Feature Article: Streamlining Solar Technology

05/31/2011

This article first appeared in Solar Today

by Mike Koshmrl

With 1000 "little cuts", SunShot aims to drop solar costs 75% in less than 10 years.

It's easy to be skeptical about the Dept of Energy's (DOE) SunShot Initiative. The goal, installing utility-scale solar at $1 per watt by 2020, would bring solar costs down to 6 cents per kilowatt-hour (kWh), roughly the cost of coal-fired electricity.

The name, SunShot, is a play on President Kennedy's 1961 pledge to land a man on the moon by the end of the decade. DOE Secretary Chu announced the $27 million program in February, the funds for which will be spread among nine companies. How can $27 million make such a big impact?

To achieve $1 per watt, the solar industry needs to streamline in a big way. It will need considerable module efficiency gains and slashed costs for installation, operations and maintenance and all other system components. Photovoltaic (PV) modules will need to come down 70%, inverters 55% and construction-related costs nearly 75%.

"We'll get there," says Frank van Mierlo, CEO of SunShot grant recipient 1366 Technologies. "Look at the historical cost curve of solar. The production costs come down 10% every year."

At 1366, van Mierlo and fellow co-founder Emanual Sachs are working to commercialize a method for manufacturing crystalline silicon wafers that halves the need for hyper-pure silicon. The process, which virtually eliminates silicon waste (about 50% is currently lost), sets the stage for a dramatic wafer price drop. "If the total installed cost is going to be $1, that means wafer costs have to come down to about $0.25, from $1 today.," says van Mierlo. "And I think it's extremely doable. We're just one of many companies working on this, and our technology alone will take one of the largest cost components and slash production costs by a factor of three - at least."

Here's a closer look at what four of the SunShot grant recipients are doing to help achieve these results.

PPG Industries
Target: Thin-Film Efficiency, Durability

Thin-film PV technology has its advantages - it's lightweight, production is relatively cheap and simple, and it's not silicon-dependent.

Durability, however is a disadvantage right now. Until nanotech companies make headway on a durable, exposed cell, commercial thin-film modules will continue to require robust encapsulants.

As First Solar and other thin-film manufacturers began to ramp up, that need caught the attention of PPG Industries, a Pittsburgh-based glass and glass-coating maker with roots in the 19^th century. PPG's contribution actually predates the industry: Back in the 1930s, the company pioneered the first low-iron glass. Now, backed by $3.1 million in SunShot funding, PPG is working to perfect a glass encapsulant for modules made with cadmium telluride (CdTe) - the most advanced thin-film technology in mass production.

PPG will try to maximize CdTe module efficiency by pulling three innovations onto their high transmission glass. "About 4.5% of the sun's energy is lost on the outside of the module," says Jim McCamy, PPG's manager of solar technology. "By reducing losses from reflectivity, we're increasing the number of watts. By creating better conductive layers, we improve the number of watts."

The new encapsulants, still unnamed, will separate the first layer of CdTe from the underlying transparent conducting oxide (TCO) glass substrate with a buffer layer. A third component, an anti-reflective coating, will be applied to the module front side over the TCO glass. "These technologies exist, but they've never been combined," McCamy says. Research is taking place at PPG's research center outside Pittsburgh, at Colorado State University (whose research formed the basis for Abound Solar's CdTe technology), and at Oak Ridge National Lab in Tennessee.

During a 2009 First Solar conference, glass was named as the CdTe industry's single largest cost component. Two years later, CdTe is providing the best value proposition for utility-scale PV developers.

1366 Technologies
Target: Silicon Wafer Manufacturing, Expense

For all the hype over thin-film's future dominance of the solar industry, crystalline-silicon technologies still account for 80% of the global market.

Silicon's everywhere - it's the second most common element in the earth's crust and is found in everything from iPhones to your favorite lager. But when refined into hyper-pure silicon, necessary for wafer manufacturing, it costs around $350 per kilogram.

In North Lexington, Mass., cleantech innovator 1366 Technologies is planning to slash that expense for module manufacturers through its Direct Wafer manufacturing process.

Besides attracting $3 million from Sunshot and $4 million from Advanced Research Projects Agency-Energy (ARPA-E), 1366 has secured backing from GE, VantagePoint Venture Partners and Hanwha Chemical. In total, $46 million is being committed to help commercialize Direct Wafer technology.

Co-founder van Mierlo likens the manufacturing breakthrough to the Bessemer process, the steel mass production process that was the foundation for the Carnegie fortune. Direct Wafer reduces wafer production steps from four to one by fashioning wafers directly from molten silicon. The process eliminates silicon waste by negating the need for sawing and grinding hardened silicon.

Relative to legacy technology, Direct Wafer is thousands of times faster post-melt, four times more capital efficient and uses just half the amount of silicon. "We eliminate the waste and we streamline the product," says van Mierlo. "That's where we get our cost savings."

To meet SunShot's goals, 1366 is trying to bring down the cost of silicon wafers from $1 per watt today to 25 cents. "You never know until the factory's built, but from a technical viewpoint, we've met that goal," he says.

As soon as 1366 completes engineering and construction of its high speed manufacturing machine, it will break ground on a 100 MW demonstration plant - by as early as year's end. The plan is to scale up to a gigawatt plant. "Everything we see now leads me to believe we can do this," he says.

