Stargazing and Sunbathing

Roger Angel is busy these days perfecting a stellar system designed to help curb greenhouse gas emissions.

Angel, director of the Steward Observatory Mirror Lab at The University of Arizona, designs telescopes and has been in the astronomy field for more than 30 years. Now, he directs light on a different area of research—solar energy—but uses the same building blocks.

The Large Binocular Telescope Observatory is a large optical/infrared telescope that utilizes two 8.4 meter mirrors. When completed, it will be the world's most advanced optical telescope that will image planets outside our solar system.
Credit: ©Marc-Andre Besel, Wiphu Rujopakarn, and LBT Corporation

“The problem we have is sort of blindingly obvious and huge,” Angel said, referring to energy consumption and the effect tailpipe and industrial emissions have on Earth.

His solution requires another blinding force—the sun.

Converting sunlight to electricity has been a hot area of study. Angel and engineers are designing a system for concentrating solar power that involves collecting sunlight and focusing it on a receptor to convert solar radiation into electricity. His vision is to replace coal energy using solar power plants.

“If we can devise low cost mirrors and tracking systems, maybe we can have an economical solution with focused sunlight,” Angel said.

The Lab

Many of Angel’s designs have been created under the football stadium at the UA in the Steward Observatory Mirror Lab. It is here where innovative techniques in mirror shaping have been born.

Shape increases the efficiency of concentrating solar energy, and also explains the curved mirrors in telescopes and camera optics.

“The business of making mirrors and how to move and shape them is my territory,” Angel said.

The mirror design used for the Large Binocular Telescope, located in Arizona on Mount Graham, is a promising template for use in renewable energy. The size and curvature of the mirror reflects the similar solar design Angel has in mind.

Creating these dome-shaped mirrors, where light rays are captured and directed to a single point, has been the focus of some of the work in the lab.

The mirror lab houses telescope-making equipment the size of backyard swimming pools, dwarfing the people making mirrors that stretch 27 feet in diameter. The machinery used must be built on site since the equipment is too massive to transport.

“Most of what we do here is material science. It’s not astronomy,” Philip Pinto, astronomy professor at UA, said during a guided tour of the mirror lab. “How do you make the nuts and bolts to put things together and make everything work?”

This question is at the forefront of technological advancements taking place in the lab.

Angel’s Angle

So what do mirrors have to do with solar power? The concentrated solar power design uses mirrors to focus light on high-efficiency photovoltaic cells made of very small amounts of geranium instead of silicon, Angel noted. Photovoltaic cells, typically made of silicon, collect light to turn the sun’s radiation into energy.

Silicon—the raw material used in many photovoltaic cells—comes with a high price due to purification and refinement costs that transfer to high solar energy prices.

The concentrated solar power design may not travel far from home since sunlight concentrates in Arizona.

When it comes to maximum sunlight for solar energy, “the Southwest desert is a very good desert. There’s nowhere within Europe that has the solar resources we have here,” Angel noted. “It’s most economical to make utility solar energy in the Southwest.”

Solar thermal, a different solution to concentrated solar energy, uses the sun’s heat for steaming water to run turbines. Angel’s design, however, uses a relatively small amount of water—just enough to occasionally clean the surfaces for efficiency in capturing light.

The mirrors and photovoltaic cells “use water like a car does when you wash it, but not a lot compared to anything else,” Angel said, referring to the array of mirrors and photovoltaic cells.

Angel noted the absence of concrete as another encouraging aspect of the design. No concrete means less carbon dioxide emissions in the project development stages, and less impact on the land.

Producing two tons of cement releases two tons of carbon dioxide, a byproduct of both the energy required and chemical decomposition to make cement, according to the Commonwealth Scientific and Industrial Research Organisation.

Angel says he’s doing what he can to help provide solutions for climate change by making “more use of optics than people have done in the past.”