Flying Electric Generators
Many means have been proposed for capturing the energy available in high altitude winds, but only those people who have not carefully considered the state of current technology doubt that capturing this energy should be achievable now. After much study on the various methods for capturing high altitude winds, we settled on a “Flying Electric Generator” (FEG), or a “rotorcraft”, for addressing the world’s major energy and global warming problem objectives. This was first proposed by Bryan Roberts. In the mid-2000s, he obtained a patent for a “Windmill Kite”, a variation of which we call a flying electric generator. We believe the FEG technology will lead the way in capturing the energy at these truly high altitudes where the very high altitude wind energy exists.
We submitted a peer reviewed paper “Harnessing High-Altitude Wind Power” of the IEEE Transactions on Energy Conversion, Vol 22, No.1, in March, 2007. It was co-authored by Ken Caldeira and Elizabeth Cannon, Dean of the Schulich School of Engineering, University of Calgary.
The original Robert’s “rotorcraft” pictured below resembles a tethered elementary helicopter with no cabin. It has two rotors each fifteen feet in diameter.
In that picture, the craft is almost horizontal, the two contra-rotating rotors having been powered by electricity from the ground to have the craft reach that altitude.
In the next picture, the craft has been tilted by command, and the wind on this unusually windy day is turning the rotors, thus both holding up the craft and generating power which is transmitted back to the ground.
And here’s a photo of the Australian Demonstration Site (click to enlarge):
Below is the video of this demonstration in Australia many years ago.
We get many questions about weight and electrical losses in the tether, and other aspects. Tether technology is not simple, but a number of vendors now compete in this field selling primarily to the military and NASA. Transmission is at high voltage, which means that small diameter, light, conductors may be used. The electrical losses which do occur, while not sought, do result in warming the tether.
Lightning and atmospheric static
discharge as they affect tethers containing conductors are problems frequently
brought to our attention, and Benjamin Franklin is often mentioned.
However, the frequency of conditions in which these atmospheric conditions
are a potential problem is close to zero in key parts of the world needing
energy the most. This includes much of the United States, as may be seen
by clicking on this NOAA link to view Vaidala’s NLDN 5 year Flash Density
Map: http://www.lightningsafety.noaa.gov/lightningmap.htm.
Even where lightning conditions do seasonally exist, with adequate warning
provided by current technology, FEGs will be grounded and returned to service
after the storm. Furthermore, lightning problems have been addressed and solved
in other tether applications and will be utilized by FEGs when conditions are
not severe.
Turbulence can be a problem for FEGs, but a tethered rotorcraft such as an FEG has the freedom to move like a kite and settle back into station rather than sit rigidly restrained by a tower. This comes about by the long tether simply changing shape when a FEG encounters a wind gust. The tether gradually will resume its natural drape, thus reducing tension at the FEG.
In addition, programmed electronic controls, using GPS and gyroscope attitude sensing information, assure that rotor pitch and airfoil control surfaces react in damping fashion to the FEG movement.
FEGS and helicoptersFEGs are not subject to the same problems as helicopters when they attempt to fly at high altitudes. Helicopters designed to hover with loads at low altitude have increasing trouble as air density decreases and the motion of the air mass has no benefit. The faster moving air mass at high altitude is a benefit to FEGS as it more than compensates for the lower air density in the case of the tethered FEGs.
GPS technology is used to assure that FEGs stay within a short distance, both horizontally and vertically, of where they are commanded to be. This assures that FEGs will stay separated enough not only to avoid collision, but also to avoid interfering with each other’s efficient access to the available wind energy, a problem also known as “wind shadowing”. Fortunately, with three dimensions in which to operate, it is easier for FEGs than terrestrial wind turbines fixed in two dimensional surface arrays.
The GPS and gyroscope combination is also used to control the rotorcraft’s attitude, i.e. pitch, roll and yaw. The use of GPS for attitude control is in use on the space station orbiting the earth as well as on Unmanned Aerial Vehicles.
Scaling
Since much smaller rotors are necessary per megawatt captured in the high velocity high altitude winds, rated capacities of FEGs may be expected to be in the multi-megawatt range and exceed the highest current tower mounted turbine capacities.
Tether strength to weight ratios improve as sizes scale up, and guidance control weight goes up less than proportionately with size. In other words, within reasonable limits, efficiency may be expected to improve with scale.
Use of more than two rotors avoids the largest component maintenance problems of two-rotor helicopters, which use “cyclic pitch”. Cyclic pitch is where the blades are change pitch back and forth during every rotation. FEGs use “collective pitch”, in which blade pitch remains constant through complete revolutions and change the pitch of pairs of rotors when direction change (left, right, up, down) is desired. The pairs are selected depending on the direction change desired.
Use of this collective pitch approach is crucial in keeping maintenance costs low and assuring FEGs being able to fly for substantial periods of time between landings for maintenance. It is fundamental to the economics.