String Ribbon Silicon Solar Panels: Complete Technology Guide

Last updated: March 2026

String ribbon silicon is a solar cell manufacturing technology that produces crystalline silicon wafers in a fundamentally different way from the standard ingot-and-saw method used to make most solar panels. Pioneered commercially by Evergreen Solar, string ribbon technology promised to slash manufacturing costs by eliminating silicon waste — but ultimately failed to achieve commercial dominance despite genuine technological promise. This is the definitive guide to what string ribbon technology is, how it works, and what happened to it.

What Is String Ribbon Silicon?

Standard crystalline silicon solar cells are made from wafers cut from large silicon ingots or bricks. Sawing these ingots into thin wafers (typically 150–200 micrometers thick) wastes roughly 30–50% of the silicon as cutting dust, called kerf loss.

String ribbon silicon eliminates kerf loss entirely. Instead of casting and cutting, the string ribbon process grows silicon ribbons directly from a silicon melt:

1. Two high-temperature strings (the “strings” in “string ribbon”) are threaded through a shallow silicon melt
2. As the strings are slowly pulled upward, molten silicon is drawn up between them by surface tension
3. The silicon solidifies between the strings as it rises, forming a continuous thin ribbon of polycrystalline silicon
4. The ribbon is cooled, and the strings become embedded in the edges of the ribbon
5. The ribbon is cut into individual wafers for cell processing

The result: silicon wafers with zero kerf waste. Every gram of silicon feedstock that enters the process becomes a wafer, not cutting dust.

The Technology Behind String Ribbon

The Strings Themselves

The “strings” in string ribbon are high-melting-point fibers — typically made from carbon, silicon carbide, or other high-temperature materials. They must survive immersion in molten silicon at approximately 1420°C (2588°F) while being pulled continuously upward at a slow, controlled rate.

The strings serve two functions: they define the width of the ribbon (the distance between the two strings), and they provide a physical boundary that the silicon surface tension bridges as the ribbon forms.

Crystal Structure

String ribbon silicon has a polycrystalline (multi-grain) structure, similar to cast polycrystalline panels. The rapid solidification at the ribbon surface creates multiple crystal grains rather than a single crystal. This is why string ribbon panels look similar to standard polycrystalline panels — the characteristic blue, slightly uneven appearance.

The crystal grain boundaries in string ribbon wafers are a source of electron recombination that limits efficiency. Research efforts to improve grain boundary passivation were an active area of development, but string ribbon never achieved the efficiencies of monocrystalline silicon.

Ribbon Thickness and Dimensions

String ribbon wafers were typically 150–250 micrometers thick and approximately 87mm wide — the fixed distance between the two strings. This defined the cell width. Multiple ribbon-growing furnaces were used in parallel to achieve production scale, with each furnace growing ribbons continuously at a slow pull rate of a few centimeters per minute.

String Ribbon vs Standard Wafer Silicon: Performance Comparison

The efficiency gap between string ribbon and cast poly was approximately 1–2 percentage points — real, but not enormous. String ribbon panels from the Evergreen Solar era typically achieved 12–14% module efficiency.

Evergreen Solar: The String Ribbon Pioneer

Evergreen Solar was founded in 1994 in Marlboro, Massachusetts, USA, and became the primary commercial developer and manufacturer of string ribbon silicon solar panels.

• 1994 — Evergreen Solar founded; begins developing string ribbon manufacturing processes
• 2000 — Evergreen goes public on NASDAQ; raises capital to scale manufacturing
• 2001–2007 — Expands Marlboro, MA manufacturing; builds string ribbon into a commercially viable production process
• 2008 — Announces a joint venture with Jiawei Solarchina to build a 200MW string ribbon factory in China, seeking lower-cost production
• 2009–2010 — Closes the Marlboro manufacturing plant; transfers production to the China joint venture facility in Wuhan
• 2011 — Evergreen Solar files for Chapter 11 bankruptcy in August 2011, citing competition from Chinese manufacturers and inability to service its debt
• 2011 — Assets including the string ribbon technology and manufacturing equipment are sold through bankruptcy proceedings

Why String Ribbon Failed Commercially

String ribbon’s zero-kerf-waste advantage was real, but it wasn’t enough to overcome several structural disadvantages:

