E-Gang: A Trick Of The Light

On The Cover/Top Stories
A Trick of the Light
Elizabeth Corcoran 09.03.07

For Christiana Honsberg and Allen Barnett, the pot of gold isn't at the end of the rainbow. It's in ripping the rainbow apart to make the world's most efficient solar cells.

In late July University of Delaware researchers Honsberg, 40, and Barnett, 67, set a world record for solar efficiency, converting 42.8% of the sun's radiation into electricity with their prototype cell. That's almost three times as efficient as commercial solar cells. "We think we can do 50%," says Barnett. He and Honsberg are working to build practical devices by 2010, with support from the U.S. military and an industrial group led by DuPont.

The first crushing problem they aim to solve is lightening a soldier's load. Soldiers are walking power supplies, lugging 20 pounds of batteries that last barely a week. Two years ago the Defense Advanced Research Projects Agency challenged researchers to create an affordable, rechargeable solar cell, about the size of a postage stamp, which could crank out a half-watt of power.

Honsberg and Barnett were eager to try; it would be their first joint project in almost 20 years. Honsberg first worked on solar cells in the mid-1980s as an undergraduate at the University of Delaware, in Barnett's lab. After earning her doctorate, she wound up at Australia's renowned photovoltaics center at the University of New South Wales. Barnett went into business, spending 14 years running solar power company AstroPower. The company fell into financial turmoil. Barnett resigned and returned to the Newark, Del. campus in 2003. A year later ge bought the assets. When Barnett went looking to staff up a solar research program, Honsberg topped the list of recruits.

Honsberg and Barnett knew that one of the most efficient solar cell designs was a sandwich of three different photovoltaic materials, each of which is triggered by a different wavelength (or color) of light. But to make those photovoltaic stacks researchers must force the crystal structure of one material to match another--a difficult and costly task.

Why struggle with single structure, asked Honsberg, when you could let the constituent parts operate independently?

Honsberg and Barnett proposed a device that uses a concentrator lens to focus light. Another device splits it into colors that are aimed at the various photovoltaic materials. High-energy (short-wavelength) photons are absorbed by one compound semiconductor; mid- and low-energy photons are bounced to other solar materials, such as gallium arsenide and silicon. They figure their device can use as many as six materials, and they can mix and match from among the best or cheapest. No other solar cell design lets engineers swap different materials in and out to balance costs and efficiency, points out Douglas Kirkpatrick, the Darpa manager overseeing the project.

The Delaware lab has built a few dozen experimental solar cells; they can be from 1 to 10 square centimeters. Wiring about three dozen together into a module would be enough to recharge a laptop. Building modules is the agenda for the next six months. Barnett predicts they will be 10 to 20 percentage points more efficient than what's on the market.

Darpa is doubling its funding for the program. With corporate dollars, too, the three-year program will have a $100 million budget. "There's no technological reason why this technology couldn't scale to rooftops," says Kirkpatrick. But first things first: The Pentagon wants solar-powered flashlights and battle gear.

http://www.forbes.com/free_forbes/2007/0903/092.html

Sphere: Related Content

E-Gang: Seeking The Light

FORBES COVER STORY:

Michael Splinter was raised on the most powerful incantation in the tech industry, Moore's Law, which roughly holds that computing power per dollar doubles every two years. During his 20 years at Intel Splinter saw this law deliver exponentially better products and profits.

Now, as chief executive of Applied Materials, the biggest pick-and-shovel maker for the semiconductor and flat-panel display industries, Splinter, 56, wants to forge a sunny-side-up version of Moore's Law. "Can we, with our customers, drive down the cost per watt of photovoltaics?" Splinter asks. "We've got to."

Currently photovoltaics cost $2 to $3 per watt to build, down from $22 in 1980. Splinter thinks he can help drive the cost of solar to under $1 a watt. At that price, even after adding a dollar or two per watt of installation costs, solar power would rival grid-delivered fossil fuel power. (Bear in mind that watts here are measured at midday peaks. Even in California an installation rated at 1 kilowatt will produce only 1,600 kwh a year.)

