June 2010
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solarpeq 2010 specialist article No. 6

Solar Production to become Greener

“Triple Green” is the new motto in photovoltaics: modules generate clean energy, are recycled and ecologically produced. This is how the solar power industry can maintain its positive image and effectively cut costs. However, this perfect triad is difficult to implement because “green factories” require high initial investment.

This time the innovation does not originate from China or the U.S. but from Osterweddingen in Germany: the Malibu company that manufactures modules from thin-film silicon now cleans its process chambers with fluorine rather than the hazardous greenhouse gas nitrogen trifluoride (NF3). This does not sound too spectacular but affords major ecological benefits: “It allows us to avoid any emission risks,” stated Malibu Production Manager Antje Bönisch. If inadvertently released into the atmosphere, NF3 is 17,200 times more dangerous for global warming than carbon dioxide. According to Antje Bönisch, fluorine has no greenhouse gas potential. In addition, operating costs are lower. “We are saving a six-digit sum every year, which gives Malibu a competitive edge on the extremely competitive thin-film market,” said Antje Bönisch.

The key to more efficient manufacturing is a so-called fluorine-on-site-generator made by the Linde company and connected to the supply lines of the plant. Malibu’s modules are made by vapour-depositing silicon onto glass in vacuum chambers. Since plenty of material ends up on the chamber walls in this process, these need to be purified after each coating cycle. The generator introduces the fluorine which then reacts with the silicon to form gaseous silicon tetrafluoride, which is pumped off, captured and reacted off.

The new method reduces climate risks and is fast: usually cleaning accounts for more than 10 % of the total process time in a vacuum chamber but fluorine reduces this time by half due to its high avidity, explained Andreas Weisheit Manager at the Linde company. This improves the line throughput and cuts costs.

Plenty of Chemistry and Energy

This makes Malibu one of the pioneers in the industry seeking not only rapid but also clean growth. Triple Green ideally means: in factories built with organic materials and supplied with energy from regenerative sources, silicon, wafers, cells and modules are produced with hardly any carbon dioxide emission or waste materials and only a minimum of energy, gas, acid and water is used.

The ambitious green motivation of the solar industry goes back to one reason in particular: its clean image is at stake because its rapid growth goes hand in hand with increased resource consumption and emissions. Over the past two years global module output has doubled to eight gigawatt (GW). And this growth is predicted to continue at the same rate according to forecasts. Eric Maiser of the German Engineering Federation (VDMA) explained that silicon generation requires high levels of chemical and energy resources: producers melt down sand to metallurgical silicon and then use hydrochloric acid to reduce it to liquid trichlorosilane. This then is thermally decomposed and in the process grows into solar-grade silicon in the form of ingots. The processes run at high temperatures and are “power guzzlers”. In most cases this power comes from nuclear and fossil-fuel fired power plants because conventional power is simply cheaper for producers and more easily available than that from regenerative sources.

The following wafer and cell manufacturing processes are just as resource consuming: when cutting the wafers out of the ingots nearly half the silicon is lost and must be melted back down for it to be re-used. For cleaning wafers, producers often use hydrochloric acid and for etching their surfaces poisonous fluoric, nitric acid and potash lye is used. The busbars applied as a rule consist of silver and aluminium. To electrically orient the crystals, companies use phosphoric acid. At the end of the day all of these chemicals end up in the waste water of the solar factories. Although this is treated, pollutants such as heavy metals and nitrates find their way into the sewage system.

Thin-film production also requires high amounts of energy and chemicals. CIS or CdTe modules are manufactured at high temperatures and in long processes from copper, indium, toxic selenium, cadmium and sulphuric acid or cadmium telluride. For thin-film silicon, manufacturers cleaned their chambers with NF3 until now. And however carefully they do this – they cannot prevent 100% of the greenhouse gas emissions. “17% are released into the atmosphere during the product life cycle,” stated Andreas Weisheit form the Linde company. According to Weisheit, this is also the reason for the rising demand for Linde’s fluorine generators in the photovoltaics industry.

