Crosswind (vertical) axis windmills have some interesting advantages over wind-aligned (horizontal) axis turbines. One is that their orientation needs no adjustment, for the wind will fully intercept them no matter where it blows from another is that the electric generator can be on the ground, its shaft directly joining that of the windmill; horizontal axis turbines either have the heavy generator way up on the tower, or if it is on the ground, it must be geared to the turbine by a long transmission train.
Further, most vertical axis turbines do not need any pitch control, i.e., adjustment of the blade angle (for "screwing" the blades into the wind). The optimum of this angle varies with the windspeed it should be high at low speeds to prevent stalling, and low at high speeds to offer little resistance.
And there is more: Vertical-axis turbines do not usually need a tower, for their shaft makes them self-supporting and they can merely be anchored with guy wires. Finally, the Betz limit does not, in theory, apply to vertical axis turbines, though in practice it is hard to beat.
Among the crosswind-axis turbines there is one that can reach an efficiency of almost 60% and that is comparatively simple; it is the Darrieus rotor, or the "eggbeater" windmill. Not many people understand the principle on which it works (but you are about to become one of them).
The Darrieus rotor is in its essence not so much a windmill as a flying machine, and one has to go back to some basics to understand it.
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Vol. 6, No. 6
Newsletter: Access to Energy Newsletter Archive Volume: Volume 6 Issue/No.: Vol. 6, No. 6 Date: February 01, 1979 04:09 PM Title: Energy and dishonor
Copyright © 2004 - Access to Energy Newsletter Archive
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