Picking up night waves

Future solar cells could operate 24 hours a day by collecting radiation emitted from the Earth at night and turning it into energy.


Future solar cells could operate 24 hours a day by collecting radiation emitted from the Earth at night and turning it into energy.

So believe researchers at Manchester University’s School of Electronic and Electrical Engineering, who are working on a new technology that would give solar cells the ability to collect light energy from multiple wavelengths.

The team has developed nano-diodes that detect terahertz waves lying at the far end of the infrared band, right before microwaves.

Project leader Aimin Song, a professor of nanoelectronics at Manchester University, said their nano-diode terahertz detector has a novel planar architecture and works at 1.5THz or 1,500GHz, the highest speed of electronic nano-devices to date.

He claimed that combining such a diode with an antenna would make it possible to collect energy from infrared waves and convert them into DC electricity.

Song said the technology would take advantage of the Earth’s greenhouse effect.

‘The Earth and the atmosphere absorb a lot of the sunlight,’ he added. ‘After absorption they slowly radiate this energy back but not in the visible light frequency range but in the infrared frequency band.’

Song said that the technology, which is known as rectenna because it combines a rectifier (diode) and antenna, has already been demonstrated to work for converting microwave energy into DC electricity with a claimed efficiency between 80 and 90 per cent. ‘If we develop this rectenna technology for the infrared frequency band, we can develop solar cells that operate at night time,’ he said. ‘This rectenna concept could potentially offer solar cells 80-90 per cent efficiency.’

Manchester University recently began a one-year commercialisation programme for the technology and Song said a spin-out company could be formed within the first half of 2010.

‘We hope at the end of this one-year programme to achieve the first prototype device to work at infrared frequencies,’ he said. ‘Our first prototype wouldn’t work for visible sunlight, but it would work to harvest energy in the night.’

Manchester University is also involved in a three-year EU-funded project beginning in January that will attempt to develop nano-devices that can both detect and emit terahertz waves.


Siobhan Wagner