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Global Solar goes back to future with thin film solar

Nothing like metal vapor for making solar cells, says Global Solar.

When it comes to CIGS (copper indium gallium selenide) solar cells, Global Solar has decided not to fight convention.

The Tucson-based company is ramping up for mass production of CIGS like a number of other companies, but the interesting thing about its tack is its manufacturing process. Global will use the vacuum evaporation process, which involves converting the active CIGS materials into a vapor and then letting them condense onto a glass substrate or thin film in a precise pattern.

The evaporation process has been extensively studied at the National Laboratory Research Lab, which has produced experimental CIGS cells that can convert a high 19.5 percent of the sunlight that strikes them into electricity.

However, it has been challenging to speed up the process to produce large volumes of materials. Thus, several CIGS start-ups have experimented with sputtering the material onto substrates (Miasole, Daystar), printing it (Nanosolar), or electroplating it onto rolls of thin film (Solopower). Some of these other processes also can provide, potentially, a better utilization of the material and higher efficiency.

Unfortunately, no one has yet perfected these alternatives, and some have had to delay production.

"Rather than reinvent the wheel, we decided to pursue a workable technology," said Global Solar's Chief Technology Officer Jeffrey Britt. "If you do evaporation right, you can get high utilization."

Global currently has the capacity to produce about 5 megawatts worth of solar cells a year, which isn't much, and says it can achieve an 11.5 percent efficiency on cells coming off of its production line. It will next try to open a 60-megawatt facility in January 2008 and raise efficiency to 13 to 14 percent.

The timing will be interesting. Most other CIGS companies are aiming to go into mass production next year, too. Right now, it's hard to say who will come in first. (Global, by the way, has been around since 1996.)

The company will initially concentrate on CIGS cells printed on glass that can fit into conventional solar panel frames. Later, it will move to thin films, which cost less. The military will likely be early customers, Britt said.

"We believe we can achieve a 30 percent cost reduction" over silicon solar cells with thin films, he added.