String Ribbon™ Modules:

Cleaner, More Efficient Silicon Technology

Imagine a way to create solar wafers, chips and panels that is less expensive, cleaner and more effective than traditional silicon production methods. Science fiction? No: it’s the reality of String Ribbon™ Technology, originally conceived in the 1980s by Emanuel M. Sachs, a pioneering professor of mechanical engineering at Massachusetts Institute of Technology, and brought into practical application by Evergreen Solar, Inc.

String Ribbon™ Technology is based on the natural science of surface tension. Think of the way a child blows a soap bubble. The surface tension between the soapy solution and the ring-shaped wand creates a bubble. This is similar to the way Evergreen Solar makes silicon wafers. The main difference is instead of using a wand, Evergreen Solar uses two parallel filaments called strings. When pulled through a silicon melt, the molten silicon spans and solidifies between the strings, creating a long ribbon that is harvested for further processing into solar cells.

One of the factors in assessing environmental impact is embodied energy, which is the energy consumed by all of the processes associated with creating a product (in this case silicon wafers), from the acquisition of natural resources to product delivery. It includes the manufacturing of materials and equipment, the transport of the materials and the administrative functions. Conventional technologies for producing silicon wafers are based on energy-intensive casting, machining and wasteful wire sawing of large silicon blocks. With String Ribbon™ Technology, the process is continuous, silent and clean, resulting in significantly less embodied energy.

Evergreen Solar produces solar wafers, cells and panels. String Ribbon™ modules are extremely efficient and produce a low carbon footprint compared with other silicon production techniques. Borrego Solar’s Chief Marketing Officer, Mike Hall, notes, “We’re excited to offer Evergreen’s String Ribbon™ solar modules as part of our goal to pursue new technologies that provide customers greater value and increased sustainability.” For more information, see www.evergreensolar.com.

Images courtesy of Evergreen Solar, Inc.