I thought you might be interested in a South African first in wind motors (rather than purely wind-driven turbines). Rotosail is a patented turbine invention (RSA patent application 2016/00808) that is conceptualised as a wind motor rather than purely a wind generator. It could be connected to a mechanical, pneumatic, hydraulic or electrical system. It is envisaged as DIY kit models at one end of the spectrum and, possibly, large grid-feeding models, the size of oil-storage tanks at the other. The latter may be barge-mounted in the North Sea, or power a weatherstation in Antarctica.
Rotosail incorporates the tried and tested configuration of hollow hemi- cylindrical shells, overlapping and rotating about a vertical axis. The principle is incorporated in many proprietary units currently available on the high-tech market. Rotosail postulates the principle of mounting a rotating space-frame turntable on the vertical axis shaft with the hemi- cylinders mounted on secondary vertical mountings on the turntable, having limited rotating ability in order to close completely or to be extended fully or staged at any intermediate point. In principle, there is no limit to the size of the shells.
The adjustment is powered by an onboard generator, rechargeable batteries and electric drives, commanded either manually, by a standard remote radio control (similar to those that operate TV sets or garage doors) or automatically by pre-set computerised parameters, related to wind velocities, rotational speed, time, duration or any other loaded parameter. This function could also be achieved, in certain circumstances, by onboard pneumatics or hydraulic circuits.
In the fully closed position, the unit is cylindrical and streamlined and could be designed to resist even hurricaneforce conditions. It is fundamental to these overrides that frontal area and rotational speed would vary and be balanced, in order to maintain power output at a given level, thereby minimising or eliminating vibration, noise and downstream turbulence such as created by propeller-type windmills. It is anticipated that, bearing in mind the unique properties inherent in Rotosail, a fairly simple gathering and spilling of wind would result, although definitive testing is not yet complete.
Harnessing of wind-power is potentially possible 24/7 all year round, almost everywhere, whereas solar power is available during daylight hours only (during winter, in high latitudes, that can be one or two hours in 24). Wind power can deliver AC or DC power, as opposed to solar power, which can deliver only DC and requires inverting conversion.
That there is an abundance of sustained wind-power is evident in the fact that, until the advent of steam, wind was the primary source of power for driving pumps and machinery, other than running water, brute manpower or draught animals. In our contemporary environment, wind farms generate considerable quantities of power, but suffer from the drawbacks of high capital cost. This is partly due to the need to elevate the horizontal shaft axis for the blades to clear the ground. Power generation and control equipment are situated high above the ground, creating logistical problems and considerable additional cost. An additional complication is the need to adjust for directional variation of the wind, with the resultant additional cost and ongoing maintenance needs, plus the facility of adjusting the pitch of the turbine blades.
Preliminary calculations for Rotosail indicate that one square metre of frontal area would produce 1 kw of “work” at a wind velocity of 10 m/sec (36 km/h). Definitive testing is not yet complete.
Anticipated savings in capital cost range from significant to huge, resulting from the concept’s simplified design and the possibility of relatively unskilled local manufacture. Installations would be far less intrusive than conventional wind turbines and could be sited on waste ground such as landfills and rugged mountain sites. Installations might even be situated above factories and high-rise buildings without significant intrusion. Offshore installations could be barge-mounted rather than on the sea-bed, with significant savings in initial costs and ongoing servicing costs.
Other possible applications range from hybrid powering of shipping to expanding the range of totally battery-powered road vehicles using independent self-powered “pit-stops” that might bridge desert areas, such as the Karoo, where perennial air movement is a norm. KEITH HONEYMAN CAPE TOWN