(Cont'd from the home page.) ......Air density at sea level is about 1.23 kilograms per cubic meter. When taken in large enough volumes, air can be more massive and heavier than even the largest ships and longest railroad trains many times over. 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 half of 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 500 feet high over it. For water, the same mass is in a volume of about 400 acre feet, which is a lake of 40 acres in area with an average depth of about 10 feet.

Just to give some idea of what a half of a million tons of mass is like, it is the combined mass of the coal in 5,000 fully loaded railroad train coal cars, or the 100 coal cars of 50 railroad coal trains.

Now let's set this amount of air in motion. At 30 mph velocity, this mass of air has the kinetic energy of 12.1 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 12.1 MWH x 30 = 362.5 MWHs per hour, which is an energy rate of 362.5 MWs. This is for energy collection along one side of this volume, or one mile long by 500 feet high.

The well-known Betz efficiency of 59.3% applies, limiting theoretical energy collection to .593 x 362.5 = 215 MWs, and practical technological capabilities can be said to further limit this to about half or 108 MWs for each square mile. 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 fossil fuel and nuclear technology power plants - if applied to heights up to 500 feet in the atmosphere over onshore land or offshore sea surfaces of as little as five miles by five miles in area or 25 square miles.

For hydro, the feet head of 400 acre feet of water that is equivalent to 12.1 MWHs - the total kinetic energy of 500,000 tons of wind in the atmosphere moving at 30 mph - is 30.1 feet. To produce the same 108 MWs of power of one square mile of wind turbines from this volume of water would require (108 / 12.1) x 30.1 = 270 feet of head behind dams on a river. The flow of 400 acre feet per hour is 6.67 acre feet per minute. While hydro water 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 for their blade designs, which tend to have lower lift to drag ratios than do the blades of the horizontals. Some successes may be found among their offerings but most verticals, with a few exceptions, continue to be relatively small.