U.S. patent application number 14/534939 was filed with the patent office on 2015-02-26 for airborne wind energy system with enhanced power transfer.
The applicant listed for this patent is Leonid Goldstein. Invention is credited to Leonid Goldstein.
Application Number | 20150054282 14/534939 |
Document ID | / |
Family ID | 48574785 |
Filed Date | 2015-02-26 |
United States Patent
Application |
20150054282 |
Kind Code |
A1 |
Goldstein; Leonid |
February 26, 2015 |
AIRBORNE WIND ENERGY SYSTEM WITH ENHANCED POWER TRANSFER
Abstract
An improved wind power device for wind energy conversion or
vehicle propulsion. Among many possibilities contemplated, the
device may have a moving sail with tethered wings (101), moving in
elliptical trajectory, utilize separate sheave (503) and cable drum
(505), use a block and tackle (411), attached to the tether and
utilize a cable having a flexible jacket with aerodynamically
streamlined cross section (603).
Inventors: |
Goldstein; Leonid; (Austin,
TX) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Goldstein; Leonid |
Austin |
TX |
US |
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|
Family ID: |
48574785 |
Appl. No.: |
14/534939 |
Filed: |
November 6, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14266765 |
Apr 30, 2014 |
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14534939 |
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PCT/US12/67143 |
Nov 29, 2012 |
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14266765 |
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61566681 |
Dec 4, 2011 |
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61577329 |
Dec 19, 2011 |
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61621535 |
Apr 8, 2012 |
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61621593 |
Apr 9, 2012 |
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61624470 |
Apr 16, 2012 |
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61662476 |
Jun 21, 2012 |
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Current U.S.
Class: |
290/44 ;
290/55 |
Current CPC
Class: |
D07B 2201/2086 20130101;
D07B 2501/2076 20130101; F03D 13/22 20160501; F05B 2240/921
20130101; Y02E 10/728 20130101; B64C 31/06 20130101; D07B 5/005
20130101; F03D 9/32 20160501; B63H 9/061 20200201; Y02T 70/00
20130101; F03D 5/00 20130101; Y02E 10/72 20130101; B63H 9/071
20200201; F03D 7/00 20130101; B63J 2003/046 20130101; D07B
2201/2087 20130101; Y02E 10/70 20130101; F03D 15/10 20160501; F03D
9/25 20160501; B63H 9/069 20200201 |
Class at
Publication: |
290/44 ;
290/55 |
International
Class: |
F03D 5/00 20060101
F03D005/00; F03D 9/00 20060101 F03D009/00; F03D 7/00 20060101
F03D007/00 |
Claims
1. A device for conversion of wind energy into electric energy,
comprising: an airborne wing, adapted to move in the air under
power of wind; a round or aerodynamically streamlined cable,
coupled to the airborne wing by one of the cable's ends; a
perforated belt, attached to another end of the cable; a ground
level platform; an electrical generator, installed on the platform;
a sprocket, rotationally coupled to a rotor of the electrical
generator, the sprocket adapted to be engaged by the perforated
belt.
2. The device of claim 1, further comprising a drum for the
perforated belt.
3. The device of claim 2, wherein the sprocket has smaller diameter
than the belt drum, thereby achieving higher angular speed of the
sprocket.
4. The device of claim 1, further comprising an electronic control
system, including a first control element installed on the
platform, a second control element, installed on the wing, and a
network link between them.
5. A method of converting wind power into electric power,
comprising: providing an electrical generator on the ground;
harvesting wind power using an airborne wing with an attached
cable, the cable having a streamlined or round section, the
airborne wing pulling the attached cable while flying mostly cross
wind; converting the pull of the cable into a linear motion of a
perforated belt by connecting a free end of the belt to the cable;
converting the linear motion of the perforated belt into rotational
motion of a sprocket by engaging the sprocket by the perforated
belt; converting the power of the rotational motion of the sprocket
into electrical power using the electrical generator through
rotational coupling between the sprocket and a rotor of the
electrical generator.
6. The method of claim 5, further comprising a step of providing a
drum for the perforated belt and further comprising two alternating
operational phases: the first phase comprising the airborne wing
moving away from the sprocket, the perforated belt reeling off the
drum and electrical power being generated by the electrical
generator; the second phase comprising the airborne wing moving
toward the sprocket, the perforated belt reeling on the drum and
electrical power being consumed; wherein significantly more
electrical energy is generated in the first phase than consumed in
the second phase.
