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During the second phase of PVMat (1992), Utility Power Group improved encapsulation and termination systems by simplifying manufacturing processes and materials. |
The Photovoltaic Manufacturing Technology (PVMaT) project was initiated in 1990. A healthy domestic PV industry would benefit the United States in many ways, from creating a technology-oriented job base to offsetting trade imbalances by shipping a valuable commodity to world PV markets. And, as a home-based energy source, PV could fill an important role in helping our nation achieve energy security and independence.
The Start-Up
By the late 1980s, the need for a method to spur domestic PV manufacturing had become clear. At that time, the manufacture of PV equipment was an infant industry, with much of the module-assembly work done by hand. PVMaT was born in 1990 when the first Bush administration allocated $1.5 million for a fact-finding mission.
A team comprised of individuals from the U.S. Department of Energy, Solar Energy Industries Association, National Renewable Energy Laboratory, and Sandia National Laboratories developed the project goals. During the years, these goals have been expanded to match the growing technical expertise of the U.S. PV industry.
Open to All Technologies
Early on, the principals decided PVMaT would be a cost-shared, subcontracted partnership between industry and government that was wide open to all technologies. The first step was the problem-identification phase, in which 22 contractors were awarded $50,000 each. The second solicitation was open only to companies that had participated in the first round. Since then, PVMaT solicitations have been open to all U.S. industrial organizations and/or teams with activities related to the manufacturing of PV products, systems, and components.
PVMaT initially focused on module manufacturing. In 1994, the scope was broadened to include manufacturing for balance-of-systems components, as well as system and component integration, to bring together all elements for a complete PV system. In 2000, the PVMaT Project was succeeded by the PV Manufacturing R&D Project as needed adjustments in the focus of manufacturing development were implemented. The result was more emphasis on manufacturing R&D needed for in-line diagnostics, intelligent processing, and improved yield necessary for large-scale manufacturing.
In 2001, a solicitation was issued for "In-Line Diagnostics and Intelligent Processing," showing a growing sophistication in PV manufacturing. Continuing that trend, the 2003 solicitation was titled "Large-Scale Module and Component Yield, Durability, and Reliability."
Thus far, there have been seven rounds of PVMaT/PV Manufacturing R&D solicitations. The total investment to date is $231 million, with a U.S. Department of Energy share of $123 million and an industry share of $108 million. This investment has resulted in major dividends, as shown by funding-recapture data for both U.S. taxpayers and domestic industries.
Project Highlights
ENTECH's 100-kW concentrating PV system was modified under PVMaT. In west Texas and other bright-sunlight areas of the world, a four-row system provides about 220,000 kWh per year. |
These were the start-up years for the PVMaT Project, with activities centered on building the foundation for a successful domestic PV industry. The project methodology was established, under which multiyear projects would be carried out through cost-shared awards resulting from competitive solicitations. Each proposal was evaluated by a panel of experts selected from technology, manufacturing, business planning, and applications areas.
An early success was achieved by ENTECH, Inc. (Dallas, TX), whose PVMaT improvements cut concentrator module costs in half. The company also took an innovative approach to module production by working collaboratively with compatible component manufacturers. Working with 3M Company, ENTECH developed an improved prismatic cell cover, reducing the material and labor costs of that processing step by 90%.
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The SPI-Assembler 5000, developed by Spire Corporation under a PVMaT subcontract, reduced the cost to assemble PV modules by a factor of five over manual assembly methods. |
In 1994 and 1995, 12 companies completed the final year of their PVMaT subcontracts, which had been awarded in 1992. Among the many highlights during those years, Solarex Corp. (now BP Solar) of Frederick, MD, increased the size of ingots and wafers, resulting in a 73% increase in capacity. The company also introduced a wire saw for cutting wafers, which saved on material costs by reducing the amount of silicon that ended up as "saw dust." The wire saw has since been adopted by many other PV manufacturers—to the extent that it is now standard equipment for the majority of the PV crystalline silicon industry.
Two companies made important contributions to the PV industry as a whole. Spire Corp., Bedford, MA, developed the SPI-Assembler™ 5000, a machine that assembled and soldered silicon cells into strings, replacing a step that had formerly been done manually. The equipment could be programmed to accommodate the module designs of various manufacturers. Springborn Materials Science Corp. (now Specialized Technology Resources, Inc.), Enfield, CT, developed a formulation that prevented the "yellowing" of encapsulants, which had been a common problem in the manufacture of PV modules.
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This 15-kW PV system near the Pentagon in Arlington, VA, comprises 60 SunSine PV modules, developed by Ascension Technology under a PVMaT subcontract. The innovative modules feature built-in microinverters that produce alternating current. |
In 1996, Ascension Technology, Inc., Waltham, MA, in partnership with ASE Americas (now RWE SCHOTT Solar, Inc.), Billerica, MA, developed an alternating-current PV module called the SunSine™ 300. PV modules naturally produce direct current and require an inverter to produce the alternating-current used by the electrical grid. The SunSine 300 represented the first time a PV module and inverter were sold as a self-contained unit.
AstroPower, Inc. (now GE Energy), Newark, DE, made major accomplishments in 1997. The company fabricated the world's largest production silicon solar cell (240 cm2), initiated a continuous Silicon-Film™ production process that was 10 times faster than competing processes, and established a record efficiency of 16.6% for a 1-cm2 solar cell.
