oC 

over a nickel-based catalyst: 

Bio-Oil/Gases + H2O ➞	CO + H2

The CO is converted into additional 

H2 by the water-gas-shift reaction, resulting in the overall reaction:

Bio-Oil/Gases + H2O ➞ CO2 + H2

As the final step in both gasification and pyrolysis, the H2 and 

CO2 are separated to yield H2

that is 99.99% pure, meeting 

the requirements for use in a fuel cell.

Co-products. Although well understood, 

the processes of biomass gasification and 

 pyrolysis face challenges. To be competitive, 

The ultimate goal is a sustainable cycle of hydrogen production and use. In the first stage of the 

cycle, hydrogen is produced from renewable resources, such as via photoelectrolysis of water, 

in which energy from the sun is used to convert 

water into hydrogen and oxygen. The hydrogen 

is then used to power a fuel cell, in which hydrogen and oxygen from air recombine to produce electricity, heat, and water. This cycle produces no pollution and no greenhouse gases. 

Advanced technologies that produce renewable 

hydrogen as part of this cycle will play a leading 

role in the future hydrogen economy. 

NREL explores several options for producing hydrogen from renewable resources, including biomass conversion; electrolysis using electricity 

from renewable resources, in particular from 

wind energy; and direct water-splitting using 

microorganisms or semiconductors. Some technologies are ready for real-world demonstrations. Others are just emerging and will require 

long-term R&D investment. But all are focused 

on the same goal — producing clean, sustainable hydrogen.

Hydrogen from Biomass

Since the Laboratory opened in 1978, NREL 

has been developing methods for converting 

biomass to fuels, chemicals, heat, and power. 

Building on the successes of these efforts, biomass is now one of the best near-term options 

for producing renewable hydrogen.

Biomass resources are abundant and widely distributed throughout the United States. And because biomass consumes atmospheric carbon 

 dioxide (CO2) during growth, it can have a 

small net CO2 impact compared with fossil fuels, effectively sequestering carbon and reducing 

our nation’s greenhouse gas emissions.

Biomass feedstocks like agricultural and forest 

residues, consumer wastes, and crops specifically grown for energy production are composed of 

three interconnected polymeric materials — cellulose, hemicellulose, and lignin. Of the technologies used to break down this biomass structure and produce hydrogen, perhaps the ones 

closest to being competitive with conventional 

means are the thermochemical processes of gasification and pyrolysis.

Gasification is a two-step process in which biomass is thermochemically converted into a combustible gas. In the first step, the volatile components of the fuel are vaporized (in the presence 

of oxygen, air, or steam) at temperatures below 

600°C by a set of complex reactions. This yields 

a mixture of CO2, carbon monoxide (CO), tar, 
Biomass Resource Potential

Excellent

Good

Concentrating Solar Power

Resource Potential

Excellent

Good

Wind Resource Potential

Excellent

Good

Page 4

higher process efficiencies and better heat and 

mass integration are needed. The processes must 

be flexible enough to handle a range of low-cost 

feedstocks and their variations in chemical and 

physical characteristics. Large-scale technology 

demonstrations of the entire biomass-to-hydrogen process are needed to optimize the process 

and prove its viability. Plus, we must be able to 

derive other valuable products from biomass. 

This is where pyrolysis has an advantage over 

gasification. Because bio-oil is made up of two 

distinct fractions, it can be separated based on 

water solubility. The water-soluble fraction can 

be converted to hydrogen via catalytic steam reforming, and the water insoluble fraction can be 

used to make high-value adhesives. While this 

approach is not yet cost-competitive, it remains 

a long-term strategy for converting biomass to 

hydrogen. Meanwhile, NREL is investigating 

other coproduct opportunities.

Other feedstocks. In the lab, researchers are evaluating low-cost, potentially high-yield renewable feedstocks — agricultural residues, mixed 

plastics, trap grease, textiles, and other organic 

materials in the post-consumer waste stream — 

for their potential to produce hydrogen using 

pyrolysis/steam-reforming technology. 

New catalysts. Scientists are designing cost-effective, feedstock-flexible reforming catalysts. 

Commercially available catalysts cannot withstand the harsh conditions required to produce 

hydrogen from pyrolysis liquids, resulting in 

catalyst losses of 10%–20% by weight per day. 

NREL has developed new nickel-based catalysts 

to withstand reaction conditions. Testing on pyrolysis oils from pine and mixed hardwoods verified that the new catalysts can produce hydrogen with efficiencies as good as or better than 

those of the best commercial catalysts. These catalysts are being modified for 

use with other feedstocks.

All of these investigations 

— co-products, feedstock evaluation, and catalyst development — are contributing to the 

development of an optimized, 

reliable, cost-effective process 

for producing hydrogen from biomass.

Wind Electrolysis 

Many renewable technologies — 

photovoltaics, wind, biomass, hydroelectric, and geothermal — can 

generate the clean and sustainable 

electricity needed to run an electrolyzer. But for 

electrolytic hydrogen production to be cost-effective, we need a low-cost source of renewable 

electricity. During the past 25 years, advances in 

wind turbine technology have dramatically reduced the cost of wind power. Today, the cost of 

wind electricity typically ranges from 3–7¢/kWh 

for utility-scale projects. This puts wind electrolysis in a good position to be the first economical 

renewable hydrogen-production system.

In wind electrolysis, the wind turns the blades 

of a wind turbine, and the blades spin a shaft, 

which connects to a generator to make electricity. An electrolyzer uses this electricity to separate water into hydrogen and oxygen:

2H2O + electricity = 2H2 + O2

Proton exchange membrane (PEM) electrolyzers, which are being investigated for this application, consist of a membrane sandwiched between two catalyst-coated electrode plates. At 

the positively charged electrode (anode), water 

is split into protons (H+), electrons (e-), and oxygen. The oxygen is collected or released, and 

the electrons move through an external circuit under the influence of an applied electric 

field. The protons move through the membrane 

and combine with electrons at the negatively 

charged electrode (cathode) to form H2.

Producing both electricity and hydrogen from 

wind turbines offers the promise of optimizing electrolysis and power-system efficiencies 

and lowering costs. For example, producing hydrogen with wind power can improve the ability to dispatch electricity when needed, which is 

a limitation associated with the intermittent nature of wind energy. When the wind turbine is 

producing electricity, hydrogen can be produced 

via electrolysis and stored for later use. The 

stored hydrogen can then be used in a fuel cell 

Renewable Resources 

for Hydrogen

We have enough renewable resources throughout the United States — 

from wind, solar, biomass, etc. — to meet the 

energy needs of the entire country. The wide 

distribution of renewable resources allows the 

use of decentralized hydrogen production from 

coast to coast. For example, in Iowa, hydrogen could be produced as 

a byproduct of the corn 

ethanol production process; and in Massachusetts, it could be produced from electricity 

generated by off-shore 

wind farms. Decentralized hydrogen production using renewable 

resources available regionally reduces or eliminates the cost associated 

with hydrogen storage 

and delivery. (Storage is 

a major challenge, however — see sidebar “Storing Hydrogen in Carbon 

Nanotubes,” page 8.)
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In a PEM electrolyzer cell, water is split into protons (H

+), 

electrons (e

-) and O

2 at the anode. The protons move 

through the membrane to the cathode, where they 

combine with electrons to form H

2

.

Page 5

to produce electricity during times of low power 

production or during peak demand.

Coupling wind turbines with low-cost electrolyzers can also reduce the cost of a system by 

minimizing redundancy. For example, variable 

speed wind turbines rely on power electronics 

to convert the “wild AC” (variable frequency, 

variable voltage) produced at the generator to 

DC, which, when connected to the grid must be 

converted back to AC at grid frequency (60 Hz). 

Electrolyzers designed for grid-connected operation also incorporate power electronics to convert AC from the grid to DC power required by 

the electrolyzer cell stack. These power converters represent a significant percentage of the total 

cost of the wind turbine and electrolyzer. 

To make wind electrolysis cost-effective, researchers will have to lower the cost of wind 

electricity itself, design more efficient electrolyzers, and optimize the wind/electrolyzer integrated system. Once they’ve done this, they will 

still need to resolve the logistics of integrating 

wind electrolyzer systems with utility systems at 

local, regional, and national levels.

One step toward meeting these challenges is a 

planned demonstration of integrated electrolysis systems at NREL’s Wind Hybrid Test Facility. For this demonstration, NREL is designing a 

single power-electronics package and controller 

that will eliminate redundancy in the wind electrolysis system and allow the power output of 

wind turbines to match the power requirements 

of electrolyzers. Success here will help pave the 

way for commercializing the concept.

Direct Hydrogen Production 

Direct water-splitting technologies — using 

photoelectrochemical devices or photosynthetic microorganisms — are the “Holy Grail” 

of the hydrogen economy. These processes use 

 energy from sunlight to dissociate water into 

 hydrogen and oxygen. They are the ultimate 

clean and sustainable hydrogen production 

methods. Although not ready for prime time, 

photoelectrochemical and photobiological technologies show great promise for the future and 

are the focus of long-term R&D efforts at NREL.

Photoelectrochemical research. A photoelectrochemical (PEC) hydrogen system integrates 

photovoltaic (PV) material with an electrolyzer 

to produce hydrogen directly from water, using 

 only sunlight. This system offers many benefits 

over two-step processes in which the PV cells 

and electrolyzer are separate components of the 

system. Combining the two components in a 

single PEC device can eliminate most of the electrolyzer costs and reduce semiconductor processing because surface contacts, interconnects, and 

wiring are no longer necessary. It can also increase the efficiency of the process by 30%, further reducing the cost of delivered hydrogen. 

The basic PEC hydrogen production system consists of two electrodes — a semiconductor electrode and a platinum metal electrode — immersed in an aqueous electrolyte. But instead 

of using electricity from an external source like 

wind power, the semiconductor absorbs light 

energy and generates the electrical current that 

drives the electrolysis reaction, splitting water 

into hydrogen at the semiconductor surface and 

oxygen at the metal electrode surface.

Although simple in concept, the challenge is to 

find a material that can drive this one-step process. For it to be viable, two criteria must be met 

— the light-harvesting system must have the correct energetics to drive the electrolysis, and the 

system must be stable in an aqueous environment (see sidebar “The Right Energetics,” page 6).

So far, no single semiconductor has been identified that satisfies all of the criteria for use in a 

hydrogen-evolving PEC system. The most stable 

semiconductors in aqueous solution are oxides, 

but their band gaps are too large for efficient 

light absorption, or their semiconductor characteristics are poor. Semiconductors with better 

solid-state characteristics are typically thermodynamically unstable with respect to oxidation.

Finding a material that can drive the process is 

the key to the success of PEC hydrogen production. Materials now under evaluation — gallium 

nitrides, amorphous silicon, and copper indium 

gallium diselenide films (CIGS) — build on 

materials developed for PV. A variety of surface 

treatments — protective coatings and bandedge engineering — are also being evaluated to 
Page 6 

address energetic issues, corrosion problems, 

and catalysts for the water-splitting reactions.

