03 August 2012
Researchers at The University of Arizona in Tucson, Arizona (US) have pioneered a new technology for making highly concentrating solar mirrors for concentrating solar power (CSP). With $1.5 million US from the US Department of Energy (DOE), the University’s Steward Observatory Mirror Laboratory, the same lab that builds the world’s largest mirrors for astronomical telescopes, now aims to optimise the mirror production process for cost-efficient mass production and extend it to solar thermal applications.
While most mirrors in CSP are cylindrical and are used for thermal power generation, The University of Arizona has build the prototype of a fully automated sun tracking structure that supports two dish-shaped, highly reflective glass mirrors, each measuring 10 square meters. “We developed a glass shaping technology for dish CPV, which is an unusual way of doing CPV. You take a large dish and you take the light off the focus and put it on a small array of CPV cells,” explains J. Roger P. Angel, PhD, Director at the Steward Observatory Mirror Laboratory and Regents Professor of Astronomy and Optical Sciences. “But the interest of the DOE is in our shaping process, because it actually is pretty accurate. We have slope errors close to one milliradian, which is about as good as it gets. And we are also able to shape reflectors by moulding process to basically any shape.”
In addition to the novel glass shaping technology, Angel’s Mirror Lab has also developed a process to increase the reflectivity of the mirror surface, which it will continue to perfect with the DOE money. “We made experimental reflectors with a different type of glass that has no iron in it,” Angel says. Their test mirror is over 95% reflective; an increase of about 1% over existing reflectors.
The DOE grant involves a collaboration with Arizona-based Rioglass Solar. Together, the University and the commercial glass manufacturer will continue to optimise the precision and reflectivity of the reflectors to beam even more sunlight at the PV receiver. Angel sees the potential in his technology to go into a high-volume production line and eventually be adapted to make tempered glass.
Angel’s dish mirror prototype, which focuses sunlight onto a glass ball the size of a grapefruit and from there onto a small array of 36 highly efficient spacecraft PV cells, generated 2.5 kilowatts of electricity in a recent test. The university projects that an array of sun trackers on an area measuring about seven square miles (about 18 square kilometers) would generate 10 gigawatts of power during sunshine hours, which is roughly equivalent to the amount of electrical energy the biggest nuclear power plant in the US is generating.
Written by Sandra Henderson, Research Editor, Solar Novus Today