Driving Solar Innovations from Laboratory to Marketplace

Driving Solar Innovations from Laboratory to Marketplace

Disruptive innovation is making solar cost competitive with non-renewable energy.

Photo of a satellite in space showing a wide solar panel with the sun in the background in the upper right and the crescent moon in the background on the lower left. Enlarge image

The success of Bell Laboratory's solar-powered satellite technology provided a foundation for worldwide commercialization.
Courtesy of NASA

Few would have thought in the 1970s that U.S. military-funded core technologies would someday lead to the internet. Or that a solar photovoltaics (PV)-powered satellite would give rise to the technology that powers all of our modern wireless communications. The idea of transferring technology from laboratory to market is nothing new.

As a U.S. Department of Energy (DOE)-funded renewable energy research laboratory, the National Renewable Energy Laboratory (NREL) serves a unique role of developing promising technologies past the high-risk stage of nascent research, to the point where private companies can take them to market.

"Most companies cannot invest in research that could be a decade away from a commercial product," said NREL's Associate Laboratory Director of the Innovation Partnering and Outreach Directorate Bill Farris. "We have the facilities and the expertise to address the fundamental scientific questions and to accelerate the pace of these innovations—but it takes commercial partners to build the concepts at a manufacturing scale."

Accelerating the pace of transfer from lab to marketplace is a key component of DOE's SunShot initiative, which aims to make solar power cost competitive with traditional sources of electricity by the year 2020. With several trillion dollars at stake worldwide, SunShot aims to strengthen the United States' position in the global clean energy race, fostering competition among the most promising innovators and technologies.

Since its early beginnings, PV has grown to be a serious contender among the world's sources of electricity with a steady evolution that has raised efficiencies and reduced system costs. But to compete with entrenched and commoditized incumbents, it must find more disruptive, or groundbreaking, advancements while weathering an economy that has challenged investment and manufacturing.

The Clean Energy Race

Photo of two workers wearing hardhats exchanging tools during installation of a panel of thin-film photovoltaics. Enlarge image

NREL's partnership with a number of thin-film PV companies have supported tremendous growth in the industry.
Credit: Dennis Schroeder

In the 35 years since its inception as the Solar Energy Research Institute, NREL has gained worldwide recognition for its work addressing the challenges unique to the energy sector. Its solar research has yielded 34 solar cell conversion efficiency records, 153 issued patents, and thousands of contributions to peer-reviewed science journals. The laboratory has also driven key discoveries in solar cell materials, devices, fabrication, characterization, and production.

By performing basic research and development (R&D), NREL works to bridge the energy sector's first unique barrier, known as the "technological valley of death." This is the phase when investments in time and capital are needed to prove the market viability of a promising technology. NREL also helps bridge the later barrier, known as the "commercialization valley of death," by supporting industry partners in scaling up technology to attract private funding for manufacturing.

Farris likened the clean energy race to the Olympic 4 x 100 sprint relay—the transfer of baton from one runner to the next is a brief but critical part of the race. "For several meters, the two race hand in hand, but there has to be a well-executed handoff. We establish the momentum, but the commercialization partner has to finish the race, and they ultimately do the work of building a business around the technology."

A Progression of Technologies

A photo of two men wearing suits and ties displaying a small gray panel of cadmium telluride-coated photovoltaic material. Enlarge image

An early prototype of a CdTe module developed by NREL and Golden Photon in 1991

Throughout the lab, scientists and business staff alike are eager to see their technologies leave the nest. The technologies are not pitted against each other, but instead, progress on different tracks depending on their maturity. Technologies considered to be evolutionary, such as crystalline silicon (Si), comprise most of today's PV. For the past several decades, NREL has also advanced second-generation technologies such as thin-films made from amorphous silicon (a-Si), copper, indium, gallium, and diselenide (CIGS), or cadmium telluride (CdTe). These technologies have the potential to be disruptive—that is, with continued improvements to cost and efficiency, they could help meet our energy needs and targets for over the next five to ten years, or beyond. These types of changes are much like going from corded telephones to wireless cell phones or from laptop computers to tablets.

NREL also advances high-efficiency III-V multijunction technologies, including inverted metamorphic multijunction (IMM) cells that have the potential to bring revolutionary changes in the more distant future. Changes of this magnitude are akin to moving from megahertz computer processors to gigahertz processors.