Suppliers with Clean Solutions

However, solar system producers can do a lot more than just change their gas suppliers. Suppliers offer a number of possibilities to make the production greener. State-of-the-art production equipment increases the yield while reducing consumption levels. Suppliers of thin-film production equipment such as Applied Materials or Von Ardenne offer machines that apply the absorber material faster to larger surfaces. Machinery manufacturers specialized in crystalline systems such as Schmid supply plants that can process thinner silicon wafers. And there are also more and more recycling specialists that offer their services to PV. For instance, the Italian company Saita has recently begun offering cell producers a system that recycles 96% of the process water for reuse in a closed loop system. This reduces the fresh water requirements for cell production by 75% and thanks to this recycling no waste water ends up in the sewage system, explained Marketing Manager Carlo Enrico Martini.

Berlin factory planner ib vogt goes even one step further: he has developed a so-called “Greenfab” that is built and operated ecologically. It can produce up to one GW of solar energy. The energy required, is generated by solar or geothermal systems on site, explained Project Manager Lino Garcia. Waste heat is used for heating and cooling. Less dirty water ends up in the sewage system since a large proportion is recovered. Integrated logistics and transport concepts shorten distances and also boost energy efficiency. This means solar system manufacturers can use “Greenfab” to produce large amounts of PV technology efficiently and cleanly. Sippliers will present some of their green innovations and approaches from September 28 September - October 1, 2010 at solarpeq, International Trade Fair for Solar Production Equipment, taking place in Düsseldorf, Germany. glasstec, the leading international trade fair for the glass industry, will be held concurrently, offering the relevant solutions for solar glass.

However, as big as the benefits of green manufacturing are – the eco-breakthrough is a gradual rather than a sudden one. Though developed three years ago, ib vogt has not sold a single complete “Greenfab” yet according to Lino Garcia but always just single, ecologically very critical manufacturing components such as concepts for waste-water recycling. “In contrast to the chip industry, PV has not embarked upon the green manufacturing voyage yet,” remarked Carlos Lee of SEMI, the global semi-conductor association.

Green in Small Doses

So what is inhibiting the breakthrough of Triple Green in the solar sector? A decisive aspect is the high investment required for sustainable production. A Greenfab with one GW capacity is “definitely somewhat more expensive” than a regular 1 GW factory, explained Lino Garcia. This investment does pay off through energy and raw material savings, he says, but the exact amortisation period differs from case to case. What is key though: those investing many millions of Euros must know the time for their return on investment. After ten years it would probably be too late since the factory design and fittings would be obsolete considering the high speed of innovations in PV. As a result, the green factory would be fit for demolition before it yields a profit.

Moreover, recession has slowed down investment. Many producers have faced declining sales and profits. “At a time like this major spending is taboo,” said Kevin Reddig of the Fraunhofer Institute for Manufacturing Engineering and Automation in Stuttgart. The introduction of green manufacturing technologies and processes currently suffers the same fate as the implementation of novel cell concepts: the commercialization of complex solutions associated with high financial spending such as the back contact cells are being postponed. Instead, manufacturers focus on the less expensive optimization of standard cells and are satisfied with moderate efficiency gains.

Since “green” is expensive, its profitability is vague and the sector is forced to save, there will be a rather gentle transition to Triple Green. “Green will come carefully dosed,“ stated Maiser of VDMA. Lee at SEMI refers to the developments in the semi-conductor industry, which took years to sizeably reduce its consumption. By their own accounts, it took STMicroelectronics, Europe’s largest semi-conductor producer, from 1994 to 2009 to reduce its CO2-emissions by 65%, its energy consumption by 54%, its water consumption by 70% and its waste by 71%.

Today, the solar sector stands where the chip industry used to be 15 years ago. The solar group Solarworld does not build a Greenfab but first creates transparency in its Sustainability Report for all its relevant environmental data and that of its suppliers thereby paving the way for green investment. Module maker Solon pursues the same avenue: it has spent EUR 200,000 on a new environmental management system to gain an overview of where sustainable solutions make business sense at all. These companies are guaranteed to reach the next green milestone – but presumably only after the crisis.