String Ribbon

String Ribbon solar cells is proprietary technology developed by Evergreen Solar.

Technology Description

String Ribbon describes a method of producing high grade silicon wafers suitable for the photovoltaics industry. The name describes the manufacturing process, where strings are pulled through molten silicon and pressed to form a ribbon of silicon crystals. The ribbon is then cut into lengths to form solar cells.

String Ribbon is advantageous to other wafer production methods as wafers are manufactured to the correct specification avoiding the need for wire sawing of silicon blocks. Silicon accounts for more than 50% of manufacturing costs in producing first generation solar cells, where most of the silicon is discarded as waste at the sawing stage of manufacture. Evergreen are able to manufacture silicon wafers to the appropriate dimensions avoiding the expensive sawing process meaning that this technology requires 1% the silicon when compared to mainstream products.

String Ribbon technology offers a cheap manufacturing technique however is not capable of achieving the same electrical performance as wafer technology. Typically a wafer will convert 15-16% of the incoming light into electricity where String Ribbon Solar Cells are capable of converting 8-10%. In research laboratories the technology has reached as high as 17.8% however cannot be produced commercially to this specification. Wafer technologies have reached as high as 25% in laboratory conditions.

Production Estimates

Year	Production Capacity	Production	Installed Capacity
2006	-	28 MW	-
2007	107 MW	66.2 MW	-
2008	188 MW	125 MW