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Posted on April 30, 2009 by  & 

Pollution challenges for photovoltaics

The annual report of Linde, the global leader in gases, is just out. It reveals what a fine job the company is doing to solve the challenging gas problems of conventional thin film solar cells as we await scale up of printed alternatives that do not have these problems. It says:
"In times of economic struggle, optimistic forecasts are few and far between, especially on the scale of this one: our experts anticipate that revenue from gases for solar power generation will increase by at least 30 percent year on year - or possibly even more. This prediction is based on the dynamic growth of the photovoltaic industry, and particularly thin-film photovoltaics.
Our expectation is that from 2012, producers of photovoltaic modules will already be spending more on gases than flat-screen manufacturers, for instance. And from 2017, the photovoltaic sector even looks set to overtake microchip manufacturing - previously by far the largest consumer of electronic and specialty gases.
These forecasts stem from the likelihood that solar energy will continue to gain in importance worldwide - both to reduce carbon dioxide emissions, and as a replacement for dwindling fossil fuel resources. The management consulting firm Frost & Sullivan anticipates that revenue from solar cell and module manufacturers will more than double by 2012, increasing from the current level of around USD 7bn to USD 16.4bn. The deciding factor here will be further technical innovations in solar module production.
The emergence of thin-film technology as a viable bulk production method for large-scale solar modules unleashed a veritable global race to set up the necessary facilities. Germany is a hotspot here, but solar plants have also been constructed in Southern Europe, Japan, China and India. And with the US energy policy set to change course under the new administration, North America may also become a major market for solar power.
Our subsidiary Linde Nippon Sanso and other Linde Group companies present in Asia are all set to participate in this dynamic growth. Linde is already market leader in the silicon-based thin-film solar cell segment and a partner to almost all the solar cell manufacturers in the world.
Linde has collaborated on more than 20 thin-film cell production projects across the globe to date, from initial engineering to plant expansion. The facility in Ourense (Spain) is a notable example. This is where the T-Solar company constructed the first Spanish thin-film solar cell plant. It opened for operation in mid-2008 and produces solar modules with dimensions up to 2.2 by 2.6 metres (5.72 square metres) - five times the size of conventional silicon wafer-based modules. Following a start-up phase, T-Solar will manufacture modules with a total power capacity of 40 megawatts (MW) per year here, employing a staff of around 190 and generating revenue in excess of EUR 100m.
Linde's contribution to this facility extended from designing the gas supply concept through engineering and project management to turnkey delivery. The supply equipment includes gas tanks and air compressors, a kilometre-long pipeline system, numerous valves and dependable safety installations. Among the latter are 150 gas detectors, for instance, to prevent unchecked leakages."
In another section it says:
"The solar cell industry experienced a major growth spurt in 2008, with new production facilities springing up across the globe, especially in Europe and East Asia. This is of great significance to the industrial gases sector, because gases play a key role in the manufacture of solar cells and it is impossible to imagine several of the steps in the process (etching, doping, layer removal) without them. However, gases which are harmful to the climate are also used in the process, particularly for cleaning the process chambers. This applies in particular to sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3). An SF6) molecule has a global warming potential which is 22,000 times greater than that of a CO2) molecule and an NF3) molecule 11,000 times greater.
Therefore, the research and development activities in our Electronics Global Business Unit are focusing on reducing or even preventing the discharge of these gases into the atmosphere, by recycling them or by performing the steps in the process using other less harmful gases. We have devised a solution to recycle around half of the unused SF6) (unused for environmental protection reasons) from the epitaxy chamber, feeding it back into the production process following purification. This closed-loop technology recaptures 100 percent of the residual gas for cost-effective reuse. Two of these SF6) recycling systems are already in operation in solar cell plants in Germany.
Another option is to eliminate completely the use of greenhouse gases for cleaning purposes and instead to generate fluorine, the active cleaning agent, directly where it is required. Unlike NF3), pure fluorine does not contribute to the greenhouse effect. Tests in Linde's development laboratory in San Marcos, California, have shown that pure fluorine significantly speeds up cleaning, as well as improving the results. The use of fluorine therefore increases productivity and cuts NF3) consumption. It is possible to switch from NF3) to a fluorine generator without major modifications to existing distribution systems. Linde had already developed the enabling technologies by the end of the 1990s and has been gathering experience with on-site fluorine generators for semiconductor customers since 2003. From there it was just a short step to implementing this process in solar-cell production, and over 20 customers across the semiconductor, solar-cell and LCD industries are now using our fluorine generators."
Top image: Spain's first facility for thin-film solar cell production opened for operation in Ourense in mid-2008.
For more attend Photovoltaics Beyond Conventional Silicon USA 2009 Dec 2-3, San Jose, USA.

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Posted on: April 30, 2009

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