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  • 2009-12-22 09:00:00
  • Article ID: 559859

Glitter-Sized Solar Photovoltaics Produce Competitive Results

  • Credit: Murat Okandan

    Representative thin crystalline-silicon photovoltaic cells – these are from 14 to 20 micrometers thick and 0.25 to 1 millimeter across.

  • Credit: Randy Montoya

    Sandia project lead Greg Nielson holds a solar cell test prototype with a microscale lens array fastened above it. Together, the cell and lens help create a concentrated photovoltaic unit.

  • Credit: Randy Montoya

    From left to right, Sandia researchers Murat OKandan, Greg Nielson, and Jose Luis Cruz-Campa, hold samples containing arrays of microsolar cells.

Neal Singer, nsinger@sandia.gov (505) 845-7078

ALBUQUERQUE, N.M. — Sandia National Laboratories scientists have developed tiny glitter-sized photovoltaic cells that could revolutionize the way solar energy is collected and used.

The tiny cells could turn a person into a walking solar battery charger if they were fastened to flexible substrates molded around unusual shapes, such as clothing.

The solar particles, fabricated of crystalline silicon, hold the potential for a variety of new applications. They are expected eventually to be less expensive and have greater efficiencies than current photovoltaic collectors that are pieced together with 6-inch- square solar wafers.

The cells are fabricated using microelectronic and microelectromechanical systems (MEMS) techniques common to today’s electronic foundries.

Sandia lead investigator Greg Nielson said the research team has identified more than 20 benefits of scale for its microphotovoltaic cells. These include new applications, improved performance, potential for reduced costs and higher efficiencies.

“Eventually units could be mass-produced and wrapped around unusual shapes for building-integrated solar, tents and maybe even clothing,” he said. This would make it possible for hunters, hikers or military personnel in the field to recharge batteries for phones, cameras and other electronic devices as they walk or rest.

Even better, such microengineered panels could have circuits imprinted that would help perform other functions customarily left to large-scale construction with its attendant need for field construction design and permits.

Said Sandia field engineer Vipin Gupta, “Photovoltaic modules made from these microsized cells for the rooftops of homes and warehouses could have intelligent controls, inverters and even storage built in at the chip level. Such an integrated module could greatly simplify the cumbersome design, bid, permit and grid integration process that our solar technical assistance teams see in the field all the time.”

For large-scale power generation, said Sandia researcher Murat Okandan, “One of the biggest scale benefits is a significant reduction in manufacturing and installation costs compared with current PV techniques.”

Part of the potential cost reduction comes about because microcells require relatively little material to form well-controlled and highly efficient devices.

From 14 to 20 micrometers thick (a human hair is approximately 70 micrometers thick), they are 10 times thinner than conventional 6-inch-by-6-inch brick-sized cells, yet perform at about the same efficiency.

100 times less silicon generates same amount of electricity

“So they use 100 times less silicon to generate the same amount of electricity,” said Okandan. “Since they are much smaller and have fewer mechanical deformations for a given environment than the conventional cells, they may also be more reliable over the long term.”

Another manufacturing convenience is that the cells, because they are only hundreds of micrometers in diameter, can be fabricated from commercial wafers of any size, including today’s 300-millimeter (12-inch) diameter wafers and future 450-millimeter (18-inch) wafers. Further, if one cell proves defective in manufacture, the rest still can be harvested, while if a brick-sized unit goes bad, the entire wafer may be unusable. Also, brick-sized units fabricated larger than the conventional 6-inch-by-6-inch cross section to take advantage of larger wafer size would require thicker power lines to harvest the increased power, creating more cost and possibly shading the wafer. That problem does not exist with the small-cell approach and its individualized wiring.

Other unique features are available because the cells are so small. “The shade tolerance of our units to overhead obstructions is better than conventional PV panels,” said Nielson, “because portions of our units not in shade will keep sending out electricity where a partially shaded conventional panel may turn off entirely.”

Because flexible substrates can be easily fabricated, high-efficiency PV for ubiquitous solar power becomes more feasible, said Okandan.

A commercial move to microscale PV cells would be a dramatic change from conventional silicon PV modules composed of arrays of 6-inch-by-6-inch wafers. However, by bringing in techniques normally used in MEMS, electronics and the light-emitting diode (LED) industries (for additional work involving gallium arsenide instead of silicon), the change to small cells should be relatively straightforward, Gupta said.

Each cell is formed on silicon wafers, etched and then released inexpensively in hexagonal shapes, with electrical contacts prefabricated on each piece, by borrowing techniques from integrated circuits and MEMS.

Offering a run for their money to conventional large wafers of crystalline silicon, electricity presently can be harvested from the Sandia-created cells with 14.9 percent efficiency. Off-the-shelf commercial modules range from 13 to 20 percent efficient.

A widely used commercial tool called a pick-and-place machine — the current standard for the mass assembly of electronics — can place up to 130,000 pieces of glitter per hour at electrical contact points preestablished on the substrate; the placement takes place at cooler temperatures. The cost is approximately one-tenth of a cent per piece with the number of cells per module determined by the level of optical concentration and the size of the die, likely to be in the 10,000 to 50,000 cell per square meter range. An alternate technology, still at the lab-bench stage, involves self-assembly of the parts at even lower costs.

Solar concentrators — low-cost, prefabricated, optically efficient microlens arrays — can be placed directly over each glitter-sized cell to increase the number of photons arriving to be converted via the photovoltaic effect into electrons. The small cell size means that cheaper and more efficient short focal length microlens arrays can be fabricated for this purpose.

High-voltage output is possible directly from the modules because of the large number of cells in the array. This should reduce costs associated with wiring, due to reduced resistive losses at higher voltages.

