During the day, the sun provides the Earth with a steady stream of energy, while at night, the Earth returns heat to the cold outer space in the form of infrared radiation. Conventional solar technology has long taken advantage of the former, converting daytime sunlight into electricity. "Nighttime" solar power is only theoretical.
Two scientists from the School of Photovoltaic and Renewable Energy Engineering at the University of New South Wales in Australia have developed a device that provides the first demonstration of the possibility of nighttime "solar" power generation. The research has been published in the journal ACS Photonics.
The core device of the "night" solar technology is still the P-N junction of the semiconductor, but the function, working principle and direction of operation are totally opposite to that of traditional solar cells. The transfer of energy across this temperature difference is converted into an electromotive force by receiving heat energy radiating upward from the Earth (or other heat source) to a cooler region.
The emitted energy collector is not original in theory. It was first proposed in 2014, but this latest study is the first to prove it.
The two scientists developed a semiconducting device called a thermal emitting diode, a material similar to that used in night-vision goggles, which simulated the Earth radiating heat into space at night, demonstrating for the first time that measurable power was generated in the process.
The application of this technology is not limited to the use of infrared radiation in the environment at night, but it may have a wide range of applications in the future.
The technology could be applied to more or less any object that glistens under a thermometer, giving off infrared radiation, including energy from industrial waste heat and possibly even biomimetic devices that use the body's own heat to power implantable devices such as artificial hearts.
In the long-term, the technology could help wean some devices off batteries and photovoltaic cable, or recharge their batteries.
The technology is still in its infancy, however, because of its limited capacity to generate electricity from cold radiation, which is only one-hundred-thousandth the power of current solar panels.
When the temperature difference is only 12.5℃, the peak thermal radiation electrical power density per square meter is only 2.26 milliwatts, and the estimated radiation efficiency is 1.8%.
But researchers believe the technology is only the beginning, and that future power generation could be improved. There is still a long way to go in the development and optimization of the "night" solar power technology, and it will take time to achieve mass production and reduce the cost of using the technology, and new materials will need to be found for widespread use.
The future may include a combination of photovoltaic devices, or the solar panels and thermal emitting diodes widely used today, for "night solar" power generation.