Crystal Systems, Inc., Salem, MA, launched a PVMaT project in 1998 that promised to benefit a major segment of the U.S. PV industry by reducing the impurities in metallurgical-grade silicon and converting it to solar-grade silicon. The company's goal was to reduce the cost of silicon feedstock to less than $20 per kilogram. By the end of its subcontract, Crystal Systems had actually produced the solar-grade silicon for a projected price of less than $10 per kilogram.
In 1999, a year that can be viewed as a coming of age for the U.S. PV industry, BP Solar International, LLC, Frederick, MD, demonstrated a fully automated cell-processing system. By automating the cell-contact process, throughput was increased, as well as the efficiency of the finished product. As more PV manufacturers instituted continuous processing, productivity increased dramatically and companies were able to produce more product in less factory space.
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ASE Americas experimented with growing a cylindrical version of its hollow crystalline Si tube. This demonstrated growth potential for edge-defined film-fed growth (EFG) tubes with reduced wall thickness down to 100 microns. |
PowerLight Corp., Berkeley, CA, focused on product redesign, plant operations, and efficiency improvements. This resulted in a doubling of production of its PowerGuard® PV roofing tiles from 200 to 400 tiles a day. The company estimated an overall cost reduction per board foot of tile of nearly 60% compared to costs in 1999. The most impressive result, however, was that PowerLight increased production capacity from 5 to 20 megawatts per year.
In 2000, ASE Americas, Inc., Billerica, MA, (now SCHOTT Solar, Inc.) developed an approach for manufacturing large diameter cylinders using its edge-defined film-fed growth (EFG) process to produce crystalline silicon wafers for PV applications. The cylindrical format enabled the tube wall (and hence, wafer) thickness to be reduced to about 100 microns. While the cylinders proved to have too much built-in stress to successfully allow for cutting into wafers with high yield, the work paved the way toward future development of larger diameter polygonal-shaped tubes with increased face widths. 125 mm EFG wafer production has since been achieved. The company also began using improved lasers for higher speed cutting of PV wafers.
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Energy Conversion Devices built this machine for United Solar Ovonic. It is used to deposit amorphous silicon PV thin films. |
During this period, project participants reported major technical progress in scaling up manufacturing, as part of the "In-Line Diagnostics and Intelligent Processing" (IDIP) solicitation.
Evergreen Solar, Inc., Marlboro, MA, developed a unique approach to manufacturing crystalline silicon wafers through the string-ribbon growth process. The company moved a dual-ribbon growth system (called Project Gemini) from R&D concept to pilot phase to production. One element of the system, a new contact-printing machine, increased throughput by 70%.
Several PV companies benefited from work performed by Sinton Consulting, Inc., Boulder, CO, which developed an in-line monitoring tool that measures indicators of cell performance during manufacture of silicon wafers and cells. Use of the WCT-100 tool allows unacceptable materials to be pulled from the manufacturing line before incurring the expense of converting the wafer to a cell. Several of these tools have been sold to industry, and feedback suggests that the equipment saves enough to pay for itself in less than one month.
Energy Conversion Devices, Inc, Rochester Hills, MI, developed control, monitoring, and diagnostic systems that allow quality control during production of each of nine layers of an amorphous silicon PV device.
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Awards and Recognition
Siemens Solar Industries, Camarillo, CA, and NREL received an award in 2001 from the Federal Laboratory Consortium for technology transfer for work to improve manufacturing in this facility. |
AstroPower, Inc. (now GE Energy) received an R&D 100 award in 1995 for its Silicon-Film product, which was conceived and manufactured under a PVMaT subcontract. The product combined the performance and stability of conventional crystalline-silicon-based solar cells with the low cost of sheet-material production.
In 1998, Popular Science published its "100 Best of What's New" technological advances, and two of the winners had strong PVMaT ties. Ascension Technology was cited for its SunSine 300 AC PV modules, with a built-in microinverter that eliminated the need for DC wiring. Advanced Energy Systems, Inc. was recognized for its microinverter, which was small, easy to install, and compatible with PV modules made by several manufacturers.
In 2001, Siemens Solar Industries, Inc. (now Shell Solar) and NREL were awarded a prestigious Federal Laboratory Consortium Award. By developing a technique to reprocess oils and solvents used in cleaning and etching silicon wafers, the company decreased by nearly 80% over two years the amount of caustic wastes from PV manufacturing that enter the environment.
In 2005, NREL and Sinton Consulting, Inc. were jointly awarded an R&D 100 Award for the development of a silicon testing system that helps manufacturers determine the quality of silicon in the early stage of solar cell production. For more than 40 years, the prestigious R&D 100 Awards have been helping companies provide the important initial push a new product needs to compete successfully in the marketplace. The winning of an R&D 100 Award provides a mark of excellence known to industry, government, and academia as proof that the product is one of the most innovative ideas of the year.
The Sinton QSSPC Silicon Evaluation System is a method of detecting impurities and defects in silicon boules—the material from which solar cells are made—before it is sliced into waters to be used in silicon solar cell manufacturing lines. A boule tester sends short pulses of infrared light into the boule and measures minority-carrier lifetime in p- or n-type silicon. Using radio frequency (RF) sensing, the tester determines quasi-steady-state photoconductance (QSSPC), then uses this information to calculate the bulk minority-carrier lifetime. Next it calibrates the results of the photoconductance analysis to determine the absolute lifetime and then determines grain structure and calculates levels of unwanted impurities. This process gives manufacturers information to identify substandard silicon before it is made into cells, thereby increasing the number of efficient cells produced, boosting yields and reducing manufacturing costs. The evaluation system will enable the solar industry to keep up with product demand and growth and to produce consistently better silicon at the lowest possible price.
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