Ambitious enough to be on Intel's shortlist of future chief executives, Splinter leaped at the chance to run his own show at Applied in 2003. The growth in solar captured Splinter's attention early on. Slowdowns at computer chip makers, who buy nearly all of Applied's equipment, hit hard. The $9.2 billion (revenue) company has a price-to-earnings ratio below that of Kraft Foods.

The solar cell manufacturing industry for years made do with hand-me-down tools from the computer chip industry. But last year solar cell manufacturers bought more silicon wafers than chipmakers--and solar's demand for wafers is growing three times as fast as demand from the rest of the electronics industry. Applied will likely hit $400 million in contracts for solar manufacturing gear by year-end; Splinter wants $1 billion by 2009.

Applied intends to trim the industry's costs in four ways: boost solar factory throughput, improve the productivity of every tool, cut materials costs by using photovoltaic materials more sparingly and raise solar cell efficiencies. Splinter has already spent close to $1 billion to hire hundreds of people for his solar group, buy two small thin-film equipment makers and invest in a silicon wafer firm in California.

Charles Gay, who is leading Applied's solar business, obsesses about speed. Computer chips are made in batches; solar cells are produced continuously. Coating tools once used to put films on sheets of glass are being tweaked so they can also rapidly coat thousands of individual wafers. Thin-film solar makers want to work with the 64-square-foot sheets of glass used by Applied's LCD customers, but solar glass is four times as thick as display glass. So Applied is strengthening the arms of the robots it sells to hold glass sheets. "We'd like to move one ton of silicon wafers through a line in an hour," Gay says. At that speed one factory could produce a gigawatt of solar modules per year, ten times as much as the U.S. is now installing. "This is like the 1970s in the computer chip business," says Splinter, flashing a 200-watt smile.

http://www.forbes.com/free_forbes/2007/0903/080.html

Sphere: Related Content

FORBES: Bright Ideas

FORBES MAGAZINE

A handful of young companies

are producing new ways

to harness solar energy.

The sun never shines in the basement laboratory on the University of California, Berkeley campus, where graduate students Delia Milliron and Ilan Gur spend their days. But that isn't stopping them from doing some of today's most advanced work in solar-cell technology.

In one corner of the lab Gur brews toxic ingredients to make a half-vial of crystals, each measuring a millionth or so of an inch, of cadmium selenide, a light-sensitive semiconductor. He covers a postage-stamp-size piece of glass with the nanocrystal goop and hands it over to Milliron. In a mini-vacuum-chamber she adds tiny strips of aluminum. Finally they carry the tiny chip into a black room and shine light on it:The chip spews back power--1.5 milliwatts for this fledgling solar cell, which on some bright future day could translate to 15 watts per square meter.

Even brighter days are ahead. The pursuit of an improved photovoltaic cell, the cornerstone of solar energy production, has the whiff of a gold rush about it. Since 1999 shipments of photovoltaic cells and modules have been growing an average of 30% a year, reaching $3.5 billion in 2002, according to Clean Edge, a San Francisco research group.

Manufacturers, led by Japanese companies such as Sharp, are convinced that within sevenyears traditional solar-cell technology will deliver power as cheaply and conveniently as steam turbines. The economics of solar, once derided as hippie wishful thinking, are getting pretty compelling. "When I started in the early 1970s, the going price for solar modules was about $200 per watt," recalls Arthur Rudin, director of engineering for Sharp's solar systems division in Huntington Beach, Calif. "Today the average price for solar modules is about $5 a watt."

That is, a solar cell that generates a watt of power when the sun is at its peak for four hours a day sells for about $5. Figure in night, clouds, winter, various supporting hardware and the depreciable lives of cells, and you find that sun-made electricity is still pretty expensive, between 20 cents and 50 cents per kilowatt-hour. Get the $5 cost down to $1, though, and the sun could compete with natural gas.

