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Engineers at UCLA and Stanford University have designed a generator that harnesses heat energy from the cool night air to ...

This clean energy invention runs on nothing but cold, night air

When Hurricane Dorian smothered the Grand Bahamas and Abaco Islands for 41 hours this month, it knocked out power and plunged nearly 70,000 people into darkness. Two years ago, Hurricane Maria smashed Puerto Rico’s electrical grid, leaving 3 million people without working lights, many of which stayed off for months.

Yet for 1.6 billion people worldwide, those bleak conditions are not the result of a natural disaster, but instead, part of everyday life without stable electricity. Even in the U.S., where energy access is universal, rural communities that lack the electrical infrastructure for less expensive power can struggle to keep the lights on.

A new project wants to illuminate this void — by making energy through the use of nothing other than the cold, night air.

A product of work by engineers at UCLA and Stanford University, the invention can be made with $30 of materials found at hardware stores and hobby shops. It is a modern twist on a technology that has existed for nearly 200 years, called thermoelectric generators.

As the name suggests, these generators harvest energy from heat, as it naturally moves from a hot place to a cold place. People have used thermoelectric generators to power devices off sources like body heat and campfires.

“What’s common in all of those examples is that they depend on a source of heat,” said Aaswath Raman, an engineer and materials scientist at UCLA who co-led the study published Thursday in Joule. “We kind of invert the problem. Instead of looking for a source of heat from which we can draw power, we’re instead taking advantage of a source of cold.”

Right now the device can only power simple LED lights or charge a phone, but Raman said a few tweaks could increase its energy output.

That’s a nifty idea, especially for emergency situations. But whether the invention ever reaches the wider public is questionable, according to one energy expert, given the current trends in renewable energy investments.

The new generator works by capturing heat energy in the air, which is warmed by the sun during the day. Heat in the air naturally wants to escape the planet into the cold of outer space. The device harvests the energy created by this heat transition, turning it into electricity. Photo by Jan Skowron/University of Warsaw/Handout via REUTERS.

The new generator works by capturing heat energy in the air, which is warmed by the sun during the day. Heat in the air naturally wants to escape the planet into the cold of outer space. The device harvests the energy created by this heat transition, turning it into electricity. Photo by Jan Skowron/University of Warsaw/Handout via REUTERS.

What the scientists did and how the device works

Raman said part of the project’s inspiration came from a trip to Sierra Leone that he took as graduate student about a decade ago. His group had partnered with a local NGO, and as they drove around at night, he was struck by how many of the smaller cities and towns had very little lighting.

“At one point, we’d been driving through what seemed like the forest or rural area. And I realized we’d actually been driving through a large town,” Raman said. “It was so dark we didn’t even notice that there were homes and businesses around us.”

Around this time, Raman and his colleagues were working on a concept called radiative cooling. When something becomes hot — whether it be solid, liquid or air — it naturally wants to move toward a place of being cold.

“It’s a natural phenomenon. It happens all the time,” Raman said. “If you’ve ever seen frost on the ground after a clear night, even though the air temperature was not below freezing, that’s often due to this effect.”

Watch: In the Bahamas, how relief groups are tackling ruined infrastructure and lack of power.

Raman had previously designed a coating — for air-conditioning units, refrigerators and roofing material — that expel heat and, in the process, cool what’s inside of them.

He said he was intrigued by this effect “and being able to use it to generate at least a small amount of power for an application like lighting.” From there, Raman’s mind turned to thermoelectric generators.

The thermoelectric generator, invented by Thomas Johann Seebeck in 1821, harvests power from periods of transitioning heat — but typically requires consistent high heat. Some spacecraft use nuclear-powered Seebeck generators because their heat and energy output can theoretically last for centuries.

Raman and his colleagues’ version of the thermoelectric generator works like a car windshield. The sun warms the glass all day. Once nightfall arrives, the heat begins escaping upwards from the glass in an attempt to head toward cooler spaces. (That’s why your car windshield sometimes fogs after nights that aren’t especially cold.)

