New Kind of 'Solar' Cell Shows We Can Generate Electricity Even at Night

Traditional solar technology absorbs incoming sunshine photons to generate a voltage. Some materials, strange as it may seem, have the ability to function in reverse, creating power while radiating heat back into the frigid night sky.

A group of Australian engineers has now shown the theory in reality, generating power using the same technology found in night-vision goggles.

The prototype currently only produces a small amount of energy and is unlikely to become a competitive source of renewable energy on its own – but when combined with existing photovoltaics technology, it could harness the small amount of energy provided by solar cells cooling after a long, hot day's work.

"Photovoltaics, the direct conversion of sunlight into electricity, is an artificial process that humans have developed in order to convert the solar energy into power," Phoebe Pearce adds, a physicist from the University of New South Wales.

"In that sense, the thermoradiative process is similar; we are diverting energy flowing in the infrared from a warm Earth into the cold Universe."
You may force electrons in any material to emit low-energy ripples of electromagnetic radiation in the form of infrared light by jiggling them with heat.

Even though this electron-shimmy isn't particularly impressive, it has the ability to start a sluggish stream of electricity. All that's required is a diode, which is a one-way electron traffic signal.
A diode, which is made up of the correct components, may shuffle electrons along the street while slowly losing heat to a colder environment.

The mercury cadmium telluride diode is used in this example (MCT). MCT's capacity to collect mid- and long-range infrared light and convert it to a current has already been shown in systems that detect infrared light.

What's not obvious is how this specific method may be employed as a reliable power source.

One of the MCT photovoltaic detectors tested produced a power density of 2.26 milliwatts per square meter when warmed to roughly 20 degrees Celsius (almost 70 degrees Fahrenheit).

Granted, boiling a pitcher of water for your morning coffee isn't quite enough. For that simple operation, you'd probably need enough MCT panels to cover a few city blocks.

But that's not really the point, considering that the area is still in its early stages and that the technology has the potential to advance greatly in the future.

"Right now, the demonstration we have with the thermoradiative diode is relatively very low power. One of the challenges was actually detecting it," states Ned Ekins-Daukes, the study's lead researcher.

"But the theory says it is possible for this technology to ultimately produce about 1/10th of the power of a solar cell."

With such high efficiency, it may be worthwhile to weave MCT diodes into more traditional solar networks so that they may continue to charge batteries long after the sun has set.

To be clear, engineers have been mulling about the possibility of harnessing the planet's cooling as a source of low-energy radiation for some time. Different strategies have produced various outcomes, each with its own set of costs and advantages.

Yet, by pushing each technology to its limits and fine-tuning its ability to absorb additional infrared bandwidth, we may create a suite of technologies capable of extracting every last drop of energy from virtually any type of waste heat.

"Down the line, this technology could potentially harvest that energy and remove the need for batteries in certain devices – or help to recharge them," Ekins-Daukes adds.

"That isn't something where conventional solar power would necessarily be a viable option."
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