Gallium nitrides, although expensive, are good 

candidates for PEC hydrogen systems because 

they show high efficiencies, are chemically stable, and their band gaps can be adjusted by altering their composition to produce alloys of 

gallium nitride. Gallium phosphide nitride and 

indium gallium nitride are being evaluated to 

determine if they can be tailored to meet the requirements for solar water-splitting.

Amorphous silicon (a-Si) multijunction systems 

developed for PV offer a lower-cost alternative 

to gallium nitride materials. Triple-junction aSi devices have voltages sufficient for water splitting, and the cells can be tailored to produce 

voltages matched to the energetic requirements 

of water-splitting, maximizing overall efficiency. But a-Si is unstable in aqueous solutions and 

must be protected by a corrosion-resistant coating in a PEC-hydrogen system. To maintain the 

function of the semiconductor, the coating material must be stable, transparent, and conductive. For this, researchers are evaluating silicon 

nitride compositions.

Semiconductor materials based on polycrystalline thin films, such as CIGS, are also promising 

alternatives. They are made with inexpensive 

techniques and can reach efficiencies greater 

than 15%, both of which help reduce costs. Incorporating sulfur into CIGS increases the band 

gap into the range required for PEC water-splitting. Making a viable CIGS water-splitting device would greatly decrease PEC hydrogen production costs.

Once we identify a semiconductor material with 

the ideal band gap and chemical stability, it still 

won’t split water unless the semiconductor band 

edges overlap the water redox potential. This energetic mismatch can be overcome by using a 

tandem semiconductor system or by modifying 

the semiconductor band edges. NREL researchers have demonstrated 

a solar-to-hydrogen 

conversion efficiency of 12.4% using 

a unique structure 

based on a gallium 

indium phosphide/

gallium arsenide 

(GaInP2/GaAs) tandem system. In this 

configuration, the 

GaAs cell generates 

the additional voltage needed to overcome the energetic 

mismatch between 

the GaInP2 semiconductor and the water 

redox reactions. Researchers are investiNREL scientist 

John Turner 

demonstrates the 

ability of a PEC 

cell to produce 

hydrogen from 

water using 

energy from a 

light source. 

The Right Energetics

For a PEC-hydrogen structure, system energetics are a 

function of the intrinsic electronic properties of the semiconductor material and the electrochemistry at the interface of the semiconductor and the electrolyte. 

According to the band theory of solids, which describes the 

electrical conductivity of solid materials, the available energy levels for electrons in a material form two bands — a 

valence band and a conduction band. The energy difference between the two bands is called the band gap energy. When a semiconductor absorbs light (photon) energy, 

electrons from the valence band are excited into the conduction band to generate a current. Only photons with energy equal to or greater than the band gap of the material 

can free an electron from the valence band to the conduction band. To absorb a large portion of the solar spectrum, 

the band gap must be less than 2.2 electron volts (eV). For 

PEC applications, the electrical output must also be large 

enough to drive the water-splitting reaction (greater than 

1.23 eV). The ideal material for a PEC-hydrogen system has 

a band gap of 1.6–2.2 eV. 

In a PV system, a solid-state junction is the active layer 

where charge transfer occurs. In a PEC system, the interface between the semiconductor and the electrolyte is the 

active layer. The characteristics of the band edges (i.e., the 

top edge of the valence band and the bottom edge of the 

conduction band) at this interface determine whether water splitting takes place. For a given semiconductor material, the energetic positions of the bands at the semiconduc-
Page 7

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gating the effects of adsorption of organometallic compounds on the band-edge properties of 

GaInP2. In theory, these materials should shift 

the band edges into the water-splitting range, 

and speed up the charge transfer rate at the surface. Understanding and controlling the interfacial properties of semiconductor electrodes 

is key to successfully producing hydrogen from 

PEC systems.

The development and characterization of new 

semiconducting materials and systems are critical for the future viability of PEC-driven hydrogen generation. Continuation of the collaborative relationship between PV and PEC hydrogen 

R&D will accelerate progress in identifying and 

synthesizing more efficient, lower-cost, and 

electrochemically stable solid-state materials 

and systems.

Photobiological research. The green alga, Chlamydomonas reinhardtii, is one of several microorganisms that uses sunlight to produce hydrogen directly from water. Like all green plants, 

this green alga also produces oxygen during 

photosynthesis. Unfortunately, oxygen inhibits 

the function of algal hydrogenase, the enzyme 

in Chlamydomonas that catalyzes the release of 

 hydrogen gas. So under normal conditions, i.e., 

in sunlight, the alga cannot sustain hydrogen 

production for more than a few minutes. 

Before photobiological hydrogen production 

can become a viable commercial-scale option, 

scientists need to find ways to control the oxygen sensitivity of the hydrogenase. Researchers are attacking this problem on two fronts — 

by isolating new forms of the organism that can 

sustain hydrogen production in the presence of 

 oxygen and by developing processes that separate the oxygen and hydrogen production reactions in the algae.

In the first approach, researchers are using 

advanced molecular engineering to design 

hydrogenase enzymes that are more resistant 

to oxygen inactivation. Past research indicates 

that the oxygen inactivation occurs when oxygen binds directly to one of the iron species located at the catalytic center of the enzyme. Researchers developed a model of the hydrogenase 

structure to help identify regions in the enzyme 

most likely to be involved in access of oxygen to 

the catalytic site. This led to the discovery that 

the gas channel, which allows hydrogen to diffuse out of the catalytic center of the enzyme, is 

large enough to allow oxygen to flow back into 

the catalytic site and deactivate the enzyme. Researchers inserted bulky amino acid molecules 

along the gas channel walls to reduce the size of 

the channel so that hydrogen, but not oxygen, 

could flow through it. This modified enzyme 

appears more resistant to oxygen deactivation 

than the original. Researchers are continuing 

this molecular engineering approach to further 

improve oxygen tolerance of the alga.

In the second approach, researchers are identifying and characterizing the process conditions 

that allow the algae to produce either oxygen or 

hydrogen, but not both simultaneously. They 

designed a metabolic switch to cycle algal cells 

between a photosynthetic growth phase, which 

produces oxygen, and a hydrogen production 

phase. The switch is based on withholding sulfur, essential for maintaining normal photosynthesis; without it, the algae decrease their 

photosynthetic activities to low levels (such 

that any oxygen evolved is immediately consumed by the respiratory activity of the culture) 

and become anaerobic in the light. As a consequence, they switch to a different metabolic 

pathway — one that utilizes the reductants generated by water oxidation — to produce hydrogen gas instead. This pathway, which involves a 

In a PEC hydrogen system, 

a semiconductor cell and a 

platinum metal electrode 

are immersed in an 

aqueous electrolyte. The 

semiconductor absorbs 

light energy to generate 

the current that drives the 

electrolytic reaction, with 

hydrogen produced at the 

semiconductor electrode and 

oxygen at the metal electrode. 

For this confi guration to 

work, the band gap of the 

semiconductor must be 

between 1.6 eV and 2.2 eV, 

the band edges must straddle 

the water redox potential, 

the system must be stable in 

solution, and charge must be 

transferred quickly from the 

semiconductor surface to the 

water.

tor surface are fixed. For water splitting to occur, the band 

edges must overlap the energy levels of the hydrogen- and 

oxygen-evolving reactions (the water oxidation-reduction 

potential). Specifically, the conduction band edge must be 

higher in energy than the hydrogen-evolving half reaction 

(-0.41 eV), and the valence band edge must be lower in energy than the oxygen-evolving half reaction (0.82 eV). 

In addition, charge transfer from the semiconductor surface to the water must occur quickly. If electrons build up 

on the surface of the semiconductor, they shift the band 

edges in a negative direction and possibly out of the range 

required for water-splitting. To accommodate this possibility, band-edge characteristics can be shifted to the required energetic positions through chemical modification 

of the semiconductor electrode surface.
Page 8

conversion processes, power 

system integration, electrochemical materials development, metabolic engineering 

of algae, and more. These advanced technologies are varied 

and complex, and each comes 

with its own set of challenges 

that must be addressed before 

they are ready for commercialization. It will take the creativity, hard work, and collaboration of scientists, engineers, and 

analysts from many disciplines 

throughout the Laboratory to 

meet these challenges and continue to move toward a sustainable hydrogen future.

For More Information

Kosourov, S.; Seibert, M.; Ghirardi, M.L. “Effects of Extracellular pH on the Metabolic 

Pathways in Sulfur-Deprived H2-Producing 

Chlamydomonas Reinhardtii Cultures.” Plant 

and Cell Physiology. Vol. 44(2), 2003; pp. 146–

155.

Khaselev, O.; Turner, J.A. “A Monolithic 

Photovoltaic-Photoelectrochemical Device 

for Hydrogen Production via Water Splitting.” 

Science; Vol. 280, April 17, 1998; pp. 425–427.

Dillon, A.C.; Jones, K.M.; Bekkedahl, T.A.; 

Khiang, C.H.; Bethune, D.S.; Heben, M.J. 

“Storage of hydrogen in single-walled carbon 

nanotubes.” Nature, Vol. 386, 1997; p. 377.

Milne, T.A.; Elam, C.C.; Evans, R.J. “Hydrogen 

from Biomass: State of the Art and Research 

Challenges.” IEA/H2/TR-02/001. International Energy Agency, 2001.

hydrogenase enzyme, is responsible for releasing 

large amounts of hydrogen, even in the presence 

of limited photosynthetic oxygen evolution.

The process is reversible, and the cycle can be 

repeated over and over. To optimize hydrogen 

production, researchers are investigating cell 

density in the photobioreactors, the level of sulfate deprivation, the light intensity, the pH of 

the medium, and the presence of organic substrates in the medium.

Researchers are making steady progress in their 

endeavors to understand and direct the metabolic activity of Chlamydomonas reinhardtii, but 

photobiological hydrogen production is still an 

emerging technology with much to learn. Further investigation and optimization of both 

 approaches will determine the most cost-effective, efficient route to hydrogen.

Conclusion

The success of renewable hydrogen is directly 

tied to advances in renewable technologies under development at NREL — thermochemical 

Storing Hydrogen in Carbon Nanotubes

Developing safe, reliable, cost-effective ways to store 

hydrogen — with the ability to carry enough hydrogen 

on-board a vehicle to enable a 300-mile driving range 

— is critical to the success of the president’s Hydrogen 

Initiative. But today’s methods for storing hydrogen — 

under high pressure as a compressed gas, or as a liquid at extremely low (cryogenic) temperatures — cannot meet the performance requirements of on-board 

storage. Promising advanced solid-state materials like 

complex metal hydrides may provide a breakthrough 

in hydrogen storage. Another promising avenue, which 

NREL researchers are exploring, is nanostructured carbon materials that adsorb hydrogen gas reversibly at 

high efficiencies and energy densities. 

The basic mechanism that drives carbon-based hydrogen storage — gas-on-solid adsorption — is a safe, 

potentially low-cost method. However, high-surfacearea carbon materials produced by conventional methods — pyrolysis of coal, biomass, or carbon carrying 

gases — do not adsorb significant amounts of hydrogen at room temperature. But carbon materials produced at the nanoscale (1 billionth of a meter) have 

dramatically different characteristics — large surfaceto-volume ratios, unique size-specific chemistry, and 

short bulk diffusion lengths — that favor enhanced 

hydrogen adsorption. 