7. The method of claim 5, further comprising the step of utilizing
an electronic control system to control the electrical generator,
the drum, the motion of the airborne wing and to synchronize reel
on/reel off of the belt with the motion of the airborne wing.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a continuation of U.S. patent
application Ser. No. 14/266,765, filed on 30 Apr. 2014, which is a
continuation of PCT Application No. PCT/US12/67143, filed 29 Nov.
2012, which claims the benefit of U.S. Provisional Applications No.
61/566,681, filed 4 Dec. 2011, No. 61/577,329, filed 19 Dec. 2011,
No. 61/621,535, filed 8 Apr. 2012, No. 61/621,593, filed 9 Apr.
2012, No. 61/624,470, filed 16 Apr. 2012, No. 61/662,476, filed 21
Jun. 2012 by the same inventor as herein. All of the foregoing
applications are hereby incorporated herein in their entirety.
BACKGROUND OF THE INVENTION
[0002] This invention is generally directed to wind power utilizing
systems and methods, using airborne wings or sails.
[0003] Recently, a novel approach to wind power utilization has
appeared. A computer controlled kite, flying crosswind, harnesses
power of the wind, which is further converted into electric energy
or into propulsion of a ship. One example of former is U.S. Pat.
No. 8,080,889 by Ippolito et al (assigned to KiteGen). One example
of later is U.S. Pat. No. 7,672,761 by Wrage (assigned to
SkySails). The common part is that the kite moves cross wind with
high speed in so-called `figure 8` trajectory. The tether of the
kite also moves crosswind and experiences very large drag, which
can exceed the drag of the kite itself. This drag wastes energy and
limits possible length of the tether.
[0004] The crosswind flying airborne wing develops high lift
forces. In the electricity generating applications, the speed of
the tether, transferring this lift to the rotor of the electric
generator, is relatively low (typically about 1/3 of the wind
speed), resulting in relatively low power output for the force.
This issue is further exacerbated by unwinding the tether from a
tether drum, and using the same drum as a rotational element,
converting linear motion of the cable into rotational motion. The
drum is wide, and its width further increases when the tether's
thickness increases. Consequently, drum's RPM is low and it
requires an expensive gearbox with high input torque and large
conversion ratio in order to achieve 1,500-1,800 RPM, required by
most conventional electric generators.
[0005] One attempt to solve the problem of high cable drag is U.S.
patent application Ser. No. 12/154,685 Faired Tether for Wind Power
Generation Systems by Griffith et al. Unfortunately, the tether in
that application is prohibitively expensive or inefficient.
[0006] This invention is directed to solving these problems and
more.
SUMMARY OF THE INVENTION
[0007] One embodiment of the invention is a moving sail for use in
systems, utilizing wind power, comprising at least two airborne
wings; a platform at the ground level; a pulled element attached to
the platform; a tether, connecting the wings to the pulled element;
an anti-twist device, preventing twisting of the tether by motion
of the wings; and the wings move under influence of the wind in the
same clockwise or counter clockwise direction, if viewed from the
platform, and the motion of the wings has substantial cross wind
component. Another embodiment of the invention is a moving sail for
use in systems, utilizing wind power, comprising two or more two
airborne wings; a platform at the ground level with a pulled
element attached to it; an airborne attachment device, having two
sides, allowed to freely rotate one relative to another; each wings
is attached to one side of the attachment device by a flexible
cable; and a tether, attached to another side of the attachment
device and to a pulled element of said platform; the wings move
under influence of the wind in the same clockwise or counter
clockwise direction, if viewed from the platform, and the motion of
the wings has substantial cross wind component.
[0008] Related method of utilizing wind power, comprising steps of
providing at least two airborne wings, attached to a tether by
cables; providing a platform having an element, pulled by the
tether at the ground level and controlling the wings to move at
least partially cross wind, in the same clockwise or counter
clockwise direction relative to the platform for multiple loops,
while preventing twisting of the tether.
[0009] Another aspect of the invention is a device for conversion
of wind energy into electric energy, comprising an airborne wing or
sail, moving under power of wind; a cable, attached to this wing or
sail; a block and tackle system, attached to the cable; a ground
level platform with a rotational element (like a sheave, a pulley
or a sprocket) on it, coupled to the block and tackle system and an
electric generator with a rotor rotationally connected to the
rotational element.
