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Innovation for Our Energy Future

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Innovation for Our Energy Future

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Innovation for Our Energy Future

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Innovation for Our Energy Future

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Innovation for Our Energy Future

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National Renewable Energy Laborato

Innovation for Our Energy Future

From 

Research 

Discoveries 

to Market

RESEARCH REVIEW

2007

National Renewable Energy Laboratory

Innovation

Technology Development

Product Development

Commercial Demonstration

Large-Scale Deployment
The National Renewable Energy Laboratory is operated by Midwest Research Institute and Battelle for the Office of Energy Efficiency and 

Renewable Energy (EERE) at the U.S. Department of Energy (DOE). NREL is funded by EERE, the DOE Office of Basic Energy Sciences, and other 

funding sources. NREL is the nation’s primary national laboratory for renewable energy and energy efficiency research and development. 

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.

This year’s Research Review staff includes Kim Adams, Karen Atkison, Howard Brown, Ray David, Kevin Eber, William Gillies, Don Gwinner, 

David Hicks, Anne Jones, Erik Ness, Trixie Phelps, Paula Pitchford, Julie Tuttle, and Theresa von Kugelgen.

Cover photo: NREL researchers Eric Knoshaug and Kim Christensen (PIX15693)

Director’s Perspective: Transforming Our Energy Enterprise 2

From Research Discoveries to Market: Five Steps to Commercialization 3

Innovation

Are Silicon “Quantum Dots” a Key to High-Efficiency Solar Cells? 4

NREL’s Research in Bioenergy Science Gets a Boost 5

NREL-Chevron CRADA Cooks Up a Super Fuel 6

Marrying Nanotechnology and Biology to Boost Hydrogen Production 7

Technology Development

Squeezing More Sugar from Cellulosic Biomass 8

A Silver Bullet for Organic Solar Cells 9

Product Development

NREL Effort Leads to New Solid-State Lithium Battery Company 10

Commercial Demonstration

Setting the Foundation for Gigawatt-Scale Renewable Energy 11

Large-Scale Deployment

Building New Markets for Energy Efficiency 13

NREL Sows the Seeds for a Thin-Film Solar Cell Bounty 17

Investing in Energy for the Future 22

Table of Contents
2007 Research Review | Director’s Perspective www.nrel.gov/research_review/ 2

Director’s Perspective: 

Transforming Our 

Energy Enterprise

Aggressively pursuing innovation, commercialization at speed, 

and deployment at scale.

By now, we are all familiar with the statistics: Global 

demand for energy is projected to increase 50% 

or more by the year 2030, and energy demand in 

developing countries is likely to double in that time.

The rapid growth of energy demand, the uncertainty

of future supplies, the increasing reliance on oil 

from unstable regions, and the resulting dramatic 

rise in fossil fuel prices—all of these are creating formidable challenges to our economy and our energy 

security. At the same time, the growing concentration of carbon dioxide in the Earth’s atmosphere is a 

looming threat to our environment.

Without fundamental changes in how we generate—

and how we use—energy, these challenges threaten 

our livelihoods, our lifestyles, and our planet.

I strongly believe that these changes cannot be incremental. The world must transform its current 

energy system on a global scale, and in order to help 

achieve this transformation, our nation must focus 

on moving next-generation energy technologies into 

the marketplace far more quickly than we are doing 

now.

At NREL, we refer to this fast-moving approach as 

commercialization at speed. We have been preparing for it for decades, so that today, we have many 

technologies that are mature enough to make a compelling business case. The challenge is to move these 

technologies into the marketplace more quickly by 

breaking down the remaining barriers.

At the same time, we must create an infrastructure 

in which our current technologies have far-reaching 

and significant impacts. We call this deployment 

at scale, and it means that we must identify and 

remove the structural barriers that are preventing 

advanced energy technologies from being adopted 

quickly and easily.

We can achieve these two imperatives by aggressively pursuing innovation while accelerating our 

commercialization and deployment efforts. All three 

pursuits are needed to achieve the necessary transformation of the world’s energy system.

At NREL, we are studying the energy marketplace 

and developing innovative technologies that are targeted to meet the needs of the marketplace. We are 

managing our intellectual property to help it reach 

its full commercial potential and are working closely with entrepreneurs who will help commercialize 

our technologies. We aim to provide consumers not 

just with clean energy options, but also the tools that 

will help them integrate advanced energy technologies into their everyday lives.

NREL’s research provides a pathway for new solutions in the form of a steady flow of technological 

advances. New concepts and systems are emerging 

that will allow renewable energy industries to become more cost competitive, expand their markets, 

and keep moving forward.

Our work covers the spectrum—from promising, 

but as-yet unproven, technologies that could still 

require years of research, to the relatively near-term 

cost-cutting improvements needed to accelerate 

the market acceptance of well-demonstrated new 

technologies.

And as the most opportune concepts move to commercialization, we continue to find still more ways 

to improve advanced energy systems and to integrate them into our existing infrastructure. In this 

way, research continues to feed the technology pipeline, providing industry and society with the best 

options for solving our energy problems.

This work is enormously challenging, yet it’s essential to our energy future. We continually ask 

ourselves, “How can we ensure that our initial steps 

toward a sustainable energy economy will take us 

where we need to go?” The answer, I feel, will be 

found through balanced efforts that simultaneously 

address aggressive innovation, commercialization 

at speed, and deployment at scale. As director of the 

national laboratory at our nation’s epicenter of clean 

energy research and development, I am confident 

we can—and will—get there.

Dr. Dan Arvizu, 

Director of the 

National Renewable 

Energy Laboratory

PIX15749
3 2007 Research Review | From Research Discoveries to Market

From Research Discoveries to Market: 

Five Steps to Commercialization

The meaning of the word “commercialization” is 

simple: it means moving a new technology, product, or process from its conceptual stage to the marketplace. At a research laboratory like NREL, that 

“conceptual stage” is usually a research discovery, 

but the ultimate goal is still a commercial product. 

And though we take stock of our progress in the 

number of technical reports published, patents 

awarded, and technologies licensed, we realize 

that these are just milestones on the path toward 

commercialization.

However, that path to commercialization can be 

quite complex. We know the general path to follow 

to bring our innovations to the marketplace, but we 

also acknowledge that the path for any one product 

is rarely linear. Most entrepreneurs have plenty of 

tales to tell us about challenges that were overcome, 

seemingly simple steps that involved significant efforts, and frustrating setbacks that were completely 

unforeseen. We’ve learned to handle setbacks along 

the way, because they often result in a better product. Finding new paths around roadblocks is part of 

the commercialization effort.

Accepting the possibility of hitting roadblocks, it 

is still possible to broadly trace the route to commercialization that most technologies will follow. 

Generally speaking, there are five major steps in this 

path: innovation, technology development, product 

development, commercial demonstration, and largescale commercial deployment.

Let’s take a closer look at those five steps, beginning 

with innovation. At NREL, innovations often spring 

from our research, which is our primary mission. 

An innovation could be a scientific finding that suggests the possibility of a commercial product, with 

no clear path to getting there, or it could be just a 

good new idea with commercial potential. So innovation can be the result of years of painstaking 

research or a single moment of brilliance.

Technology development is often the most 

challenging step, because it involves taking a 

discovery or idea and finding a way to make it work 

in the real world. But it’s another area where NREL’s 

scientists and engineers really shine. As the nation’s 

applied research and development laboratory for 

renewable energy and energy efficiency, it is our 

forte and a central part of our mission for DOE. 

After all, for more than three decades, we have been 

starting with raw materials and knowledge and 

creating solar cells, wind turbine designs, biofuels, 

and a panoply of other energy technologies.

However, developing a commercial product out of 

a new technology is not our role, so that’s when we 

bring in industry partners. These partners supply 

the business and manufacturing experience needed 

to create a successful product, and they also help 

take us to the next step, commercial demonstration. 

Along the way, we provide our technical expertise 

when needed, and we serve as objective experts who 

can analyze and test prototypes, validating their 

performance and suggesting areas for improvement, 

while also helping our partners to integrate their 

products into today’s energy infrastructure.

When a demonstration is successful, the final step 

is the holy grail of commercialization, large-scale 

commercial deployment. That’s what we’re really 

after: not just making a niche product, but actually 

changing the way the world produces and uses energy. This is yet another area where NREL shines, as 

we have plenty of engineers with real-world experience who serve as advisors to project developers. 

Our work in high-performance buildings is a good 

example: we introduce designers and builders to 

new ideas, methods, and technologies that can lower 

the net energy use of buildings to near zero. If we’re 

successful, those designers and builders carry those 

practices to every new building they work on.

And that’s what NREL is all about—moving innovations from concepts to commercial products 

using our deep technical knowledge. The articles 

that follow present examples of this five-step path to 

commercialization.