To optimize the hydrogen adsorption capacity of carbon materials, we must understand the mechanism 

of the hydrogen adsorption, including the interplay 

between the chemical and molecular forces in bindStructural model of the 

hydrogenase enzyme 

from the green alga 

Chlamydomonas reinhardtii. 

The different colored lines 

depict individual atoms that 

constitute the enzyme: dark 

blue for nitrogen, red for 

oxygen, white for hydrogen, 

yellow for sulfur, and light 

blue for carbon. The catalytic 

center for the hydrogenase 

— the portion of the enzyme 

that synthesizes hydrogen 

gas — is depicted in ball 

form, showing atoms of iron 

(green) and sulfur, along 

with carbon, nitrogen, and 

oxygen.
ing hydrogen to carbon materials. Hydrogen can be 

adsorbed onto the carbon surface through physisorption, in which the physical attraction between molecular hydrogen and the carbon surface forms a weak 

physical bond, or through chemisorption, in which 

molecular hydrogen (H2) is dissociated into atomic 

hydrogen (H), forming a strong chemical bond with 

the carbon surface. To meet DOE’s hydrogen storage 

requirements with this approach, the binding energy must permit strong but reversible immobilization 

of hydrogen atoms or molecules, and the density of 

the binding sites must be sufficient to ensure a system 

weight fraction of hydrogen of at least 8%.

During the past decade, NREL’s R&D has focused primarily on the carbon nanostructure known as “single-wall nanotubes” (SWNTs), long, thin cylinders of 

graphite with a diameter of just a few hydrogen molecules (1-2 nm). The carbon atoms in the graphite 

structure are connected together in a hexagonal lattice similar to chicken wire. Researchers can control 

the synthetic conditions to produce tubes of different 

diameters, with different carbon bonding, and electronic type (semiconducting or metallic, a function of 

the nanotube lattice). They can also introduce defects, 

dopants, and catalysts into the nanotube structure to 

alter properties and tailor the performance of nanotubes.

In 1997, NREL researchers demonstrated that SWNTs can 

store hydrogen at a range they speculated to be 5%–

10% by weight. More recently, they showed that SWNTs 

can adsorb up to 8% by weight hydrogen when catalytic 

metal species are present. However, other laboratories 

have not been able to duplicate these results. To resolve 

this controversy, NREL is now focused on improving the 

reproducibility of the measured performance and fully 

characterizing the SWNTs to understand the mechanism 

and extent of hydrogen adsorption. 

Poor reproducibility is attributed in part to the small 

sample sizes currently available. Typically, NREL’s 

SWNT samples weigh just a few milligrams. It is difficult to measure the performance of such small samples. NREL has established a group to define and 

disseminate measurement and sample-handling protocols for carbon nanomaterials. In addition, NREL scientists are developing repeatable and scalable methods for producing larger quantities of active materials.

They are also performing experimental and theoretical studies of carbon nanomaterials to uncover the 

fundamental science that drives the gas-on-solid 

adsorption process and to ultimately control and 

optimize hydrogen storage. As part of this 

endeavor, they are synthesizing, testing, 

characterizing, and evaluating a variety of different types of SWNTs and 

other carbon materials. They are 

investigating the impact of 

SWNT electronics and 

structure on the 

thermodynamics, 

kinetics, and 

capacity of 

hydrogen storage, the role of defects and catalysts, 

and the nature of interactions at the SWNT wall/

hydrogen interface. And they are exploring other nanostructured carbon materials, which could provide additional information on what governs adsorption interactions with hydrogen.

A number of new concepts have been proposed to 

explain and manipulate the hydrogen adsorption characteristics of carbon nanomaterials. One possible 

approach to increasing the hydrogen storage capacity of SWNTs is to enhance chemisorption with reversible hydrogen spillover. In this approach, a catalyst in 

contact with the nanotube wall dissociates molecular 

hydrogen. Because the nanotube is curved, the attractive forces of the carbon atoms in the lattice overlap. 

This results in a higher number of carbon atoms interacting with the hydrogen, which lowers the activation 

energy for hydrogen addition and permits surface diffusion of the hydrogen away from the catalyst. Atomic 

hydrogen diffuses from the catalyst onto the SWNT 

where it is stored. If the carbon-hydrogen binding 

energy is not too large, the process could be reversible.

Researchers still have a long way to go before this 

technology is fully understood. Significant improvements over currently available hydrogen storage 

technologies are required if hydrogen is to become 

a viable energy carrier. Innovative new approaches, improvements in synthesis and analysis techniques, and scale-up of optimized cost-effective processes are critical for determining the 

potential of these materials to store and 

release adequate amounts of hydrogen 

under practical operating conditions. 

Hydrogen storage represents a difficult but exciting challenge — success in unlocking the mysteries of hydrogen storage in 

nanoscale carbon materials 

could open the door to 

the hydrogen future. 

Page 9

One concept for increasing 

the ability of carbon singlewall nanotubes (blue) to 

store hydrogen is to use 

a metal catalyst (silver) in 

contact with the surface 

of the nanotube. Here, the 

catalyst dissociates hydrogen 

molecules to hydrogen 

atoms (yellow), which then 

diffuse into 

the nanotube 

lattice and 

reversibly 

bond with 

carbon atoms 

(blue).
Unraveling

the Structure

of Plant Life

To Make Sustainable Fuels and Chemicals To Make Sustainable Fuels and Chemicals

Page 10 

used to make chemicals or ethanol fuel for 

our cars and trucks. According to NREL scientists, lowering the cost of the cellulases in that 

enzyme cocktail is the most promising avenue 

toward a competitive and domestic renewable 

alternative to gasoline. It is also a key element 

for developing a U.S. biorefinery industry that 

could make a wide range of chemicals and products from biomass — plants and organic wastes 

— as an alternative to chemicals derived from 

petroleum (see sidebar “What is a Biorefinery,” 

page 12). 

Imagine the look on the bartender’s face if you 

asked for your happy-hour cocktail to be 19 

parts endoglucanase, 90 parts exoglucanase, 

and 1 part betaglucosidase. If you wanted a 

wood chips hors d’oeuvre, or to get energy 

from the fiber in your wheat crackers or corn 

chips, that enzyme cocktail would be just the 

thing. Endoglucanase, exoglucanase, and 

betaglucosidase are cellulases, a family of 

enzymes that act in concert to hydrolyze 

(decompose in water) the cellulosic fiber in 

plant material to sugar. The sugar can then be 
Page 11

Bringing in the 

Big Guns 

To reduce the cost of 

cellulases, NREL and 

DOE contracted with 

the two largest enzyme 

companies in the world 

— Genencor International and Novozymes. 

 Genencor sells enzymes 

and other biotechnology 

products for the health 

care, agri-processing, industrial, and consumer markets. Novozymes 

produces enzymes for a 

 variety of markets and 

performs biotechnology 

research for the pharmaceutical, agricultural, and 

 biochemical industries. 

Both companies have 

 already exceeded their 

initial objective, which 

was to reduce the cost of 

producing cellulases to 

one-tenth of what it was 

to start with. Having met 

their initial objective, 

they are performing follow-up work that could 

cut costs another several fold — to about $0.10/

gallon of ethanol produced. This will make enzymatic hydrolysis more 

cost-competitive and 

overcome a critical barrier for making cellulosic ethanol an economic 

reality along with grain 

ethanol. And, with the 

promise of the ongoing 

research to engineer 

even cheaper and more 

efficient cellulases, combined with advances in 

other aspects of biomass 

 conversion technology, 

 cellulosic ethanol may 

even become competitive 

with gasoline.

So-called “cellulosic biomass” (trees, 

crop residues, municipal solid wastes, 

grasses, etc.) is primarily made up of 

cellulose, hemicellulose, and lignin. The 

proportion of these constituents varies 

with the type of biomass.

and hemicellulose are carbohydrates. But the 

sugars of which they are made are linked 

together in long chains called polysaccharides, 

which form crystalline structures — nature’s 

plastics. Unraveling those polymeric structures is the key to economic biological conversion of cellulosic biomass to valuable fuels and 

chemicals. NREL scientist and cellulase expert 

Mike Himmel likes to refer to this complex and 

 highly protective structure (the plant cell wall) 

as “nature’s cunning plan” to keep plants standing and resistant to microbes. He refers to the 

resulting challenge for bioconversion as the 

“recalcitrance of biomass.” 

Cellulose consists of a loose crystalline structure of thousands of strands, with each strand 

containing hundreds of glucose sugar molecules 

(C6H12O6). The cellulose is, in turn, wrapped 

in a sheath of hemicellulose and lignin, which 

further protects the cellulose. Hemicellulose is 

easier to hydrolyze than cellulose. A combination of heat, pressure, and acidic or basic conditions (each a way of causing hydrolysis, contributing an element of “severity”) breaks 

down hemicellulose into its component sugars. (Hemicellulose sugars are different from 

the glucose of cellulose and harder to ferment 

— but that’s another story). NREL researchers 

use dilute sulfuric acid for this thermochemical 

“pretreatment,” which hydrolyzes hemicellulose 

to its component sugars, making them soluble in water along with some of the lignin. The 

“solubilized” hemicellulose liquid can then be 

separated, leaving the cellulose and remaining 

lignin as solids. This pretreatment step not only 

hydrolyzes the hemicellulose, but also effectively removes the hemicellulose/lignin sheath 

from the cellulose, leaving the cellulose accessible to further hydrolysis.

Currently, cellulose is hydrolyzed in a similar 

fashion to the hydrolysis of hemi cellulose, 

but with far greater severity, which is typically 

The United States already makes more than 

2 billion gallons of ethanol per year from the 

starch in corn kernels and other grain. This is 

added as a 5% to 10% mixture to about one out 

of eight gallons of gasoline sold. But the primary use of corn is as animal feed, so it is relatively 

expensive, and there is a limit to how much ethanol can be made from it. NREL is developing 

technology to produce “cellulosic ethanol” from 

the fibrous material that makes up the bulk of 

plant matter. This dramatically increases the 

 potential supply, adding inexpensive materials 

such as corn stalks and cobs, municipal wastes, 

sawdust and wood chips, and “energy crops” 

like grasses and fast-growing trees. Although 

the materials are relatively cheap, the conversion technology is not — yet. Currently, one of 

the biggest costs is for the cellulase enzymes 

used to convert cellulose to sugar. Although 

grain ethanol plants are sophisticated industrial operations, their underlying technology is 

 relatively simple, similar to that used for moonshine stills. A common and inexpensive enzyme 

with a long history of industrial use for ethanol 

production — amylase — efficiently converts 

starch to sugar. Cellulases, however, are highly 

complex and do not have that history. 

So NREL and DOE contracted with the world’s 

two largest enzyme companies, Genencor International and Novozymes — to reduce the cost 

of producing cellulases. The goal is to bring 

the cost of the enzymes down to about $0.10/

gallon of ethanol produced, which is key to 

making ethanol derived from cellulose economically competitive. Both companies are reporting excellent progress, but the goal is ambitious 

(see sidebar “Bringing in the Big Guns”) and the 

natural resistance of cellulose to decomposition 

makes the task challenging.