[0010] Another aspect of the invention is a device for conversion
of wind energy into electric energy, comprising an airborne wing or
sail, moving under power of wind; a cable, attached to this wing or
sail; a ground level platform with a rotational element (like a
sheave, a pulley or a sprocket) in contact with the cable; an
electrical generator, having a rotor rotationally connected to the
rotational element; and means for holding excess of said cable
(like a cable drum). The cable may comprise two dissimilar
sections, a top section and a bottom section, and only the bottom
section is exposed to said rotational element.
[0011] Related method of converting linear motion of a cable into
rotational motion in a wind energy conversion device, comprising
steps of providing an airborne wing; a cable, coupled to the
airborne wing; a rotational element coupled with a rotor of an
electric generator; coupling the cable with the rotational element;
storing excess of the cable separately from the rotational element.
Further, the top part of the cable, which normally does not come in
contact with the rotational element, may have round or streamlined
section; and the bottom part of the cable, which does come in
contact with the rotational element, may have flat or flattened
section. An electronic control system may be utilized to control
the electrical generator and/or the rotational element and/or to
synchronize reel on/reel off of said cable with the motion of the
airborne wing.
[0012] Another aspect of the invention is a cable with
aerodynamically streamlined profile, comprising a load bearing core
and a flexible jacket having aerodynamically streamlined profile
around the core, placed in such way that the center of aerodynamic
pressure on the jacket is behind the center of the core, when the
profile of the cable is not oriented straight into the relative
airflow.
[0013] A method of manufacturing a cable with aerodynamically
streamlined profile, comprising steps of providing at least one
core cable made of a material with high tensile strength and
wrapping a flexible jacket, having aerodynamically streamlined
profile, around it.
[0014] Various objects, features, aspects, and advantages of the
present invention will become more apparent from the following
detailed description of preferred embodiments of the invention,
along with the accompanying drawings in which like numerals
represent like components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings illustrate the invention. The
illustrations omit details not necessary for understanding of the
invention, or obvious to one skilled in the art, and show parts out
of proportion for clarity. In such drawings:
[0016] FIG. 1 is a schematic view of a vehicle propulsion system
with a dynamic sail according to one aspect of the present
invention
[0017] FIG. 2 is a schematic view of a rigid wing when used in the
dynamic sail
[0018] FIG. 3 is a schematic view of a flexible wing when used in
the dynamic sail
[0019] FIG. 4 is a schematic view of a wind energy conversion
system according to one aspect of the present invention
[0020] FIG. 5 is a perspective view of a wind energy conversion
system with a separate pulley or sprocket and a cable drum
[0021] FIG. 6A is a sectional view of one form of a aerodynamically
streamlined cable
[0022] FIG. 6B is a perspective view of one form of the
aerodynamically streamlined cable
[0023] FIG. 7 is a sectional view of another form of the
aerodynamically streamlined cable
[0024] FIG. 8 is a sectional view of one more form of the
aerodynamically streamlined cable
[0025] FIG. 9 is a sectional view of yet another form of the
aerodynamically streamlined cable
[0026] FIG. 10 is a perspective view of another form of the
aerodynamically streamlined cable
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Unless stated otherwise, term "cable" here includes usual
mechanical cables, ropes and lines of any form and material. It
also encompasses belts, including perforated belts, flat belts,
round belts, toothed belts, ribbed belts, grooved belts and
V-belts. A tether is a kind of a cable, lower end of which is
attached to an object on the ground level.
[0028] FIG. 1 shows one embodiment of the invention, in which a
system of airborne wings utilizes power of the wind to pull a ship.
This embodiment comprises a pair of wings 101, attached by cables
102 to an anti twist device 103. Anti twist device 103 is attached
to a ship 110 by a tether (or another cable) 105. A control system
104 is provided. Ship 110 has a hull 106 and a rudder 107. Anti
twist device 103 is provided in order to allow circular motion of
wings 101. Anti twist device 103 comprises a top part 109 and a
bottom part 108 with a ball bearing between them, allowing
unlimited rotation of top part 109 relative to bottom part 108.
Optionally, it can be provided with its own direction sensor
(gyroscopic, magnetic or GPS) and a servomotor, compensating
remaining twisting moment.