3M
Target: Thin-Film Installation Costs, Versatility

A number of roofing companies now partner with installers to provide building integrated PV (BIPV) systems that low-lying, lightweight, non-penetrating and - depending on your preferences - more physically attractive. Copper-indium gallium (di) selenide (CIGS) thin-film technology is on the cutting edge of this expanding niche market.

In the past, CIGS module manufacturers trying to tailor a product to the BIPV market have been restricted by the limited availability of flexible polymer encapsulants, used in lieu of conventional rigid glass encapsulants. No manufacturer has mass-produced a proven polymer based product for CIGS panels - anything that's made its way onto a rooftop came off a pilot manufacturing line.

Now, propped up by $4.4 million in SunShot funding, 3M is planning to scale up and fill that hole. The Minnesota-based company is on schedule to begin mass production of a multi-layer, fluoropolymer-based encapsulant early next year, leading the thin-film industry's shift toward versatile, flexible modules.

"3M has been working on this for over a decade," says Arnie Funkenbusch, thin-film solar program manager. "But it's only recently that we've begun to focus on the solar application." For years, 3M's flexible polymer films have been used in organic light emitting diodide displays, found on cell phones and other hand-held electronic devices. In adapting its film for the solar industry, 3M has laser-focused its research on improving weatherability. "Unlike with electronics, in a solar application our film is subject to sunlight and temperature extremes," he adds.

Manufacturing of a first-generation film, Ultra Barrier Solar Film, is underway at a pilot line in Minnesota, and what's been produced to date has been sold to CIGS module manufacturers. The final product will be tweaked slightly, Funkenbusch says, as accelerated life-time testing is still underway at National Renewable Energy Labs.

Using feedback from NREL and the CIGS module manufacturers, Funkenbusch expects the redesign to have increased light transmission, better durability and lower cost. "We want to make sure we

have a product that lasts 25 years," he says. "That's where SunShot helps us out."

The new manufacturing line will be at an existing 3M factory in Columbus, Missouri. According to the Columbus Daily Tribune, the line will add 120 solar jobs to a plant that's shed jobs for years.

Construction of the line is underway and production Construction of the line is underway and production is set to begin in early 2012. There are indications that CIGS module manufacturer

SoloPower, which recently secured a $197 million DOE loan guarantee for a new factory in Wilsonville, Oregon, will be the first customer.

Varian Semiconductor
Target: IBC Cell Production, Cost

Recent NREL tests have measured SunPower's interdigitated-back-contact solar (IBC) cells at the highest conversion efficiencies to date. The only factor preventing SunPower's technology from becoming the industry standard is cost.

The principle is very simple: IBC cells eliminate frontside metallic conductors, which typically cover 5-8% of the physical surface of a wafer. Move the wiring to the backside, more sunlight gets absorbed, and cell efficiency spikes.

"Currently, IBC solar has the highest efficiencies, but it's very expensive to make," says Jim Mullin, general manager for solar products at Varian Semiconductor. "In solar manufacturing, every step adds cost, adds complexity, and can result in potential yield loss." In Gloucester, Mass., Varian is using $4.8 million in SunShot funding to develop an ion-implant tool that promises to slash the number of manufacturing steps from 21, necessary in the IBC process today, to eight.

Ion implantation is far from a novel concept - implanters are integral to semiconductor device fabrication and have long been used to make computer chips. Varian's been selling the tools to the electronics industry since 1975 and has an ion implanter, the Varion Solion, for conventional PV cells that's already running in high-volume production. SunShot backing will be used to redesign the Solion so that it can to do backside wafer patterning necessary for IBC cell production.

"We're the first ones to do this," Mullin says. "We are in a unique position because we're the only ones that can do it without impacting the tool's productivity - because we own the intellectual property."

Mullin says that Varian has matched its DOE funding with internal investments well north of $20 million. He expects the tool to be commercially ready within three years.

It's unclear how much the reduction in production complexity will reduce IBC costs, however. Module manufacturers have some ground to make up before IBC solar is cost-competitive with other PV technologies.

SunPower is the only company commercially producing IBC modules today and is operating at a production cost of around $1.70 per watt, while Chinese crystalline-silicon manufacturers are producing at about $1.20 per watt, and First Solar, a CdTe thin-film manufacturer, is now down below the $0.75 mark.

NREL Incubator Program

Not all SunShot funding is going toward projects at 1366 Technologies, 3M, PPG, Varian Semiconductor and Veeco, a fifth recipient. Another $7 million is being injected into the National Renewable Energy Lab's Photovoltaic (PV) Technology Incubator program.

Started in 2009, the incubator program is primarily tasked with hastening nascent PV technologies' transition from the drawing board into the lab. There are two funding tiers: The first supports development of commercially viable prototypes; the second helps companies scale up to the pilot-project manufacturing stage.

SunShot funding targets four companies:

Tier One

Caelux (Pasadena, CA) - $1 million: developing a flexible PV-manufacturing process that minimizes the amount of semiconducting material used.

Solexant (San Jose, CA) - $1 million: developing a new printable nanoparticle thin-film ink from common nontoxic substances.

Stion (San Jose, CA) - $1 million: developing a technology consisting of two stacked high-efficiency thin-film devices, offering improved absorption of light.

Tier Two

Crystal Solar (Santa Clara, CA) - $4 million: commercializing single-crystal silicon wafers, four times thinner than standard cells.

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This article first appeared in Solar Today, a SustainableBusiness.com Content Partner. Read the digital edition of the full magazine.