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2007 Research Review | Innovation www.nrel.gov/research_review/ 4

Are Silicon “Quantum 

Dots” a Key to HighEfficiency Solar Cells?

Research shows new promise for “nanoscale” particles of silicon.

Art Nozik, who was 

recently named a fellow of the American 

Association for the 

Advancement of 

Science, is leading 

NREL’s research of 

quantum-dot solar 

cells.

One photon of solar energy excites one electron in conventional PV cells, but possibly more than one “exciton” in 

quantum dots. Also, by varying their size, quantum dots can 

be “tuned” to different wavelengths, dramatically increasing 

their efficiency in capturing solar energy.

PIX15750

 NREL’s research shows new promise for “nanoscale” particles of silicon—particles on the scale 

of a billionth of a meter, or nanometer. These submicroscopic dots of material are called “quantum dots” 

because they are small enough to exhibit unexpected characteristics as a result of their quantum mechanical behavior. For instance, quantum dots made 

from the same photovoltaic solar cell material can 

capture different frequencies of light, depending on 

their size. This unique characteristic has led many 

researchers to try building quantum-dot solar cells.

It’s tricky, though. When a normal photovoltaic material captures a photon of sunlight, it produces a 

negatively charged electron, which leaves behind a 

positively charged “hole” in the material. Under the 

solar cell’s electrical field, the two charge carriers 

migrate to the terminals of the cell and produce a 

current. But quantum dots produce “excitons,” consisting of electrons loosely bound to positive holes. 

Solar cells employing quantum dots must dissociate 

the excitons into electrons and holes that must then 

migrate to the cell terminals without recombining.

On the plus side, researchers have found that quantum dots of certain materials can produce more than 

one exciton per photon of light. That finding would 

hold promise for solar cells if it weren’t for one problem: those quantum dots were made of materials not 

commonly used in solar cells.

That all changed in July 2007, when NREL researchers found the multiple-exciton effect in 

quantum dots made of silicon, the material used in 

most of today’s solar cells. The finding, published 

in the August 8, 2007, edition of Nano Letters, suggests we are on a path toward solar cells that will 

produce more electrical current from the same 

amount of sunlight.

The NREL team discovered the effect using silicon 

quantum dots and exposing them to solar wavelengths from violet visible light into the ultraviolet. 

The research validated a prediction made by NREL 

Research Fellow Arthur 

Nozik in 1997. But despite 

the promise of the discovery, 

Nozik remains cautious about 

its practical applications.

“This is a significant scientific 

advance,” says Nozik, “but for 

this discovery to be converted 

into a useful and technologically important solar cell, it 

is necessary to dissociate the 

excitons and collect the resulting free electrons and holes with high efficiency.”

In other words, it’s one thing to find a material that 

efficiently produces excitons from sunlight, but it’s 

another thing altogether to build a device that can 

produce a current from those excitons. NREL and 

other laboratories are trying to tackle that challenge, 

knowing that the payoff could be great. Calculations 

by Nozik and NREL scientist Mark Hanna have 

shown that the maximum theoretical conversion 

efficiency of such quantum-dot solar cells would be 

about 44% under normal sunlight 

and about 68% under sunlight concentrated by a 

factor of 500. That’s 

a big leg up over 

today’s conventional solar cells, 

which have maximum theoretical efficiencies of 

33% and 40%, respectively, under 

the same solar 

conditions.
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5 2007 Research Review | Innovation

NREL’s Research in 

Bioenergy Science 

Gets a Boost

NREL is part of a new DOE Bioenergy 

Science Center.

PIX15751

PIX15746

NREL’s ability to pursue new discoveries in basic 

bioenergy science received a major boost in 2007, 

when DOE announced funding for a new Bioenergy 

Science Center. NREL will play a major role in the 

new center.

For more than 30 years, NREL researchers have been 

working to increase our knowledge of the science 

underlying renewable energy technologies. But according to Mike Himmel, manager of the NREL 

Biomolecular Science Group, new gains in bioenergy 

science will have to come from a renewed focus on 

a deeper understanding of the fundamental science 

underlying biotechnologies. The DOE Bioenergy Science Center will provide that ability.

In August 2006, the DOE Office of Science Genomics: GTL (formerly, Genomes to Life) Program issued 

a solicitation for genomics-related investigations 

that will accelerate basic research in the development of cellulosic ethanol and other biofuels. To respond to the solicitation, NREL teamed with DOE’s 

Oak Ridge National Laboratory (ORNL) and several 

universities, bioenergy companies, and other institutions to propose a DOE Bioenergy Science Center. 

In June 2007, DOE announced that the proposal was 

one of three successful ones among more than 20 

submitted. The center will be based at ORNL and is 

slated to receive $25 million per year for five years 

from the Genomics: GTL Program.

The new center’s goal is to develop the science and 

technology that enables cost-effective conversion 

of cellulosic biomass to biofuels. To that end, the 

center will focus on two major research pathways, 

both involving recombinant genetics. For the first 

pathway, the center will develop plants that can 

be broken down more easily into their component 

sugars for fermentation, while the second pathway 

will focus on the microorganisms employed in biofuel production.

“The microorganisms we now use for biomass 

conversion tend to either be good at producing enzymes for breaking biomass down to sugar or good 

at fermenting those sugars, but not 

both,” Himmel says.

The effort will develop new microorganisms that can do both well, 

so that today’s multiple-step process can be carried out in a single 

step, called “consolidated bioprocessing.” This achievement should increase process 

efficiency and reduce capital equipment costs.

NREL’s three contributions to the work of the center 

will include advanced analysis and imaging, rapid 

analyses of large numbers of samples, and improvements in the biochemistry of cellulosomes. Cellulases are enzymes used to break cellulose down 

into its component sugars, and cellulosomes are 

complexes of cellulases that work together in the 

breakdown process.

“This funding will allow us to work on the entire 

process in a way that we have not been able to do 

before,” Himmel says.

Each spherical shape on the surface of this Acetivibrio cellulolyticus

bacterium is a cellulosome containing several different enzymes 

active in breaking cellulose down to its component sugars. With new 

Bioenergy Science Center funding, NREL researchers can research the 

overall action of the cellulosome in a way that they have not been 

able to before.

Researcher Shi-you 

Ding images cellulosome enzymes in 

NREL’s Compositional 

Analysis Laboratory.
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2007 Research Review | Innovation www.nrel.gov/research_review/ 6

NREL-Chevron CRADA 

Cooks Up a Super Fuel

Collaboration will convert rapid-growing, oil-rich 

microscopic algae into renewable “green” diesel, jet 

fuel, or even gasoline.

PIX15605

Put some algae in a shallow pond of water unfit for 

agricultural uses, stir in some simple nutrients and 

an exhaust gas that’s threatening the Earth’s climate, 

and let it all cook in the sun for a few days.

That’s NREL’s recipe for a new sustainable fuel 

resource. If the recipe works, you can harvest a 

bumper crop of microscopic algae, or “microalgae,” 

extract its oil, and ship the oil to a petroleum refinery, which can turn it into renewable-source “green” 

diesel, jet fuel, or even gasoline. The production of 

oil from microalgae could also be dramatically higher per acre than it is for soybeans and other oil seed 

crops—perhaps as much as 20 times higher.

Many species of microalgae naturally produce up to 

20% of their body weight as lipids, fats, or oils that 

can be converted to fuel. When these microalgae are 

starved of the nutrients they need, their lipid content 

can increase as much as 60%.

To make good use of this extraordinary oil-producing capability, NREL and Chevron Corporation 

signed a DOE Cooperative Research and Development Agreement (CRADA) in October 2007. Under 

the agreement, NREL will develop ways to increase 

the productivity of these microalgae. Chevron anticipates using the resulting oil as a feedstock for 

renewable transportation fuels.

Microalgal oil production has everything going for 

it in terms of being an environmentally ideal recipe 

for biomass energy. For example, microalgae can be 

grown on land that’s not suitable for conventional 

crops and in salty water that’s unfit for conventional 

agricultural or domestic uses.

Growing microalgae could also be one of the most 

effective ways of reducing carbon dioxide emissions. 

Algae, like terrestrial plants, take up carbon dioxide 

directly from the atmosphere as they convert light 

energy into chemical energy by means of photosynthesis. But algae can be stimulated to grow more 

vigorously by being “fed” with carbon-dioxide-rich 

air streams from power plant flue gases or other 

sources.

NREL is uniquely and highly qualified for advanced 

R&D in microalgal oil production. From 1978 to 

1996, the laboratory was a pioneer in the field with 

the Aquatic Species Program. In it, researchers 

screened and characterized more than 3,000 potential strains, shed light on the growth conditions 

that stimulate lipid production, demonstrated open 

ponds for mass production of biomass, and made 

significant breakthroughs in genetic engineering. 