[0029] Wings 101 move cross wind in a circle in the same direction
(clockwise or anti clockwise, when viewed from ship 110) under
power of wind for long time. The circle lies in a plane--the plane
of rotation. In FIG. 1, the plane of rotation is inclined about 45
degrees to the horizon. The aerodynamic forces (mostly aerodynamic
lift) act on wings 101 and are transferred to anti twist device
103. There, force components, parallel to the plane of rotation,
compensate each other. The remaining force component, normal to the
plane of rotation, pulls tether 105, which pulls ship 110. The
projection of tether 105 on horizontal plane does not usually match
direction of the desired motion. Rudder 107 and hull 106 compensate
sideways component of the pull force. Control system 104 selects
direction of the tether to maximize the component of the pull
force, matching the desired direction of ship motion (tractive
component). Control system 104 can vary angle of attack of the
wings depending on the wind condition and desired pull, and angle
of inclination. Angle of inclination of the plane of rotation to
the horizon can vary in wide range, from 30 to 85 degrees.
[0030] This system can be used either as an auxiliary propulsion
system, as a main propulsion system with an auxiliary engine or, on
a small boat, as a sole propulsion system. This system cannot pull
ship 110 directly upwind. If upwind motion is desired, the system
should be either depowered (wings are let to move with a minimum
lift, required to keep wings 101 in the air) and a conventional
engine used, or the ship should be tacking.
[0031] More than two wings can move in the same plane of rotation.
Multiple anti twist devices 103 can be connected with long tethers
on top of each other, with a system of wings connected to each anti
twist device 103 and moving in parallel planes.
[0032] Lateral axis of wings 101 have slight inclination to the
plane of rotation. Wings 101 are cambered. In one particular
embodiment, the lateral axis of the wings 101 are inclined 100 to
the plane of their rotation, and the angle of attack is 3.degree..
The angles change, depending on strength of the wind and the
required force. In another example, longitudinal axis of each wing
101 has constant angle 5.degree. to the plane of rotation, and
angle of attack changes with the position of the wing in the
circle.
[0033] The system of wings 101 plays role of a conventional sail,
with a big advantage: fast crosswind motion of the wings allows to
develop force, many (possibly hundreds times) bigger than wind
pressure on static sails of the same size. Another advantage is
that it can catch stronger and more regular wings at the altitude
above the sea level. Further, tether 105 does not exhibit
significant motion and does not create significant drag. Also,
circular motion of wings 101 requires lower centrifugal
acceleration (compared with figure 8 motion).
[0034] Wing 101 can be any of the following: a rigid wing, like
planes, gliders or ground based wind turbines have; a flexible
wing; a soft wing; an inflatable wing; an inflatable wing, inflated
by the ram air, entering it through holes; a kite wing; a
paraglider wing; a wing, using soft materials, spread over a rigid
frame or cables; a wing made of elastic fabric, receiving airfoil
form from relative air flow; and/or a mixed wing, using different
construction techniques in different parts of the wing.
[0035] Wing 101 can be made of various materials, including carbon
fiber, fiberglass, wood, aluminum, aramids, para-aramids,
polyester, high molecular weight polyethylene, nylon and others.
Wing 101 may have wingtips to decrease turbulence and noise. Wing
101 has stabilization and control surfaces and their actuators and
possibly its own control system. An example of a rigid wing is
shown in FIG. 2. It comprises horizontal stabilizers 201, rudders
202, a vertical stabilizer 203 and an elevator 204 on a double boom
206, spoilers 205 and a control system 207. An example of a kite
wing is shown in FIG. 3. It comprises flexible inflatable canopy
301, 4 combined control and suspension cables 302 and a control
device 303. In this form, position of the wing relative to the wind
and to the horizon is controlled by dynamically changing the
lengths of cables 302. Wing 101 can be aerodynamically unstable and
its stability can be assured by frequent application of corrective
forces.
[0036] Control system 104 comprises a central processor or a
microcontroller, actuators, sensors and communication means for
communicating with the control elements of wings 101. Preferable
communication means is a wireless network, although optical or
copper wires, going through cables 102 and tether 105 can be used
too. The sensors may include an anemometer, barometer, radar,
hygrometer, thermometer, GPS, cable tension meter, RPM meter,
cameras for observing the wings and other.
