By Bruce Flickinger
Solar energy companies are ready for their day in the sun
Companies operating in the solar energy/photovoltaics (PV) marketplace are facing what is often called a good problem to have: how to meet growing demand for its products. The call from public and private sectors for sun-derived power has been increasing steadily for decades, and while worldwide capacity is there to meet it, the challenge is cost effectively putting it to use. Solar energy companies are poised to address the issue, moving from under the shadow of semiconductor manufacturing to flourish on their own and bring the necessary advances in materials and manufacturing technology.
The numbers attest to accelerating activity. According to Solarbuzz, a solar energy market research firm with offices in Aachen, Germany, the global solar industry spent some $2.8 billion on plant and equipment in 2006, adding 548 MW to bring worldwide capacity to 2,204 MW, a 33 percent jump from the previous year. Solar sales (equipment and installations) reached $10.6 billion in 2006 and will likely grow to somewhere between $18 billion and $31 billion by 2011.
A majority of this growth is occurring in Europe, and Germany is its heartbeat. Germany’s grid-connect PV market grew 16 percent to 960 MW in 2006 and now accounts for 55 percent of the world market. Spain and the U.S. were the strongest growth performers last year, with the Spanish market up more than 200 percent in 2006 and the U.S. market up 33 percent.
Industry wide, “solar markets, manufacturing, and equipment are largely located in Germany,” says Charles Gay, vice president and general manager of the Applied Materials Solar Business Group, Santa Clara, CA. “It’s the hotbed of solar activity right now.” About half of Applied Materials’ solar employees are based in Europe, with about 40 percent of these in Germany.
Like Applied Materials, many companies, ranging from small R&D consortia to the world’s largest materials and technology suppliers, are committing themselves to solar energy development. Their collective goal is to make solar cells more efficient and more durable, while reducing manufacturing costs by 40 to 50 percent over the next three years–a critical touchstone cited by several stakeholders.
Manufacturing matures
While solar power has a lot to offer in terms of being a reliable, renewable source of energy, it is currently somewhat cost prohibitive to generate. Current PV technology is based primarily on borrowed technology and off-specification material from semiconductor manufacturing and has been characterized by incremental innovation. The industry clearly is in its formative years, but observers say the future will be characterized by more radical innovations, particularly in manufacturing and equipment, along with higher quality silicon or the use of alternate materials that will bring the price-per-watt to sustainable levels.
To achieve this, all stages of advanced PV product development are being targeted for improvement, from material and device concepts to system development and manufacturing. Noah Kaye, with the Solar Energy Industries Association (SEIA; Washington, DC), points to two key areas: the “need to identify fabrication processes to improve material properties during manufacture, and improved diagnostic techniques to identify properties and quality of solar cells materials during manufacturing.”
Another requirement is true in-line, high-throughput processing of PV films and modules. Current lines involve mechanical tool connections and are not very flexible; advanced manufacturing techniques, such as smart automation, computer integrated manufacturing, manufacturing execution systems (MES), maintenance schedules, logistics, and sophisticated work in process (WIP), are beginning to be adopted.
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M+W Zander FE (Stuttgart, Germany) is considered in front of the curve in designing large-scale PV manufacturing facilities, and expects to have one manufacturer’s silicon-based facility onstream next year capable of producing 1 GWp. “We call this type of an integrated gigawatt factory a Gigafab,” says managing director Robert Gattereder. “It includes wafering, cell manufacturing, and module assembly, and it could be realized with three parallel production lines. In the thin-film sector a Gigafab will be realized around about 2011, with four parallel production lines.”
The key challenge, Gattereder says, is improving manufacturing cost efficiency, particularly by reducing the number of pieces of equipment, which reduces the manufacturing area and allows more efficient distribution of supply and disposal systems. Large-scale manufacturing also means “greener” manufacturing, with trigeneration plants “that provide all their own energy requirements in terms of electricity, steam, and hot and chilled water,” he says. Overall, “about 25 percent of initial investment costs could be saved by large-scale manufacturing.”
In terms of critical controls, solar cell/module manufacturing generally is much more forgiving than integrated circuits, although environmental contaminants will be a larger concern as material and tool tolerances tighten. For now, ambient conditions in a solar cell fabrication facility are similar to those found in a typical office space.
