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Schott Takes a Shot at Solar

Photonics.com
May 2009
ALBUQUERQUE, N.M., May 12 2009 – In little over a year’s time, Schott Solar planned, contracted, built and began operations at the first production facility in the world to manufacture both photovoltaic modules and receivers for concentrated solar power (CSP) installations. According to the company, the solar industry is able to support both technologies at a large scale.

CSP.jpg
A demonstation of a CSP receiver and parabolic mirror setup. (Photos: Melinda Rose, Photonics Media)

At the new, 200,000-sq-ft facility, which celebrated its grand opening on May 11, the bulk of the space is devoted to making steel-and-glass tubes that act as receivers in CSP operations. The 13-ft-long tubes consist of a glass tube that surrounds and protects a second tube made of steel. The inner cylinder is filled with an oily heat-transfer fluid that absorbs the brunt of the sun’s rays, which are directed – concentrated – onto each tube by a parabolic mirror.

Several companies produce similar tubes, but Schott says that its product stands out because of the quality of the glass and the proprietary way in which it joins the steel and glass tubes. The life span of a CSP receiver tube can be adversely affected by differences in the way that metal and glass materials expand and contract due to swings in temperature. According to Schott, the bellows-like mechanism that holds the steel cylinder inside the glass one enables the company to offer a long warranty on the product, thus assuring easy calculation of the costs associated with generating electrical power with a CSP installation.

CSPCloseup.jpg
Closeup of a sample Schott Solar CSP receiver tube. The raised edge visible at the far left is where the main tube and the end cap are joined together.

As with any solar product, efficiency is essential to profitability. Another way that Schott addresses this issue is through a specialized sol-gel antireflection coating that is placed on the steel tubes. Inside the factory, the metal cylinders are dip-coated in the sol-gel material, which passes 96 percent of the Sun’s radiation that strikes it to the steel and further inside to the heat-transfer fluid. The coated tubes are then annealed, inspected and assembled with the glass tubes, bellows and end caps. The air between the two tubes is pumped out to create a partial vacuum to further increase efficiency.

When assembled into a typical 50-MW power-generating installation, 18,000 to 22,000 receiver tubes are connected in series in a closed-loop system. In operation, the thermal-transfer fluid passes through the receiver tubes at about 435 psi, parabolic mirrors concentrate sunlight onto the center of each tube assembly, heating the fluid inside to about 750 °F. The fluid is pumped continuously, eventually reaching a water storage unit; the hot thermal-transfer fluid heats the water, which produces steam that drives turbines that generate electric power.

LynnPVPanels.jpg
Photonics Media's Lynn Savage (foreground) and Schott North America's Brian Lynch examine Schott's PV panel test bed outside the company's new facility in Albuquerque. The plant is the first in the world to manufacture both PV panels and concentrated solar power receivers.

While these CSP receivers are being built, the other part of the plant is making the better known photovoltaic modules, also known as solar panels. Bigger than the panels used for domestic rooftops, the modules made at the Albuquerque plant are commercial-grade electricity producers. The photovoltaic panels vary in size, but typically 60 cells are tied together to form each module, providing a total output of approximately 240 W. Depending on the number of cells, each panel weighs 25 to 30 lbs and produces 210-250 W. Designed for a lifetime of abusive weather, the modules incorporate a glass substrate that can take a hammer blow with no effect.

Schott expects the new factory to annually produce enough photovoltaic modules to provide 65 MW of power, enough to furnish electrical power to thousands of commercial buildings.

Lynn Savage
lynn.savage@laurin.com


GLOSSARY
mirror
A smooth, highly polished surface, for reflecting light, that may be plane or curved if wanting to focus and or magnify the image formed by the mirror. The actual reflecting surface is usually a thin coating of silver or aluminum on glass.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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