Blu-ray Discs Can Enhance Solar Efficiency

Monday, December 8th, 2014
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One of today’s most popular audio-visual storage mediums could double as an ideal means of enhancing the efficiency of solar PV cells.

Engineers have uncovered a novel and unexpected method for enhancing the performance of solar photovoltaic cells the at makes use of a commonplace hi-tech device from an unrelated field.

An interdisciplinary research team from Northwestern University has discovered that Blu-ray discs, a opular medium for the storage of high-defintion audio-visual data, could also double as outstanding means for boosting the light absorption  and efficiency of solar cells.

Engineers have long known that the scattering of light by the variable texture of a solar cell’s surface can significantly raise its efficiency. To this end, they have long sought textures which are capable of maximising this effect for moderate cost.

The researchers suspected from the outset that the dense, quasi-random patterns of the Blu-ray discs would provide an ideal texture for light scattering.

These algorithm-based patterns have been improved and refined by engineers over the course of decades, enabling them to store far more data than their predecessors, the CD and the DVD.

Jiaxing Huang

Jiaxing Huang

“We had a hunch that Blu-ray discs might work for improving solar cells, and, to our delight, we found the existing patterns are already very good,” said Jiaxing Huang, associate professor of materials science and engineering at the McCormick School of Engineering Applied Science.

“It’s as if electrical engineers and computer scientists developing the Blu-ray technology have been subconsciously doing our jobs too.”

Huang and his colleague Cheng Sun, an associate professor of mechanical engineering at McCormick, led a team of researchers in testing a variety of Blu-ray discs across the full gamut of film and television genres – including action, dramas, documentaries, cartoons and black-and-white materials.

They discovered that irrespective of content, the Blu-ray discs all proved capable of increasing the light absorption of solar cells to a greater extent than other similar options.

“We found a random pattern or texture does work better than no pattern, but a Blu-ray disc pattern is best of all,” said Huang. “Then I wondered, why did it work? If you don’t understand why, it’s not good science.”

Huang’s wife, Shaorong Liu, a database engineer at IBM, speculated that the improved scattering of light was most likely related to the enhanced data compression achieved by Blu-ray discs.

This prompted Huang and Sun to seek advice from one of their colleagues at McCormick, Dongning Guo, an associate professor of electrical engineering and computer science, as well as an expert in information theory.

Working with Guo, the researchers managed to determine that the algorithms employed by the Blu-ray standard are the key to their enhanced light trapping capabilities.

Blu-ray standard algorithms serve two main purposes – achieving the maximum degree of compression by converting video signals into an ostensibly random binary sequence of zeroes and ones, and increasing error tolerance by introducing controlled redundancy into these sequences, thus restricting the occurrence of consecutive zeroes and ones.

These algorithms just happen to result in microscopic strings of bumps and pits on the surface of Blu-ray discs which are excellent at scattering light, thus optimising light absorption across the full range of the solar spectrum.

According to the researchers, a Blu-ray patterned solar cell can achieve an overall broadband absorption enhancement of as high as 21.8 per cent.

The research provides an outstanding reason to recycle discarded Blu-ray discs, which are huge in number given the immense popularity of the medium, and could have applications for light absorption across a broad range of solar cells.

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