WHAT IS IN THE WIND?

But in practice. only a few square feet of windswept area can be tapped at a time; and then it becomes apparent that the energy density of the wind is small. Besides. it fluctuates in time to an extent that makes it far less useful than other sources of energy.

The power (in watts) available form a well designed wind driven generator is about

W = 0.016 D2 v3

where D is the diameter of the propeller blades in feet. and v is the wind speed in miles per hour. For 8 foot blades. that means a laughable 100W for windspeeds of 10 mph; to get 100 kW, you need (and the structure would have to withstand) a gale of 100 mph. The cost of a low power generator, including installation of the tower, is $3,000 up; and when one considers the available windspeeds, even in the windsuept Midwestern plains, the annual available energy comes to between 10 and 50 kWh per square foot of swept surface an almost negligible fraction of what the average American family consumes per year. Besides. to be available when needed, the energy has to be stored in batteries, pumped water, or other energy reservoirs.

These figures make it clear why wind driven generators make sense only where power lines would be too costly (mountain tops, deserts, jungles), and why they are in demand in South America or India; in the US they were largely killed off in the thirties by the expanding power net.

But large scale conversion is another matter. It has been proposed to mount wind turbines on the already existing towers of the high voltage power distribution lines for a supplementary feed into these lines. The generators driven by random windspeeds would have to be synchronized with the 60 cycle power net, but a constant frequency wind generator has been developed at Oklahoma State University by a team under Dr. William Hughes. Operating costs would be low, but capital costs might be prohibitive. Also, such a system suffers from low efficiency due to lack of energy storage.

Another proposal is to use wind power to pump water to a high reservoir, then use the water to run a hydro electric turbine. (This system, with electrically driven pumps, is widely used by power companies to cope with demand fluctuation; the water is pumped during the night and drives the turbine during the peak demand hours.)

Probably the most viable proposal is to use wind generated electricity to produce hydrogen from water, then use the hydrogen as a fuel (pollutionless, see September AtE) in conventional power plants. Dr Hughes considers this the most efficient alternative. Prof. W.E. Heronemus of the University of Massachusetts shares this opinion. He proposes offshore turbines using the Westerlies off the east coast, which are moderate to strong throughout the year. Windgenerated power would first distil sea water, then electrolyze it to produce hydrogen to be sent ashore or stored in collapsible sea bed tanks. Prof. Heronemus estimates that about one half of the predicted 1990 electricity demand of the New England States could be met in this way at a price competitive with nuclear power.

There is plenty of wind, and it comes free, so that the operating costs tend to be low. However, the investment is very large, and the question is whether it is worthwhile when compared to the capital costs of harnessing nuclear, solar or geothermal energy. Most experts at present think not; yet tapping the energy of the wind remains an intriguing possibility which no expert is quite willing to reject completely.

[More information: Basic literature is old and mostly out of print. As a starter, we recommend vol. 7 of the Proceedings of the UN conference on new sources of energy, Rome, l961, United Nations, New York, 1964. For information on small wind driven generators, contact Solar Wind Co., RFD 2, East Holden, Me., which distributes Australian and Swiss models for home use.]