When the program ended, the technology was considered to be highly promising but not yet cost competitive with petroleum-based fuels.

Today, however, it’s time to take the microalgal-fuel 

recipe off the back burner. While petroleum prices 

are up, new petroleum refinery processes are better 

able to handle algal-derived oils.

Algae farming techniques have also changed. NREL 

used to grow algae in large, shallow outdoor ponds. 

Today, microalgae are grown within inexpensive 

plastic tubes or similar enclosed bioreactors. In fact, 

more than 50 companies have sprung up over the 

last several years to research microalgal oil production, focusing primarily on developing novel bioreactors while using existing algal strains. The most 

exciting change for NREL’s researchers, however, is 

that the science has improved.

“In the ‘80s and ‘90s, efforts to increase oil production in algae were largely based on the Edisonian 

approach: ‘try something and observe what happens.’ Now, new biotechnologies give us far greater 

capability to understand how an organism responds 

to various environmental factors that influence 

growth,” says Al Darzins, who is directing the 

Chevron CRADA work.

“The new excitement about microalgal oil has lots 

of people looking at engineering better bioreactor 

systems, but not as many at the underlying biology 

of the organisms, and that is crucial,” says Darzins. 

“We look forward to making substantial gains.”

Researchers Eric 

Knoshaug and Kim 

Christensen are using fluorescence of 

lipids under laser light 

to analyze and sort 

algae samples for oil 

content.
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7 2007 Research Review | Innovation

Marrying Nanotechnology 

and Biology to Boost 

Hydrogen Production

“Biohybrids” could replace expensive precious-metal catalysts 

in electrolyzers and fuel cells.

NREL-developed “biohybrids” made of bacterial 

enzymes and carbon nanotubes—carbon tubes 

on the scale of a billionth of a meter—could one 

day allow hydrogen-producing bacteria to be put to 

work for either hydrogen production or for oxidizing fuels within fuel cells.

The goal of the hydrogen economy involves using 

hydrogen fuel cells to power vehicles, buildings, and 

portable devices. Unfortunately, it can be an expensive business, as both fuel cells and electrolyzers—

devices that run a current through water to produce 

hydrogen—require expensive precious metal catalysts such as platinum.

“Hydrogen and fuel-cell technologies address the 

need to both mitigate greenhouse gas emissions 

and develop energy alternatives to fossil fuels,” says 

NREL researcher Mike Heben. “Hydrogen gas is 

scarce, however, and cheap, efficient hydrogen production technologies will be required for its widescale deployment.”

One inexpensive approach is found in nature. Microbes have had billions of years to figure out efficient ways to catalyze hydrogen reactions. Their 

solutions involve enzymes called hydrogenases, 

which use more abundant metals like iron and 

nickel to activate hydrogen. For years, scientists 

have searched for ways to employ hydrogenases in 

electrolyzers and fuel cells.

One challenge for scientists is their inability to electrically tap into the workings of the hydrogenase 

enzyme, but new research led by Heben and NREL 

researcher Paul King may point the way to a solution to that problem. The researchers found that 

under certain conditions, carbon nanotubes will 

spontaneously combine with hydrogenases to create 

an electrical connection.

In the experiment, the NREL team 

used photoluminescence and 

Raman spectroscopy to look at what 

happens when hydrogenase from 

the anaerobic bacterium Clostridium 

acetobutylicum interacts with singlewalled carbon nanotubes. Carbon 

nanotubes normally absorb and 

re-emit light at wavelengths that can be measured 

using photoluminescence spectroscopy. After 

hydrogenase was added, the photoluminescence 

disappeared.

“This suggests that the enzyme is feeding electrons 

into the nanotubes as it catalyzes the oxidation of 

hydrogen,” says King.

The resulting biohybrid has the catalytic properties 

of hydrogenase and the excellent electrical conductivity of carbon nanotubes. The team found that 

they could control the catalytic reaction by changing the pH balance and oxygen concentration of the 

solution. When they added oxygen, which inactivates hydrogenase, the nanotubes lit up again. In 

the absence of oxygen, the hydrogenase-nanotube 

connections continued to work for up to a week.

“Our research indicates that combining hydrogenase with carbon nanotubes may offer an inexpensive alternative to noble-metal catalysts,” says 

King. “The results suggest the possible construction of functional biohybrids of hydrogenase and 

single-walled carbon nanotubes for applications in 

a variety of hydrogen-production and fuel cell technologies. Such biohybrids could replace expensive 

precious-metal catalysts in electrolyzers and fuel 

cells.”

Researcher Maria 

Ghirardi purifies biological catalysts for 

hydrogen production 

using fast protein 

liquid chromatography 

within an oxygen-free 

chamber.

PIX15753
2007 Research Review | Technology Development www.nrel.gov/research_review/ 8

Squeezing More 

Sugar from 

Cellulosic Biomass

DOE’s goal is to move from a batch process 

to a continuous reactor and to reach 90% 

conversion by 2012.

Researcher Noah Weiss 

feeds raw corn stover 

into a pretreatment 

reactor (left) and 

examines the product 

(right) after the 

reactor has extracted 

the hemicellulose as 

xylose.

PIX15646

PIX15634PIX15752

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NREL researchers recently achieved an important 

goal in breaking down long molecular chains of 

xylan—a significant component of biomass plant 

material—into their component xylose sugar molecules. This is a very important step toward the goal 

of making ethanol from cellulosic biomass cost competitive with fossil fuels.

Bioenergy technology is focused on taking biomass 

plant matter apart and making useful products from 

it. But taking biomass apart can be quite difficult. 

Over millions of years, plants have evolved highly 

sophisticated structures to keep themselves intact.

Up to 50% of biomass is cellulose and up to 32% is 

hemicellulose, and these two carbohydrates are nature’s main storehouses of sugars that researchers 

want to tap to make ethanol and other products. Although perhaps the easier of the two to break down, 

hemicellulose is by no means easy to take apart. It 

consists largely of xylan, long molecular chains of 

xylose sugar molecules, which are wrapped around 

cellulose to protect it.

To make cellulosic ethanol cost competitive by 2012, 

which is a goal of the President’s Advanced Energy 

Initiative, NREL developed a set of specific annual 

goals for various aspects of biomass conversion 

technology. A key goal for 2007 was to be able to 

convert 75% of xylan to xylose. To do that, NREL 

used a dilute acid, high temperature, and pressure 

to “pretreat” biomass, breaking down the hemicellulose and making the cellulose more accessible 

for the next step in the process, called enzymatic 

hydrolysis.

Pretreatment expert Nick Nagle describes realizing 

the 75% xylan conversion goal—up from 63% the 

previous year—as “a big step in the right direction.” 

And fellow researcher Andy Aden says it was a 

great challenge for a number of reasons.

“One, we are now working at 30% solids—kind of 

like oatmeal or paste—which is much more difficult 

than our earlier work with more free liquid, but it’s 

also a key step toward making the overall process 

economically competitive,” says Aden. “Two, our 

research has shown that the xylan release process 

occurs in two distinctly different segments, with 

the first step occurring swiftly and the second occurring much more slowly. This was the first really 

big gain with xylan release that draws on the slower, 

more difficult second step.”

Key steps included thoroughly impregnating the 

biomass with acid before putting it into the pretreatment reactor and then reducing the actual reactor 

time to less than two minutes. The shorter time in 

the reactor limited the subsequent degradation of 

the xylose. The goal for 2008 is to move from a batch 

process to a continuous reactor, while the ultimate 

goal is to reach 90% conversion by 2012.

The non-edible 

portions of corn, 

known as corn stover, 

can be converted 

into ethanol, but the 

process is much more 

difficult than today’s 

processes to convert 

corn kernels into 

ethanol.
9 2007 Research Review | Technology Development

A Silver Bullet for 

Organic Solar Cells

Researchers boost conversion efficiency of 

plastic and fullerene molecules by adding silver.

Centuries ago, stained-glass makers developed a technique for creating luminous colors by mixing minuscule droplets 

of metals into molten glass. Today, scientists at NREL are using a related concept to 

boost the efficiencies of organic solar cells.

Made largely from plastic, organic solar 

cells have the potential to be manufactured more 

easily and less expensively than solar cells made 

of silicon and other materials. They can be made 

of lower-cost materials in processes that are amenable to high-throughput manufacturing and that 

do not require high-temperature or high-vacuum 

conditions.

To explore this potential, Jao van de Lagemaat and 

his colleagues at NREL and the University of Colorado at Boulder are studying organic solar cells 

known as polymer-fullerene cells. The active layer 

of these cells consist of a mixture of plastic and 

fullerene molecules, which are molecules of 60 carbon atoms arranged in the shape of a soccer ball.