The Recalcitrance of Biomass

The name of the game is hydrolysis, breaking 

down complex carbohydrates (compounds of 

carbon, hydrogen, and oxygen) into their component sugars — analogous to how petroleum 

refineries break down complex hydrocarbons 

(compounds of carbon and hydrogen) into simpler chemicals, which are then built back up into desired fuels, plastics, and other chemicals. 

The difference is that, unlike petroleum, plant 

carbohydrates are renewable. The vast bulk of 

plant material (most anything that is considered 

fibrous) consists of cellulose, hemicellulose, 

and lignin, with substantial starch and sugar 

found primarily in fruits and certain roots and 

tubers. Like starch and sugar, however, cellulose 
Page 12

What is a Biorefinery?

Once cellulase enzymes and bioprocessing technology are cost-effective enough to produce inexpensive sugar from cellulosic biomass, that sugar can become a “platform” chemical from which various fuels and chemicals can 

be made in “biorefineries.” The biorefinery concept is analogous to today’s petroleum refineries, which produce multiple fuels and products from petroleum. Industrial biorefineries have been identified as the most promising route to 

the creation of a new domestic biobased industry.

Wet-mill corn refineries now make ethanol, beverage sweeteners, and a variety of other food and animal feed products 

from cornstarch. Industrial giants Cargill-Dow (a joint venture between Dow Chemical and Cargill, Inc.) and DuPont 

are already making biomass plastics for clothing and other 

uses from lactic acid and 1,3 propanediol, both of which can 

be made from sugar or from cellulosic biomass. With lignin 

and hemicellulose sugars, as well as glucose from cellulose, 

the biorefinery will be even better positioned to make a variety of products. 

achieved with strong acid or higher temperature. This requires more expensive processing 

equipment — one reason why NREL researchers 

determined that biological (enzymatic) hydrolysis could be more cost-effective in the long run. 

(Another reason is that acid hydrolysis is fairly well developed, with little room for further 

cost saving, whereas enzymatic hydrolysis has 

great potential for cost reductions.) And cellulose can certainly be broken down biologically. 

Although humans cannot digest cellulose, cattle, termites, beaver, and mushrooms can. Some 

bacteria, fungi, and insects produce cellulases 

themselves; other animals host cellulase-producing bacteria in their digestive tracts. But, in 

keeping with the complex, recalcitrant structure 

of cellulose, even after the hemicellulose/lignin 

sheath is removed, enzymatic conversion is not 

simple. 

A Marvel of Nanomachinery

Most cellulases are systems of three types of 

enzymes, proteins that work together to catalyze biological conversion processes such as 

cellulose hydrolysis. First, an endoglucanase 

attacks one of the cellulose chains within the 

crystal structure, breaking it via hydrolysis, 

and creating new chain ends. During this hydrolysis, a molecule of water is consumed, and 

one of the chain ends becomes “reducing” and 

the other “non-reducing.” Then — in what is 

a remarkable example of nanoscale machinery — an exoglucanase attaches to a loose end, 

pulls the cellulose chain out of the crystal structure, and then works its way down the chain, 

breaking off cellobiose (dimers of two glucose molecules) as it goes. Actually, there are 

two types of exoglucanase to match the two 

types of loose chain ends. A cellobiohydrolase 

I (CBH I) attaches to the “reducing” end, and 

a cellobiohydrolase II (CBH II) attaches to the 

“non-reducing” end. Finally, a betaglucosidase 

splits cellobiose into two separate glucose molecules, making them available for processing into 

chemicals or fuels. 

The dominant cellulase systems considered thus 

far for industrial processing have come from 

fungi, in particular from Trichoderma reesei.

Cellulase researchers, however, also explore 

 enzymes produced by other fungi and bacteria for traits or capabilities that might improve 

the enzymatic hydrolysis process. NREL scientists, for example, have investigated Acidothermus cellulolyticus, a bacterium they found in 

hot springs in Yellowstone National Park. Even 

though bacterial exoglucanases are not usually 

as good as fungal ones, they have a tolerance for 

high temperatures that could be used to speed 

up bioprocessing. The problem then becomes 

one of taking a fungus that normally grows on 

rotting wood scattered through the forest, mass 

producing it in a factory setting, extracting enzymes for industrial processing, and making the 

enzymes more effective by incorporating features such as the high-temperature tolerance of 

NREL’s hot springs bacterial enzymes.

The High-Tech World of Protein Engineering

The two goals NREL set for Genencor and Novozymes (see sidebar “Bringing in the Big Guns,” 

page 11) are: (1) reduce the cost of producing 

the cellulases; and (2) make them more effective, so that less enzyme is needed. While the 

first avenue may include such mundane measures as optimizing growth conditions or processes, both lie predominantly in the high-tech 

world of protein engineering and production.

With genetic manipulation, you seek to turn 

genes on or off or to import genes that express 

a particular trait. In metabolic engineering, 

which NREL scientists practice to develop more 

effective fermentative organisms, researchers 

manipulate a series of different genes to give the 

organism the ability to digest a new food source 

or to produce more of a desired product such as 

ethanol. But NREL, Genencor, and Novozymes 

scientists are also going beyond these techniques. Instead, they are actually creating enzymes that never existed in nature and getting 

organisms to produce them.
Cellulase enzymes break down cellulose to sugars in three steps. First, endoglucanase (top 

left) attacks a cellulose chain and severs it via hydrolysis; second, exoglucanase (top right) attaches to a cellulose chain end, works its way along the chain, and breaks off cellobiose molecules (bottom right); third, betaglucosidase splits the cellobiose into two glucose molecules.

Endoglucanase Exoglucanase

Glucose Cellobiose

Page 13

The ability of an enzyme to 

catalyze a biochemical reaction is partly a function of the 

physical shape of the enzyme. 

In the illustration (right) of an 

exoglucanase — which Himmel refers to as “one of the 

most important proteins in 

the biosphere” — the “tadpole 

body” is the catalytic domain, 

and the “tail” is a binding site 

that “grabs onto” the cellulose 

and draws it into the body. The 

CBH I catalytic domain contains ten active subsites that 

physically adjoin to the cellulose and initiate the chemical reactions that break the 

chains apart into cellobiose. 

The question is, Can this 

nanomachine be improved? 

Assuming that improvement 

is possible, how do you get a 

fungi to produce a more efficient protein? To see how this 

may be done, it is necessary 

to understand how cells produce proteins. Ribonucleic acid (RNA) provides the code for 

producing proteins. But RNA 

itself is synthesized from a 

gene’s DNA (deoxyribonucleic 

acid), a polymer comprised 

of two strands of sequences 

of four nucleotides connected and wound around each 

 other in a double helix configuration (see illustration, next page). The four 

nucleotides are guanine (G), cytosine (C), adenine (A), and thymine (T). Nucleotides on 

each strand attach to their complementary 

nucleotides on the other strand: G connects to 

C and A to T. To synthesize RNA, a polymerase 

enzyme attaches to a DNA and travels along the 

double helix.

As is does so, it unzips the double helix into two 

strands, which zip back together as the polymerase passes along the DNA. One of the unzipped DNA strands serves as a template that 

the polymerase reads as it travels along, synthesizing a strand of RNA, whose sequence 

of nucleotides are the complements of the 

nucleotides read on the template. As the polymerase reads the sequence of nucleotides on 

the DNA template, it performs 

the trick of synthesizing a uracil 

(U) nucleotide for each adenine 

nucleotide it reads on the DNA 

(rather than producing the complementary thymine).

By producing many products, biorefineries take advantage 

of differences in biomass components and intermediates 

and maximize value derived from biomass. For example, a 

biorefinery might produce several low-volume, high-value 

chemical products and a low-value, high-volume liquid fuel, while generating electricity and process heat for its own 

use and perhaps enough to sell electricity. High-value products enhance profitability. High-volume fuel helps meet national energy needs. Power production reduces costs and 

avoids greenhouse-gas emissions.
Sequenced triplets of RNA nucleotides, or codons, provide the code for a cell’s 

ribosomes to manufacture chains of amino acids to make proteins. RNA itself 

is synthesized via copying the sequence of nucleotides of one of the strands 

of a gene’s DNA. Hence, to engineer a protein, a fi rst step is to devise a way to 

induce variations during the copying of a DNA’s nucleotides.

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NREL scientists use a robotics deck such as this to quickly 

culture genetic variants of fungal genes for producing 

enzymes and screen them to identify the variants with the 

most promising characteristics.

Protein Engineering 

Page 14

Thus, the synthesized RNA is comprised of a sequence of A’s, C’s, G’s, and U’s — such as UGC 

UCA GUG; the sequence of which is divided 

 into functional triplet nucleotides known as 

codons. Each codon codes for one of 20 amino 

acids. The codon UGC, for example, codes for 

the amino acid cysteine, while UCA codes for 

serine and GUG for valine. The codons on the 

RNA strand are read by the cell’s ribosome machinery, which are “factories” that use the information provided by the codons to produce the 

amino acids. The string of amino acids thus produced is the primary structure of a protein. This 

primary structure then twists and folds to become a functional three-dimensional protein. 

By manipulating the nucleotide sequence in 

the gene that codes for producing a particular cellulase in the fungi, scientists can change 

the sequence of amino acids in the cellulase, 

and thus alter its effectiveness — producing a designer protein. One way to change the 

nucleotide sequence is to use a bacterial polymerase that has been genetically engineered 

to incorrectly copy the genetic sequence to be 

modified. Or, scientists can subject a polymerase to abnormal conditions, such as high 

salt concentrations, which will induce the polymerase to produce variations when copying a 

DNA nucleotide. Using polymerases, researchers apply several techniques to engineer proteins, such as directed evolution and site-directed mutagenesis. 

Directed evolution. In directed 

evolution, researchers randomly alter the nucleotide sequence 

of the particular fungal gene 

that codes for the exoglucanase 

or other protein produced. They 

then grow and test cultures of 

each of the altered fungi and 

select those with more desirable traits, such as greater enzyme production or enzymes 

with stronger hydrolysis activity. 

They tackle this Herculean task 

of seemingly infinite possibilities by using robotic equipment 

that can automatically culture 

the possible genetic variants and 

screen them to identify the ones that exhibit the 

most desired characteristics. Researchers can 

then test the top candidates more thoroughly.

Site-directed mutagenesis. In contrast to the rapid-screening-of-random-changes approaches, 

with site-directed mutagenesis, researchers (1) 

build molecular models of the enzymes; (2) use 

computer simulations to examine the enzyme’s 

structure and predict how it could be altered 

to more effectively interact with the cellulose 

strands; (3) identify the amino acid responsiWhat if Biomass Was Not So Recalcitrant?

The crystalline structure of cellulose and resulting fibrous 

nature of biomass may be one of nature’s key features for 

protecting plant life in the biosphere — imagine a 200-

foot-tall tree or even an 8-foot cornstalk otherwise — but 

that is not to say there are not other possibilities. NREL researcher Steve Thomas, who has worked on improving 

cellulases for breaking down cellulose, talks about starting 

to look at the other side of the coin — altering the structure 

and composition of biomass. Thomas and colleagues are 

already examining many of the thousands of varieties of 

corn that seed companies have developed over the years to 

find ones that might be better for cellulose bioprocessing. 