[0037] FIG. 4 shows another embodiment of the invention. A pair of
wings 101 connected by cables 102 to anti twist device 103 are is
placed in the air and are flying cross wind with a speed, exceeding
speed of the wind. Wings 101 can have a high L/D ratio, and move
with speed is 4-20 times higher, than the speed of the wind. A
cable 401 is attached to anti twist device 103 at one end and to a
sheave 403 at another end. A ground platform 410 is installed on
the ground, or slightly above the ground. An electric generator
408, having a rotor and a stator, is installed on the platform. A
pulley 407 is rotationally connected to the rotor of electric
generator 408. The connection can be via a gearbox, or pulley can
be co-axial with the rotor, or another way of mechanical
transmission can be utilized. Platform 410 can be able to rotate in
horizontal plane (yaw) to order accommodate changes in direction of
wind and movement of the wing. A sheave 405 is installed on
platform 410. A belt 406 is attached by its one end to platform
410, goes around another sheave 403, then around sheave 405, then
around one more sheave 404, and comes into contact with pulley 407.
Belt 406 wraps around pulley 407 at a number of times, necessary to
avoid slippage (this number can be between 0.25 and 20, depending
on used materials, cable form and other conditions). Remaining part
of cable 406 is wound around a spool 409.
[0038] Usual mechanical cables, ropes and lines of many forms and
materials can be used for belt 406. Also, various belts, including
perforated belts, flat belts, round belts, toothed belts, ribbed
belts, grooved belts, V-belts and other can be used for belt 406.
Control system 412 is provided.
[0039] Operation of this embodiment is controlled by control system
412. Operation comprises two phases: the active phase and the
passive phase. The active phase starts when anti twist device 103
is in a position, closest to platform 410, sheave 403 is closest to
sheave 405, and almost all of cable 406 is wound on spool 409. In a
coordinate system, moving with anti twist device 103, wings 101
move in the rotation plane. Relative to platform 410, wings 101
move in ascending downwind spiral with constant radius, getting
away from the platform. Aerodynamic lift of wings 101 pulls cable
401, which pulls sheave 403. Belt 406 is pulled up, unwinding from
spool 409 and rotating pulley 407, which rotates the rotor of
electrical generator 408, which produces electric energy. When all
cable 406 is unwound from spool 409, an electric motor or some
other means stop spool 409 and start rotating it in the opposite
direction, winding cable 406 back on. Winding cable 406 pulls in
sheave 403 and extension cable 102. Wings 101 stop flying cross
wind and are commanded by control system 412 to fly in general
direction of platform 410, creating minimum resistance, only to
keep cables 102 and 103 stretched. In the end of passive phase, the
device returns into the initial position, and a new active phase
starts. The passive phase is much shorter than active phase and
consumes very little energy.
[0040] Optional block and tackle 411 is employed to mechanical
disadvantage. It is used here for two purposes:
[0041] a) increase velocity of belt 406 in contact with the pulley,
thus decreasing forces, acting on the pulley and other mechanisms,
connected to it, for the same power;
[0042] b) decrease tension of belt 406, thus allowing to decrease
its thickness and, consequently, diameter of pulley 407, while
increasing durability of the belt.
[0043] Increasing velocity of cable in contact with pulley 407 and
decreasing diameter of pulley 407 allow to increase angular speed
of pulley's rotation. A gearbox may still be required, but less
expensive one than without use of block and tackle 411. FIG. 4
shows block and tackle system with mechanical disadvantage ratio of
4 (i.e., velocity of the cable near the pulley, attached to the
rotor, is 4.times. higher than the speed, with which distance
between wing 101 and generator 408 increases). By changing number
of the sheaves, it is possible to change mechanical disadvantage
ratio from 2 to 20. Block and tackle system 411 or its analogies (a
differential pulley, Z-drag line, Spanish bartons etc.) can be used
in any wind energy conversion system with airborne blades, where
the motion transfer is performed by a cable. Alternatively, belt
406 can be connected directly to cable 401. If belt 406 is
perforated, a matching sprocket can be used instead of pulley
407.
[0044] An example system with cross wind wing trajectory, in which
anti twist device 103 is moving away from platform 410 with an
average speed 2 m/s, pulley 407 has diameter 0.25 m and block and
tackle provides 10.times. mechanical disadvantage has 1,500 RPM on
pulley, sufficient for almost every 50 Hz electric generator
without gearbox.