The two materials form interpenetrating phases 

within the active layer, and when blue light is absorbed by that layer, it forms “excitons,” which are 

weakly bound pairs of a newly freed electron and 

the positive “hole” left behind in the material when 

the electron was freed. As the excitons diffuse to 

a boundary between the two materials, they split, 

and electrons move through the fullerenes to the 

back contact, while holes move through the plastic 

to the front contact. The result is a flow of electrical 

current.

There is one big roadblock to achieving high conversion efficiencies with these types of cells, however: The active layer does not absorb the low-energy 

red and infrared portions of the solar spectrum. But 

van de Lagemaat and his associates have overcome 

that obstacle. Their solution was to add a layer of 

silver with a thickness on the scale of a billionth of a 

meter (a nanometer).

“We are using a nanoscale layer of 

discontinuous silver particles, which 

boosts cell performance by exploiting 

a phenomenon called surface-plasmon resonance,” van de Lagemaat 

says. “Surface plasmons are free electrons that 

move in unison on the surface of the silver layer 

when excited by light. These plasmons greatly enhance the electromagnetic energy transmitted to 

the underlying active layer. The result is a boost in 

current generation and hence, improved conversion 

efficiency of the cell,” van de Lagemaat says.

The team has demonstrated that building a nanoscale silver layer within an organic solar cell can 

increase the output current of the device at long 

wavelengths. In experiments using a silver layer 

one nanometer thick, the solar energy conversion 

of the solar cell improved by a factor of 1.7. Finetuning will produce devices with even higher 

efficiencies.

Organic solar cells might not look quite as beautiful 

as a stained-glass window. But the performance improvement in these plastic cells—gained by using 

this silver “bullet”—will be very much appreciated 

by those wanting more affordable, clean electricity.

Surface plasmons are 

free electrons that 

move in unison on the 

surface of the silver 

layer when excited by 

light. The plasmons 

greatly enhance the 

electromagnetic 

energy transmitted to 

the underlying active 

layer.

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NREL Effort Leads to 

New Solid-State Lithium 

Battery Company

NREL technology allows for a breakthrough in manufacturing 

highly compact batteries that last virtually forever.

Researchers from 

Planar Energy Devices, 

Inc., insert a sample 

into the vacuum 

chamber of the 

company’s thin-film 

deposition system.

Planar Energy Devices 

has advanced the 

solid-state lithium 

battery from NREL’s 

crude prototype 

(below) to a miniaturized, integrated 

device (bottom).

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It can take decades to move from research and development to a commercial enterprise. But in one case, 

NREL’s research has rather quickly led to a new 

start-up company that is developing solid-state batteries for use in sensors, medical devices, and other 

products that require safe power sources with high 

capacities and long lifetimes.

It all began when NREL researchers Ed Tracy, 

Se-Hee Lee, and Ping Liu decided to take their thinfilm expertise from window technology research 

and apply it to a solid-state, thin-film lithium 

battery.

“Thin-film batteries have a problem with respect to 

being degraded very fast,” says Tracy. “That’s because the lithium metal anode is always on top, and 

if there were a way to get it on the bottom, it would 

be a much more durable device.

“We had a concept to construct this device by electrochemically plating the lithium anode on a lower 

layer of the battery, forming a ‘buried’ anode.”

Although the team made progress, their work accelerated when Battelle Ventures visited NREL looking 

for new technologies. Battelle Ventures is a $220 million independent venture fund that aims to leverage 

the technologies and expertise of the national laboratories managed or co-managed by Battelle.

Coincidentally, the Battelle Ventures team had earlier visited DOE’s Oak Ridge National Laboratory 

(ORNL), which was trying to commercialize a thinfilm lithium battery. The Battelle Ventures team recognized the synergies between the two laboratories’ 

work and provided funding for NREL to demonstrate working prototypes.

With Roland Pitts leading the task, the team found 

that their battery technology was very durable and 

had a high charge capacity, suggesting that it was 

commercially viable. Meanwhile, Battelle Ventures 

and entrepreneur Scott Faris jointly founded a 

company called Planar Energy Devices, Inc., which 

licensed both the NREL and the ORNL technology. 

Since then, Roland Pitts has taken sabbatical leave 

to work at Planar and oversee the transfer of the 

technology from the labs to Planar.

“We are currently in the stage of acquiring equipment and building out our prototype laboratory, 

and we’re just starting to try to make some prototype batteries,” says Pitts. “We recently acquired 

the facilities and equipment of another ORNL battery licensee, which will allow us to get to market 

much sooner than we had originally planned.”

Planar’s batteries will be highly compact and last 

virtually forever, changing the way electronic devices are used and designed. And because the solidstate lithium batteries are made from inorganic 

materials, they don’t suffer from potential thermal 

runaway and fires, as do lithium-ion batteries. The 

NREL technology allows for a breakthrough in 

manufacturing as well.

“With the NREL technology, we can deposit all of 

the thin films at ambient temperatures, enabling 

the use of polymers and flexible substrates, as well 

as new types of high-capacity cathode materials,” 

says Pitts. “Now we can make highcapacity, solid-state batteries on a 

true roll-to-roll manufacturing line, 

making it a very low cost approach.”

The technology certainly has 

Battelle Ventures convinced. In June 

2007, the fund committed $4 million 

in venture financing for the new 

start-up, providing the critically 

needed capital to keep the company 

going as it develops its promising 

technology.

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11 2007 Research Review | Commercial Demonstration

Setting the Foundation 

for Gigawatt-Scale 

Renewable Energy

A joint venture between NREL and Xcel Energy is studying 

how wind, solar, and hydrogen technologies can best be 

integrated with the electric grid.

Sitting on an exposed, wind-blown plateau along the front range of Colorado’s Rocky Mountains, a 

40-foot by 40-foot concrete pad may hold a key to 

our energy future. This is the home of the “wind to 

hydrogen” project, a unique facility that uses electricity from wind turbines and solar panels to produce hydrogen from water.

In chemical nomenclature, hydrogen is “H2,” and 

researchers at the “Wind2H2” facility are working to solve some of the biggest problems facing 

the world today: how to generate electricity and 

produce transportation fuels without accelerating 

climate change.

“The ultimate goal is to get more wind power onto 

the grid and provide cost-effective hydrogen for 

vehicles in an environmentally conscious manner, 

although economical and robust fuel-cell-powered 

cars are still years away,” says project leader Kevin 

Harrison.

Producing electricity from renewable resources like 

the wind and the sun is an environmentally friendly 

way to meet our future needs for power. But there’s 

a major drawback: these resources don’t produce 

electricity when the wind isn’t blowing and the sun 

isn’t shining, and this variability has hampered 

their development and wide-scale adoption. So, 

the major goal of Wind2H2 is to improve the reliability, dispatchability, and economics of renewable 

energy by storing it as hydrogen, opening the door 

for gigawatt-scale renewable energy deployment. 

The hydrogen could then be converted to electricity 

when it’s needed or used as a vehicle fuel.

Hydrogen is a flexible energy carrier that can be 

generated from coal, natural gas, biomass, water, 

and other hydrogen-rich materials. Using renewable energy to produce hydrogen from water allows 

inherently clean energy to be stored for later uses. 

Hydrogen can be stored and converted back to 

electricity or used to run vehicles while producing 

little or no greenhouse gases. That’s why hydrogen 

is often regarded as the fuel of the future. There are, 

however, quite a few technical challenges to be overcome before that vision becomes a reality.

The Wind2H2 facility at NREL’s National Wind 

Technology Center is a joint venture between NREL 

and Xcel Energy, the largest provider of wind energy in the country. Xcel provided most of the capital 

equipment, while NREL, designed, built, and now 

operates the facility, which had to comply with stringent safety codes and standards governing sites that 

produce and store hydrogen.

The hydrogen is produced by electrolysis, which 

is the process of splitting water into hydrogen and 

oxygen using electricity. The electricity needed for 

this process comes from utility-supplied power and 

three renewable sources:

•	A 10-kilowatt wind turbine that produces alternating current (AC) that varies in magnitude and 

frequency as the wind speed changes

•	A 100-kilowatt wind turbine, from which some 

direct current (DC) electricity is directed toward 

electrolysis before the remaining energy is inverted back to regulated AC for the grid

•	An array of solar electric photovoltaic panels capable of producing 10 kilowatts of DC electricity.

The electricity from these sources is run through 

power converters—designed and built by NREL—

that provide the electrolyzers with the DC power 

they need to operate efficiently. Two polymer electrolyte membrane (PEM) electrolyzers and one 

alkaline electrolyzer produce hydrogen and oxygen 

from an onsite water supply. The PEM electrolyzers 

Wind energy ... or solar energy ...

