Wind Fights Solar; Triangle Wins

Editor’s Note: EarthTechling is proud to repost this article courtesy of Do The Math. Author credit goes to Tom Murphy, an associate professor of physics at University of California, San Diego.

For me, the most delightful turn of events in the ultimate nerd-song “Particle Man” by They Might Be Giants, is that after introducing (in order of complexity) particle-man, triangle-man, universe-man, and person-man—and learning that triangle-man naturally beats particle-man in a match up—we pit person-man against triangle-man to discover that triangle wins—again. In this post, we’ll pit solar against wind and see who wins.

do the math

image via Shutterstock

I will take my usual approach and estimate what I can—as opposed to researching the results of detailed studies. It’s part of the process of personal mastery of the big-picture issues, while also providing a sanity-check. In exploring useful reactions to the loomingpeak oil crisis (or pick your favorite rationale for weaning ourselves from fossil fuels), an appropriate strategy is to assess ballpark capacities of the various options. Some will prove to be orders-of-magnitude more prodigious than we need, others will be marginal, and many will show themselves to be woefully inadequate to match the required scale. So the goal is to perform this crude sorting process into abundantuseful, and waste of time.

Earth’s Energy Budget

Since many of the options I will discuss in the coming weeks ultimately derive from the Sun, it is useful to throw up an energy budget.

earth's energy budget, nasa, do the math

image via NASA

Of the 1370 W/m² incident on the upper atmosphere from the Sun, 30% is reflected straight away without pausing long enough to say hello. About 20% is absorbed in the atmosphere and clouds, and 50% gets absorbed at ground level. Note that 7% of the energy budget goes into conduction and rising air (separate phenomena; the latter relating to wind). Virtually no heat is able to conduct through the thick atmosphere, so really this figure is all about convection, or moving air.

For comparison, the energy consumption (conversion) rate of the human race is about 13 TW (13 trillion Watts), which works out to an average of about 2,000 W per person on the globe (Americans are 10 kW). We can also divide by the area of the globe to get a power density of 0.025 W per square meter, or 0.09 W/m² if we just count land area.

1 Comment

  • Reply February 28, 2012


    DoTheMath – very impressive.  I too have been working the numbers – to be honest you are much more thorough than I.  My goal is to use rough math to determine the impact of man on Global Warming.  Your map with the black dots – required area needed to meet all energy needs with PV is instructive.  I estimated that the sun delivered 8K to 10K times more energy per day than we generate.  Based on that – man is not warming the earth (total additional heat added is small) – the impact of CO2 as a “greenhouse” gas is far less than H2O as a greenhouse gas – so reasonable “scientists” neglegect its impact. 

    As an aside – your number of 50 to 51% of the Suns energy being absorbed by the surface – is that based on the current configuration with mans impact?  Roads, roofs, plowed fields, cities, etc. or was it based on a rural non developed landscape?  If the portion of the energy previously reflected by the surface is now absorbed (south facing houses, dark roofs, etc.) this could be a huge factor in retained vs reflected energy.

    Lets say of the land mass (1/7 of the surface = .142) times the 1370 yeilds an additional =195 w/m sqd equals the potential increase in the suns energy if it was all abosrbed.  Due to mans impact lets say an additional 2% is absorbed (roads, roofs, cities, etc.) that would equal about 4 w/m sqd for the land portion – not an insignificant number.

    Of course all this additional energy would be dissipated (greater driving force for the heat engine, increased convection, etc.)

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