A new renewable energy source generates power from the net emission of infrared radiation from the surface of Earth to space, "a vast and untapped energy source." This "strange and new" device is "something akin to a photovoltaic solar panel, but instead of capturing incoming visible light, the device would generate electric power by releasing infrared light" to the atmosphere, and ultimately to space.
How is this possible? Based upon the 2nd law of thermodynamics, heat only flows from hot to cold, i.e. from the hot +15C Earth surface to the average -15C cold atmosphere and then to very cold -455F [= -270C = 2K] outer space. This device generates electricity by releasing infrared radiation to the cold atmosphere, which causes cooling of the device and generates flow of current. In similar fashion, a solar cooker pointed at a clear night or day sky acts as a refrigerator to make ice when the ambient temperature is 10 degrees above freezing, by increasing cooling at the focal point.
The ancient Romans also used this principle to make ice [and some speculate ice cream] at ambient temperatures well above freezing by digging a hole and putting a pan of water at the bottom. The hole allows increased loss of heat from the warm water since it is only pointed at the -15C sky, thus causing the water to freeze at ambient temperatures higher than freezing.
What significance does this have for the conventional explanation of the 33K greenhouse effect on Earth? The conventional explanation claims infrared radiation from greenhouse gases or "radiative forcing" is forcing Earth's surface temperature to warm from the equilibrium temperature with the Sun of 255K up to the measured surface temperature of 288K [15C]. Per the Stefan-Boltzmann Law, this increase in temperature requires a net increase of heat flux from the atmosphere to the Earth surface of 150W/m2 [390-240]. This is absolutely impossible, because net heat flux must always be from hot to cold and entropy always increases per the 2nd Law of Thermodynamics. The fact that these devices work by cooling to the atmosphere proves the net effect of the atmosphere is cooling, not warming. Heat flow from cold to hot requires a decrease of entropy, which is impossible without work input [like in a refrigerator], and greenhouse gases cannot add any work input whatsoever.
Does this mean I'm a greenhouse effect denier? No, absolutely not. On the contrary, the 33K greenhouse effect absolutely does exist, but it is due entirely to the adiabatic compression of all gases [Earth's atmosphere is >99% non-greenhouse gases] within a gravity field, and is completely independent of man-made CO2. An atmosphere without greenhouse gases would be even warmer than one with greenhouse gases, because greenhouse gases increase radiative surface area and increase the emissivity of infrared radiation to space.
The ancient Romans also used this principle to make ice [and some speculate ice cream] at ambient temperatures well above freezing by digging a hole and putting a pan of water at the bottom. The hole allows increased loss of heat from the warm water since it is only pointed at the -15C sky, thus causing the water to freeze at ambient temperatures higher than freezing.
What significance does this have for the conventional explanation of the 33K greenhouse effect on Earth? The conventional explanation claims infrared radiation from greenhouse gases or "radiative forcing" is forcing Earth's surface temperature to warm from the equilibrium temperature with the Sun of 255K up to the measured surface temperature of 288K [15C]. Per the Stefan-Boltzmann Law, this increase in temperature requires a net increase of heat flux from the atmosphere to the Earth surface of 150W/m2 [390-240]. This is absolutely impossible, because net heat flux must always be from hot to cold and entropy always increases per the 2nd Law of Thermodynamics. The fact that these devices work by cooling to the atmosphere proves the net effect of the atmosphere is cooling, not warming. Heat flow from cold to hot requires a decrease of entropy, which is impossible without work input [like in a refrigerator], and greenhouse gases cannot add any work input whatsoever.
Does this mean I'm a greenhouse effect denier? No, absolutely not. On the contrary, the 33K greenhouse effect absolutely does exist, but it is due entirely to the adiabatic compression of all gases [Earth's atmosphere is >99% non-greenhouse gases] within a gravity field, and is completely independent of man-made CO2. An atmosphere without greenhouse gases would be even warmer than one with greenhouse gases, because greenhouse gases increase radiative surface area and increase the emissivity of infrared radiation to space.
