US breakthrough promises "solar panels" that work in the dark

As every good physicist knows, just because it is dark does not mean there is no light.

Or, to put it another way, we are constantly surrounded by infrared light that the earth radiates as heat after absorbing energy from the sun during the day.

Now researchers at the US Department of Energy's Idaho National Laboratory (INL) claim to have unlocked the secret of harnessing that energy through the development of microscopic nanoantennas, each with a diameter 1/25 the size of a human hair, capable of absorbing infra red energy. And they are confident commercial products based on the technology could be available within five years.

Speaking to BusinessGreen.com, INL physicist Steven Novack explained that the microscopic antenna work in the same way as conventional antenna such as those used by televisions or cell phones, but because of their size they can soak up energy in the infrared spectrum that is invisible to the human eye. " This is not a new idea," he said. "But advances in nanotechnology in recent years have finally allowed us to build these structures."

The development, which was debuted today at the American Society of Mechanical Engineers International Conference on Energy Sustainability in Jacksonville, has been heralded as a major breakthrough that has the potential to revolutionise the solar industry and provide a cost effective, highly efficient "solar panel" capable of generating energy day or night.

The INL team claimed that while conventional solar panels typically capture up to 20 per cent of the sun's energy, computer models suggested that nanoantenna boasting the right combination of materials, shape and size could harvest up to 92 per cent of the energy at infrared wavelengths.

Prototype silicon-based nanoantennas built using conventional nanotechnology production methods backed up these computer models, absorbing more than 80 per cent of the energy from the intended wavelength range. Initial experiments have also shown that the antennas continue to work effectively when embedded into sheets of plastic to create a panel or "skin" capable of capturing energy, potentially paving the way for "solar panels" that work during both the day and the night.

Novack admitted the technology still faces one major technical challenge in turning the captured energy into usable electricity. He explained that the nanoantennas create alternating currents that oscillate trillions of times a second, and harnessing such high frequencies is beyond the existing rectifier technologies typically used to convert alternating to direct currents.

However, he added that the researchers were working on using the same nanotechnology manufacturing techniques used to create the antennae to create a means for harnessing the energy and were confident the energy could be harnessed.

"We believe it is achievable," said Novack, adding that the team were aiming to delivering a complete, commercially viable cooling device based on the technology within five to seven years, and a device capable of turning infra red rays into to usable electricity within seven to 10 years.

Should the researchers deliver a means of harnessing the electricity the applications for the technology are potentially limitless.

Novack said that embedding the antennae into plastic-based "skins" would allow the technology to be integrated into everything from cars to clothes and buildings to electronic devices. Meanwhile, their ability to capture heat could be harnessed to waste heat generated by electronic devices or even power stations is captured and reused.

He added that because the antennae are mechanical devices they should also prove far cheaper to manufacture than chemical-based solar photovoltaic cells making it easier for them to attain commercial viability.

"The applications are potentially huge," he concluded. "I envision this being the technology that allows us to deliver a genuinely decentralised energy grid. "