|Some machines for aeolian energy|
|Multi-blade air-pump |
This type of windmill is simple, strong, cheap, reliable and quick to install; in view of its simplicity it is predominantly used in developing countries. With sheet metal blades, it can be used for pumping water even at depths of over a hundred metres. Equipped with a large number of blades of an extremely simple profile made from curved sheet metal, which can be activated even by weak and medium winds of between 3 and 6 metres per second, these machines are consequently ideal even in areas without strong ventilation.
These wind systems are used to power electric generators, and require a more sophisticated technology than that of the multi-blade air-pump. The current produced by the wind engines is transformed into unidirectional current to enable accumulation in the batteries, and the blades have to be similar to those of aircraft to provide a high rotation velocity. They are generally constructed with two or three blades with a streamlined profile which enables the system to function in medium and strong winds. To set them in operation, the wind has to have a speed of at least 5 metres per second.
This air-pump, invented by the Finn Sigurd J. Savonius in the thirties is an aeolian system of extreme simplicity, inspired by the principle of the ancient vertical-axis Persian windmills. Also known as the “S Rotor” it can even be constructed using 50, 100 or 200-litre bins. The top and bottom are removed and the bin cut in two vertically, creating two symmetrical blades. These are then attached to supporting disks and erected on a vertical axis. This is a system which works well with weak winds, while it becomes extremely vulnerable in the presence of strong air-currents.