A new renewable energy source? Device captures energy from Earth's infrared emissions to outer space
Date: March 3, 2014
Source: Harvard School of Engineering and Applied Sciences
Summary:
When the sun sets on a remote desert outpost and solar panels shut down, what energy source will provide power through the night? A battery, perhaps, or an old diesel generator? Perhaps something strange and new. Scientists now envision a device that would harvest energy from Earth's infrared emissions into outer space. Heated by the sun, our planet is warm compared to the frigid vacuum beyond. Thanks to recent technological advances, the researchers say, that heat imbalance could soon be transformed into direct-current (DC) power, taking advantage of a vast and untapped energy source.
"We’re talking about the use of physics at the nanoscale for a completely new application," says Federico Capasso.
When the sun sets on a remote desert outpost and solar panels shut down, what energy source will provide power through the night? A battery, perhaps, or an old diesel generator? Perhaps something strange and new.
Physicists at the Harvard School of Engineering and Applied Sciences (SEAS) envision a device that would harvest energy from Earth's infrared emissions into outer space.
Heated by the sun, our planet is warm compared to the frigid vacuum beyond. Thanks to recent technological advances, the researchers say, that heat imbalance could soon be transformed into direct-current (DC) power, taking advantage of a vast and untapped energy source.
Their analysis of the thermodynamics, practical concerns, and technological requirements will be published this week in the Proceedings of the National Academy of Sciences.
"It's not at all obvious, at first, how you would generate DC power by emitting infrared light in free space toward the cold," says principal investigator Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard SEAS. "To generate power by emitting, not by absorbing light, that's weird. It makes sense physically once you think about it, but it's highly counterintuitive. We're talking about the use of physics at the nanoscale for a completely new application."
Challenging convention
Capasso is a world-renowned expert in semiconductor physics, photonics, and solid-state electronics. He co-invented the infrared quantum-cascade laser in 1994, pioneered the field of bandgap engineering, and demonstrated an elusive quantum electrodynamical phenomenon called the repulsive Casimir force -- work for which he has received the SPIE Gold Medal, the European Physical Society Prize for Quantum Electronics and Optics, and the Jan Czochralski Award for lifetime achievement. His research team seems to specialize in rigorously questioning other physicists' assumptions about optics and electronics.
"The mid-IR has been, by and large, a neglected part of the spectrum," says Capasso. "Even for spectroscopy, until the quantum cascade laser came about, the mid-IR was considered a very difficult area to work with. People simply had blinders on."
Now, Capasso and his research team are proposing something akin to a photovoltaic solar panel, but instead of capturing incoming visible light, the device would generate electric power by releasing infrared light.
"Sunlight has energy, so photovoltaics make sense; you're just collecting the energy. But it's not really that simple, and capturing energy from emitting infrared light is even less intuitive," says lead author Steven J. Byrnes (AB '07), a postdoctoral fellow at SEAS. "It's not obvious how much power you could generate this way, or whether it's worthwhile to pursue, until you sit down and do the calculation."
As it turns out, the power is modest but real.
As Byrnes points out, "The device could be coupled with a solar cell, for example, to get extra power at night, without extra installation cost."
Two proposed devices -- one macro, one nano
To show the range of possibilities, Capasso's group suggests two different kinds of emissive energy harvesters: one that is analogous to a solar thermal power generator, and one that is analogous to a photovoltaic cell. Both would run in reverse.
The first type of device would consist of a "hot" plate at the temperature of the Earth and air, with a "cold" plate on top of it. The cold plate, facing upward, would be made of a highly emissive material that cools by very efficiently radiating heat to the sky. Based on measurements of infrared emissions in Lamont, Oklahoma (as a case study), the researchers calculate that the heat difference between the plates could generate a few watts per square meter, day and night. Keeping the "cold" plate cooler than the ambient temperature would be difficult, but this device illustrates the general principle: differences in temperature generate work.
"This approach is fairly intuitive because we are combining the familiar principles of heat engines and radiative cooling," says Byrnes.
The second proposed device relies on temperature differences between nanoscale electronic components -- diodes and antennas -- rather than a temperature that you could feel with your hand.
"If you have two components at the same temperature, obviously you can't extract any work, but if you have two different temperatures you can," says Capasso. "But it's tricky; at the level of the electron behaviors, the explanation is much less intuitive."
