Salient White Elephant

April 27, 2009

Airborne Wind Turbine Energy Multiplier

Filed under: Airborne Wind Turbine — Tags: — Salient White Elephant @ 6:22 pm

Suppose an airborne turbine can choose its altitude, as in the various blimp supported turbines proposed on this blog. In this case, the blimp may choose to hover in the clouds if it’s a cloudy day. Since the air in the clouds is wet, won’t its density be greater? And since the energy in the wind is proportional to density, then won’t this mean that the wind in the clouds will have more energy? Of course, the blimp may not be able to reach that altitude, but if it can, then here’s a possible option for increasing the amount of energy harvested.

About an hour after I posted this, I read in Wikipedia that the density of air actually decreases as a function of humidity. I was quite surprised to read this, but if you don’t believe me, check out the Wikipedia article for yourself. The reason it decreases is that “the molecular mass of water (18) is less than the molecular mass of air (around 29)”. One of my earlier posts suggested increasing the energy density of wind approaching a turbine by injecting a fine mist into the wind in some upstream location. (I was thinking of those misting devices they have to cool people down on the patios of some coffee shops and restaurants.) The Wikipedia article raises an interesting question. Is air that carries a fine mist “humid air”, or is it air that is carrying droplets of water? Because for the Wikipedia analysis to apply, the water must be in a gaseous state. And what about clouds? The stuff that falls on our heads on a rainy day certainly isn’t a gas. Well… it’s late, and I hope you guys will be able to sleep without knowing the answer to this compelling mystery… because I’m going to sleep! More on this later…


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