FRYlNG EGGS BY WINDPOWER

Windmills are also highly interesting from a theoretical point of view. For example, it follows from mechanical principles (conservation of momentum) that a windmill with its axis parallel to the wind direction cannot extract more than 16/27, or just under 60%, of the kinetic energy in the wind intercepted by the blades; the rest remains in the wind emerging from the mill. (A 100% efficient windmill would have a "shadow" of total calm behind it, since it extracted all the energy in the wind crossing the area swept out by the blades.)

The 16/27 or "Betz" limit (after the German scientist who derived it mathematically in the 1920's) is, of course, not achieved in practice; a well-designed two-bladed rotor can achieve an efficiency of about 79% (of Betz's 60%, or an overall efficiency of about 47%, and even that only at certain windspeeds.

But whatever the efficiency, the energy is now in the motion of the windmill, and if we want to heat domestic water with that energy (in the many places where there is more wind than sun), we can either go via electricity, or via mechanical friction (e.g., by stirring water in a vessel). Which is the better way?

Although, of course, the most advantageous way for a consumer is usually to buy the energy as either centrally distributed fuel or centrally distributed electricity, the question is not without merit, for it sheds some light on the theories of the disciples of thermodynamic mysticism. To use electricity for heating, preaches Lovins, is like using a chainsaw to cut butter; but the yawns must have got very wide, for he has recently changed this to "using a forest fire to fry an egg." In fact, of course, heating by electricity is more efficient in some cases and less efficient in many others; there is no thermodynamic principle passing judgement on its use under all conditions.

In the present case, for example, the energy extracted by the windmill can be realistically converted to electricity and thereafter to heat where it iswanted (inside the house) with an efficiency well over 90%; that is a value difficult to attain by mechanical means if no more than 10% of the heat is to be lost in transmission to its intended destination. Even so, it would be difficult to provide this heat at a desirable temperature; the easy way would be to provide oodles of lukewarm water.

As for frying eggs, electricity is the obvious, easy and efficient way to do it with wind power. To fry an egg by the wind, but not via electricity well,perhaps a forest fire would be one of the simpler ways.