• Silicon prices crashed: String ribbon’s key advantage was silicon efficiency — using less feedstock per watt. When polysilicon prices crashed from $400/kg in 2008 to $15–20/kg by 2012, the silicon savings advantage largely disappeared.
• Throughput limitations: The continuous ribbon-pull process had lower throughput per furnace than batch wafer production. High-volume Chinese manufacturers investing in parallel casting and sawing lines could produce more wafers per capital dollar invested.
• Efficiency gap: String ribbon cells were 1–2% less efficient than the best cast poly and significantly behind mono. As the market standardized on 60-cell and 72-cell module formats optimized for cast wafers, string ribbon’s fixed cell dimensions became a constraint.
• Scale economics: Evergreen never achieved the manufacturing scale needed to drive down costs below Chinese commodity panel pricing. The 2010 move to China came too late to save the business.

String Ribbon Solar Panels Available Today

Commercial string ribbon solar panel production effectively ended with Evergreen Solar’s 2011 bankruptcy. No major manufacturer is currently producing string ribbon silicon panels for the commercial market as of 2026. The technology exists in research contexts and may appear in academic papers, but it has not been revived as a commercial manufacturing approach.

String ribbon panels can still be found on secondary markets — primarily Evergreen Solar ES-A-195 and similar models that were installed in residential and commercial systems between 2005 and 2011. These used panels occasionally appear on eBay and from solar salvage dealers.

The following historical price data covers string ribbon panels sold in North America during the 2008–2011 period:

Related Solar Technologies

String ribbon is part of a broader family of ribbon silicon research that included several related approaches:

• Edge-defined Film-fed Growth (EFG): A similar ribbon growth technique using a shaped die to define the ribbon geometry. Developed by ASE Americas (later RWE Schott Solar). Produced octagonal silicon tubes that were then cut into wafers.
• Dendritic Web: A ribbon growth technique developed at Westinghouse in the 1960s–1970s. Very thin ribbons with good crystal quality but difficult to scale.
• RGS (Ribbon Growth on Substrate): A more recent ribbon approach developed in Europe where silicon solidifies on a moving substrate.
• Kerfless wafer approaches (current): The zero-kerf-waste problem string ribbon tried to solve is still an active research area. Modern approaches include epitaxial liftoff and ion implantation kerfless wafering.

Frequently Asked Questions

What is string ribbon silicon solar technology?

String ribbon silicon is a method of manufacturing solar cell wafers by pulling continuous ribbons of crystalline silicon from a silicon melt using high-temperature strings. Unlike the standard method of casting ingots and sawing them into wafers, string ribbon produces wafers with zero silicon waste from cutting. The technology was commercialized by Evergreen Solar in the 2000s but is no longer in commercial production.

What happened to Evergreen Solar?

Evergreen Solar filed for Chapter 11 bankruptcy in August 2011. The company had accumulated significant debt funding its manufacturing operations and could not compete with rapidly falling Chinese solar panel prices. After closing its Massachusetts plant in 2009–2010 and moving production to a China joint venture, the company still could not achieve profitability. Its assets, including the string ribbon technology and patents, were sold through bankruptcy proceedings.

Are string ribbon solar panels good?

String ribbon panels were competent, functional polycrystalline panels — slightly less efficient than cast poly panels but otherwise similar in real-world performance. Evergreen Solar panels installed in 2005–2011 that are still operating should continue to produce electricity. The technology wasn’t bad; it simply couldn’t compete economically with the scale advantages of Chinese crystalline silicon manufacturing.

What are solar panel ribbons?

“Solar ribbon” or “solar panel ribbon” can refer to two different things: (1) string ribbon silicon — the manufacturing technology described on this page; (2) tabbing ribbon — the thin metal strips (typically tin-coated copper) used to connect solar cells together within a module. Tabbing ribbon is a component used in manufacturing all types of solar panels, not a panel technology itself. Suppliers of solar tabbing ribbon are separate from solar panel manufacturers.

Where can I find string ribbon solar panel specifications?

Evergreen Solar, the primary manufacturer, published datasheets for their ES-A series (195W, 200W, 205W) panels. These can sometimes be found through solar industry archives and the Internet Archive (web.archive.org). The main models were the ES-A-195-fa3b (195W), ES-A-200-fa3 (200W), and ES-A-205-fa3 (205W), all featuring 85 string ribbon cells per panel.