How Do You Measure Industry Impact?

As part of the "Startup America" initiative supporting high growth entrepreneurship, President Obama in 2011 issued a directive to foster innovation by increasing the rate of technology transfer and the economic and societal impact from federal R&D investments.

In 2009, NREL began working to spur clean energy entrepreneurship by increasing the number of CRADAs, patents, licensing transactions, rewards to inventors, and innovations transferred to the private sector. NREL's innovative output increased dramatically and in 2011 alone NREL generated 134 invention records, 55 filed U.S. patents, 16 issued patents, and 21 royalty-bearing commercial licenses. NREL's solar research portfolio represents approximately a third of the laboratory's overall inventions and more than half of the commercial licenses.

NREL's Innovation Spectrum at Work

Among NREL's many innovations, one that demonstrates the lab's proficiency in transferring technology from research through commercialization and into large-scale deployment is cadmium telluride (CdTe). Thin film technology is highly valued by private investors because it uses less semiconductor material than silicon solar cells and can also be quickly deposited onto various glass, metallic, or even plastic substrates, providing both cost and production advantages.

When the project started in 1990, CdTe was considered suitable for thin-film PV because it was a semiconductor with a band gap of around 1.5 eV, which closely matches the terrestrial solar spectrum for optimum conversion efficiency. This meant that it could absorb more of the spectrum of the sun's energy, which allowed it to convert more than 10% of the sun's energy to electricity—a threshold that made it attractive to explore for manufacturing.

In 1991, NREL and Golden Photon earned a prestigious R&D 100 Award from Research and Development (R&D) Magazine for the development of a CdTe PV module manufacturing process. Over the next several years, NREL's collaborations with the industry to further develop CdTe seeded technology and process improvements alike.

"In the early years, our primary goal was to understand all the roadblocks the industry was encountering," said Principal Scientist Tim Gessert. "We visited the sites to learn about the challenges and there were many first meetings. Sometimes, we would simply help the companies understand what kinds of skills and expertise they needed to bring onboard."

By 1996, Golden Photon was able to provide the U.S. Navy with a 25-kW array of CdTe modules, which at the time, was the largest CdTe array in the world. Another early partner, Solar Cells, Inc., proved a thin-film cost structure that gave rise to more than a dozen start-up thin-film PV companies. This ultimately led to the creation of First Solar LLC, a leading worldwide PV manufacturer that uses CdTe technology optimized at NREL.

A photo of a bearded worker, wearing safety goggles, hardhat and work gloves, carrying a panel of CdTE-coated glass. Enlarge image

A First Solar associate handles photovoltaic materials at the company's Ohio manufacturing plant
Courtesy of First Solar

In 2003, First Solar installed CdTe modules at NREL's Outdoor Test Facility for long-term, outdoor performance monitoring. The company also enlisted NREL's deposition expertise to aid their efforts to improve light transmission into the electrical junction, thereby forming lower cost and higher efficiency thin-film modules.

Together, NREL and First Solar developed a unique process for manufacturing high-efficiency thin-film CdTe cells on low-cost commercial soda-lime glass. The process, which quickly deposits uniform layers of semiconductor material for photovoltaic (PV) modules, won a 2003 R&D100 Award and was considered a significant milestone in the race to produce cost-competitive solar energy.

NREL's research team also explored transparent conducting oxides (TCOs), which are doped metal oxides used as a front electrical contact in thin-film devices. By optimizing the light transmission through the TCOs, NREL was able to boost the cell efficiency to set a new CdTe cell efficiency record of 16.7%.

Commercialization and Deployment—Impacts on a Global Scale

A diagram showing the breakdown of materials layered onto glass in the cadmium telluride process. Layers from top to bottom are glass, SnO2Cd4Sn04, CdS, CdTe, and C-Paste with Cu or Metals. Enlarge image

A CdTe thin-film PV device showing the layers that are deposited onto a glass superstrate that allows sunlight to enter.
Illustration by Al Hicks

CdTe's increasing cell efficiency was a large driver behind the formation of PrimeStar Solar, a company that participated in the PV Technology Incubator program. In 2007, NREL signed a Cooperative Research and Development Agreement to allow PrimeStar to transition NREL's CdTe technology to commercial production and PrimeStar also received a $3 million incubator award to commercialize its low-cost PV panels. In 2011, PrimeStar was acquired by General Electric (GE), which had made large investments in the company since 2008. The acquisition accelerated the pace of commercialization and represented a key step in GE's plan to build a large-scale solar PV module plant in Colorado.

