Could Earth's Infrared Emissions Be a New Renewable Energy Source? 78
Zothecula (1870348) writes "Could it one day be possible to generate electricity from the loss of heat from Earth to outer space? A group of Harvard engineers believe so and have theorized something of a reverse photovoltaic cell to do just this. The key is using the flow of energy away from our planet to generate voltage, rather than using incoming energy as in existing solar technologies."
Power density? (Score:5, Insightful)
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Re:Power density? (Score:4, Insightful)
The diurnal mean of the energy emitted is equal to the energy received (otherwise the oceans would quickly boil away).
The difference is that the energy emitted has a much higher entropy than the energy received: solar energy comes from a source with a temperature around 6000 K, i.e. low entropy, Earth emits the same amount of energy at a temperature of around 300 K, i.e. high entropy.
Hence, it is much harder to get any useful work from the emitted than from the received energy.
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Score 5: Interesting/Insightful. WTF?
*) Diurnal. Does it mean what you think it means?
*) Energy received and energy emitted by the Earth aren't equal. You might have heard of global warming.
*) The energy emitted by the Earth isn't all infrared radiation.( http://en.wikipedia.org/wiki/F... [wikipedia.org] and http://www.eoearth.org/view/ar... [eoearth.org] )
*) Temperature doesn't have color, pressure doesn't have speed and energy doesn't have entropy. You can only define entropy for a thermodynamic system (i.e. Earth, or Earth + atmosphe
A stupid idea. (Score:3)
Correct: it's a mostly useless idea.
The problem really is in the laws of thermodynamics.
The total energy radiated is indeed equal to the sunlight energy (although the power density is less by a factor of 4: the Earth absorbs sunlight on an area pi r^2, but radiates heat over an area 4 pi r^2)-- but usable energy is produced not by a heat source, but by the transfer of energy from a heat source to a heat sink-- the Carnot efficiency. The difficulty is that in intercepting the outgoing radiation, you necessa
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I never get why people are so set on Solar-> Electricity.
Solar -> Heat is a lot more efficient and takes a lot less technology.
Absolutely. Solar heating (and hot water) is low tech, and easy to do-- it's been cost effective for quite a while.
Re:Power density? (Score:5, Informative)
Energy received and energy emitted by the Earth aren't equal. You might have heard of global warming.
True, they're not equal. To a reasonable approximation, they are equal: the heat picked up via global warming is tiny compared to the amount of heat added by the Sun each day (and subsequently lost to space by radiation).
The energy emitted by the Earth isn't all infrared radiation.( http://en.wikipedia.org/wiki/F [wikipedia.org]... [wikipedia.org] and http://www.eoearth.org/view/ar [eoearth.org]... [eoearth.org] )
True, though it's mostly infrared and albedo.
Temperature doesn't have color
No, but a distribution of radiation does. When, in physics, someone says that radiation is "X Kelvin", it's shorthand for "a distribution of radiation very close to the ideal black-body radiation at X Kelvin". The great bulk of the Sun's and Earth's radiation is black-body radiation.
You can only define entropy for a thermodynamic system (i.e. Earth, or Earth + atmosphere).
Radiation certainly does have entropy. See, for example, Planck's "the Theory of Heat Radiation" or some more modern text.
All oher things being equal, the entropy goes up with the temperature (0 at 0K, higher at 6000K than at 300K)
This is just a misunderstanding of the meaning of 6000K vs. 300K light. Though it's incorrect to just assume zero entropy at 0K.
Entropy more or less describes the disorder of a system.
It's enormously more complicated than that. That's a Brian-Greene-level description.
You're probably talking about exergy
... Are you an engineer?
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The total heat produced by radioactivity in Earth is 44.2 TW (Wikipedia).
The total solar power received by Earth by the upper atmosphere is 174 PW (Wikipedia).
This means 3937 more solar energy is received by Earth than produced by radioactivity in its interior.
Furthermore geothermal energy is high entropy energy in regard of solar energy since the temperature difference between
ground (~287K) and nearby space (>10K) (DT=277K) is much less than the temperature difference between
sunlight (5778K) and ground
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The total heat produced by radioactivity in Earth is 44.2 TW (Wikipedia).
Which means if we can capture 5% of it, that would be enough energy to power the entire world's energy needs.
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Check your numbers - 2008 global energy usage, 142,300TWh(wikipedia) /365/24 = 16.2TW average instantaneous energy consumption.
We'd need to capture 37% to satisfy 2008s energy requirements, and today's are even higher.
Then we need to worry about efficiency - assuming we could manage to get up to 10% efficiency, we'd need to blanket 370% of the planet with thermal energy collectors to satisfy current energy demands from georadiothermic sources.
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If nothing else, it's surely enough to power a small TED.
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Hmm, well, I have a hand held sterling engine that runs a dynamo and lights up several LEDs. It runs off the thermal difference between my hand an the room temperature air.
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Just how many watts per square meter are capturable this way?
It seems that if you're after the earth's heat energy, you drill a deep enough hole and get it.
No space lift required.
Dyson Sphere? (Score:2)
A mini Dyson Sphere around the earth?
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Yes, we become a world of programmers and gamers. The whole is is our mothers' basement.
Re:Dyson Sphere? (Score:4, Funny)
We might use some system that lets most of the sun's rays pass through but that blocks the infrared from getting back out. You know, like a greenhouse. Maybe we could produce some kind of gas that has these properties?
