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Terrawatt years

  1. Jun 25, 2012 #1
    This comes from Robert Zurin's the Case for Mars

    What is a Terrawatt year? Is that 1 terrawatt produced in one year? I don't see why it's measured in terrawatts. Why not just terrawatts?

    Further down he says

    That's more understandable.

    Tell me if this calculation is correct. To get 120 millibars of oxygen you need to multiply 2200 by 120 since 2200 TW are needed for 1 millibar of oxygen.

    2200 * 120 = 264,000 terrawatts

    It looks like he thinks you can produce 100 TW a year with 90 coming from reflectors and 10 coming from factories. If that's 100 TW a year that would take 2640 years, so there is something that I'm not understanding.

    But I should also point out that I don't really trust this guy. He has an agenda, going to Mars and quick, so he's motivated to minimize all the obstacles and make everything seem easier than it is.
  2. jcsd
  3. Jun 25, 2012 #2


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    Terrawatt-year is a unit of energy. His 2200 terawatt-years is expressing how much energy would be needed to produce 1 millibar of oxygen. So if you could produce 2200 terawatts of power it would take 1 year, or if you could produce 1 terawatt of power it would take 2200 years to obtain that 1 millibar.
    It is the same as your electrical company charges you - they charge for energy usage as kw-hour.
    Just stating a power level is insufficient - you have to know the length of time that power level would be sustained.

    He says "By combining the efforts of such biological systems with perhaps 90 TW of space-based reflectors and 10 TW of installed power on the surface ... " I believe he includes some biological organizisms helping out to produce the oxygen to get his figure of about 900 years.
    What he does say previous to the quote may be the clue you are looking for in the diecspancy of your result versus his.
  4. Jun 25, 2012 #3
    Let me just go ahead and quote the whole thing. Remember I'm trying to figure out how he got the 900 year figure.

    I'm sure there is some chart out there that shows how much energy humans are able to produce per human over the course of the last 200 years in, say, UK and USA, most likely it grows at a very steady tick, just as computing power doubles every 18 months. I think someone should track that chart down and come up with a reasonable extrapolation of how much energy we'll be able to produce in the next 500 years. I know they have charts of worker productivity. Also France is building a fusion generator which is supposed to be up and running in 2018. If it works we'll be able to get 10 units of energy for every unit we put in.
  5. Jun 25, 2012 #4


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    I found this graph http://articles.businessinsider.com/2011-07-22/markets/30001486_1_energy-growth-growth-trend-solar-energy [Broken], which gives a factor of 10^4 in ~300 years or (conservative) a factor of 10 per 100 years.
    I would not trust any extrapolation over 500 years, but if you like to do this, you could add 5 orders of magnitude and try to add a "mars factor", as mars is more remote than conventional power plant locations. 5 orders of magnitude are the difference between 1 GW (usual power plant size) and 100TW. However, keep in mind that conventional power plants need cooling water, which is tricky at mars.
    Last edited by a moderator: May 6, 2017
  6. Jun 25, 2012 #5


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    There is your answer - 200 TW from plants and 100 TW from humans.
  7. Jun 25, 2012 #6
    ok, good, 264,000/300 = 880 years, that's reasonable.
  8. Jun 26, 2012 #7


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    Fwiw, the word is terawatt, one 'r'. It has nothing to do with terra = earth (Latin), but much to do with tera = monster (Greek). I do hate searches failing because technological terms are misspelt. Or misspelled if you prefer.
  9. Jun 26, 2012 #8

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    Terawatts are units of power. The power output of the world's most powerful laser is measured in petawatts, or 1000 terawatts. However, the energy output was only 680 joules because the laser fired for less than a trillionth of a second. Energy is power times time.

    A terawatt-year is a huge amount of energy. The total electrical power generated by all of the electrical power generators in the US during 2009 was 0.44 terawatt-years. Another way to look at it: That 2,200 terawatt-years figure is equal to 5,000 times the total electrical power output for all of the US for all of 2009.

    Yet another way to look at it: It's pure science fiction.
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