[0045] It should be noted, that in the active phase cable 401 moves
steadily in the direction of its length and neither it nor block
and tackle system 411 experience significant sideways motion (thus
saving power losses due to air resistance and excessive wear of
cable 406). Different strategies for control of wings 101 can be
utilized by control system 412 in the active phase. One strategy is
to attempt to keep wing's angle of attack in the air constant and
low. Another strategy is to attempt to keep constant the wing's
angle to the wings' plane of rotation. These controls actions can
be combined with cyclical changing angle of the lateral axis of the
wings to their plane of rotation (over each 360 degrees rotation
cycle). Anti twist device 103 prevents twisting of cable 401.
[0046] FIG. 5 shows another aspect of the invention--an enhanced
mechanism for conversion of linear motion of a cable into
rotational motion of a rotor of electric generator. In one
embodiment, this aspect of the invention comprises at least one
wing 501, moving in the air under power of wind and pulling a cable
502. On the ground, there is an electric generator 504, comprising
a rotor and a stator. A pulley (or a sheave, or a sprocket for a
perforated belt) 503 is rotationally attached to the rotor of
generator 504. Optionally, it can be attached through a gearbox
(not shown on the picture). Cable 502 is wrapped around pulley 503
at least pre-defined number of turns. Pre-defined number of turns
can be fractional and is usually small, typically between 0.5 and
20. After wrapping around pulley 503, cable 502 is wound around a
spool 505, and cable's end is attached to it. Means are provided to
wind and unwind cable 502 accurately and to maintain pre-defined
force on cable 503 in direction from pulley 503 to spool 505 in
order to ensure sufficient friction. In FIG. 5, these means are a
small electrical motor 506, attached to spool 505, and a ball screw
507 with associated small electric motor 508. Further, an optional
section of cable 509 of a different kind can be inserted between
wing 501 and cable 502. For example, cable 509 can be a standard
round cable, while cable 502 can be a perforated belt. If cable 502
is perforated belt, a sprocket is used instead of pulley 503.
[0047] Operation of the system consists of two phases--the active
phase and the passive phase. In the active phase, wing 501 is
moving away from pulley 503, while rotating the rotor of generator
504, which generates electricity. It should be noted, that
trajectories of the wing may differ as long as the cable length
between wing 501 and pulley 503 increases. In the passive phase,
wing 501 moves toward pulley 503, while cable 502 is winding on
spool 505. Electrical energy is not generated in the passive phase,
other way around--small amount of electrical energy may be
consumed. The arrows on the picture show direction of movement of
cable 502, spool 505 and direction of rotation of pulley 503 and
spool 505 in the active phase. In the passive phase these
directions are opposite.
[0048] In the beginning of the active phase, spool 505 is in its
left most position, wing 501 is in the position, closest to pulley
503 and most of cable 502 is wound on spool 505. In the active
phase wing 501 is moving away, pulling cable 502. Cable 502 rotates
pulley 503 and unwinds from spool 505. Small motor 506 resists
rotation of spool 505, creating a force on the segment II of cable
502, opposite to direction of cable movement. Force, acting on
segment II, is much smaller than force of wing's pull, acting on
segment I, so that cable unwinds, while rotating pulley 503 without
slippage. As cable 502 unwinds from spool 505, spool 505 moves
toward right on ball screw 507, pushed by motor 508. Spool 505
moves to right with such speed that unwinding cable remains aligned
with pulley 503. In the end of active phase, spool 505 is in its
right most position, wing 501 is in the furthest position from
pulley 503 and only few wraps of cable 502 remain on spool 505.
Then passive phase starts. In this phase, motor 506 rotates pulley
506 in the opposite direction, winding cable 502 on pulley 505,
while motor 508 moves spool 505 to the left. In the end of the
passive phase, positions of the parts of the system correspond to
the positions in the beginning of the active phase.
[0049] The benefits of this embodiment are due to the fact, that
forces, acting on segment II of cable 502 are much smaller than
forces, acting on segment I of cable 502. The ratio is determined
by belt friction equation:
T.sub.load=T.sub.holde.sup..mu..phi.