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each produce approximately 2.3 kilograms of hydrogen per day, and the alkaline electrolyzer produces 

12 kilograms per day, for a total of 16.6 kilograms of 

hydrogen, equal in energy content to about 16.6 gallons of gasoline.

After the hydrogen is compressed, it’s stored in 

tanks at 3,500 psi (pounds per square inch) for later 

use. When the demand for electricity is at its peak, 

the stored hydrogen is fed to an internal combustion engine connected to a generator, producing 

AC electricity that is fed into the utility grid. Future 

plans for the facility include adding the equipment 

necessary to compress and store hydrogen at the 

5,000 psi or more needed for vehicle refueling. Another option would be a fuel cell, which could be 

used to convert the hydrogen back to electricity at 

nearly twice the efficiency of the internal combustion engine.

Today, the research focus is on developing the power electronics and control systems required to integrate all these different components into a single, 

smoothly functioning entity. The ability to do this is 

one of NREL’s great strengths and the primary reason that Xcel chose the lab as a partner. NREL has a 

strong track record in integrating multiple generators and battery storage systems for village power 

grids in both the United States and the developing 

world.

Wind2H2 project partners hope to reduce the complexity of an integrated renewable hydrogen system 

and improve its overall efficiency. The first challenge is to convert the variable energy output from 

the wind turbines and photovoltaic array into a form 

that can be used by two different kinds of commercially available electrolyzers. Additional challenges 

involve creating a control system for integrating 

multiple electrolyzers of both PEM and alkaline 

technologies, which produce hydrogen at different 

pressures. If Wind2H2 facilities are to operate costeffectively and propagate throughout the country, 

it is essential that they operate safely and smoothly 

without needing onsite monitoring.

“One of our major challenges is designing a fully 

autonomous system that does not require human 

input,” says Harrison.

The design concept of the Wind2H2 facility is exquisitely simple, but the real-world challenges associated with operating it are legion. Despite those 

challenges, the pressing need for clean, autonomous 

energy systems has placed this project on a fast 

track. At the facility’s inauguration in December 

2006, NREL director Dan Arvizu emphasized a key 

advantage of joint ventures like this.

“Our growing strategic partnership with Xcel Energy helps us reduce the time and effort between research discoveries and sharing the benefits of what 

we learn with energy consumers,” Arvizu said.

And according to Harrison, we won’t have long to 

wait for the results of NREL’s research on the optimal ways to integrate and control wind, solar, and 

hydrogen systems. “Expect answers by late 2008,” he 

says. Now that’s the power of partnership in action.

for subsequent 

electrical generation.

to electrolyze water and stored ...

to hydrogen ...

which is 

compressed ...

is converted to the 

appropriate current ...

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13 2007 Research Review | Large-Scale Deployment

Building New Markets 

for Energy Efficiency

NREL experts are teaming up with schools, the military, retailers, disaster 

recovery teams, and others to develop energy-efficient buildings.

NREL engineers 

contributed to a new 

publication that will 

help design teams 

plan and construct 

energy-efficient 

schools.

That clothing store you shop in, the office where you 

work, and even the garage where you take your 

car for service—all those buildings, and more, present great opportunities to save energy through improved energy efficiency and the use of clean, 

renewable energy.

Many of those energy- and money-saving opportunities are available to us today as a result of 30 years 

of building energy research and development at 

NREL. Today, engineers and researchers in NREL’s 

Center for Buildings and Thermal Systems continue 

to share their expertise in advanced technologies 

with the commercial building industry.

“We have developed the analysis, model simulation 

and optimization, and field monitoring capabilities 

that enable us to best answer the industry’s questions about the most cost-effective ways to save 

energy in buildings,” says Center Director Ronald 

Judkoff.

Commercial buildings account for about 17% of all 

of the energy consumed in the United States and 

represent great potential for energy and cost 

savings. More and more businesses are beginning 

to realize that potential by applying energy-efficient 

technologies in both their new construction and in 

current facilities.

In recent years, many organizations have knocked 

on NREL’s door to ask for help in moving advanced 

building energy technologies into the marketplace. 

As a result, NREL’s technical specialists are now 

working with energy managers, builders, and marketing staff in some of the nation’s largest commercial building organizations.

NREL is now a partner in some exciting projects that 

are helping DOE achieve its goal of transforming the 

commercial building industry. We have been assisting in the development of advanced energy guides 

for schools, hospitals, and retail buildings; helping 

the U.S. Army deploy energy-saving technologies 

in Army facilities; working alongside some of the 

largest retail companies in the country to cut energy 

costs; and helping 

distressed communities rebuild 

in the wake of a 

natural disaster.

Providing 

Energy 

Efficiency 

Guidance for K-12 Schools

What better place to save money by 

increasing energy efficiency than in 

our public schools? Today, fully 16% 

of the controllable cost of running a 

school district is spent on energy. Energy-efficient technologies and building practices 

can mean that a chunk of this money will be put to 

better use.

NREL engineer Paul Torcellini is helping to define 

the energy cost savings potential of our schools. 

He chaired a committee that developed a new publication written specifically for schools that serve 

students in kindergarten through twelfth grade 

(K-12). The guide will help design teams plan and 

construct energy-efficient schools using off-theshelf technologies that can cut energy use by 30% or 

more, in comparison to the amount of energy used 

by buildings meeting minimum energy efficiency 

requirements.

“Many schools throughout the country have increased energy efficiency, cut costs, and reduced 

their environmental footprints through energy efficiency measures,” says Torcellini. “Many others, 

however, still spend more money on energy than 

they do on educational supplies. Just think of all the 

things a school could do each year with the money 

it saves on energy: buy more books and computers, 

increase teachers’ salaries, upgrade the media center and gymnasium . . . the list goes on and on.”

The Advanced Energy Design Guide for K-12 School 

Buildings is published by the American Society of 

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2007 Research Review | Large-Scale Deployment www.nrel.gov/research_review/ 14

Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). It was written in partnership with 

the American Institute of Architects, the Illuminating Engineering Society of North America, the U.S. 

Green Building Council, and DOE. This same collaboration is developing an entire Advanced Design 

Guide series, which also includes design guides for 

small retail and office buildings. The series will soon 

feature a guide that addresses energy efficiency in 

warehouses.

The guide for schools builds on NREL’s extensive 

experience in developing and advancing the concept 

of integrated building design. Integrated design consists of looking at a building as a system and then 

designing and using energy-efficient and renewable 

energy technologies on a system-wide basis.

“To build a highly energy-efficient building, you’ve 

got to focus on early design from a whole-building 

systems perspective,” says NREL engineer 

Shanti Pless.

The school building guide features easy-to-follow 

recommendations for various climate zones and a 

series of case studies of actual school construction 

projects. It also includes suggestions for garnering 

green building energy credits, as well as supplemental strategies for achieving advanced energy savings 

beyond the target of 30% better than code.

To encourage schools to follow the new K-12 design 

guide, ASHRAE and its partners have sent free 

printed copies to 16,000 school boards throughout 

the United States. Following the guide’s suggestions 

will result in more energy-efficient school buildings 

and help to create safe and comfortable environments that enhance learning.

Teaming with the Army to Boost Energy 

Efficiency

The U.S. Army Corps of Engineers has joined the 

fight to broaden the use of energy-efficient and 

renewable energy technologies in the Army’s facilities worldwide. According to the Energy Policy Act 

(EPAct) of 2005, new federal buildings must be 30% 

more energy-efficient than buildings complying 

with standard building codes. To meet that goal, the 

Corps of Engineers is getting help from engineers 

and analysts at NREL.

NREL engineer Michael Deru is creating models 

and running simulations for eight different building types used by the Army. The results will help 

the Army with new construction, and they can be 

applied to the same types of buildings in other organizations as well as in industry.

“What’s exciting is that several of these building 

prototypes use NREL’s optimization methods, 

which analyze thousands of building variations 

looking for the best energy solutions,” Deru says.

The Corps of Engineers sent NREL specifications 

for two types of barracks, a dining facility, a vehicle 

maintenance building, headquarters office buildings for battalion and company personnel, a child 

development center, and an Army Reserve center. 

Using NREL-developed software, Deru and other 

NREL engineers are using the specifications to 

create models and run thousands of optimization 

simulations across 15 climate subzones. These simulations allow them to find innovative applications of 

a series of technologies that meet the EPAct requirements on a broad scale.

Like much of the U.S. commercial building industry, 

the Army recognizes NREL’s analysis and simulation capabilities. These include the publicly available 

EnergyPlus software program, developed in part by 

NREL, which can model a wide range of parameters 

and provide comprehensive analytical results, as 

well as NREL’s in-house software tool, Opti-E-Plus, 

which is a complex optimization program that will 

run tens of thousands of simulations to find the 

optimal energy-saving combination of products 

and technologies. NREL has also built a powerful 

distributed computing environment that effectively 

manages and performs the intricate calculations that 

create these models and simulations.

