Silicon-free thin-film photovoltaic solar cells are now commercially available in early production runs. These differ from the next generation thin film cell described in a previous post in that they are applied to the substrate by a sputtering process that was developed in the semiconductor industry and is been adapted for use in producing solar cells, rather than by adapting a printing process as is being done in the next generation of thin-film cells. Silicon-free solar cells could easily gain momentum from the current world wide shortage of silicon. These cells are currently applied to a stainless steel substrate, although there is indication that they could be applied to a plastic substrate in the future. These may well be the low cost cells for the next few years until the potential of silicon-free, thin-film cells produced by printing can be evaluated.
The two companies that I have researched both use Copper Indium Gallium diSelenide (CIGS) cells. CIGS cells are very efficient having higher efficiency than the crystalline Silicon cells now in common use. CIGS cells are very stable showing little if any degradation over their long life. Cells have been in the field for 17 years and exposed to the rigors of space with very stable performance. Life expectancy is projected to be 20-30 years, among the longest if not the longest of all cell types. This material exhibits "self-healing" properties that may correct for very small manufacturing defects and operational damage which may help explain their long life span. No toxic materials are used in the manufacturing process unlike some other silicon-free cell materials.
The claim of the companies in this business is that the manufacturing process being used is the key element in being able to produce low cost solar cells. They use a continuous roll-to-roll vacuum process in which the solar cell material is sputtered on the moving substrate. The cell material can be applied in layers with each layer having different properties that can enhance the cells performance. Similar process are used in the architectural glass industry, in producing hard drives, making optical filters and in making flat-panel displays.
DayStar Technologies was founded in 1997 and has been developing its solar cell and manufacturing techniques since that time. According to DayStar "Sputtering is used extensively in the flat-panel display and computer hard-drive industries. Sputtering is easily scaled to large dimensions (on the order of 3-4 meters in some cases) and, when combined with DayStar’s other proprietary film deposition methodologies, enables a highly reproducible, and hence inexpensive, Photovoltaic Foil™ manufacturing process."
DayStar describes sputtering as follows: "Sputtering is a vacuum evaporation process which physically removes portions of a coating material called the target, and deposits a thin, firmly bonded film onto an adjacent surface called the substrate. The process occurs by bombarding the surface of the sputtering target with gaseous ions under high voltage acceleration. As these ions collide with the target, atoms or occasionally entire molecules of the target material are ejected and propelled against the substrate, where they form a very tight bond. The resulting coating is held firmly to the surface by mechanical forces, although, in some cases, an alloy or chemical bond may result."
"The Company is performing low risk, incremental manufacturing development steps to reach its Gigawatt scale, roll-to-roll manufacturing goal avoiding development of singular, high cost and risk manufacturing line development." The company started selling products in early 2005 and has made announcements on three purchase agreements:
On March 14, 2005 DayStar and Auxilia, Inc. signed a Memorandum of Understanding (MOU) regarding design and development of fully integrated photovoltaic power systems for the unmanned airship (lighter-than-air vehicle) marketplace. Low cost, serviceability and range of coverage make airships ideal for a variety of communications, surveillance, data relay, and broadband applications for military and commercial telecommunications. DayStar and Auxilia will focus on integrating DayStar's proprietary LightFoil™ photovoltaic power product with Auxilia's products. LightFoil’s™ lightweight, high performance and form factor flexibility is derived from a unique design which consists of high efficiency CIGS solar cells deposited on thin titanium foil less than the thickness of common household aluminum foil.
On June 9, 2005 the company announced that they had signed a purchase agreement with Blitzstrom, GmbH for Blitzstrom’s purchase of DayStar’s exclusive TerraFoil™ solar cells. Samples for module and array testing will be delivered in the near future, with initial product shipments slated for the third quarter of 2005. Full realization of the purchase agreement would result in revenues of up to $60 million using today’s market price for the silicon cells they replace. Near term costs are likely to exceed projected revenue under this contractual arrangement until DayStar transitions its production of TerraFoil™ solar cells from the existing Gen II line to its planned lower cost Gen III production. TerraFoil™ solar cells are their alternative to to silicon wafer solar cells currently used in flat plate PV modules. They can be assembled into modules of the same size and capacity as current Silicon cells. A previous post discusses this sale in more detail.