Other possible applications for the technology include satellites and remote sensing.

The project combines expertise from Sandia’s Microsystems Center; Photovoltaics and Grid Integration Group; the Materials, Devices, and Energy Technologies Group; and the National Renewable Energy Lab’s Concentrating Photovoltaics Group.

Involved in the process, in addition to Nielson, Okandan and Gupta, are Jose Luis Cruz-Campa, Paul Resnick, Tammy Pluym, Peggy Clews, Carlos Sanchez, Bill Sweatt, Tony Lentine, Anton Filatov, Mike Sinclair, Mark Overberg, Jeff Nelson, Jennifer Granata, Craig Carmignani, Rick Kemp, Connie Stewart, Jonathan Wierer,

George Wang, Jerry Simmons, Jason Strauch, Judith Lavin and Mark Wanlass (NREL).

The work is supported by DOE’s Solar Energy Technology Program and Sandia’s Laboratory Directed Research & Development program, and has been presented at four technical conferences this year.

The ability of light to produce electrons, and thus electricity, has been known for more than a hundred years.

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Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, an autonomous Lockheed Martin company, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.

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Cold and Bubbly: The Sensory Qualities that Best Quench Thirst

New research from the Monell Center finds that oral perceptions of coldness and carbonation help to reduce thirst. The findings could guide sensory approaches to increase fluid intake in populations at risk for dehydration, including the elderly, soldiers, and athletes.

J.R. Macdonald Lab receives nearly $8 million DOE grant renewal

MANHATTAN -- A nearly $8 million grant from the U.S. Department of Energy is supporting the "bread and butter" physics research at Kansas State University's James R. Macdonald Laboratory. The grant is a three-year renewal award, "Structure and Dynamics of Atoms, Ions, Molecules and Surfaces." "This big operational grant is our bread-and-butter," said Itzik Ben-Itzhak, university distinguished professor of physics and director of the J.

University contributes art to the new downtown arena

A number of Sac State artworks are joining Jeff Koons' "Coloring Book" in exhibits at the new Golden 1 Center. (Sacramento State/Rob Neep) More photosSac State Professor Rachel Clarke and alumnus Bryan Valenzuela check out the installation of Valenzuela's "Multitudes Converge" glass sculpture at the Golden 1 Center.

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New Method for Reporting Solar Data

A straightforward new way to calculate, compile, and graphically present solar radiation measurements in a format that is accessible to decision makers and the general public has been developed by researchers at the University of Texas at Austin and is described in the Journal of Renewable and Sustainable Energy.

Trapped Sunlight Cleans Water

High energy costs are one drawback of making clean water from waste effluents. According to an article in the journal Biomicrofluidics, a new system that combines two different technologies proposes to break down contaminants using the cheapest possible energy source, sunlight.

Report: Policies to Spur Renewable Energy Can Lower Energy Costs

The South could pay less for its electricity in 20 years than is currently projected if strong public policies are enacted to spur renewable energy production and use, according to a report released today by researchers at the Georgia Institute of Technology and Duke University.


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Citi Grant Helps University Students Succeed

Citi Community Development, part of the Citi family of businesses, supports an innovative Academic Success Program at South Dakota State University. The program is designed to help students who have been re-admitted to SDSU following suspension due to low academic achievement.

Iowa State Engineer and Goodrich Partner to Develop Fuel Nozzles

Hui Hu, an Iowa State University associate professor of aerospace engineering, is working with engineers from the Goodrich Corp. to test and characterize the next generation of fuel nozzles.

CSB to Hold Public Hearing Tomorrow, December 15, as Part of the CSB Deepwater Horizon Investigation

CSB Board Will Hear Testimony on how Offshore Drilling is Managed and Regulated in Other Countries

Cornell Joins Team Taking Head-first Plunge Into Algae Biofuels

Cornell University researchers have joined other scientists and a biofuel research company on a mission to develop a commercial-scale algae-to-fuel facility by 2015. The effort is backed by a $9 million award from the U.S. Department of Energy.

Engineering Researchers Partner With Toyota; DOE Grant Will Further Work Toward a More Efficient Charger for Hybrid-Electric Vehicles

A $3.9 million award from the U.S. Department of Energy will allow electrical engineering researchers at the University of Arkansas to continue contributing to the development of a compact and highly efficient silicon-carbide charger for hybrid electric vehicles. The benefits of the project extend beyond vehicles into other areas, such as wind and solar power, and could lead to reduced energy consumption in the United States.

Research Looks at Alternative Power for Military

South Dakota State University has a major role in a $10 million project to deliver alternative power technologies to help the U.S. military supply power to units in the field. The three-year project began in May 2009.

Mixing Blood and Oil: Conference Tackles Similar Challenges from Two Major Industries

Scientists and engineers from two of the nation's largest industries - medicine and energy - came together this week to explore the synergies in moving oil and pumping blood.

Time Ripe to Move Energy Storage Idea Off Drawing Board

Need has caught up with Case Western Reserve University researcher Gerhard Welsch's design for a self-healing, high-energy capacitor he patented a decade ago. ARPA-E has granted Welsch $2.25 million to start producing the small and lightweight device for hybrid and electric cars and more.

Registration Open for Sandia-Sponsored 4th International Conference on Integration of Renewable and Distributed Energy Resources

Registration is open for the 4th International Conference on the Integration of Renewable and Distributed Energy Resources, the premier event for technical discussion of electric integration of new energy resources.

Advanced Energy Conference To Illuminate Latest Technologies For 21st Century Clean Energy Economy

Leading Energy Organizations to Highlight Latest Job-Producing Energy Technologies at Nov. 8-9 Conference in N.Y.C.


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