NREL engineer 

Michael Deru is 

creating models and 

running simulations 

for different building 

types used by the 

Army. The results 

will help the Army 

build energy-efficient 

buildings around 

the world.

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NREL has been 

monitoring and 

evaluating more 

than 50 different 

technologies that 

Wal-Mart installed 

in its experimental “Supercenter” 

store in Aurora, 

Colorado, including 

daylighting.

Showing Retailers the Value of EnergyEfficient Technologies

U.S. retail buildings account for approximately 20% 

of commercial energy consumption. They range 

from the small shops on the corner to huge retail 

stores of more than 200,000 square feet. Whatever 

the size, the retail industry is in general a highly 

competitive one characterized by slim profit margins, closely watched costs, and smart marketing.

A successful retail store understands and meets the 

needs of its customers. Whatever those needs might 

be, retailers are now seeing that good energy management is a vital part of providing cost-effective, 

customer-oriented goods and services. Many retailers have been looking at more energy-efficient and 

renewable energy technologies and coming to NREL 

for help in using them.

For example, for more than two years NREL has 

been working with one of the leaders in the construction and operation of large-scale retail outlets—

Wal-Mart. Engineers are helping this retail giant 

find the most effective technologies for reducing its 

energy costs. They have been monitoring and evaluating more than 50 different technologies that WalMart installed in its experimental “Supercenter” 

store in Aurora, Colorado. NREL’s analyses determine which technologies are the most effective and 

which are ready to be applied to stores now being 

either built or retrofitted.

As one result of the monitoring, Wal-Mart recognized that using LED (light-emitting diode) lights in 

their refrigerated and frozen food cases achieved as 

much as a 70% energy savings in comparison to the 

energy consumed by fluorescent lights. LED lights 

do this by reducing the amount of installed wattage 

required.

Then, Wal-Mart staff found that adding motion 

sensors to LEDs allows them to program the lights 

so they go on only when a customer is standing in 

front of the door to the refrigerated case. Turning the 

lights off the rest of the time saves a 

significant amount of energy. NREL’s 

work showed this technology to be so 

effective that Wal-Mart is rolling out 

the LED case lighting to 1,000 stores 

nationwide.

NREL’s work with Wal-Mart and 

other retail stores has led to a 

separate, ground-breaking project, the Retailer 

Energy Alliance. As an outcome of retailers’ 

ever-growing recognition of the value of energy 

management, NREL and DOE coordinated the 

formation of this Alliance to aid the retail industry 

in adopting energy-efficient and renewable energy 

strategies and technologies. The retailers who 

joined this Alliance recognize that not one of them 

is large enough by itself to bring about dramatic 

changes in the construction and operation of 

commercial buildings. Together, however, they can 

have an impact not only on the building industry, 

but also on the supply stream of materials used in 

construction.

Remarkably, the 12 companies that initiated the 

Alliance operate 1.25 billion square feet of retail 

store space and include some of the largest retail 

operators in the nation, such as Wal-Mart, Target, 

Food Lion, Whole Foods, Home Depot, Lowe’s, 

and Best Buy. Large retailers tend to build multiple 

structures having the same design. Because of the 

similarities in the design and operation of stores 

among the companies, the Retailer Energy Alliance 

has great potential to implement successful technologies quickly and widely.

Helping Stricken Communities Rebuild 

and Renew

The “renew” part of “renewable” takes on a different 

meaning when it comes to disaster recovery efforts. 

To the cities of New Orleans, Louisiana, and Greensburg, Kansas, it means resolving to start over and 

rebuild with energy efficiency and renewable energy 

Wal-Mart recognized 

that using LED (lightemitting diode) lights 

in their refrigerated 

and frozen food cases 

achieved as much as 

a 70% energy savings 

compared to standard 

fluorescent lights.

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in mind. In both of these cities, NREL has been working with DOE and other federal, state, and local agencies to help people recover and rebuild.

The category 3 Hurricane Katrina and its aftermath 

began devastating 80% of New Orleans on August 

29, 2005, but rebuilding efforts are still going on. For 

Greensburg, the fateful date was May 4, 2007. That 

night a level EF5 tornado, the highest level in the 

National Weather Service classification system, destroyed 95% of the town and changed the lives of its 

1,500 residents forever.

Neither of those disasters has escaped the attention 

of staff at NREL. The laboratory has been providing 

recovery assistance to New Orleans since the fall 

of 2007, when Technology Manager Mary Colvin 

joined DOE officials in visiting the area and then 

began meeting with state and local officials. NREL 

has been managing $1 million in DOE funding 

directed at bringing energy-efficient and renewable energy technologies and expertise to the Gulf 

Coast rebuilding effort. As part of that effort, two 

NREL employees, Joe Ryan and Phil Voss, have been 

placed in New Orleans to provide direct assistance 

to the community.

In Greensburg, NREL has been involved with local 

and state officials, the Federal Emergency Management Agency, and other federal agencies to provide 

resources for energy-efficient rebuilding and greater 

use of renewable energy. The mayor of Greensburg, 

its city council, and the Kansas governor’s office 

have all pledged to rebuild Greensburg as a green 

city. They do not just want to rebuild their community to have energy-efficient buildings, however. 

They also plan to construct a new renewable power 

generation facility, advance the use of renewable 

fuels and vehicles, encourage distributed solar and 

wind power, and establish green industries to bring 

investment and employment to the community.

In fact, NREL assisted the city in writing an ordinance that requires all buildings in excess of 4,000 

square feet to be constructed to meet LEED Platinum 

certification. LEED is the U.S. Green Building Council’s Leadership in Energy-Efficient Design program, 

and platinum is its highest rating. Many projects are 

now reaching for LEED levels on their own.

“A 32-unit townhome project for low-income seniors is going to be LEED Gold certified and very 

cost-effective,” says Lynn Billman, NREL project 

lead. “Everything NREL is doing is based on costeffectiveness. We help them understand real-world 

solid business models for efficiency and renewable 

energy.”

Assistance to Greensburg also includes designing 

strategies for energy-efficient commercial buildings, 

a school, a hospital, and homes; evaluating options 

for renewable power generation and fuels; and 

developing sustainable community strategies. The 

NREL team of staff and contractors has provided 

expertise through a wide range of activities—from 

identifying big-picture efficiency and renewable 

opportunities to leading daily on-the-ground rebuilding efforts and offering energy efficiency training to residents, commercial building owners, and 

builders.

We might say that NREL and its partners are changing the nation’s built environment one building at a 

time—but through its work on new design guides 

and collaborations with military agencies, retail alliances, and entire cities, NREL is finding efficient 

ways to be sure those changes happen to as many 

buildings as possible.

Greensburg, Kansas, 

was hit by an EF5 

tornado on May 4, 

2007, destroying 

95% of the town and 

changing the lives of 

its 1,500 residents 

forever.

When BNIM Architects 

designed this new 

school for Greensburg, 

NREL provided technical advice about the 

use of solar electric 

systems, daylighting, 

and other energy efficiency and renewable 

energy features. 

Credit: Associated Press

Credit: BNIM Architects
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NREL Sows the Seeds 

for a Thin-Film 

Solar Cell Bounty

A crop of new thin-film solar cell companies is now 

gaining prominence worldwide.

 Arecent crop of thin-film solar cell companies is growing in influence in the U.S. solar cell industry, thanks in part to years of care and nurturing by 

NREL.

Solar cells work by capturing photons of sunlight in 

a photovoltaic material, which is generally a semiconductor with at least one loosely-bound electron 

that can be freed from its atom by sunlight within a 

narrow range of wavelengths. Most of today’s solar 

cells are made from wafers of crystalline silicon, 

which is also used in computer chips. But NREL has 

long been involved in the development of alternative 

solar cells made from thin films of semiconductors 

such as amorphous silicon, cadmium telluride, and 

alloys of copper, indium, gallium, and selenium 

known as “CIGS.”

These thin-film solar cells have a number of advantages over traditional crystalline silicon solar cells: 

they use less semiconductor material, so they are 

generally less expensive, and they can be deposited 

rapidly onto a variety of substrates, such as glass, 

stainless steel, or even plastic. And while crystalline 

silicon is used to form individual solar cells, which 

are then assembled into large rectangular modules, 

thin-film manufacturers actually deposit the entire 

module at one time, avoiding some of the labor-intensive assembly that individual solar cells require. 

This provides potential cost savings while allowing 

for a wide range of possibilities for the form of the 

final product.

