Turning on the sun offers bright future01 December 2006

Increasing demand for photovoltaic solar cells has taken production at Sharp's factory in Wrexham from producing just 200 working modules in the first month of production in March 2004 to 2,400 panels per 24 hours on three production lines in February 2006, representing 110MW per year.

The manufacturing process is fraught with potential problems arising from the need to connect together and mount very fragile silicon wafers that are only 180 microns thick - with plans to reduce this thickness to 150 microns in the near future.

Growing demand means the factory, which used to make VCRs, is likely to be fully occupied, with further opportunities offered not only by its current range of products, but also its latest 'Tandem Structured Thin Film' technology, which involves vapour deposition of silicon on to areas of window glass in such a way that the silicon is in a microcrystalline, rather than amorphous, film. Efficiencies are in the range of 6% to 9%, approaching that of polycrystalline silicon wafers at 8% to 12% and monocrystalline wafers at 20%.

With shortages of electronic grade single crystal silicon arising because manufacturers can get a better price supplying chip makers, the potential to make office windows into solar cells - workers inside can still see out - opens up the possibility of manufacturing the devices on a scale that would start to make real inroads into world energy needs. It has been calculated that the world's entire requirement for all kinds of energy could be met by 20% efficient photovoltaic cells covering an area of 360,000km2 of desert: ie, an area 600km x 600km. In practice, it's more likely offices with south-facing frontages could easily power themselves, as could many homes.

Even in the UK, there is sufficient solar insolation that about six polycrystalline panels with a total area of 8m2 would generate 1kWp, or 850kWh per year, out of a total annual electricity requirement of around 3000kWh. The problem is the installed cost - about £8,000 for 1kW, partly arising from the cost of using trained professionals to carry out any task on a house roof, but also from the actual cost of the panels. Yet these come with a 25-year performance guarantee and indeed the first panels made by the company and installed in lighthouses off the Japanese coast in the early 1950s are still working.

The present manufacturing process involves robotically lifting the wafers with suction cups and then connecting the presumably diffusion-bonded conducting tapes to each other. Bus bars then have to be soldered on to the tapes, so the cells are all connected in series. This is followed by inspection, lamination between sheets of acetate, curing, framing, connection and testing. There are presently two semi-automated production lines and one manual line to try to keep up with demand.

"Inspection and soldering are critical," says Gordon Butler, general manager of the solar panels department. "In the first month of production in March 2004, we only produced 200 working modules. Now we can install a new line and it goes into production right away." Each employee works two day shifts and two night shifts, each shift being 12 hours long, with four days off.

The robotic machines, which are a mix of Japanese and Chinese, all bear the slogan, 'Share your wisdom to take us upward'. The company is now working on ways to re-use some of the broken, dirty and distorted wafers that are rejected by robotic inspection.

SOE

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