capacity factor

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 should be consistently higher. 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.


Location State 15,000 ft. 10 km.
Aberdeen South Dakota 75% 92%
Albany New York 73% 87%
Amarillo Texas 66% 82%
Bismarck North Dakota 68% 87%
Brownsville Texas 57% 72%
Buffalo New York 71% 87%
Chatham Massachusetts 79% 89%
Denver Colorado 44% 77%
Detroit Michigan 72% 90%
Jacksonville Florida 55% 74%
Medford Oregon 54% 83%
Miami Florida 34% 61%
Midland Texas 60% 75%
Morehead City North Carolina 64% 77%
Oakland California 50% 80%
Quillayute Washington 62% 83%
Rapid City South Dakota 64% 86%
San Diego California 40% 71%
Topeka Kansas 77%* 91%
Tucson Arizona 42% 69%

*See below

Topeka Monthly Capacity Factors
For Year 2001 at 15,000 ft. Altitude

Month Actual Readings in Month Readings at Rated Capacity SubCapacity Power Capacity Factor
January 60 43 8.52 0.86
February 56 50 5.26 0.99
March 61 36 8.44 0.73
April 60 50 9.20 0.92
May 62 42 11.31 0.82
June 60 35 12.26 0.76
July 56 19 15.47 0.62
August 61 16 15.64 0.52
September 60 23 13.29 0.57
October 62 43 6.13 0.79
November 60 42 9.09 0.85
December 62 51 6.47 0.96
Total 720 437 129.69 0.77
Capacity Factor for Year

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.

Location Country 15,000 ft. 35,000 ft.
Gough Island South Atlantic 78% 95%
Misawa Japan 63% 94%
Gagetown N.B. Canada 70% 92%
Nottingham England 64% 85%
Beijing China 46% 85%
Tasmania Australia 60% 84%
Buenos Aires Argentina 50% 82%
Moscow Russia 51% 78%
King Fahad Int Airport Saudi Arabia 46% 78%
Lyon France 40% 78%
Munich Germany 38% 73%
Madrid Spain 32% 73%
Patiala India 23% 72%
Milan Italy 24% 70%
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