Ceramic Industry

Tubular Glass Solar Energy Advancement

August 1, 2011
Glass tubes improve the performance of a new rooftop solar panel system.

A new proprietary rooftop solar panel system has been designed that uses glass tubes rather than traditional flat panel systems.* Compared to previous technologies, the system is easier to install and replace, as it is ideally set flat on rooftops with no anchors. The module design also enables a greater concentration of panels per square foot of rooftop area.

In addition, the cylindrical structure of the tubes creates a greater incident angle for light absorption, since it captures sunlight across a 360° photovoltaic surface. The new panels are also very durable. Each module is designed to produce electricity for more than 25 years while surviving the harsh rooftop environment. The modules are more resistant to weather impact than traditional systems; snow and dirt generally do not accumulate.

System Development

The new technology required R&D efforts and technological improvements for the glass tubes, which were traditionally used for pharmaceutical applications like vials and ampoules, starting with the chemical composition. The glass used for the solar panels is soda-lime neutral flint glass. Classified as Type III, this glass offers many advantages for solar applications.

One of the primary reasons for the use of soda-lime glass is the chemical reaction between the CIGS coating (copper, indium, gallium, selenium) and the glass chemistry of the inside tube. Consequently, in order to match the thermal expansion between the inside and outside tubes, the outer tube must be composed of soda-lime glass. In addition, since worldwide glass capacity is much higher for this type of glass, it offers greater ramp-up potential for the technology.

Technological developments were required to manufacture this glass to the standards needed for this process. The furnace used to manufacture the soda-lime glass is based in a tube drawing facility responsible for making other chemical compositions. New forming equipment and technologies were implemented to optimize the manufacturing process for this particular application. Several primary proprietary changes were made to improve strength and allow better resistance and durability of the solar modules while minimizing surface flaws. Equipment was also installed to continually monitor modulus of rupture.

Another improvement was made to optimize the tube-end stress patterns in order to minimize tension in crucial areas without eliminating beneficial compressive forces. Advanced stress measuring equipment, designed specifically for this application, was used to control this critical attribute.

The end finish of the solar tube is a very critical dimension for the achievement of its hermetic seal. A unique end shape has been designed for the solar application, which resulted in the development of advanced measuring equipment.

In addition to the dimensional requirements, the glass' chemical and physical properties had to be defined to optimize the tubing's glass light transmission performance. In an effort to optimize glass transmission, the tube drawing team reduced glass colorants (e.g., iron and copper), properly managed the glass colorant oxidation state, shifted the index of refraction (reduction in reflection losses), and continually conducts research in advanced anti-reflective coatings.

Manufacturing for Tomorrow

Manufacturing glass for solar energy tubes requires an elaborate quality system based on controlled processes, mechanical vision inspection and statistical process control (SPC) systems. In this case, all manufacturing lines are producing with 100% visual tube cosmetic and near-100% visual dimensional inspection systems for all conceivable parameters. Additional measured attributes include stress measurements and dimensional requirements for the ends, tube strength, and light transmission.

This American-made cylindrical tubing-based solar panel provides clean renewable energy, helps reduce CO2 emissions and is more aesthetically appealing than traditional flat panels. This new technology has the potential to improve the quality of life for everyone.

For more information, contact Nipro Glass Americas at 1200 N. 10th St., Millville, NJ 08332; call (856) 825-1400; or email glasstubing@amcor.com. Solyndra's website is located at www.solyndra.com.

*Designed by Solyndra.