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>Glass (of a greenhouse) does pass solar radiation but reflects thermal radiation
Actually, mostly not. notably IR-reflective glass is a very recent invention that is still generally considerably more expensive that normal glass, much less plastic, etc. Most greenhouses primarily rely on retaining a mass of heated air separate from the outside environment, a job done fairly efficiently by gravity on Earth. Basically as an analogy "greenhouse gasses" is an unfortunate misnomer created by someone apparen
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For this to work we'd may need to have a "hindmost" central world that was almost all arcologies. Nothing we need to worry about soon. I mean, I've been to Montana.
Better way (Score:2)
I've got a better way, lets release some greenhouse gases, trap the heat until the oceans boil, reuse old steam engines. WIN!
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Then we could put steam vents at 90 degree angles and spin the earth faster. The increased spin could then be used to generate power off of the magnetic field of the Van Allen belt.
Profit!
Seems like a bad idea, intuitively (Score:1)
If you're capturing the earth's radiant energy...
Wouldn't you already have needed to solve the climate change problem?
Because this seems guaranteed to cause manmade global warming - that thermal radiation never escapes, we're harvesting the energy which creates heat...
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We'll just use some of the energy to run giant refrigerators.
Sheesh, it's tiring doing all the thinking.
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No. It's supposed to work day AND night. That's its advantage.
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It doesn't (really) matter how efficient A is compared to B.
In the real world it (really) matters how much each option costs. Given use of term "nanofabrication" and lack of available energy density likely this costs more than anyone is willing to pay into foreseeable future.
The answer: (Score:1, Interesting)
No!
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Actually, the answer is "yes", but isn't very efficient. It sounds like he's stumbled upon the idea of peltier coolers (or TEC). It could convert the released heat energy into electricity. It would work great, if we could build a wall roughly the size of the planet. :)
Just get (Score:2)
Just get Congress to abolish the Laws of Thermodynamics
By rule (Score:2)
No.
Not New (Score:4, Informative)
a photovoltaic cell converts light into electrical (Score:1)
a reverse photovoltaic cell converts electrical current into light, i.e. a light bulb!
Is this a case of stupid journalism?
Re: a photovoltaic cell converts light into electr (Score:2)
Partly though thermovoltaic cells do exist.
Cue the bad sci-fi movies... (Score:2)
It'd be amazing if there were a hollywood blockbuster that theorises that doing this will make the Earth run out of rotational energy and fall into the Sun.
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That's kind of what happened to my machine-planet powered by the tidal forces of its moon. It eventually just slung the moon away.
In a simulation of course. There's no sentient machine race monitoring this planet's technical progress. Nope, this isn't a violation of any galactic statutes (not like I wouldn't need a vacation if it were though).
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Orbital energy. Or, you know, just forward motion.
Rotational energy maintains the night/day cycle.
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You obviously have axes to grind...
Very useful ON THE MOON (Score:2)
Ok, even if this is just marginal on earth (because of the low temperature gradient due to the atmosphere), it should be GREAT on the moon.
During the long lunar night when temperatures drop hundreds of degrees, it should be much easier to generate significant power from the still warm lunar soil. Coupled with the solar power from the long lunar day, it should make long term lunar exploration much more feasible (and prevent problems like the shutdown of "Jade Rabbit" due to freezing).
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I'm not sure this is actually going to get you that far. The difference in radiant flux (moon vs sun) is T^4, so you're talking about a 200-300K source vs a 6000K source, or (if I inverted correctly) about 8.7mW per m^2 power at 100% efficiency, compared to 1400W/m^2 of solar.
To help Jade Rabbit "not freeze" would have required (?) an acre of array, I'm guessing. It would have been better to use a deployable MLI canopy as a secondary shield against the radiative losses to space and capture the heat directly
Scientists love their hammer (Score:1)
Or you know, we could just use the basics of passive solar heating. Capture the sun's energy with a large thermal mass and then use the concentrated energy.
I don't know, covering a quarter of an acre of land to heat my place, or some nice statues inside the greenhouse half of my dome with passive piping to a large thermal mass underground. One of
Suburban rooftops (Score:2)
Bedouins used to make ice by leaving shallow pans of water open to the desert night air, with a blanket under the pan to keep the heat of the ground from soaking into the water. This idea is essentially using a thermocouple in place of the blanket and exploiting the temperature differential to generate electricity.
Can we dream of suburban rooftops that harvest photoelectric power by day plus whatever small amount of back-seepage of heat into the air can be reclaimed at night?
Runaway heating (Score:2)
So, the earth is too hot. It absorbs energy, and then radiates it away. It reaches an equilibrium so it maintains a cyclical average temperature.
So you want to capture the radiating energy and release it on the earth?
Do you see a problem here?
Source temp is 300K. Carnot efficiency is zero. (Score:2)
For all this theoretical work, we could think of putting a huge thermocouple with one end i
Solar Panals & Global Warming. (Score:2)
My understanding (based on a youtube video I saw once...) is the photovoltaic cells don't capture all the energy of the photons that strike them.
They absorb some energy, converting the visible wavelength photons into infrared wavelength photons.
My question is, does this basically create heat pollution, which is trapped by CO2; while if the same area were covered by white/mirror surface, more energy would exit the atmosphere into space?
How about photocells that convert UV light into energy, and give off visi
Applied To ..... (Score:2)
If this could be applied to my checking account I might be able to pay for my kids education before they graduate!
If it was applied to my weight I would loose the weight of the snack before it hit my stomach!
Hair loss could be a thing of the past?
And some environmentalist proposed this? (Score:2)
So the idea is to trap infrared for energy. But infrared is effectively heat ( crudely spoken ). So you are trapping heat. Doesn't that add to global warming?
This is why people look down on environmentalists.