‘Triple Green’ is the new motto in photovoltaics: the drive to produce modules that generate clean energy, that are recycled and – what’s more – ecologically produced. It’s an effective way for the solar industry to further boost its image and sustainably cut costs. However, this perfect triad is difficult to implement because “green factories” require high initial investment. PES investigates…
This new way of thinking does not originate from China or the USA, but from Osterweddingen in Saxony-Anhalt; a little town near Magdeburg, where a company called Malibu manufactures modules from thin-film silicon and now cleans its process chambers with fluorine rather than the hazardous greenhouse gas nitrogen trifluoride (NF3). And while this does not sound too spectacular, it affords major ecological benefits: “It allows us to avoid any emission risks,” says Malibu Production Manager Antje Bönisch. If inadvertently released into the atmosphere, NF3 is 17,200 times more dangerous for global warming than carbon dioxide. By comparison fluorine, she says, has no greenhouse gas potential. This turn towards ecological processes only becomes really attractive for the company through falling operating costs. “We are saving a six-digit sum every year,” says 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. And since plenty of material ends up on the chamber walls in this process, these chambers 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 ten per cent of the total process time in a vacuum chamber, but fluorine reduces this time by half thanks to its high avidity, explains Linde-Manager Andreas Weisheit. This improves the line throughput and cuts costs.