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Could Earth's Infrared Emissions Be a New Renewable Energy Source?

Posted by samzenpus on from the power-up dept.

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."

5 of 78 comments (clear)

  1. Power density? by gregor-e · · Score: 4, Insightful

    Just how many watts per square meter are capturable this way? Enough to power a small LED?

    1. Re:Power density? by busstop · · 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.

      --
      -- ... end of sig
    2. Re:Power density? by blueg3 · · Score: 4, 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] and http://www.eoearth.org/view/ar... [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?

  2. Not New by urgelt2 · · Score: 4, Informative

    This is not a new idea. http://web.mit.edu/newsoffice/...

  3. Re:Dyson Sphere? by michelcolman · · 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?