A perfect example of this wide range of possibilities can be found in the Uni-Solar brand of solar 

shingles, which consist of amorphous silicon deposited onto flexible stainless steel. The solar module is 

encapsulated in a clear plastic to yield a product that 

looks and functions like a shingle but also produces 

electricity.

United Solar Ovonic, a subsidiary of Energy Conversion Devices, Inc., first introduced the Uni-Solar 

shingles in the mid-1990s. The company then 

evolved the product into “peel and stick” laminates 

that can be directly bonded to the roofs of buildings. 

The solar laminates are one of the most popular examples of building-integrated photovoltaic devices, 

that is, solar cells that also serve a structural purpose for the building.

Building an Industry

United Solar Ovonic is also an example of the 

thin-film solar revolution that is now taking place. 

NREL has long supported the research efforts of 

a number of companies that explored each of the 

thin-film technologies in what could be described as 

a friendly competition. At the same time, in-house 

teams of NREL scientists and engineers also tried to 

perfect the technologies. The story of United Solar 

Ovonic (often referred to by its Uni-Solar brand 

name) is one of those cases in which industry pulls 

ahead of a national laboratory while building on the 

laboratory’s breakthroughs.

“In the thin-film area, we had national teams for 

each technology, so there was an amorphous silicon team, and Uni-Solar was the prime industrial 

member in that team,” says Bolko von Roedern, the 

NREL technical monitor for the amorphous silicon 

work. “Historically, for amorphous silicon, the industry group always had the highest efficiencies, 

whereas for CIGS and cadmium telluride, our inhouse groups were the world-record holders. In the 

U.S. amorphous silicon program, Uni-Solar was the 

champion cell maker.”

A key to Uni-Solar’s success was its ability to lay 

down three separate layers of amorphous silicon, 

each tuned to a different frequency of sunlight. This 

created a cell with three active semiconductor layers, 

called a “triple-junction” cell. The top active layer in 

a triple-junction cell captures a portion of the solar 

spectrum, and the remaining sunlight penetrates to 

the second layer, which captures another part of the 

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solar spectrum, and likewise for the third and final 

layer. As a result, the cell converts more of the solar 

spectrum into electricity, achieving a higher conversion efficiency.

But despite its technical leadership, Uni-Solar still 

learned from NREL’s research, particularly when 

it came to material characterization and the techniques for depositing the amorphous silicon onto a 

substrate. For instance, NREL pioneered hot-wire 

deposition, in which a material such as silicon is 

vaporized by a hot wire in a vacuum chamber, and 

the vapor then condenses onto the cooler surface of 

the substrate. Uni-Solar helped NREL to make highefficiency solar cells using this technique.

“NREL developed the hot-wire deposition technology and other deposition technologies, but 

Uni-Solar often collaborated with NREL to achieve 

better results,” says von Roedern.

In 1997, Uni-Solar started up its amorphous silicon 

pilot line, which had the capacity to produce enough 

solar modules in one year to generate 5 megawatts 

of power. In the solar cell industry, this is referred 

to as a 5-megawatt production line, big enough to 

provide 2-kilowatt solar power systems to 2,500 

homes each year. This Uni-Solar pilot line was the 

first significant thin-film manufacturing facility in 

the United States.

The success of Uni-Solar’s pilot line led the company 

to launch its first full-scale manufacturing plant in 

2002. The facility, located in Auburn Hills, Michigan, produces the amorphous silicon solar modules 

using a roll-to-roll process similar to the printing 

presses used by newspapers. As a result, the Michigan production plant had a 25-megawatt production 

capacity, and back then that was big enough to boost 

U.S. solar cell production capacity by 20%. The process handles 9 miles of stainless steel at one time, advancing at a rate of about 2 feet per minute through 

the machine, to deposit triple-junction cells only

1 micron thick.

Uni-Solar eventually increased its production speed 

at the Auburn Hills plant, boosting its annual capacity to about 28 megawatts. In 2007, Uni-Solar added a 

second production line and doubled the plant’s production capacity. Currently, more than 50% of the 

company’s products are used in building-integrated 

applications such as their “peel and stick” roofing 

laminates.

Uni-Solar produced 48 megawatts of solar cells 

in 2007, and the company is now building four 

30-megawatt production lines at a new facility in 

Greenfield, Michigan. When the first line begins 

production in 2008, the company will have an annual production capacity of 88 megawatts, and that 

will quickly grow to 178 megawatts. For comparison, U.S. manufacturing plants produced about 266 

megawatts of solar cells in 2007, so amorphous silicon is having a significant impact on the domestic 

front.

“It has been a dream for a long time,” says von 

Roedern, “and now a dream that has been realized.”

New Competition Arises

Uni-Solar and other manufacturers have achieved 

significant results for amorphous silicon solar cells. 

At the same time, NREL’s work with the other thinfilm technologies, CIGS and cadmium telluride, 

has triggered new industries that are growing even 

faster.

Their current growth is particularly impressive 

when you consider the humble beginnings of today’s leading companies. For CIGS, for instance, 

Global Solar Energy is currently the largest manufacturer depositing CIGS thin films onto a flexible 

substrate. But when NREL started working with 

Global Solar back in 1996, the company had a much 

lower profile.

“Global Solar was a spin-off from ITN Energy 

Systems, of Littleton, Colorado, which was also 

United Solar Ovonic 

is using a process 

similar to newspaper 

printing to deposit 

solar cells on long, 

flexible rolls of 

stainless steel.

This United Solar 

production line 

in Auburn Hills, 

Michigan, has the 

capacity to produce 

28 megawatts of 

solar modules in 

one year.

PIX15778
19 2007 Research Review | Large-Scale Deployment

supported by NREL,” says Harin Ullal, the lead 

project manager for NREL’s work with the CIGS and 

cadmium telluride industries. “They basically had 

a building with four walls when we gave them the 

contract. We helped them get started developing the 

technology for CIGS.”

NREL developed a laboratory procedure to produce 

CIGS solar cells with 19.9% conversion efficiencies 

using glass as a substrate. Global Solar licensed the 

technology from NREL and is using the same procedure, but is instead depositing the coating on flexible stainless steel in a roll-to-roll production process.

Global Solar started in Tucson, Arizona, with a 

4-megawatt pilot line. In early 2008, the company 

opened its first full-scale manufacturing line, which 

has a capacity of 40 megawatts. The company is 

also building a 35-megawatt manufacturing plant 

in Berlin, Germany, and it plans to establish a new 

100-megawatt manufacturing line in Tucson by 2010.

“NREL has been a steadfast partner to Global Solar 

throughout the changes that have occurred in our 

company and industry,” says Jeff Britt, chief technology officer for Global Solar. “The technical support from NREL has led us in new directions and 

provided capabilities we could not find anywhere 

else in the world. In particular, their work on highefficiency CIGS solar cells and the transfer of that 

know-how has directly benefited our production 

line.”

“Firsts” from First Solar

But NREL’s biggest thin-film success to date is its 

work with First Solar, Inc. This manufacturer of cadmium telluride solar modules started out as a small 

company called Solar Cells, Inc.

“We started working with Solar Cells, Inc., way back 

in 1991 when they were about a six-person operation, almost a garage-type operation, on the campus 

of the University of Toledo in Ohio,” says Ullal.

NREL’s 

Solar 

Research 

Garners 

Awards

Decades of innovative research in solar cell 

technologies has led to prestigious, internationally 

recognized awards for NREL researchers in 2007. 

Researchers Sarah Kurtz and Jerry Olson received the 

Dan David Prize for their years of research, and in 

particular, their development of the multi-junction 

solar cell. The researchers shared the $1 million prize 

for their “Quest for Energy” with climate researcher 

James Hansen of the NASA Goddard Institute for Space 

Studies. Sarah Kurtz directed her share of the prize 

toward a trust that will support concentrating solar cell 

development at the University of California, Merced.

In addition, Lawrence 

Kazmerski, the head of the 

National Center for Photovoltaics 

received the 2007 Karl W. Böer 

Solar Energy Medal of Merit. The 

Böer medal and a cash award 

of $40,000 is given every two 

years to an individual who has 

made significant pioneering 

contributions to the promotion of solar energy. 

Kazmerski plans to use the award to establish a trust 

that supports graduate student research using NREL’s 

new Process Development and Integration Laboratory.

Last but not least, NREL earned an R&D 100 award in 

2007 for its work with Spectrolab, Inc. to develop a 

triple-junction solar cell that exceeded 40% conversion 

efficiency. The cell uses an innovative approach to 

combine layers of semiconducting materials with 

different lattice spacing in their crystal structure, a 

technical challenge that previously resulted in cells 

with significant defects, which limited their efficiency 

and durability.

