Vertical-axis wind turbines (VAWT)

Vertical-axis wind turbines (VAWT) are a type of wind turbine where the main rotor shaft runs vertically. VAWTs work somewhat like a classical water wheel in which water arrives at a right angle (perpendicular) to the rotational axis (shaft) of the water wheel. Vertical-axis wind turbines fall into two major categories: Darrieus turbines and Savonius turbines.

Savonius Turbine
invented in Finland, the Savonius turbine is S-shaped if viewed from above. This drag-type VAWT turns relatively slowly, but can produce a high torque. It is useful for grinding grain, pumping water and other works that need high torque, but if this kind of turbine connected with electric generator, it only can produce a little electricity
picture below shown schematics Savonius Turbine
The commonest VAWT is a Savonius VAWT which is an extended version of an anemometer (wind speed measuring tool). VAWTs can offer up to 15% efficiency and they work equally well no matter which direction the wind is coming from.


Darrieus wind turbine
A Darrieus machine, a VAWT, is a vertical axis wind turbine. It acts much like a windmill except that a windmill has a horizontal axis
Darrieus wind turbines are not self-starting. Therefore a small powered motor is required to start off the rotation, and then when it has enough speed the wind passing across the aerofoils starts to generate torque and the rotor is driven around by the wind.

In overall comparison, while there are some advantages in Darrieus design there are many more disadvantages, especially with bigger machines in MW class. The Darrieus design uses much more expensive material in blades while most of the blade is too near of ground to give any real power.

others type that derivaties from Darrieus wind turbine are
The giromill was included in Darrieus's 1927 patent for vertical aerofoil powered vertical axis wind turbines, however development is now starting again on new giromills which take advantage of modern ultra strong light materials to produce turbine blades robust enough to cope with the stresses they are put under.


Another variation of the Giromill is the Cycloturbine, in which the blades are mounted so they can rotate around their vertical axis



below is interesting concept for callobaration between Darrieus and Savonius