(Cont'd from the home page.) ......Air density at sea level is almost exactly two pounds per cubic yard or 1.23 kilograms per cubic meter, about the weight of a quart of water. Atmospheric air pressure is 14.7 pounds per square inch, which multiplies out to 1.06 tons or about one ton per square foot. What this actually is, is the weight of all the air above to the top of the atmosphere.

Let's compare windpower and hydropower. A million tons of air is contained within the volume a little less than that over one square mile of geographical area and up to 1000 feet high over it. For water the same mass is in a volume of 784.3 acre feet, which is a lake of 80 acres in area with an average depth of about 10 feet.

Just to give some idea of what one million tons of mass is like, it is the combined mass of 23 ships the size of the Titanic, which sank as a great tragedy in the North Atlantic in April of 1912, or about the mass of 100 railroad coal trains of 100 fully loaded coal cars each.

Now let's set this amount of air in motion. At 30 mph velocity, this mass of air has the kinetic energy of 24.2 megawatthours equivalent of electrical power, subject to the practical efficiencies of collection.

This is not the end of the story. To account for the number of such volumes moving over one specific location in a specified period of time, the above energy must be multiplied by 30, which is the distance in miles this air is covering in one hour and bringing energy with it. So 24.2 MWH x 30 = 725 MWHs, which is an energy rate of 725 MWs. This is for energy collection along one side of this volume, or one mile long by 1000 feet high.

The well-known Betz efficiency of 59.3% applies, limiting practical energy collection to .593 x 725 = 430 MWs, and current technological capabilities limit this still further. However the fact remains that it is conceivable for wind energy to produce electrical energy with typical windspeed ratings at the level of 1000 MWs - a standard for non-renewables technology - if applied to elevations up to 1000 feet over no more than four square miles of land or water.

For hydro, the parallel would be to multiply a water head of 30.1 feet by the same number, that is, 30 to result in 903 feet, the sum of the heads of a number of dams on the same river. The river flow necessary to replenish this amount of water, that is, 784.3 acre feet in one hour is 13.07 acre feet per minute. While hydro may provide substantial amounts of power when stored behind a dam, it still requires upstream flow to replenish it.

This is quite a good story. Ordinary air is not so "thin" and its mass is not to be dismissed lightly. The largest steam railroad locomotives ever built, the famed "Big Boys" of the early '40s, which were 4-8-8-4s, reputedly weighed 386 tons each. At wind velocities of 30 mph, the 1.5 MW wind turbines with rotor diameters of about 75 meters see this same 386 ton mass of air flow through the blades in just under 5 seconds.

"Dutchy" the Windmill

The "Verticals"

The verticals turbines have several desirable properties but the world yet awaits better answers to their blade designs. Some successes may be found among their offerings but most verticals, with a few exceptions, continue to be relatively small.