The best commercial solar cells today convert 15% of sunlight into electricity, but they are made of brittle, expensive materials such as silicon. Cells can be made from cheaper, more malleable plastics, but those typically now turn a mere 3% of light into electricity. "We know it's possible to do better," contends Paul Alivisatos, the chemist who oversees that lab at UC-Berkeley.

In March 2002 Alivisatos put his reputation--and his venture capitalists' money--where his mouth is, turning over much of his research to a Palo Alto firm called Nanosys. The company has amassed $75 million and is devoting much effort to figuring out how toembed nanofilaments of semiconductors in cheap, bendable plastic sheets. Nanosys' goals: 10% efficiency, $1 per watt.

Solar energy cells are typically made of crystalline silicon, the kind used in computer microprocessors, sandwiched between electrodes (see box).Silicon's orderly atomic structure allows electrons to shoot rapidly through the crystal to the electrodes. But silicon is expensive and must be processed in elaborate clean-room facilities, just like computer chips. Organic materials such as light-absorbing polymers are easier and cheaper to process, but typically fritter away 97% of the sun's energy because the electrons must navigate a tortuous path.

Solar entrepreneurs have many ways to attack the problems. In Los Gatos, Calif. a nine-person startup called Solaicx is building a furnace for making cheap crystalline silicon substrate. Pour in elemental silicon and out will come little bricks that are the foundation material for 90% of today's solar modules. "We have far less waste than the usual manufacturing process, lower labor costs--we're just attacking every factor of production," says Robert Ford, chief executive of the company.

He says that Solaicx's furnace may be able to cut the cost of making wafers by as much as 50% when the company is in full-scale production, about two years from now. He bets that Solaicx will make it possible for solar modules to generate power at 8 cents per kilowatt-hour by 2007.

Nanosys and two other new firms, Konarka and Nanosolar, are taking the radical approach of replacing chunky solar-cell modules with rolls of flexible plastic that have photovoltaic elements built in. "You don't have to invent a new factory to do this. You use coating and printing machines," says William Beckenbaugh, chief executive of Konarka. Production costs would drop by maybe 80%.

Which light-sensitive nanomaterials to use? Nanosys' solar-cell work is based on Alivisatos' tinkering with so-called nanorods in his Berkeley lab. When embedded in plastic, the rods act like roads for the electrons, shortening their route toward the electrode andproducing power more efficiently. Early batches of nanorods were as organized as pickup sticks. In a happy accident Milliron and other Berkeley postdocs made an errant batch of nanorods that looked like jacks--with four legs--rather than rods. No matter which end was up, one leg always pointed toward the electrode. Another perk:Nanorods can be "tuned" to absorb light from different parts of the spectrum just by growing them bigger or smaller. Although Nanosys is still exploring just the right shape for its nanorods, it has committed to a deal with Matsushita Electric Works to make plastic photovoltaic laminate for materials like Spanish-style roof tiles, slated for the Japanese market by late 2006.

In Lowell, Mass. two-year-old Konarka is using titanium dioxide nanocrystals coated with a thin layer of a light-sensitive dye. The dye-sensitized solar cells suck up photons even in dim light. Konarka's work is based on a decade of research by Michael Graetzel at the Ecole Polytechnique Fédérale de Lausanne. Konarka's plastic-based solar modules have already shown efficiencies of up to 6.5%, beating the scores of thin- film (or amorphous) silicon solar cells, Beckenbaugh says. (For a story on a thin-film enthusiast, see p. 86.) Konarka has teamed up with Groupe Electricité de France, ChevronTexaco and Eastman Chemical to make products by 2005. Earlier this year Aisin Seiki, in Japan, demonstrated a solar module that's more efficient than the best silicon versions and can be made for one-tenth the cost.

Nanosolar, in Palo Alto, is building "brushes" of semiconducting metal oxide nanowires that it says improve efficiency even more. Its work is based, in part, on technology developed at Sandia National Laboratories, with the help of former students from Alivisatos' laboratory. R. Martin Roscheisen, the company's founder, says Nanosolar has a working prototype and plans to raise funds to build a factory.

http://members.forbes.com/forbes/2003/1124/222.html

--##--

Sphere: Related Content