Very few people would disagree with Jocelyn Newmarch's sentiment (Rather turbines than coal mines, Letters, July 9). The impossibility of turning this into a reality, especially in SA, lies in physics and nature.

Around the world wind turbines are being found sadly unviable. From an engineering point of view, mainly dictated by physics, an annual average wind speed of about 23km/h is needed to make a wind generation farm workable. From a natural point of view very few such areas exist in SA, and the few that exist are all far from where the power is needed. This results in the need for long, expensive and losscausing power lines.

Also, to make the wind farm acceptably efficient the wind needs to be steady all year around and at all times during the day and night, something that does not occur in SA. This is important because every time the wind drops, the power that the wind turbine can supply is reduced and must be instantaneously provided by a coal or nuclear-fired steam turbine which is running with idle capacity and is "waiting" for this dip to occur. This means that the steam turbine is running at an inefficient load factor and is wasting coal just to back-up the wind farm. The bigger the wind farm, the more idle steam capacity that must be on line.

Also, the big power capability of a typical coal or nuclear power station needs to be considered. A typical Eskom coal-fired power station is capable of producing 3000MW continuously for decades.

A typical wind turbine produces a maximum of 2,5MW, but because of wind fluctuations it produces only about one third of this continuously. This means that in order to replace just one Eskom power station 4300 wind turbines would be needed. This is totally impractical and confines the use of wind turbines to that of a very expensive placebo to the Greenies.

SR Becker