New renewable energy-powered light bulbs that work even at night

Researchers have developed a relatively inexpensive way of providing a renewable source of electrical energy for an LED light bulb even during the blackest night, which may be vital to solving how we power homes with little to no sunlight.

Recently, solar cells have emerged as a growing market to provide renewable energy that could provide electricity. Compared to a decade ago, solar cells have become cheaper, more reliable, and more accessible to people looking for a greener way of powering their homes.

In a critical time where more and more people demand to cut carbon emissions, the call for greener alternatives have multiplied. However, solar cells are only an efficient source of renewable energy during the day; there is currently no similar renewable approach to generating power at night.

Notably, solar lights can be outfitted with batteries to store energy produced in daylight hours for night-time use, but the addition drives up costs.

Fortunately, researchers Aaswath Raman, lead and an assistant professor of materials science and engineering at the University of California, Los Angeles, and Stanford University scientists Wei Li and Shanhui Fan have developed a device that cuts through the issue of powering electrical devices even at night.

In their study published September 12 in the journal Joule, they detailed that their device uses thermoelectric technology, which harnesses the cold of space without active heat input to produce energy strong enough to power an LED light bulb.

This thermoelectric generator developed by Aaswath and fellow scientists harnesses temperature differences to generate renewable electricity. In this photo taken by Aaswath, the device is powering a small LED light.
Source: Aaswath Raman

Researchers have tested a theory where they harnessed a phenomenon known as radiative cooling, which happens when surfaces on the ground radiate heat into the atmosphere. This process can make a surface cooler than the air surrounding it, which explains why frost forms on the grass even if the air temperature is above freezing.

Researchers say their device is a useful form of renewable energy, primarily because of lighting demand peaks at night. “Beyond lighting, we believe this could be a broadly enabling approach to power generation suitable for remote locations, and anywhere where power generation at night is needed,” lead author Raman, said in a statement.

The prototype device was tested on a table 3 feet (1 meter) above the ground on a rooftop in Stanford, California, in late December. It was placed in a polystyrene enclosure covered in aluminized mylar (which minimizes thermal radiation) and protected by a wind cover. Inside the protective layers, researchers made the device draw heat from the air and send it back into the atmosphere, using a black emitter.

During the course of the said experiment, researchers noted that their make-shift device was able to power an LED using a voltage boost converter passively, and measured that over 6 hours the device can generate as much as 25 milliwatts of energy per square meter.

The researchers noted that their device, with some modifications, can easily be scaled to increase performance and produce a more substantial amount of energy. They also emphasized that their device is an inexpensive product to create since the radiative cooler consists of a simple aluminum disk coated in paint, while all other components can be purchased off the shelf.

However, compared to typical solar cells, their device remains to underperform, and the amount of electricity it generates per unit area remains relatively small, limiting its widespread applications for now, but the researchers predict it can be made twenty times more potent with improved engineering.

For example, the researchers suggest increasing heat-exchange efficiency by reducing heat gain in the radiative cooling part of the device. The device may also work best in hotter and drier climates, the team noted.

It is also worth developing since the device p to be able to work during the night, while solar cells have no sunlight to convert into energy.

“Our work highlights the many remaining opportunities for energy by taking advantage of the cold of outer space as a renewable energy resource,” Raman said. “We think this forms the basis of a complementary technology to solar. While the power output will always be substantially lower, it can operate at hours when solar cells cannot.”

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