Two potential sources of contamination that manufacturers must control, however, are the water and detergents used to clean the glass surfaces and the purity of feedstock gases used for deposition on the surfaces. “The automation of glass handling and cleaning are leveraging considerations in optimizing how a factory works,” Gay says.
Another benefit of automated, larger scale manufacturing is the ability to produce integrated large-area modules that contain the necessary wiring and circuitry; smaller panels, conversely, need to be wired together in the field. “The market is hungry for these larger area modules, both for commercial buildings and solar farms,” Gay of Applied Materials says. “There are significant cost savings in installing larger modules because there is less wiring in the field and less mounting hardware involved in assembling the panel.”
 Figure 2. PV wafer fabrication line developed by M+W Zander in Stuttgart, Germany. Photo courtesy of M+W Zander. |
Applied Materials is now able to apply a thin film to a glass substrate about the size of a garage door. Five or six years ago, Gay says, the largest panel the industry was able to produce was about 10 square feet. “The size of the manufacturing lines needed in solar has risen to a scale today such that each new line has to have a throughput of 50 MW a year,” he says.
This is accomplished through a cost-of-production metric driven by the interplay of decreasing cell thickness and increasing panel surface area.
Optimizing efficiency
PV-based solar cells convert sunlight directly into electricity. They are made of semiconductor materials, notably silicon. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity. The process of converting light to electricity is called the photovoltaic effect.
Industry averages for cell efficiency–how well the cells convert light to energy–continue to increase steadily at tenths of percentage points, according to SEIA, with some significant outliers and breakthroughs being made above the average. The average for crystalline silicon-based solar products is about 15 percent; the highest efficiency panel on the market, about 22 percent, comes from a company called SunPower, headquartered in San Jose, CA, Kaye says.
Kaye adds that researchers at the University of Delaware are working under a grant from DARPA to manufacture a 50 percent-efficient cell. They recently reached the 42.8 percent mark using a lateral optical concentrating system that splits solar light into high, medium, and low energy bins, and directs them onto cells of various light-sensitive materials to cover the solar spectrum.
Still, Gay and others say that, while solar efficiency obviously is a concern, the overriding issue by far is cost-per-watt.
“Efficiency is a good metric, but not the first-order metric,” Gay says. “In developing countries, where a solar panel might provide electricity for an entire home, users can work with larger, less efficient panels, but in countries like Germany, for example, you want to put as many watts as possible on the roof.”
“At the end of the day, it’s about the price of the panel: Users are looking for the best return on investment for the total installed system cost,” Gay says.
While thin films are less expensive than crystal silicon, they are about half as efficient, but they can be used in applications where there is limited space or unusual geometries to accommodate, and the films can be applied in tandem layers of materials that respond to different frequencies in the solar light spectrum.
“The potential is there for thin films to meet or exceed the efficiency of silicon,” Gay says, adding that Europe “tends to be out in front” in the development and application of thin-film technologies.
A future in films
Aggressive R&D into other materials and substrates notwithstanding, crystalline polysilicon still carries roughly 90 percent of the overall PV market, according to SEIA, but polysilicon is expensive and supply constraint looms as a near-term growth issue. Suppliers are poised to fill the gap.
Dow Corning (Midland, MI), for example, has developed a metallurgical-grade silicon called PV 1101, which is designed to be blended with traditional polycrystalline silicon so that users can extend their available supply of silicon. This product was released last year and has been tested in independent institutes and at several Dow Corning Solar Solutions’ customer production sites worldwide. Customer shipments of PV 1101 began last August.
“Customers have been successful using PV 1101 at various levels without losing any of the efficiency of the cells,” says Jarrod Erpelding, corporate communications manager with Dow Corning.
For many, though, thin films are the future. United Solar Ovonic (Auburn Hills, MI), for example, is exploring the use of amorphous silicon (a-Si) alloy thin-film technology to reduce materials costs. The material’s efficiency at absorbing light means the thickness of an a-Si solar cell can be 100 times less than that of cells made of crystalline or polycrystalline silicon. The company uses a flexible, stainless-steel substrate and polymer-based encapsulates; the cell is deposited using a vapor-deposition process at low temperatures, meaning the energy payback time is comparatively short.
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