Rather than just valuing high starch content in the kernels 

and tall and straight growth, cellulose bioprocessing could 

benefit from other traits. For example, corn plants with 

more cellulose in the stalk could benefit bioethanol 
Page 15

One way in which 

researchers gain insight 

into how cellulases 

function is through the 

development and use of 

models, such as this one 

of the dynamic interaction 

at the interface between 

water and cellulose.

production, or ones with more lignin could benefit biomass 

power generation. Using NREL’s rapid analysis technology 

for biomass and sophisticated economic models, researchers have already found that ethanol production could be 

more than $0.30/gallon less expensive using stover with 

different composition.

Going a step further, many plants produce enzymes that 

break down their own cell walls, with the enzymes serving 

functions such as ripening fruit or allowing leaves to break 

off in the fall. We could breed plants with high natural 

cellulase production, genetically engineer higher or earlier 

production of the cellulases, or import cellulase production genes from fungi. One possibility is plants that already 

start to break themselves down before they are harvested. 

Another possibility could be one part of a plant producing 

enzymes needed to break down other parts. Either would 

make the work of the biorefinery easier and less costly.

On the other hand, NREL 

cannot begin to develop 

the real-world improvements associated with 

actual industrial operations that can come from 

enzyme producers such 

as Genencor and Novozymes NREL researchers are validating the 

achievements of the enzyme companies. And, of 

course, research understanding will do no good 

unless industry incorporates it into practice. So, 

overcoming the recalcitrance of biomass with 

economical enzyme production — which will 

lead to more cost-effective production of ethanol and other products from cellulosic biomass 

— must come from a combination of basic research at NREL and universities and from steady 

improvement by the enzyme industry. 

For More Information

ble for the portion of the enzyme where change 

is desired; (4) identify the codon of nucleotides 

in the organism’s genes that correspond to those 

amino acids in the enzyme, and; (5) set out to 

make the specific desired change in the DNA. At 

this point, they are back to inducing somewhat 

random changes. They know, however, that they 

have targeted the right site and more precisely 

what they are looking for in screening the variants.

Modeling for Fundamental Understanding

Techniques such as site-directed mutagenesis 

require understanding the fundamentals of 

how cellulases function. One way to do this 

is through 3-D animation (see images of 

endoglucanase and exoglucanase, page 13), 

which can help researchers hypothesize how 

cellulases interact with cellulose. The hypotheses may then be tested to hone the picture. Another way is via modeling dynamic interactions, 

such as the surface layer interaction between 

water and cellulose, believed to be a key factor in the resistance of cellulose to hydrolysis 

and therefore in designing effective methods to 

overcome that recalcitrance. Modeling activities 

are invaluable in helping to understand the fundamentals of cellulase action. NREL researchers 

will continue to work in this vein, developing 

thermodynamic, mathematic, and mechanistic models of the molecular machinery of enzymatic hydrolysis.

Moving to Eureka! and a Biomass Economy

Just as understanding basic science behind 

cellulase activity is critical for specific applications such as site-directed mutagenesis, it 

is also where dramatic changes in approach 

could come from. Himmel expects the “Voila!s” 

and “Eureka!s” of enzymatic hydrolysis to 

come from fully understanding the way the 

exoglucanases work. Industry does not generally 

do such basic research, so DOE has asked NREL 

to lead in this area. NREL’s work to gain understanding of this crucial research area is supported by collaborations with Cornell University, 

the Colorado School of Mines, the University of 

California at Davis, Rutgers University, the University of Arkansas, and research institutes in Japan, Israel, and Sweden. 

NREL Biomass Research. “Alternative Fuels 

Users Facility (AFUF).” http://www.nrel.gov/

biomass/workingwithus.html#afuf. Accessed 

January 27, 2004.

Himmel, M.E.; Baker, J.O.; Saddler, J.,eds. “Glycosyl Hydrolases for Biomass Conversion.” 

ACS Symposium Series 769, Washington, DC: 

American Chemical Society, 2001: Distributed 

by Oxford University Press.

Sheehan, J.; Himmel, M.E. “Enzymes, Energy, 

and the Environment: Cellulase Development 

in the Emerging Bioethanol Industry.” Biotechnology Progress (15:3), 1999; pp. 817–827.

Hames, B.R.; Thomas, S.R.; Sluiter, A.D.; Roth, 

C.J.; Templeton, D.W. “Rapid Biomass Analysis: 

New Tools for Compositional Analysis of Corn 

Stover Feedstocks and Process Intermediates 

from Ethanol Production.” Davison, B.H., et al., 

eds. Applied Biochemistry and Biotechnology. Proceedings of the 24th Symposium on Biotechnology 

for Fuels and Chemicals. 28 April–1 May, 2002, 

Gatlinburg, TN. Vol 105–108, Spring 2003; pp. 

5–16.
Offsetting CO Offsetting CO2 2 Emissions with Wind Energy Emissions with Wind Energy

Page 16 

Roughly 84% of the anthropogenic contribution to climate change is due to CO2 ; the rest 

comes from gases such as methane, which traps 

23 times more heat per gram of gas than CO2, 

and nitrous oxide, which traps 296 times more 

heat. Even if all anthropogenic emissions were 

to stop tomorrow, the concentration of greenhouse gases in the atmosphere would take centuries to return to preindustrial levels. The IPCC 

has estimated that, to maintain stable atmospheric conditions in the long run, anthropogenic emissions of greenhouse gases must be cut 

60% to 70%. 

The United States itself produces about 23% of 

global greenhouse gas emissions. Plus, with a 

growing economy, U.S. emissions continue to 

increase at a rate of about 1% per year. 

“Climate change is occurring, “ says John H. 

Marburger III, director of the White House Office of Science and Technology Policy. The Intergovernmental Panel on Climate Change 

(IPCC), a group of 2900 leading climate scientists from 120 countries, agrees. Climate change 

could lead to rising sea levels, ecological instability, and a growing incidence of weather 

anomalies such as floods and droughts — 

changes that are likely to have consequences for 

the world environment and economy. 

IPCC scientists agree that climate change is the 

result of growing emissions of carbon dioxide 

(CO2) and other greenhouse gases from anthropogenic (human) activities — deforestation, industrial processes, and fossil fuel combustion. 

As these gases accumulate in the atmosphere, 

they trap heat, creating a greenhouse effect. 

Winds

of Change
Page 17

Calculating Energy Output 

from Wind Turbines

Wind turbines are usually classified according to their rated electric power output, e.g., 1 MW. This 

means the turbine can produce 

a maximum of 1 MW of power in 

 ideal wind conditions. But because 

wind is an intermittent resource, 

the wind turbine won’t be operating at its maximum rated capacity 

all of the time. The average capacity at which the turbine operates 

during the course of its lifetime is 

called its capacity factor. 

The question is how much electric 

energy (electricity) a wind turbine of 

a rated power output could produce 

over time. Energy production is usually determined by the equation: Energy = Power x Time. For electricity 

generating plants, this can be more 

accurately be restated as: Energy 

= Power x Time x Capacity Factor, 

where the capacity factor is the ratio 

of the amount of energy produced 

over time to the amount of energy 

that could have been produced if the 

turbine operated at its maximum 

rated output 100% of the time. 

For example, with a capacity factor 

of 30% and 8760 hours in a year, 

the energy produced by a 1-MW 

wind turbine over the course of a 

year would be: 8760 h x 0.30 x 1 

MW = 2628 MWh.

A turbine’s capacity factor is affected by the amount of down 

time required to service the turbine and by the site-specific wind 

 conditions. The more time the turbine spends in service, and the lower the average wind speed at the 

site, the less energy the turbine 

produces, hence the lower the turbine’s capacity factor.

Capacity factors can vary widely. Today’s nationwide fleet of wind turbines is operating at an average 

 capacity factor of 30%, and this 

 ratio is improving. The American 

Wind Energy Association (AWEA) estimates that turbines installed since 

2001 are operating at an average 

 capacity factor of about 33%, and 

EIA estimates that, by 2020, some 

new turbines will be operating with 

capacity factors of 42% to 48%.

The Energy Connection

Most U.S. greenhouse gas emissions come from 

our reliance on fossil fuels, which are made 

up primarily of hydrogen and carbon. When 

burned, the carbon combines with oxygen to 

yield CO2. In 2002, electricity production was 

responsible for 2249 Tg (teragrams, or million 

metric tons) of CO2 emissions, or 39% of the 

U.S. total. 

The U.S. government is considering ways to mitigate the problem, including voluntary measures 

to decrease U.S. greenhouse gas intensity — 

the ratio of emissions to economic output — by 

18% during the next decade. In February 2003, 

speaking about the need to curb emissions, Energy Secretary Spencer Abraham said “We will 

also need to develop the revolutionary technologies to make these reductions happen. That 

means creating the kinds of technologies that . 

. . actually transform the way we produce and 

consume energy.” 

Wind energy is such a breakthrough technology. Because wind power plants produce virtually 

no CO2 emissions during operation, grid-connected wind power reduces overall greenhouse 

gas emissions by displacing the need for natural 

gas- and coal-fired generation. 

The Wind Resource

Wind power is among the world’s fastest-growing sources of energy. In 2003, U.S.-installed 

wind generation grew by 1687 MW (greater 

than 30%) to 6374 MW. Worldwide, more than 

8000 MW of wind capacity was added, bringing 

the international total to 39,000 MW. 

The United States has enough wind resources to 

meet more than twice the nation’s total electricity demand. Wind resources are characterized 

by wind-power density classes, ranging from 

Class 1 (lowest) to Class 7 (highest). Fair to 

good wind resources (Class 3 and above), which 

have an average wind speed of at least 13 mph 

at a 50-m hub height, are found along the East 

Coast, the Appalachian Mountains, the Great 

Plains, the Pacific Northwest, and other areas. 

North Dakota alone has enough Class 4 and 

higher winds to supply a third of the electricity 

needs of the lower 48 states. 

Using Wind Energy to Cut Emissions

Although a wind plant produces no CO2 while 

generating electricity from wind, it does take fossil energy to mine, transport, and fabricate materials used in plant construction; build the power 

plant; operate and maintain the plant during its 

service life; and decommission the 

plant at the end of its useful life. 

According to a 1989 DOE study, when 

all energy requirements are taken into 

account, a wind plant adds about 7.4 g 

of CO2 to the atmosphere per kilowatthour of electricity generated. But this 

is lower than 964 g/kWh for a typical 

coal-fired plant, 484 g/kWh for a natural gas turbine plant, and 611.7 g/kWh 

generated by the average U.S. utility 

mix (which takes into account the electricity generated by a weighted mix of 

hydropower, nuclear power, coal, natural gas, and other generating technologies). Wind power thus can displace 

956.6 g/kWh of CO2 from coal plants, 

476.6 g/kWh from natural gas plants, 

and 604.3 g/kWh of CO2 from the average U.S. supply mix.

