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 Power-Out Intermittency Notes

The problem of inherent Wind Intermittency v. Baseload is not our central AWE problem. Thousands of engineers with billions in investment are working on utility-scale storage, so we need only await the winners.

Most intermittency is a trivial design issue. KiteLab's AWECS with a Seiko self-winding chronometer "ground station" produces super-smooth output from the wildest input. "Clockwork" is legacy tech.

Our problem is AWE power-cycle intermittency. Pierre is right that its mostly just a cost, but any cost is bad. If a generator is inherently only producing 60% of the time and motoring retract 40%; that is not great ROI compared to a continuously driven generator.

Running generators hot with lots of cycling loads, G-forces, etc, will greatly reduce reliability and life due to accumulating mechanical wear of the insulation in the coils. The best and most profitable generator regime is steady operation at just the right temperature.

Looping kiteplanes, as we have seen them so far, have high amplitude variation in power-out during the loop. The solution is counter-intuitive: the loop must be laid back downwind just as Dutch windmill rotors are tilted back (and also angled sideways to cancel g-force asymmetry). One needs a lifter kite (incl. arrays) to hold up tilted-back loops and it is the kite's "jellyfishing" that buffers the power signal. The reason for back-tilt is the surface wind gradient. Only a back-tilted loop experiences a level "apparent crosswind". The side angle needed allows the (struggling) rising kiteplane to see more apparent wind, while mostly just using free-fall force for the descending side.

Figure-of-eight patterns are best with a brief retract at the top of each ear of the eight. Pump-retract optimal frequency is at the fundamental harmonic of the kite-tether, based on biomimetic models.

CoolIP                       ~Dave Santos           May 15, 2011              M3576

Comment and development of this topic will be occurring here.       
All, send notes, drawings, and photographs!

Terms and aspects:   

  • Distinguish between variability and intermittency.
  • Distinguish between AWECS production of energy and the problem of storage of energy.
  • Smoothing electricity characteristics from intermittent and variable inputs for feed to a consumption grid
  • g-force  
  • AWE power-cycle intermittency
  • jellyfishing
  • power signal

Related links:

  • Energy storage

Commentary is welcome:

  • Recall that an AWECS may be designed to produce electricity or heat or traction or fluid pumping or lifting of objects (for transport, moving position, or storage of potential energy). Intermittency and variability of wind plays differently as challenge in the various types of energy production or task set for an AWECS.        JpF May 15, 2011
  • M3575    PierreB  brings forward the period of time for storage of energy as a special consideration.   May 15, 2011
  • The very tether set of a KES stores some potential energy in its elasticity. Consider how bungee launch of a glider works: store energy in the stretched bungee and then release the anchored glider and watch the glider use the stored potential energy for its kited launch; the elastic potential energy is converted mostly to increasing the kinetic and positional potential energies of the glider for airspeed increase and altitude increase. JpF  May 15, 2011
  • DougS supports focus on AWE, not the storage challenge: HERE.   May 15, 2011   
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