greentechZONE Products for the week of June 2, 2003
SunPower Announces World's Most Efficient, Low-Cost Silicon Solar Cell
The A-300 High-Performance Solar Cell Achieves 20% Efficiency on 2-MW Pilot Line; Affiliation With Cypress Semiconductor to Bring Competitive Advantage in High-Volume Manufacturing
SunPower Corporation has announced sampling of the A-300, the world's most-efficient, low-cost silicon solar cell. Based on a unique rear-contact design-which maximizes the working cell area, hides unsightly wires and makes automated production easier-the A-300 achieves over 20 percent efficiency compared with currently available cells in the 12% - 15% range. The National Renewable Energy Laboratory (NREL) has verified 20.4 percent conversion efficiency for the A-300.
The 125-mm, single-crystal A-300 cell generates three watts of electricity providing the most efficient cost-per-watt solution in the photovoltaic (PV) industry. Additionally, the A-300 silicon solar cell delivers 3-kW in less than 17 square meters, allowing SunPower's customers to trump the world's best area-efficient construction designs. The A-300 solar cells are ideal for rooftop systems, communications, building integrated PV systems, and consumer applications.
Cypress Semiconductor Corporation is sharing its expertise in technology development and high-volume manufacturing with SunPower, providing the solar cell company with a substantial competitive advantage in a silicon-intensive, highly cost-sensitive business. The 2-megawatt manufacturing line that yielded the A-300 cells is adjacent to Cypress's manufacturing facility in Round Rock, Texas. A future SunPower manufacturing facility is under consideration for a site nearby Cypress's high-volume assembly and test facility in the Philippines.
"The A-300 cell marks a major milestone both for SunPower and for the photovoltaic industry," said Dick Swanson, SunPower president and CEO. "The cell's innovative design, high-efficiency and low manufacturing cost will enable our customers-the companies that design and build solar modules-to create superior products at a cost capable of accelerating the rate of conversion to clean, solar solutions."
"SunPower cells have been used in a broad range of high-profile, high-performance products, including NASA's Helios solar airplane, which set an altitude record of 96,863 feet in 2001," Swanson said. "But our partnership with Cypress has been key in enabling our transition from a small scale solar supplier to a world-class manufacturer of solar cells for high-volume applications."
"Performance and cost are key to making solar power a commercial success," said T.J. Rodgers, SunPower chairman, and president and CEO of Cypress Semiconductor Corporation. "The A-300 provides an entirely new class of cost-effective solutions to the clean energy industry.
"The solar cell business represents a great opportunity for several reasons," Rodgers added. "Even without the negative effects of political volatility, the production of conventional sources of energy, such as oil, is expected to peak over the next decade, requiring renewable forms of energy to begin to take its place. "After more than 30 years of continuous improvement, the science of solar power has matured to the point where it has become highly cost-effective."
About A-300 Solar Cell
The A-300 cells eliminate front-side metallization by utilizing a patented rear-contact design to provide more cosmetic uniformity and maximize energy generation. These products have been developed on a 2-MW pilot line in preparation for a full-scale manufacturing facility to be established in the near future. This production line enables SunPower to manufacture solar cells with less raw material and higher throughput. Until now, this level of efficiency and aesthetic value was unattainable for commercial applications.
In researching this story, I had the privilege of meeting the Chair of SunPower's Advisory Board, Dr. Charles Gay, a person to whom the adjective "interesting" does not do justice. Even if the solar cell he and the company developed were not such an important breakthrough, the work he does with renewable energy solutions for improving economic conditions in developing nations would have made him one of the top 20 interviews of my career. Unfortunately, the stories of solar-powered sewing machines in India, and Dr. Gay's other exploits will have to wait for another issue of green-techZONE because their A-300 solar cell represents such a significant achievement.
With a real-life efficiency of 20+%, the A-300 may have the potential to accelerate the economics of the photovoltaic industry and hasten the day when solar power can compete directly with fossil-based generating systems. Since this represents a quantum leap from the 12 - 14% efficiency I normally expect from a non-concentrated silicon cell, I was naturally skeptical of SunPower's claims. But, after a closer look it seems as though the manufacturer has combined a series of solid, well-conceived improvements that work in concert to coax the cell's efficiency towards the neighborhood of the 25% theoretical maximum.
When you take a look at the A-300 the first thing you notice is the absence of metal contacts on the front surface. SunPower has spent quite a while learning how to move the diode junctions, and the metal contacts that collect the current from them, to the back of the wafer. This arrangement yields several advantages, including uncovering 5% f the cell that would normally be shadowed by the contacts. It also allows for use of thicker, wider metal, something that almost eliminates the resistive losses that eat up as much as 5% of a conventional cell's energy.
Forming the junction at the rear of the cell, combined with a clever surface treatment allows it to trap and convert much more of the available photons into mobile electrons - yielding another jump in efficiency. The cell employs several other tricks to boost efficiency, including an oxide passivation layer on the backside to deny regions for unwanted hole-electron recombination. For more details, see the short white paper provided by SunPower.
The resulting cell is not only more efficient, it is also easier to assemble into a solar array, thanks to its rear-mounted attach points. The rear contacts allow for much simpler automated bonding and attachment processes, something that translates into lower panel manufacturing costs. SunPower also attacks the overall solution cost of a PV panel by reducing the area required to deliver a given amount of power. Now that photovoltaic cells are coming down in price, the materials and labor required to produce the panel enclosure are becoming a significant fraction of the assembly.
This means that even though the A-300 will cost more in terms of dollars-per-watt paid at the cell-level (at least this year), they will save customers money in the fabrication and installation process. SunPower estimates that their new design will cut assembly costs by 40% with the combination features of the backside contact and higher efficiency. Installers and large-scale generators will also benefit as they will have to mount fewer panels to achieve the same power output. Cost-per-installed-watt should continue to drop as SunPower recoups its development costs and can start to sell the cell at something closer to a conventional unit cost.
The bottom line is that even with a premium dollar-per-watt price tag, the SunPower cell should help to accelerate the price reduction curve that moves the current $6 - $8 per W of a current PV generating system (including mounting, power conversion, control, and some storage) towards the $3-$4-per W it will take to begin directly competing with current fossil-burning systems.
Given the base cost of mono-crystalline silicon wafers, it's not clear to me whether they can achieve cost parity with conventional generating technologies, or whether somewhat less-efficient poly-crystalline, amorphous, or other non-traditional materials will get there first. But if anybody has a shot at making this happen it seems to be SunPower at the moment.
Of course, I just learned from STMicroelectronics CEO Pasquale Pistorio that his company is involved in a long-term project to produce plastic solar cells that employ a matrix of carbon nanotubes to convert photons to electrical power. This could eventually lead to the low-cost "photovoltaic roofing material" that is the holy grail of the industry. But such developments are at least 5 years away from commercialization and at least, for the moment, it looks like SunPower has taken the lead in the race towards a sustainable future.
Congratulations to the SunPower team for their diligent efforts, and to their parent company Cypress Semiconductor, for having the vision to add this unique asset to their product portfolio.
Production for the A-300 in the Roundrock, TX line is expected in August 2003.