According to estimates by the DOE’s 

Energy Information Administration 

(EIA), total electricity demand will increase from 3839 billion kWh in 2002 

to an estimated 5430 billion kWh in 

2020. The great majority of this increase is expected to come from the 

use of new natural gas and coal-fired 

plants. A good portion of this increase 

is also expected to come from wind 

turbines. In fact, members of the wind 

energy industry project that windgenerated power will provide 6% or 

more of the nation’s electricity by 2020 

(roughly 326 billion kWh). This would 

entail an average yearly growth rate of 

approximately 18%. 

On the other hand, if the wind market 

grew at an annual rate of 28% (a growth 

rate that is less than that for the world 

market during the past five years), then 

in 2020 wind energy would provide approximately 20% of the nation’s electricity — which is often considered to 

be the maximum amount of wind energy that can be incorporated into the 

electricity grid without adversely affecting grid reliability (see also discussion on page 20). If wind has a 20% share of the 

electricity market in 2020, wind power plants 

will be generating about 1086 billion kWh; this 

would require roughly 413 GW of installed wind 

capacity, assuming an average capacity factor of 

30% (see sidebar “Calculating Energy Output 

from Wind Turbines”).
Page 18

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��� ��������� ���� The EIA projects that CO2 emissions from 

power plants could increase to 3322 Tg by 

2020. But if wind energy supplied between 

6% and 20% of the nation’s electricity by 

then, the expected rise in CO2 emissions 

would be reduced by 197 Tg (Wind A) to 

656 Tg (Wind B), assuming that the wind 

energy would displace the average utility 

generation mix. 

Reducing the Cost of Wind Energy

NREL is home to DOE’s National Wind Technology Center (NWTC), 

where the main focus is to work with the wind industry to improve 

wind energy technology and decrease its cost. NWTC researchers 

are working with industry to develop new breeds of wind turbines 

that will operate efficiently in Class 3 and 4 wind regimes, with the 

goal to reduce costs for Class 4 areas to 3¢/kWh on land and 5¢/kWh 

offshore by 2012, and to reduce the cost of wind energy in Class 3 

regimes to as little as 10¢/kWh by 2007. 

One strategy for exploiting lower-class wind regimes is to develop advanced large turbines (1 MW or greater). Because they have a 

higher hub height where the wind typically blows stronger, and because larger blades are used to sweep greater areas, large turbines 

can harvest more energy for a given wind class. For these advanced 

concepts, researchers are considering every component — from the 

base of the tower to the tips of the blades — for opportunities to improve the technology.

They are, for example, researching blade sizes and shapes, and better and lighter materials with which to make blades and towers that 

last longer, extract more energy, and cost less to manufacture. They 

are investigating alternative concepts for drivetrain components 

(gearboxes, generators, and associated power electronics) that 

According to Britta Buchholz of MVV Energie, 

German wind forecasters are currently able to 

predict wind strength and power output 48 

hours ahead with 90% accuracy. As wind conditions can vary significantly from one place to 

another, the geographical disbursement of turbine arrays tends to decrease the variance in 

wind power output. This is because a drop in 

output from one wind farm can be made up by 

a rise from another. 

Denmark, which gets about 17% of its electricity from wind, is starting to have some problems 

integrating wind power into its electricity grid. 

This is because Denmark is a small country that 

doesn’t have enough geographical variability in 

wind patterns to even out fluctuations in wind 

strength (and hence turbine output). Small 

wind projects of single turbines or small clusters of turbines contribute the majority of Denmark’s wind power.

If wind-generated electricity grows to comprise more than about 20% of power flows on 

the grid, the intermittency of the wind resource 

could pose a problem for grid system operators. 

Some form of backup generation (such as natural gas) or of energy storage would have to be 

used to compensate for wind’s intermittency. Although exact data are not available, it is clear 

that this would degrade the energy payback ratio somewhat and would slightly increase emissions of CO2. It is also likely that upgrades to 

the transmission infrastructure would be required for wind energy to service major load 

centers, although the cost of these improvements may not be prohibitive. NREL has estimated that 175 GW of wind capacity lie within 

5 miles of existing 230 kV or lower transmission 

lines, and another 284 GW lie within 10 miles. 

In a series of letters to Science magazine in fall 

2001, Stanford University researchers Mark Jacobson and Gilbert Masters concluded that, 

even assuming a relatively high average cost of 

$500,000 per mile to build new above-ground 

AC transmission lines, the cost of the new lines 

would add less than 1% to the cost of the wind 

Using today’s electricity supply 

mix and emission rates, CO2

emissions from the electricity 

sector in 2020 would be about 

3322 Tg, an increase of 1073 Tg. 

On the other hand, if wind energy could supply between 6% and 

20% of the nation’s electricity, 

wind would reduce the expected 

CO2 emissions by between 197 

Tg and 656 Tg — a significant 

impact under either scenario.

Getting There

A 6% market penetration of 

wind energy by 2020 not only appears to be an attainable growth 

scenario, but this amount of 

wind energy could easily be incorporated into the electricity 

grid despite an intermittent wind 

resource. 

But how realistic is it to think 

that wind could provide 20% of 

the nation’s electricity by 2020? 

In terms of achievable market 

growth, 20% is optimistic. In 

terms of resource, it could be accomplished without much difficulty — according to DOE, to provide 20% of 

America’s electricity from wind, only 0.6% of 

the land of the lower 48 states would have to 

be developed with wind power plants. Much of 

the land could be used for a dual purpose — for 

both farming and wind energy, providing farms 

with an extra “cash crop.”

What about intermittency? At deployment levels up to about 20%, wind power can be incorporated into the electricity grid relatively easily. 

The U.S. power grid already includes generating assets, such as hydroelectric power, that can 

be used to compensate for wind’s intermittency. 

And wind forecasting software can overcome 

many of the challenges associated with intermittency. 
Page 19

Calculating the Energy Payback from Wind Turbines

Power plants consume energy even before they begin making it. 

Materials to be used in the plant must be mined, shipped, and fabricated; power plant parts must be transported to the construction 

site and assembled; the plant must be operated and maintained; 

and the plant must be disassembled and decommissioned at the 

end of its service life.

The time it takes for a power plant to generate as much energy as it 

uses over the course of its life is called the energy payback time. The 

energy payback of a power plant can also be expressed as the ratio of the energy generated by a power plant during its lifetime to 

the energy required to build, operate, and decommission the power plant. 

According to European studies, a typical utility-scale wind turbine 

will produce, on average, 30 times more energy than it consumes 

during its lifetime. According to AWEA, a wind turbine’s energy payback period is typically three to eight months, depending on the average wind speed at the site. Moreover, because energy payback is 

typically a measure of how long it takes to pay back fossil fuel energy, it is also a measure of how long it takes to pay back the CO2 emitted by the consumption of that fossil fuel. In contrast, because they 

must consume fossil energy to produce electricity, fossil fuel power 

plants never achieve energy, or CO2, payback.

could result in less weight and more efficiency. And they are exploring new rotor designs to extract more energy from the wind and to 

reduce peak and fatigue loads. 

NWTC researchers are also performing field and air-tunnel tests. 

They are using the results from the tests to develop computer simulations and models that will:

• enable them to accurately project how wind turbines react to varying wind conditions;

• help them better forecast wind conditions and understand the 

characteristics and location of wind resources so that developers 

can site wind farms in the best locations; and

• allow them to predict the performance of advanced prototype designs, reducing development time and costs. 

The NWTC also provides world-class testing facilities. At the structural test facility, researchers can determine strength and durability of full-scale wind turbine blades. At the dynamometer facility researchers test the lifetime endurance of a wide range of wind turbine drivetrains and gearboxes at various speeds. Results from both 

facilities help turbine designers increase the lifetimes of blades and 

components by decreasing loads on the components, or making 

them more efficient and resistant to wear — thus increasing the life 

and reliability of wind turbine components and reducing costs. 

 power plants. (Note that their analysis assumes 

that existing transmission lines have room to 

carry the wind-generated power.)

What about the affordability of wind power?

According to DOE, new, utility-scale wind projects are being built in the United States today 

with energy costs ranging from about 3.9¢ to 

7¢/kWh or more. The lower-cost wind energy is 

typically achieved for the better wind sites, such 

as Class 6. Wind energy at Class 4 sites, on the 

other hand, is currently marketed at prices in 

the 5¢ to 7¢/kWh range. In comparison, DOE’s 

National Energy Technology Laboratory (NETL) 

reports that the average cost of electricity from 

current coal-generating facilities is 4¢/kWh and 

about 3.5¢/kWh from state-of-the-art facilities. 

NETL also projects that the cost of electricity 

from advanced coal facilities could be reduced 

to 3.1¢/kWh by 2010.

With the cost of wind power in the better wind 

regimes close to that of coal power, expanding the proportion of wind-generated electricity in the energy supply mix is not expected to 

have much of an impact on future electricity 

prices. A 2002 EIA study concluded that a federal renewables portfolio standard (RPS) requiring 10% of electricity to be generated from renewable sources by 2020 would result in a 1% 

increase in retail electricity prices, while a 20% 

RPS would result in a 3% increase. The study 

predicts that most new renewable electricity 

would come from wind, despite the fact that it 

assumes there will be no federal production tax 

credit for generation from wind plants and no 

renewable energy production incentive. 

As researchers at NREL and in industry lower the costs even more, especially for wind turbines operating in Class 3 and 4 wind regimes, 

wind could become highly competitive with all 

other sources, and may even become the power 

of choice for many areas of the United States. If 

such becomes the case, wind energy could grow 

sufficiently to supply the United States with 

20% of its electricity and could help the nation 

and the world find the means to decrease greenhouse gas emissions while meeting the energy needs of a growing economy. (See sidebar on 

“Reducing the Cost of Wind Energy.”)

For More Information

American Wind Energy Association. (2002). 

“The Most Frequently Asked Questions About 

Wind Energy.” http://www.awea.org/pubs/

documents/FAQ2002%20-%20web.PDF. Accessed Jan. 29, 2004.

Intergovernmental Panel on Climate Change. 

“IPCC Third Assessment Report — 2001.” 

http://www.ipcc.ch/. Last updated Dec. 23, 

2003; accessed Jan. 28, 2004.

Energy Information Administration. (October 

2003). “Emissions of Greenhouse Gases in the 

United States 2002.” ftp://eia.doe.gov/pub/

oiaf/1605/cdrom/pdf/ggrpt/057302.pdf. Accessed Jan. 28, 2004.

Jacobson, M.Z.; Gilbert, M.M. “Exploiting 

Wind Versus Coal.” Science; Vol. 293, Aug. 24, 

2001; p. 1438

Department of Energy. Wind Power Today & 

Tomorrow. DOE/GO-1002004-1894, March 

2004..
Page 20

Since the last publication of the Research Review, NREL, its researchers, 

and partners have received several 

awards and honors. Among these are 

four R&D 100 awards, two tech transfer awards from the Federal Laboratory Consortium (FLC), recognition by 

Scientifi c American, and a newly elected 

fellow of the American Association for 

the Advancement of Science (AAAS). 

PPS Protection

Carbon steel is tough, but not tough 

enough to withstand harsh conditions 

found in geothermal power plants, 

chemical plants, and railroad tank cars. 

To protect vital fl uid-carrying steel 

tubes in hostile environments, researchers from 

NREL and Brookhaven 

National Laboratory (BNL) developed a polymer-based coating system 

called polyphenylenesulfi de (PPS). 