On July 11, 2005 the company announced a purchase agreement for up to 500-kilowatts of TerraFoil-SP™ cells with monthly delivery beginning later in 2005 and escalating in volume through the end of 2006. The TerraFoil-SP™ cell is a small form factor product designed to be used in consumer electronic devices.
My interpretation of their status is that the Gen II line, which is in operation now, may either a batch-continuous process or a narrow width roll-to-roll line. GEN III is a roll-to-roll process with greater efficiency than the Gen II line. See their paper on manufacturing of solar cells for an explanation of how they plan on increasing production rates and efficiencies through progressively more sophisticated processes. Presumably the LightFoil™ and the TerraFoil-SP™ are relatively high margin products and could be made on the Gen II line. To deliver on the Blitzstrom agreement will require successful operation of the Gen III line and therefore involves some risk, as this line has not been proven.
Miasole is a relatively young company with somewhat similar technology. A couple of press releases are my only clues to their status.
A 5/11/2004 press release stated: "Miasole, formerly Raycom Technologies, has developed a new low cost manufacturing process for the production of solar cells on flexible stainless steel foil. Miasole's technology is based on a proprietary vacuum deposition sputtering technology which is used to apply a thin-film of light absorbing semiconductor material composed of copper, indium, gallium and selenium, more commonly known as CIGS. The CIGS material and other thin-film layers are deposited in a continuous process in the vacuum system on stainless steel foil. Miasole's CIGS solar cells offer a direct replacement for conventional silicon based cells, at a fraction of the cost.
The new funding is earmarked to transition the Company's demonstrated R&D process to an existing high volume production system rated for 5MW of annual solar cell output. Last year Miasole demonstrated solar cells with 12 percent conversion efficiency, a level competitive with market dominant multi-crystalline silicon solar cells."
They raised another $16 million according to a 6/10/05 article on SiliconValley.com. "Venture firms are enthusiastic, and Miasolé, in particular, has drawn attention -- already producing cheap, high-quality hard disks for disk drives, which Chief Executive David Pearce used at a previous optical components company. ... Last year, Miasolé's Pearce predicted his (products) would be available during the first quarter of this year. He has taken his first orders, but now plans to make his first delivery next month: "Honestly speaking, it has taken a little longer to get the bugs out,'' he said.
Miasole's strong point is their manufacturing process. Their management team has a great deal of successful experience in developing sputtering manufacturing process. They apparently have a 4 ft wide roll-to-roll process built and in operation. Their website shows a prototype roll-to-roll production line. They show a schematic of their "Dual Cylindrical Rotating Magnetrons".
As far as cost of their products is concerned, DayStar is planning on having lower cost, higher volume continuous production facilities operating by the end of 2006 which should reduce their module cost from about $3.00 per watt to about $2.00 per watt. They project that in full scale production they could reduce costs to $1.00 per watt. Miesole has a chart on the bottom of their "Benefits" page that indicates that in 2005 they could produce electricity for $.18-.19 per Kwh and by 2010 they will be able to reduce the cost to $.10 per Kwh.
DayStar Technologies, Inc., Halfmoon, NY, http://www.daystartech.com/
"Design Considerations and Implementation of Very Large scale Manufacturing of CIGS Solar Cells and Related Products", Proceedings of the 20th European PV Solar Energy Conference and Exhibit, J. R. Tuttle, et al, DayStar Technologies, June 2005
Miasole, San Jose, CA, http://www.miasole.com/solution.asp
"Miasole Closes $5.4 Million in Funding", FRESHNEWS.COM, 5/11/2004
"Vow of lower solar costs attracts venture capital", SiliconValley.com, 6/10/05