But Raman’s setup doesn’t need the sun or use windshield glass. Instead it relies on an aluminum disc, painted black and set inside what is essentially a windproof shoebox. That’s glued to a small thermoelectric plate, which can convert heat into electricity, and the whole thing is glued on top of a metal block.

At night, the metal block is warmed by the surrounding air, which passes heat upward through the thermoelectric plate and into the aluminum disc, which in turn expels that heat toward the cold of space.

A schematic (left panel) and a photo of the new thermoelectric generator. Image by Aaswath Raman

A schematic (left panel) and a photo of the new thermoelectric generator. Image by Aaswath Raman

The pros and cons of pulling power from thin air

While this proof-of-principle device unlocks the energy stored in the very air that surrounds us, this study highlights what little power exists there. If you packed this thermoelectric generator into one square meter of space, it would yield about 25 milliwatts of power. The average American energy consumer uses 7 million times that amount of power in their homes every minute.

“You’re not gonna be able to run a full load from a typical house,” Raman said. But their generator would be useful for simple electronics — like LED lights and phone charging — in places completely off-grid.

That includes extremely cold locations like the Arctic, because theoretically all you need is a setting that isn’t very humid and has a temperature difference with outer space. Humidity is a problem because water vapor absorbs warmth, which would prevent heat from escaping the device.

“The best performance you will typically see is in hot, dry climates. Polar climates tend to be very dry but cold, so we still expect reasonable performance there,” said Raman, who added the new generator works in cloudy weather as long as the clouds aren’t too low in the sky.

Early modeling by their team suggests their generator could last 20 years and its energy output could be increased 20-fold with further investments in scaling up the project.

But will those investments ever come?

Powering the future of energy

That’s because a 25 milliwatt generator isn’t likely to turn the heads of many clean energy investors, said David Victor, co-chair of the Cross-Brookings Initiative on Energy and Climate.

“I’m concerned that this device probably is not competitive with other ways of generating energy at night or providing energy at night — namely having a solar panel with a battery pack connected with it,” Victor said.

That’s partially because investors — venture capitalists specifically — are moving away from early-stage ideas like Raman’s. Between 2011 to 2016, venture capital investment in renewable technology declined by 30 percent in the U.S., from $7.5 billion to $5.24 billion, according to the Brookings Institution.

“The clean tech boom was based partly on the idea that new innovations in clean tech will scale quickly,” Victor said, which meant venture capitalists could enter the industry early but then easily sell their shares once a startup became established. That helped drive advances in areas like solar tech, but eventually some technologies that took longer to mature became unattractive.

“Fuel cells, for example, have taken a long time to get to market,” and taken a long time for investors to see a return on their investment, Victor said. But early-stage investments in clean energy software remain strong because of expected quicker payoffs, he said.

But don’t let this decline in angel investing worry you if you’re a fan of solar, wind and other renewables. It is actually a sign of clean energy’s maturation.

Victor said green tech funders tend to fall into two groups. There are angel investors who gamble on early-stage concepts, which may or may not yield success — and then there are those more interested in mature products like solar and wind technologies.

Most of the cleantech money is now flowing into the second group, and it is what is driving the clean energy boom you keep hearing about. A U.N. report published this month shows 2018 was the ninth year in row where renewable energy investments exceeded $200 billion. Victor added that big tech companies like Siemens and Tesla have also taken on a bigger role in cleantech R&D, which means a big share of early-stage investments and advances are made in-house rather than through upstarts.

But Raman wants to reach locations where even solar panels and wind farms would be less appealing energy solutions than his innovation because they require regular maintenance or new parts. And indeed, Raman has partnered on another project that might build radiative cooling technology into solar panels. The panels could convert solar energy during the day, and then switch to emitting heat-based energy at night.

“There are definitely technical constraints [with our device] but the hope is that it can be useful in certain applications,” Raman said.

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