1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Increasing earths reflection

  1. Dec 19, 2007 #1
    If one is trying to reduce earth mean temperature, why not cover it with aluminum foil?

  2. jcsd
  3. Dec 19, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    Because aliens wouldn't be able to read our minds
  4. Dec 19, 2007 #3
    Take this example:
    Cover 1 km^2 of a desert with solar panels wich produce electricity at 10% eff. Then, calculate the energy absorption in the panels, and the radiance over the full spectrum.

    Second. Calculate the energy absorption and radiance over the full spectrum for the desert.

    Calculating the dissipating heat from the two options: could not solar panels lead to global warming?
  5. Dec 19, 2007 #4


    User Avatar
    Science Advisor
    Homework Helper

    Compared to a million sq km which was covered by ice and is now sea water pretty much anything we do is going to be negligible.
  6. Dec 19, 2007 #5


    User Avatar
    Gold Member

    Of ocurse they would. They're black. The whole point of solar panels is to capture energy. That energy will contribute to the heat of the Earth somewhere along the line.
  7. Dec 20, 2007 #6
    Then the question is: does the fact that solar panels make electricity trump the negative effect given their contributing to global warming? :)
  8. Dec 20, 2007 #7


    User Avatar
    Science Advisor

    [smart alec]If we increased the reflectivity of the planet, would Al Gore be touting universal warming then?[/smart alec]

    I would fathom a guess that the heat they would contribute globally would be negligible. Can anyone compare the amount of heat they would hold over time to the heat the top foot of soil retains?
  9. Dec 20, 2007 #8


    User Avatar
    Gold Member

    But this is the case with every power source. What is the point you're making?

    It sounds like you might be refuting the claim that solar energy is "green".

    If so, I think the premise of the argument for energy is "OK, lets take it as a given that we need energy, even knowing it will increase global warming. Given that, which energy source is greenest?"

    Solar energy is excellent because it is a nearly ideal source; it takes energy othersie not being used and converts it directly into electricity, with no waste products.
  10. Dec 20, 2007 #9
    Im not sure you get my point Dave.

    When energy enters the atmosphere, and then is reflected by light sand dust, it would probably consist of pretty much the same spectrum-composition as the incident rays. These rays would then leave the atmosphere less hindered than lets say dissipating heat from black objects. Therefor it contributes to warming of the atmosphere.

    Im not saying this is a major factor. Im just wondering if the electricity generation through solar panels outweighs the negative effects of heating? :)
  11. Dec 20, 2007 #10


    User Avatar
    Gold Member

    I think I am getting your point. Solar panels trap energy; whereas not having them would mean that energy would (to some extent) be reflected by lighter objects.

    What I'm not sure about is how you propose to "value" the generation of electricity against the heat it produces. They're apples and oranges, and you're talking like they have the same measurement unit: "outeweighs" or "trumps".

    I agree that it's something worth considering, I just don't think it's particular to solar energy. All energy sources must have their cost/benefit ratio considered.
  12. Dec 22, 2007 #11
    You might try the following experiment. Place a piece of aluminum foil, a piece of something painted white, and a piece of something painted, say, red in the sunlight. After an hour, compare the temperatures of the surfaces, using your hand to make the comparison. Be careful not to burn yourself.

    We see things based on visible light, but heat has to do more with IR where things often look different.
  13. Dec 22, 2007 #12
    This is no straightforward task. Remember tvp45, the entire clue to solving this problem is not the energy, but the composition of the energy ranging the scale... So one needs accurate data over a wide range of wavelengths. For both sand and solar panels.
  14. Dec 22, 2007 #13


    User Avatar
    Science Advisor

    You could measure the amount of electricity that the panels generate, determine how much CO2 would be release when generatnig the same amount of electricity by burning coal in a power plant, which is about 2.095 lbs/kWh. Then you can compare how much heat is trapped by a solar panel in the act of generating 1 kWhr to the amount of heat that is trapped by the greenhouse effect of 2.095 lbs of CO2.
  15. Dec 22, 2007 #14
    It is not the "long term storage" of heat in the sand or the solar panel that is the problem. The problem is the temperature the sand and the solar panel radiates with. And is the radiation "black body" radiation or a modified spectrum for the individual cases? What is the time for the dissipating of the energy to space for the two cases given different variables? seems like this will be very complicated to calculate.

    Or am I mistaken?
  16. Dec 22, 2007 #15


    User Avatar

    We use solar panels [the parabolic kind] ( to power giant freezers :)

    Maybe kickstart that hydrogen infrastructure, using excess heat to pry apart hydrogen in sea water. Or not.
  17. Dec 23, 2007 #16
    True. But if one were to do this, one might learn something about emissivity of aluminum.
  18. Mar 16, 2008 #17
    You can't reflect the heat energy because the atmosphere will trapt it in.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook