Pushing against the receding darkness of basic science, researchers are looking at the physics behind capturing and producing light—work that could illuminate breakthroughs in clean energy.
In the fight against climate change, governments and private companies are focusing much of their attention on engineering devices like light bulbs and solar cells, chasing single-percentage-point efficiency gains.
These marginal improvements could have major effects: The U.N. Environment Programme estimated that 19 percent of the world’s electricity goes toward lighting, accounting for up to 8 percent of global greenhouse gas emissions.
In the United States, the residential and commercial sectors consumed 412 billion kilowatt-hours of electricity in 2014, amounting to 11 percent of total electricity use, according to the U.S. Energy Information Administration.
Meanwhile, the world has now deployed more than 178 gigawatts of solar photovoltaic power, comprising 1 percent of the world’s electricity generation, according to the International Energy Agency.
However, scientists say that there is still fundamental science to explore when it comes to harnessing light and that figuring this out could unlock completely new ways to design and build clean energy systems. And marginal improvements may be too little and too late to make a big dent in the changing climate.
Looking to plants to improve renewable power
In a study published last week in the journal Nature Communications, a group of researchers studied a device that mimics how plants use sunlight to do useful things.
Jürgen Hauer, a co-author of the report and a junior research group leader at the Photonics Institute of the Vienna University of Technology, explained that natural systems have evolved to use light efficiently, but there are some caveats before engineers can design a solar cell that works as effectively as a leaf.
“Natural systems don’t have any evolutionary pressure to make the most structured system,” he said. “They are much more complicated and flexible than anything you could dream of producing on an industrial scale.”
A living organism grows, repairs itself and adapts to its environment, while a solar panel has to remain intact for 20 years or more. Still, the researchers reasoned that there might be some useful properties in the initial steps of photosynthesis, particularly where a molecular structure captures light.
The team investigated an artificial light harvester, an aggregate of thousands of individual light-absorbing molecules arranged in a cylinder that is analogous to the antenna complex in plants that captures and transfers energy from light.
Using short laser pulses, Hauer and his collaborators watched how energy behaved in the harvester. From past experiments, two competing theories emerged to explain how plants manipulated solar energy. One held that energy was contained in vibrations within molecules. The other said quantum effects were at work, with energy held in excited electrons shared between molecules.
The experiment showed that the laser pulse created an energy oscillation in the harvester that lingered for longer than either model would predict. “What we saw was the oscillation is electronic, but it needed a vibration to be so long-lived,” Hauer said. “The truth was somewhere in the middle.”
Teasing out how plants use light could lead to improvements in renewable energy, like designing solar materials that optimize both electronic and vibrational energy transfer. “If we understand that better, we can take these design principles and apply them to a new generation of solar cells,” Hauer said.
Lighting the way to new solar panels
Another study, published last week in the journal Physical Review Letters, presented a light-emitting device that punches well above its weight, making it appear 10,000 times larger than its physical size.
The device in this case is a resonator, a structure made from materials that concentrate and amplify light, exploiting its wavelike properties. The resonator, when embedded in a material with a refractive index approaching zero (a vacuum has a refractive index of 1), produced a light cross-section orders of magnitude bigger than its actual size.
These properties are useful in a variety of applications, explained Ming Zhou, lead author of the report and a doctoral student in electrical and computer engineering at the University of Wisconsin, Madison. Because of its amplification, the resonator can improve the performance of cameras looking for tiny wisps of light, such as those used in microscopes.
Its energy scattering abilities could make the resonator a good passive cooling system, like an extremely efficient heat sink. It could also offer more efficient illumination in lighting applications.
The resonator could also improve solar panels that rely on concentrators. “The solar cell industry uses lenses, so the concentration ratio is very limited,” Zhou said. “For solar cells, you want to concentrate light in a small area to produce current.” The resonator’s light amplification drastically outperforms lenses in this task.
Both Zhou and Hauer cautioned that their work is far upstream and it will likely be years before their findings translate into better light bulbs and solar panels. However, such findings may light a path toward far superior clean technology.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500