WIND ENERGY - DESIGN IDEA FOR A SMALL VERTICAL-AXIS TURBINE

It is generally accepted that the future for very large (megawatt) capacity wind-driven generators in Britain is somewhat bleak, as climatic and environmental conditions are not particularly favorable. Prospects are rather brighter, however, for locally installed units of comparatively low power output, especially when intended for preheating the make-up water in domestic hot-water systems. For water-heating purposes, it is not essential for the voltage or frequency of the power supply to be carefully regulated, so that any natural source of energy which is variable, erratic or intermittent, such as the wind, can be utilized effectively and economically. Such a 'crude' supply, fed directly to a thermostatically controlled immersion heater, installed in an efficiently thermally insulated hot-water storage tank will always have its heat equivalent transferred to and accumulated by the water. There are many designs of wind-driven rotors, mostly of the conventional horizontal-axis type which have to be equipped with means for presenting the driving blades into the on-coming wind. Vertical-axis rotors such as the 'Darrieus' and 'Savonius' type do not require such means and possess a number of advantages over horizontal machines. A design idea for a small vertical-axis turbine is presented. A hollow cylinder fitted with end plates (similar to a cable drum) comprises the 'chassis' and this is arranged so that it can rotate freely on a vertical shaft. Wind vanes are mounted between the end plates, hinged at their outer edges on vertical spindles, so that they are free to swing independently and automatically into 'driving' or 'feathering' positions depending on wind direction but always in such a way as to afford unidirectional rotation of the assembly. By using a cylindrical form of chassis, the air stream striking it is diverted round its surface, causing an acceleration in the velocity of the air impinging upon the driving vanes. Since the energy potential of the air stream is approximately a cube function of its velocity, it will be realized that a substantial increase in power output is achieved.