Sarah Kurtz and Jerry Olson

Lawrence Kazmerski

PIX15760

PIX14909
2007 Research Review | Large-Scale Deployment www.nrel.gov/research_review/ 20

NREL was attracted to the company because it employed some experts from the glass industry as well 

as an expert in cadmium telluride technology. Solar 

Cells, Inc. was focused on depositing cadmium telluride on glass, forming rigid solar modules similar 

in appearance to solar modules made from crystalline silicon solar cells.

“We supported Solar Cells, Inc. in their early years 

through joint research projects, and after a couple 

of years or so, they produced their first prototype 

module, which was rated at an efficiency of 6% or 

so,” says Ullal.

Solar Cells, Inc. kept making steady progress and 

eventually started a pilot line with a capacity of 

about 2 to 3 megawatts. In 1999, private investors 

formed the First Solar company as a joint venture 

with Solar Cells, Inc., and later bought out Solar 

Cells’ stake in the company. In its early years, First 

Solar developed a range of novel technologies to 

make it easier to manufacture their thin-film-onglass solar modules. Along the way, the company 

continued to collaborate with NREL.

“We’ve worked with them quite closely,” says Ullal. “For example, we’ve done a lot of measurements 

and characterizations of their materials, and we’ve 

helped them with NREL’s technical knowledge. 

We’ve also helped them through testing their modules and systems at our outdoor test facilities.”

First Solar launched a plant in Perrysburg, Ohio, that 

started with one production line and soon expanded 

to three production lines, each designed to produce 

25 megawatts of solar modules per year. Today, each 

of those lines has been expanded to 45 megawatts, 

for a total of 135 megawatts of U.S. production capacity. The company has also improved the conversion 

efficiency of its solar modules to 10.6% while cutting 

its manufacturing costs from $2.96 per watt in 2003 

to $1.14 per watt today.

“NREL expertise played a key role in helping First 

Solar get established in its early days,” says David 

Eaglesham, vice president of technology at First 

Solar. “NREL plays a very crucial role for the 

photovoltaic community in the United States and 

provides invaluable expertise and learning for companies getting started in this business.”

First Solar now operates a manufacturing plant in 

Germany with four lines, for a total of 180 megawatts, making it the largest U.S.-based manufacturer of solar cells and the world leader for thin-film 

solar modules. The company is now the world’s 

fifth-largest manufacturer of solar cells, producing 

206 megawatts of solar cells in 2007.

First Solar is also constructing four new manufacturing plants in Malaysia, each one featuring four 

45-megawatt production lines. Once those plants 

begin operating, the company’s total production 

capacity will exceed 1,000 megawatts per year. For 

comparison, about 3,700 megawatts of solar cells 

were produced globally in 2007.

“It’s an amazing story,” says Ullal. “NREL and DOE 

can really be proud of those accomplishments.”

The company’s manufacturing growth is indeed 

impressive, but it was its financial performance that 

drew the world’s attention in 2007. The company 

Global Solar Energy 

is currently the largest manufacturer 

depositing CIGS thin 

films onto a flexible 

substrate.

In early 2008, Global 

Solar Energy opened 

its first full-scale 

manufacturing line, 

which has a capacity 

of 40 megawatts. 

PIX15764 PIX15763
21 2007 Research Review | Large-Scale Deployment

launched its initial public offering in late 2006 and 

garnered more than $400 million in investments. 

Then in 2007, its stock went up by a factor of 8, making it the top one-year performer on the Wall Street 

Journal’s Shareholder Scoreboard.

While NREL can’t take credit for the company’s financial success, that success is built on the cadmium 

telluride technology that NREL helped develop. 

With a number of companies now successfully manufacturing solar modules using the three main thinfilm technologies, NREL has undoubtedly helped to 

bring the nascent thin-film solar industry to life. But 

rather than resting on its laurels, NREL continues to 

work with new companies that are bringing fresh 

ideas to the thin-film solar cell industry.

The current CIGS manufacturing roster includes 

HelioVolt, which plans to build a 20-megawatt plant 

in Austin, Texas, in 2008; Ascent Solar, which plans 

to construct a 25-megawatt production line near 

Denver, Colorado, by 2009; and SoloPower, Inc., 

which is using electrodeposition to build CIGS solar 

modules on flexible thin-film substrates. SoloPower 

is in the process of building a 20-megawatt manufacturing plant in San Jose, California.

For cadmium telluride, the roster includes AVA Solar, which plans to begin pilot production in northern Colorado in 2008, and PrimeStar Solar, which 

has entered into a cooperative research agreement 

with NREL. It’s worth noting that General Electric 

Company has also made a significant investment in 

PrimeStar Solar.

The future of thin-film solar cell manufacturing 

looks promising indeed, as former start-ups are becoming manufacturing giants, while a new crop of 

start-ups hope to inject added competition into the 

rapidly growing field.

First Solar, Inc. 

is NREL’s biggest 

success to date with 

the manufacture of 

thin-film solar cells.

PIX08730

PIX10751

Engineer Keith Emery checks the 

performance of an array of First 

Solar modules at NREL’s Outdoor 

Test Facility. The facility has 

allowed First Solar and other 

solar manufacturers to test the 

long-term reliability of their 

solar modules when exposed to 

the elements.
2007 Research Review | Investing www.nrel.gov/research_review/ 22

Investing in Energy 

for the Future

NREL innovations along the pathway to commercialization are 

gaining momentum—expanding R&D partnerships with industry, from 

start-up companies and entrepreneurs to Fortune 500 companies.

 As investments in clean energy continue to grow at record-breaking numbers, efforts to move 

NREL innovations along the pathway to commercialization are gaining momentum. These efforts are 

encouraging and expanding R&D partnerships with 

industry—from start-up companies and entrepreneurs to Fortune 500 companies—and will continue 

along that path in the future.

Through the DOE Technology Commercialization 

Deployment Fund (TCDF), NREL received $4 million in fiscal year 2008 to facilitate collaborative projects between researchers and industry to develop 

commercial products based on NREL innovations. 

Commercial partners share 50% or more of the project development costs, which will typically range 

from $150,000 to $1 million.

TCDF projects are selected based on their fit with 

the program, the value of NREL’s intellectual property, and the potential for near-term commercial impacts. Project proposals can be submitted by either 

NREL researchers or our industrial partners, and 

once funded, the projects can move ahead quickly. 

NREL’s first TCDF project moved from first contact 

with the start-up company to a funded project in 

only 17 days.

“The TCDF Program gives us some wonderful tools 

to address the commercialization ‘valley of death’ 

that exists between technologies at the laboratory 

and products in the private sector,” says Tom 

Williams, NREL technology transfer director.

To further address the commercialization “valley of 

death,” NREL has two other new programs that leverage the business creation skills of the private sector. The first is the DOE Entrepreneur-in-Residence 

Program, which involves placing an entrepreneur at 

the lab to identify opportunities for spin-off companies based on NREL-developed technologies. In February 2008, DOE selected the venture capitalist firm 

Kleiner Perkins Caufield & Byers, which will identify and sponsor an entrepreneur to work at NREL. 

The program is also being piloted at DOE’s Oak Ridge and 

Sandia national laboratories.

The second program is the 

Commercialization Mentor Program, which offers 

seasoned business professionals an opportunity to 

provide a short-term contribution to NREL’s commercialization efforts. These commercialization 

mentors, who are NREL employees during their 

time at the laboratory, are working alongside the 

lab’s technology transfer staff as they evaluate new 

innovations for commercialization opportunities, 

allowing the mentors to share their commerical experience with NREL staff.

NREL also provides encouragement to clean energy entrepreneurs from outside the lab, who will 

receive feedback on their business plans from investors and energy experts at NREL’s 21st Industry 

Growth Forum on October 28-30, 2008, in Denver, 

Colorado. NREL’s Industry Growth Forum is considered the premier forum on clean energy investment. Companies participating in five of the most 

recent forums have collectively raised more than 

$1.2 billion to start up their businesses. Demonstrating industry’s support of clean energy innovations, more than 430 participants attended the 20th 

Forum.

“When people look back at the 21st Century’s greatest inventions, renewable energy technologies will 

be on that list,” said John Denniston, a partner with 

Kleiner Perkins Caufield & Byers, at NREL’s 20th 

Industry Growth Forum.

After an NREL-developed technology is licensed, 

the work doesn’t necessarily stop there. NREL 

researchers often continue to work with industry 

partners on ways to improve the technologies, 

such as increasing their performance and lowering 

manufacturing costs. This starts the innovation 

process all over again, making it another 

beginning, not an end.

Colorado Governor 

Bill Ritter spoke to 

investors and energy 

experts in support of 

NREL’s 20th Industry 

Growth Forum in 

November 2007.

PIX15762
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Notice

This report was prepared as an account of work sponsored by an agency of the 

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thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that 

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