"The key is in these beautiful circuit diagrams," he adds (see image). "We found they had been considered before for another application -- in 1968 by J.B. Gunn, the inventor of the Gunn diode used in police radars -- and been completely buried in the literature and forgotten. But to try to explain them qualitatively took a lot of effort."
Simply put, components in an electrical circuit can spontaneously push current in either direction; this is called electrical noise. Gunn's diagrams show that if a valve-like electrical component called a diode is at a higher temperature than a resistor, it will push current in a single direction, producing a positive voltage. Capasso's group suggests that the role of the resistor could be played by a microscopic antenna that very efficiently emits the Earth's infrared radiation toward the sky, cooling the electrons in only that part of the circuit.
The result, says Byrnes, is that "you get an electric current directly from the radiation process, without the intermediate step of cooling a macroscopic object."
According to the paper, a single flat device could be coated in many of these tiny circuits, pointed at the sky, and used to generate power.
Technological challenges -- and promise
The optoelectronic approach, while novel, could be feasible in light of recent technological developments -- advances in plasmonics, small-scale electronics, new materials like graphene, and nanofabrication. The Harvard team says a strength of their research is that it clarifies the remaining challenges.
"People have been working on infrared diodes for at least 50 years without much progress, but recent advances such as nanofabrication are essential to making them better, more scalable, and more reproducible," says Byrnes.
However, even with the best modern infrared diodes, there is a problem. "The more power that's flowing through a single circuit, the easier it is to get the components to do what you want. If you're harvesting energy from infrared emissions, the voltage will be relatively low," explains Byrnes. "That means it's very difficult to create an infrared diode that will work well."
Engineers and physicists, including Byrnes, are already considering new types of diodes that can handle lower voltages, such as tunnel diodes and ballistic diodes. Another approach would be to increase the impedance of the circuit components, thereby raising the voltage to a more practical level. The solution might require a little of both, Byrnes predicts.
Speed presents another challenge. "Only a select class of diodes can switch on and off 30 trillion times a second, which is what we need for infrared signals," says Byrnes. "We need to deal with the speed requirements at the same time we deal with the voltage and impedance requirements."
"Now that we understand the constraints and specifications," Byrnes adds, "we are in a good position to work on engineering a solution."
Romain Blanchard, who completed his Ph.D. at Harvard SEAS, was also a coauthor of the paper in PNAS. This research was supported in part by King Abdullah University of Science and Technology (CRG-1-2012-FRA-005-HAR).
Story Source:
The above story is based on materials provided by Harvard School of Engineering and Applied Sciences. The original article was written by Caroline Perry. Note: Materials may be edited for content and length.
Journal Reference: Steven J. Byrnes, Romain Blanchard, and Federico Capasso. Harvesting renewable energy from Earth's mid-infrared emissions. PNAS, 2014
Harvesting renewable energy from Earth’s mid-infrared emissions
- Contributed by Federico Capasso, February 3, 2014 (sent for review November 1, 2013)
Significance
Renewable energy can be generated whenever heat flows from a hotter to a colder body. One such flow is from the warm surface of Earth to cold outer space, via infrared thermal radiation. An emissive energy harvester (EEH) is a device that can generate energy from emitting thermal radiation into the clear sky. We calculate how much power is thermodynamically available, using a location in Oklahoma as a case study. We discuss two possible ways to make such a device: A thermal EEH (analogous to solar thermal power generation) and an optoelectronic EEH (analogous to photovoltaic power generation). For the latter, we propose using a rectifying antenna, and we discuss its operating principles, efficiency limits, system design considerations, and possible technological implementations.
Abstract
It is possible to harvest energy from Earth's thermal infrared emission into outer space. We calculate the thermodynamic limit for the amount of power available, and as a case study, we plot how this limit varies daily and seasonally in a location in Oklahoma. We discuss two possible ways to make such an emissive energy harvester (EEH): A thermal EEH (analogous to solar thermal power generation) and an optoelectronic EEH (analogous to photovoltaic power generation). For the latter, we propose using an infrared-frequency rectifying antenna, and we discuss its operating principles, efficiency limits, system design considerations, and possible technological implementations.
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