Wind is More Persistent at High Altitudes
It is common practice in the wind industry to talk in terms of rated capacity of wind turbines or total installed capacity at wind farms.
But this says nothing about how much energy is actually captured until "Capacity Factor" is brought in. Capacity Factor is the percentage of energy actually captured relative to what would be captured if the wind turbines were operating at full capacity all the time.
By far the biggest reason for not operating at capacity is that insufficient winds exist at the given site to generate at rated capacity. This is true at any altitude, but the percentage of the time is much less at high altitude.
In the year 1999 the average capacity factor for the wind turbines in California was 19.2 percent. Since then wind turbine efficiencies have improved, but ground based sites at which capacity factors are as high as 35 percent are difficult to find.
By contrast, capacity factor calculations for Flying Electric Generators of Roberts' design operating at high altitude typically range from seventy percent in the south of the United States up to in some cases over ninety percent at the latitude of Detroit, then starting to taper off going further north. This may be seen in the following tables, as calculated on the basis of the radiosonde readings for the listed cities during the year 2001 as discussed in a previous section. The operating characteristics of a specific but typical Roberts Flying Electric Generator design are used in these calculations. The same design is assumed in the economics section of this website. (Capacity factors can be improved by expanding rotor sizes relative to generator capacities but at increased cost, and, if carried too far, at greater cost per kilowatt hour delivered).
Very importantly, at high altitude ground topology has almost no bearing on capacity factor. Fly FEGs anyplace within about a hundred miles of a city whose capacity factor is listed in the tables and the capacity factor can be expected to be about the same.
This means that good site selection for FEG arrays depends primarily on being isolated enough not to be over populated areas but not so far as to make ground transmission to those areas too expensive.
Note in the tables below that Miami, because of its low latitude, has the lowest capacity factor of U.S. cities. However, by very fortunate coincidence, the Gulf Stream goes right by, with its tremendous potential for power generated from turbines capturing its kinetic energy.
In the tables below, capacity factors calculated at 15,000 feet and 10 kilometers (=32,500 feet) it is important to understand that the period taken for calculation was the year starting September 21, 2001 to September 20, 2002. Statistics do vary somewhat from year to year not only overall but by locality as well.
CAPACITY FACTOR TABLE FOR U.S. LOCATIONS
Topeka Monthly Capacity Factors
For Year 2001 at 15,000 ft. Altitude
CAPACITY FACTORS ELSEWHERE IN THE WORLD
The capacity factor at Misawa, in central Japan, is 94 percent. Japan has one of the most serious energy problems of the developed world. Need we say more?
The highest capacity factor we've calculated, 95 percent, is for Gough Island, in the Atlantic Ocean, between Africa and South America, administered for the U.K. by South Africa. There's no market there, but the purpose of flying there, near no air routes, might be to generate hydrogen and ship it (which also could be done by ship-based FEGs at nearby latitudes).
It should be mentioned that the high altitude winds in New Zealand may well be the most favorable in the world, but the radiosonde data are so incomplete with regard to wind statistics that reliable calculations are not feasible.
Unfortunately, high altitude winds are not good near the equator or low latitudes in either hemisphere, where geostrophic winds do not exist.
England, in spite of its northern latitude, perhaps another benefit of the gulf stream, has surprisingly good high altitude winds. Capacity factors at many other places in the world, including Europe, are also favorable for economic generation of electricity using Flying Electric Generators.