This technology, which won both an 

R&D 100 award and an FLC technology transfer award, was transferred to 

Bob Curran & Sons for further refi nement and commercialization. Within nine 

months of fi rst being 

contacted about the 

technology by NREL 

and BNL, the company had incorporated 

PPS into a commercial 

product. It now represents the primary line of business for 

Bob Curran & Sons, which has built 

a new facility near Houston to better serve its burgeoning roll of customers in the petrochemical processing industry. 

A PPS coating is not only tough, it is 

smart. Its three-layer construction divides the duties, with the innermost 

one — a zinc phosphate ceramic primer — assigned to create a strong bond 

with the steel. The second layer, typically a carbon fi ber PPS matrix, provides toughness, corrosion protection, 

and high thermal conductivity. The 

third layer, a polymer blend of PPS, 

calcium bialuminate, and Tefl on, gives 

the product a self-healing mechanism 

that repairs damage to the coating system by fi lling in small cracks due to 

physical wear. 

PPS extends the life of 

untreated carbon steel by 

fi vefold. Even when compared to stainless steel or 

titanium tubes, PPS-coated carbon steel tubes yield a 

life-cycle cost savings of up to 

82%. 

Nanofi ber Protection

New alumina ceramic nanofi bers 

developed by NREL, Argonide Corporation, and the Design Technology Center of the Russian Academy of 

Sciences can be used in bioactive fi ltration to eliminate 99.99999% of a 

variety of viruses, bacteria, and pathogens from fl uids. This includes hepatitis A, retroviruses, adenoviruses, 

coxsackle, Salmonella, shigella dysenteriae, and E. Coli. The fi bers also can 

be used in bone tissue engineering, to 

eliminate 99.99% of heavy metals in 

water, and to reduce arsenic in drinking water to well below federal and international standards. 

The fi bers’ remarkable capabilities derive from their unique combination 

of small diameter (about 2 nm), long 

length (up to hundreds of nm), a surface area of 600 m2/gm, and surface 

chemistry that can be tailored. Trademarked and marketed as NanoCeram by the Argonide Corporation, the 

nanofi bers arrive with good timing, 

in light of heightened concerns about 

bio-terrorism and national security. 

Letting in Light

BP Solar’s PowerView module, developed jointly with NREL, doubles as architectural glass and a PV module. Particularly useful for sloped glazings 

such as awnings, BP has installed it at 

hundreds of its Connect fueling and 

retail sites, where much of the electricity demand is met with their own futuristic, semi-transparent canopies.

Helping make PowerView possible was 

an innovative manufacturing method 

from BP Solar, in which programmable lasers were used to selectively remove material from the thin-fi lm PV 

module to allow light through while 

minimizing the decrease in electrical 

power. Although an innovative technology, this R&D 100-award winner 

fell victim to a BP Solar reorganization 

that dropped thin-fi lm modules from 

the company’s PV product line.

A Module a Minute

First Solar’s automated, non-stop, continuous-feed production line can crank 

out one PV module per minute — and 

these are 60 cm x 120 cm, high-quality modules made of thin-fi lm cadmium telluride (CdTe) and cadmium sulfi de (CdS). How is it done? Soda-lime 

glass is fed into vacuum deposition 

chambers where a layer of CdTe is deposited on the glass, followed by a layer of CdS. The modules are then laserscribed, metallized, and encapsulated 

in ethyl-vinyl acetate, and then another layer of soda-lime glass. 

The enabling core of this process is the 

R&D-100-award-winning high-rate vapor transport deposition technology 

developed by First Solar and NREL. 

This is a deceptively simple technology that can deposit a thin, uniform 

Awards

&Honors

Awards

 & Honors
Dr. Bhushan Sopori demonstrates PVSCAN, one of the technologies that he developed 

and helped transfer to industry, and for which he won an FLC award.

PIX12233

Dr. Arthur Nozik becomes a fellow of the 

AAAS.

Page 21

layer of CdTe or CdS on glass substrate 

in less 40 seconds — a deposition rate 

three to four orders of magnitude greater than rival thin-film PV technologies.

It is the world’s first such mass-production method for making polycrystalline thin-film modules. In its first year 

of production, the technology helped 

First Solar cut the price of PV modules 

to $2.50 per watt. A second-generation 

production line now under construction could lower the price by nearly 

another 50% in the next three years. 

Monitoring Manufacturing

By transferring two related technologies to GT Equipment Technologies, 

Inc. (GTi), a manufacturer of equipment for semiconductor and PV materials processing, NREL helped fill a 

need in the international solar energy 

community. 

One of the two technologies, PVSCAN, 

is a high-speed, optical-scanning system that maps and analyzes defects in 

PV wafers and cells. The other, the PV 

Reflectometer (marketed as the GTFabscan 6000), is used to monitor important parameters in solar-cell processes including surface roughness and 

texture, metallization, antireflection 

coatings, and back contact properties. 

The theory behind both technologies, 

as well as their design and engineering, are products entirely of NREL researchers, who also helped negotiate 

licensing of the technologies by GTi 

and worked closely with the company 

to scale them up to production. These 

efforts will yield additional benefits to 

NREL in the form of new relationships 

with R&D groups, universities, and PV 

makers and other companies from the 

United States and abroad.

Scientific American 50

In its debut issue of spotlighting the 

top 50 business and research leaders of 

the year, Scientific American magazine 

recognized NREL and Spectrolab, Inc. 

as leaders in the energy category for 

their work in increasing the efficiency 

of PV cells. 

NREL’s research in multijunction solar 

cells for more than a decade has led 

the way to ever-more-efficient cells, offering the potential of cheaper electricity from the sun. Multijunction solar 

cells use multiple layers of semiconducting material to absorb sunlight 

and convert it to electricity more efficiently than single-junction cells. 

In 2001 — using a solar-cell design licensed from NREL — Spectrolab made 

a gallium indium phosphide/gallium 

arsenide/germanium (GaInP2/GaAs/

Ge) triple-junction solar cell that converted 34% of sunlight to electricity under concentration — a world record at 

the time. Since then, the company has 

improved the conversion efficiency to 

36.9% under 309 suns concentration.

This technology has won two R&D 100 

awards. The first was won by NREL 

in 1991 for a double-junction cell 

(GaInP2/GaAs) whose primary use 

is for space applications. The second 

award was presented to both NREL 

and Spectrolab in 2001 for the triplejunction device. 

Art Nozik Elected AAAS

Fellow

Arthur J. Nozik was recently elected 

a fellow of the American Association 

for the Advancement of Science, the 

highest distinction bestowed on AAAS 

members by their peers 

Dr. Nozik is a senior research fellow at 

NREL. During his tenure at the Laboratory, he has established himself as a 

leader in photoelectrochemistry, semiconductor-molecular interfaces, quantization effects, carrier dynamics, and 

the application of these interdisciplinary sciences to the conversion of photon energy to electricity or fuels (such 

as hydrogen or alcohols). 

Dr. Nozik received his Ph.D. in physical chemistry from Yale University in 

1967 and joined NREL in 1978, where 

he has been a research fellow since 

1983 and has been recognized with 

several important Laboratory-wide distinctions, including the Van Morriss 

award, the Hubbard Award, and an 

award for outstanding achievement. 

He has published more than 160 peerreviewed publications, edited several books in his fields of expertise, been 

awarded 11 U.S. patents, and served as 

a senior editor on The Journal of Physical Chemistry since 1993.
NREL

in Focus

NREL

 in Focus

Page 22

Dr. Michael Pacheco becomes director of the National Bioenergy 

Center.

Dr. Michael Seibert is named to 

NREL’s Research Fellows Council.

First Director Joins 

National Bioenergy Center

DOE’s National Bioenergy 

Center, based at NREL, welcomed Dr. Michael Pacheco as its fi rst director in 

2003. Pacheco arrived with 

an impressive resume from 

private industry, most recently with Louisiana-Pacifi c Corp., for which he 

was manager of oriented strand board technology and product quality. He 

also spent two years as a 

corporate engineering fellow with the company.

Pacheco has led efforts to 

commercialize biocatalytic 

processes with Texas-based 

Energy BioSystems Corp., 

where he was vice president of process development. He held 

numerous supervisory R&D positions 

during 13 years with Amoco Corp. and 

three years with Conoco Oil Co. Pacheco holds a Ph.D. in chemical engineering from the University of California at Berkeley, a bachelor of science in 

chemical engineering from Clarkson 

University, and an associate degree in 

chemical technology from Thames Valley College.

Pacheco will provide strategic guidance, technical direction, and management to continue the center’s leadership role in bioenergy research. His 

responsibilities include coordinating 

NREL’s activities with bioenergy research at Argonne National Laboratory, 

Idaho National Energy and Environmental Laboratory, Oak Ridge National Laboratory, and Pacifi c Northwest 

National Laboratory. Pacheco will represent the interests of 

DOE, NREL, and the 

other labs to technical and industrial 

leaders and to various U.S. and international stakeholders.

The Bioenergy Center was created in 

2000 as the focal point for developing 

bioenergy technology and information 

in the United States. It gives industry 

“one-stop shopping” for world-class 

research and 

state-of-the-art 

laboratory facilities at several 

federal agencies. 

As the center’s 

new director, 

Pacheco replaces acting director, Stan Bull, 

who is NREL’s 

Associate Director for Science 

and Technology.

The center links 

DOE-funded 

biomass renewable energy research programs 

with the resources and capabilities of the U.S. departments of Agriculture and Interior, 

the Environmental Protection Agency, the National Science Foundation 

and several other federal 

agencies, DOE laboratories, universities, and the 

private sector. NREL’s 

biomass research program focuses on converting biomass feedstocks 

into transportation fuels, chemicals, biobased 

materials, and electric 

power. 

Seibert Named 

Research Fellow

In October of 2003, internationally recognized 

research scientist Michael Seibert was named 

as the newest member of NREL’s Research Fellows Council. An NREL employee since 1977, Seibert has devoted 

his career to researching structure and 

function problems in photosynthetic energy capture, biological water-splitting processes, and photoproduction of 

hydrogen by algae.

Before becoming an NREL research 

fellow, Seibert was elected a fellow 

of the American Association for the 

 Advancement of Science. He currently 

serves on the editorial boards of 

Advances in Solar Energy, Applied Biochemistry and Biotechnology, and the 

American Institute of Physics International Series in Basic and Applied Biological Physics. Seibert has established scientifi c and technical collaborations 

throughout the world; authored more 

than 170 scientifi c articles and reviews; 

and given more than 150 conference 

presentations. He holds eight U.S. and 

foreign patents.

Seibert holds a Ph.D. in molecular biology and biophysics, and an M.S. in 

physics, both from the University of 

Pennsylvania; and a B.S. in physics 

from Pennsylvania State University. He 

was born in Lima, Peru and grew up 

near Philadelphia.

