China tests world’s largest megawatt-level flying 'windmill' airship
interestingengineering.com
China’s S1500 airborne wind turbine completes maiden flight, becoming the world’s largest floating wind-power generator.

"High-altitude winds between 1,640 and 3,281 feet (500 and 10,000 meters) above the ground are stronger and steadier than surface winds. These winds are abundant, widely available, and carbon-free.

"The physics of wind power makes this resource extremely valuable. “When wind speed doubles, the energy it carries increases eightfold, triple the speed, and you have 27 times the energy,” explained Gong Zeqi "

  • WFloyd@lemmy.worldEnglish
    10·
    10 hours ago

    When wind speed doubles, the energy it carries increases eightfold,

    Edit: I’m wrong, see edit below!

    Huh? Kinetic energy increase is square, not cubic.

    KE=1/2 m v^2

    So every doubling of speed should increase the available kinetic energy by 4 times, not 8. 3 times the speed is 9 times the energy. Granted there are probably some efficiency gains in excess of this at the low end, but as a rule that’s just wrong.

    Edit: Cool, I learned something new! I neglected to consider it in terms of power, just thought about kinetic energy.

    So something like: KE = 1/2 m v^2

    = 1/2 ( rho V) v^2

    = 1/2 ( rho A d) (d/t)^2

    = 1/2 rho A d^3 1/t^2

    Where P = KE/t

    Thus:

    P = 1/2 rho A (d/t)^3

    = 1/2 rho A v^3

    Lots of other aspects I’m sure I have wrong, but I see how the cubic came to be.

    • DahGangalang@infosec.pubEnglish
      1·
      4 hours ago

      I’m out of practice with my physics so apologies if this is a n00b question, but:

      I’m unclear what (rho V) is and how you converted to that from mass (m). Further unclear what (rho A d) refers to.

      Can you explain / link to an explainer on this?

      • deltamental@lemmy.worldEnglish
        17·
        11 hours ago

        That’s a good link.

        During the stampede scene in the Lion King, imagine the wildebeests were stampeding twice as fast. Then Simba’s dad Mufasa would not only have quadruple the amount of energy imparted by each wildebeest, but also be trampled by twice as many wildebeests per second, so the rate of energy imparted on Mufasa per second would be 4 x 2 = 8 times greater when velocity doubles.

      • MeThisGuy@feddit.nlEnglish
        1·
        6 hours ago

        thx for the link! just spent the last hr reading about windmills. and although I live in a country full of them I’ve often wondered, but never really paused to ponder about the intricacies that go into windmill design. fascinating stuff!

    • Beaker@lemmy.blahaj.zoneEnglish
      11·
      11 hours ago

      Increasing the speed increases both the kinetic energy of the wind hitting the turbines and the amount of wind that hits the turbines each second.

    • tate@lemmy.sdf.orgEnglish
      31·
      12 hours ago

      We don’t directly harvest the kinetic energy. That increase probably has to do with how the wind provides lift to the blades. Of course, you couldn’t keep increasing like that until the harvested energy is greater than the kinetic energy. But I’m sure at any wind speed we only get a tiny fraction.

      • inktvip@lemmy.dbzer0.comEnglish
        4·
        8 hours ago

        Kinetic energy is exactly what’s harvested, which is why modern wind turbines are not far off the theoretical limit of the amount of energy that can be extracted. (Betz’s law)

        By taking energy from wind, you slow it down. Slow it down too much, and it can’t get out of the way in time for new air.

        • tate@lemmy.sdf.orgEnglish
          1·
          34 minutes ago

          I could have stated it better. What I meant was that the fraction of kinetic energy that is taken from the wind is so small that the total kinetic energy in the wind is probably not the important factor that changes with wind speed. The dynamics of how the lift depends on wind speed is probably much more important.