As it has matured, CdTe technology has achieved many additional milestones. First Solar has used the technology to produce 1 GW of PV modules in 2009, and more than 6 GW of modules to date. It also set world records for CdTe PV cell (17.3%) and PV module (14.4%) efficiency, all of which NREL has certified.

In 2012, First Solar installed its 10 millionth PV module in the 550 MW Desert Sunlight Solar Farm project in Riverside County, California. The project is part of a 2.7-GW pipeline of utility-scale projects in the U.S. and is expected to support 7,000 construction and supply chain jobs over several years. When completed in 2015, the project will be one of the two largest solar PV projects in the world.

Fundamental Science—Getting Back to Basics

In some ways, cadmium telluride has been described as a victim of its early success. Gessert explained, "It showed its potential very early compared with other technologies, so most of the resources went to figuring out how to scale it up, rather than on its fundamental properties." At the same time production was increasing, laboratory cells found only incremental increases in conversion efficiency due to limits in the material's open circuit voltage and fill factor.

In 2012, a DOE-sponsored NREL workshop convened industry, academia, and the national laboratories to discuss scientific research avenues for disruptively increasing CdTe efficiency toward a goal of 20% efficiency with processes and materials that can achieve the SunShot cost goal of less than $0.50 per watt.

Today, NREL's CdTe team, led by Principal Scientist and Thin-Film PV Group Manager Rommel Noufi is leveraging years of thin-film PV materials and devices expertise to perform the research needed to understand the material's fundamental limitations on the solar cell performance. This research aims to identify the mechanisms that limit the open circuit voltage and fill factor of CdTe PV devices and advance new processes and device designs. By addressing existing limitations to enable dramatic increases in conversion efficiency, the team is undertaking the market-relevant research needed to help solve the challenges of today's thin-film PV manufacturing industry.

Toward a Multi-Terawatt Future

The DOE SunShot Initiative's goal of reducing the installed cost of solar energy systems by 75% by the end of the decade calls for photovoltaics (PV) improvements in three main areas: solar-cell efficiencies, material processing costs, and scalability to terawatt (TW or 1012 W) levels.

According to the SunShot Vision Study the global PV market has grown at average annual rate of 53% over the past decade, with PV shipments reaching 17 gigawatts (GW) in 2010. Thin-film technologies are growing rapidly within this market, due to successes in reducing costs and advancing production.

With the rapid project growth comes the challenge of ensuring the glass industry can meet the increasing demand. Because glass is a key component of CdTe thin-film systems, NREL scientists have joined with large glass manufacturers to explore different glass compositions that may have ideal interactions with the chemical and electrical properties of the solar cells.

One large specialty glass manufacturer, Corning Inc., has called on NREL to analyze the thermal and diffusion properties of glass with multiple different compositions and the ways that chemicals diffuse differently into solar cells. "We've had a very productive CRADA with Corning," Gessert said. "They were interested in ways to tailor glass to PV applications, and through our ongoing work with them, we were able to demonstrate cells fabricated at the higher temperatures needed for PV."

While thin-film technologies currently comprise a very small percentage of the world's PV production, they have been growing at a rate of more than 35% each year. "Fast growth sneaks up on you," Gessert explained. "PV production is doubling every two years, and with this type of growth, by 2018, more than half of the glass made worldwide could go into a product that is just a blip on the chart today."

Reflecting on NREL's achievements in past decades and the amount of work left to do improving costs, efficiency, and processes to enable large-scale solar adoption across America, Gessert put the mission in an even larger context. "It took about 135 years to put the world's electricity infrastructure together. Replacing it in the next 35 years is no small task."

Learn more about NREL's photovoltaics research.

Learn more about NREL's Spectrum of Clean Energy Innovation and how the laboratory's capabilities emulate the nature of the innovation process.

— Molly Riddell

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