The Research Fellow and Senior Research Fellow positions at NREL were 

established to provide parallel or dual 

career opportunities for outstanding 

scientists and engineers who have 

achieved exceptional positions of leadership in their fi elds, but who wish to 

devote the majority of their time and 

energy to scientifi c 

and technological 

endeavors. Candidates are nominated by senior 

management and 

current research 

fellows. Seibert 

joins Art Nozik, 

Alex Zunger, Tim 

Coutts, Dick Ahrenkiel, and Ralph 

Overend on the 

NREL Research Fellows Council.
NREL’s new Science and Technology Facility will be used to support R&D in photovoltaics, hydrogen, solid-state lighting, electrochromic windows, nanotechnology and other basic sciences, 

and process research on thin films and nanostructures.

Page 23

S&TF Plans Move Ahead

NREL’s much-needed Science and 

Technology Facility (S&TF) took a big 

step closer to becoming reality in November 2003, with $4 million in funding for its first phase of construction 

approved in the Energy and Water 

Development Appropriations Act of 

2004. Construction is expected to begin in the late summer of 2004 and be 

completed in approximately two years.

Construction of the proposed semiconductor research facility is estimated 

to cost a total of $20.2 million. It will 

be located 80 feet to the east of the existing Solar Energy Research Facility 

(SERF) and will include 71,000 square 

feet of laboratory, office, and support 

space on three levels. The building will 

be connected to the SERF via an elevated bridge that links the service corridors of the two buildings, thereby 

facilitating collaboration between researchers in the two facilities. Approximately 75 research staff will work in 

the new facility.

The facility-design process — completed on time and within budget — 

was no small feat, says Pete Sheldon, 

a division manager who represented 

the National Center for Photovoltaics 

in designing the facility. The process 

solicited input from an NREL team 

of experienced researchers, chosen to 

ensure that current and future research 

requirements will be met. The team 

also included representatives with 

expertise in energy-efficient building 

design, daylighting, sustainability, and 

environmental health and safety.

Research capabilities within the new 

S&TF, combined with those of the 

existing SERF, will enable new and 

expanded work in photovoltaics, 

hydrogen, solid-state lighting, electrochromic windows, and basic sciences, 

including nanotechnologies.

The S&TF will support process research 

on thin films and nanostructures for 

DOE and for U.S. companies developing energy technologies. It is designed 

around a process research concept specifically developed to accelerate the 

time required to transfer research developed in the laboratory to manufacturing and use, Sheldon says. The centerpiece of the building is the Process 

Development and Integration Laboratory — an open 11,000-square-foot lab 

space specifically designed to accommodate a new class of thin-film deposition, processing, and characterization 

tools. These tools will provide new 

ways to bridge the gap between laboratory and commercial success, by allowing researchers to flexibly prototype 

processes in a controlled environment. 

The facility was designed with sustainability in mind. The multi-story 

design reduces the building footprint 

to approximately 45,000 square feet, 

thereby conserving valuable land for 

future expansion opportunities. It exploits a state-of-the-art energy efficient 

mechanical design that reduces energy 

use by 50%, compared with a DOE 

10CFR434 compliant building. And it 

will provide 100% of the ambient light 

requirements in the open office and 

circulation areas, while maximizing 

daylighting opportunities in the laboratories.

Lab Takes on Hydrogen 

Systems Integration 

With the nation’s high expectations for 

hydrogen as an important energy carrier comes a new, high-profile responsibility for NREL. The Laboratory was 

designated the central systems integrator for DOE’s hydrogen efforts as of 

March 2003. 
Page 24

The role includes documenting technical requirements of a future hydrogen energy system for the United 

States, and linking these requirements 

to DOE’s programs. It also covers independent analysis, developing and 

maintaining an integrated baseline, 

hydrogen infrastructure modeling and 

simulation, confi guration control and 

management, integrating scheduling, 

budgets, scope of work, and other important areas.

NREL supports the President’s Hydrogen Fuel Initiative in many ways, some 

new and some long-standing. It performs basic research and development 

in numerous hydrogen areas, verifi es 

the performance of hydrogen technologies in development, validates emerging technologies, and helps establish 

codes and standards for hydrogen safety. 

The Laboratory leads nationwide R&D 

efforts in:

• production of hydrogen from renewable energy sources; 

• delivery and storage of hydrogen in a 

national infrastructure; 

• uses of hydrogen in fuel cells, both 

in stationary and transportation applications; and

• validation of emerging technologies. 

Dale A. Gardner joined NREL on December 1, 2003 to direct the Laboratory’s hydrogen systems integration work 

for the U.S. Department of Energy. The work he 

leads will directly inform Steve 

Chalk, manager of 

DOE’s Hydrogen, 

Fuel Cells and Infrastructure Program.

Gardner came 

to NREL from 

Northrop Grumman Mission Systems, where he 

managed the company’s operations 

in Colorado 

Springs, Colorado. He has more than 

30 years of experience with industry, NASA, and the military in systems 

management, design, development, 

and integration. He began his career 

with the Navy and the Naval Air Test 

Center and fl ew on two space shuttle missions as a mission specialist. 

Gardner supervised implementation 

of a worldwide space-sensor network 

at U.S. Space Command in Colorado 

Springs before managing engineering 

support programs for TRW, Inc. and 

Northrop Grumman Corp.

Computational Sciences 

Center Aids R&D

Along with theory and experiment, 

computation is considered an equal 

and indispensable partner in advancing scientifi c knowledge and engineering practices. Enormous computational capacity is needed to study 

the details of complex systems at everhigher levels of detail and realism.

Recognizing this, NREL has taken several steps toward establishing a fi rstclass computational capability. First 

came its Computational Sciences Initiative, adopted in 2000. It is a Labwide commitment to establish appropriate levels of computing power, data 

storage, applications software, and 

skilled support to all centers in the 

Laboratory. Next was the creation of 

the Computational Science Center. Situated in Building 16 in Golden, Colorado, the center has fi ve staff members. 

Its director is Steve Hammond, who 

joined NREL in March 2002.

Shortly thereafter came the installation of a supercomputer: a 64 processor IBM SP parallel computer with 64 

gigabytes of total memory and a peak 

speed of 96 billion fl oating point operations per second (gigafl ops). The system is similar in character to machines 

at Oak Ridge National Laboratory, Pacifi c Northwest National Laboratory, 

and Lawrence Berkeley National Laboratory’s National Energy Research Scientifi c Computing Center.

Equipment such as this is essential to 

many NREL scientists, says Hammond. 

“It enables them to study complex systems and natural phenomena in a virtual environment that would otherwise 

be too expensive or dangerous, or even 

impossible, to study by direct experimentation.” Scientists from NREL’s Basic Sciences Center, for example, use the 

IBM system to simulate and model the 

electronic structure of materials for PV 

devices and hydrogen storage.

Hammond came to NREL from the National Center for Atmospheric Research 

in Boulder, Colorado, where he managed the Computational Sciences Section and led a number of R&D efforts 

to improve the computational effi ciency of climate models. He holds a Ph.D. 

in Computer Science from Rensselaer 

Polytechnic Institute in Troy, New York, 

and master and undergraduate degrees 

from the University of Rochester.

Dr. Steven Hammond directs NREL’s Computational Sciences 

Center.

Dale Gardner directs the Laboratory’s 

 hydrogen systems integration work for 

the DOE.
PPatents P atents Patents P atents atents

Page 25

NREL 2003 Research Review Staff

Executive Editor Gary Cook

Writers Howard Brown, Erik Ness,

Tom LaRocque, Debra Sandor,

Gary Cook

Design/Layout Raymond David

Cover Design Al Hicks

Editors Michelle Kubik, Amy Vaughn, 

Gary Cook

Photography Warren Gretz, Raymond David

Additional Graphics Al Hicks, Raymond David

Contributors/Reviewers NREL Staff Members

Method for Improving the Durability 

of Ion Insertion Materials, Se-Hee Lee, 

et al, U.S. Patent 6,420,071, July 16, 2002. 

Dilute Acid/Metal Salt Hydrolysis of 

Lignocellulosics, Quang A. Nguyen and 

Melvin P. Tucker, U.S. Patent 6,423,145, July 

23, 2002. 

Passivating Etchants for Metallic Particles, Douglas L. Schulz, et al, U.S. Patent 

6,536,305, August 20, 2002. 

Method and Apparatus for Measuring 

Spatial Uniformity of Radiation, Halden Field, U.S. Patent 6,441,896, August 27, 

2002. 

Electrochromic Projection and Writing Device, Howard M. Branz and David 

K. Benson, U.S. Patent 6,441,942, August 27, 

2002. 

System for Rapid Biohydrogen Phenotypic Screening of Microorganisms 

Using a Chemochromic Sensor, Michael Seibert, et al, U.S. Patent 6,448,068, 

September 10, 2002. 

Plasma & Reactive Ion Etching to Prepare Ohmic Contacts, Timothy A. Gessert, U.S. Patent 6,458,254, October 1, 2002. 

Deposition of Device Quality, Low 

Hydrogen Content, Hydrogenated 

Amorphous Silicon at High Deposition Rates, Archie H. Mahan, et al, U.S. 

Patent 6,468,885, October 22, 2002. 

Purifi cation and Deposition of Silicon 

by an Iodide Disproportionation Reaction, Tihu Wang and Theodore F. Ciszek, 

U.S. Patent 6,468,886, October 22, 2002. 

Dish/Stirling Hybrid Receiver, Mark S. 

Mehos, et al, U.S. Patent 6,487,859, December 3, 2002. 

Pentose Fermentation of Normally 

Toxic Lignocellulose Prehydrolysate 

with Strain of Pichia Stipitis Yeast Using Air, Fred A. Keller Jr. and Quang A. 

Nguyen, U.S. Patent 

6,498,029, December 24, 2002.

Alkaline Tolerant 

Dextranase from 

Streptomyces Anulatus, Stephen R. Decker, et al, 

U.S. Patent 6,509,184, January 21, 2003. 

Processing Approach Towards the 

Formation of Thin-Film Cu(In,Ga)Se2,

Markus E. Beck and Rommel Noufi , U.S. 

Patent 6,518,086, February 11, 2003. 

Use of a Region of the Visible and 

Near Infrared Spectrum to Predict 

Mechanical Properties of Wet Wood 

and Standing Trees, Robert R. Meglen 

and Stephen S. Kelley, U.S. Patent 6,525,319, 

February 25, 2003.

Recombinant Zymomonas Mobilis 

with Improved Xylose Utilization, Min 

Zhang, U.S. Patent 6,566,107, May 20, 2003. 

Synthesis of Acid Addition Salt of DeltaAminolevulinic Acid from 

5-Bromo Levulinic Acid Esters,

Luc Moens, U.S. Patent 6,583,317, June 24, 

2003.

Refrigeration System with Liquid Injections Desuperheating, Christopher J. 

Gaul, U.S. Patent 6,584,784, July 1, 2003. 

Method of Predicting Mechanical 

Properties of Decayed Wood, Stephen 

S. Kelley, U.S. Patent 6,593,572, July 15, 

2003.

Ultra-Accelerated Natural Sunlight 

Exposure Testing Facilities, Alan A. 

 Lewandowski and Gary J. Jorgensen, U.S. 

Patent 6,604,436, August 12, 2003.

Ethanol Production with Dilute Acid 

Hydrolysis Using Partially Dried Lignocellulosics, Quang A. Nguyen, et al, 

U.S. Patent 6,660,506, December 9, 2003.

U.S. Patent