[0050] where T.sub.load the force on segment I, T.sub.hold is the
force on segment II, mu is the coefficient of friction and phi is
the angle of cable wrapping. It is desirable to have higher ratio
of forces. In many cases ratio 20:1 is sufficient (i.e., force on
segment II is 5% of force on segment I). To achieve such ratio with
a high friction ribbed belt over ribbed sheave(mu=0.9), only half
turn of the cable is required. To achieve such ratio with Dyneema
over smooth steel (mu=0.05), full 20 turns are required. In any
case, the force should be sufficient to prevent slippage. Since
force, acting on segment II of cable 502 is relatively small and we
do not care about angular velocity of spool 505, spool 505 can be
wide and long and cable 502 can be laid in multiple layers on
it.
[0051] Among advantages of this aspect and embodiment: very long
cables and very long cable motion are allowed (up to tens of
kilometers) due to large capacity of spool 505; cables and belts,
withstanding high tension are allowed due to large capacity of
spool 505; cable fatigue is decreased due to large diameter of
spool 505; flat cables and belts can be used; rotational velocity
of pulley 503 can be increased for the same linear velocity of
cable 502 by decreasing diameter of pulley 503; higher power output
at lower cost is achieved.
[0052] As a variation of this embodiment, a second wing can be used
instead of spool 505, creating resistance in segment II of cable
502 in its active phase, and pulling cable 502 in the passive phase
of the first wing. Also, drag based wind capturing devices can be
used instead of wings in this embodiment.
[0053] Another aspect of the invention is a streamlined cable and
method of its manufacturing, combining high strength with low drag
in cross flow and low disturbance of laminar air flow. The high
drag of a usual cable is caused by it being round in section. This
causes disturbance of air flow in the area behind the cable. Thus,
aerodynamic cable should have a section in the form of a
streamlined body.
[0054] FIG. 6A shows one embodiment of such aerodynamic cable in
section. It consists of an off-the-shelf load bearing rope 601
inside of a streamlined jacket or coating 603, with the remaining
space occupied by polyethylene foam 602. Rope 601 is placed in the
widest place inside jacket 603 (or jacket 603 is wrapped around
rope 601). In some variants of this embodiments, especially when
the rope diameter is small, polyethylene foam 602 is replaced by
air. Also, electrical or optical wires can pass in the space
between core 601 and jacket 603. Other light weight flexible
material can be used instead of polyethylene foam. Rope 601 is made
of aramid (including poly aramid or meta aramid) fibers, ultra high
molecular weight polyethylene fibers, carbon fibers or another
strong material. jacket 603 is made of nylon or other material,
sufficiently durable and flexible. Material of jacket 603 should
also be smooth from outside, resistant to water and ultra violet
radiation, or have coating with these properties. When the
aerodynamic cable is attached to another cable or surface, jacket
603 and foam 602 are removed at the end, and rope 601 is attached
as usual.
[0055] FIG. 6B shows perspective view of the aerodynamic cable
according to this embodiment, with rope 601 exposed at the end. In
most cases, the cable needs to orient itself correctly in the air
stream. The cable in this embodiment does orient itself in the air
stream, when it is attached by its end and sufficiently long. In
some variations, additional strips 604 are attached to the rear end
of the cable at constant intervals, to provide additional
stabilization in the air flow. Strips 604 can be rigid or
flexible.
[0056] FIG. 7 shows another embodiment of the aerodynamic cable in
section. It comprises multiple ropes 601, possibly of different
diameters. In this embodiment, ropes or yarns 601 can fill part or
whole space inside of jacket 603. FIG. 8 shows another embodiment
of such aerodynamic cable in section. It uses one or more sideways
compressed ropes 601. As the result of asymmetrical compression,
rope 601 should be wider in the direction of the airfoil axis and
narrower in the perpendicular direction. FIG. 9 shows another
embodiment of such streamlined cable, in which sectional form is
not airfoil, but round in the forward part and angular in the rear
part. FIG. 10 shows another embodiment, in which a small section of
jacket 603 is removed at equal intervals (for example, each one
hundred diameters of rope 601). It is done for better flexibility
and self orientation in the air flow.
[0057] These embodiments of invention will have aerodynamic drag
many times (5.times.-50.times.) lower, than round cable of the same
strength and weight, due to lower form drag coefficient in all
embodiments and lower cross section in some embodiments for the
same strength. The applications of the streamlined cable are in the
airborne wind energy conversion devices, tethered aircraft,
suspension cables for airplanes and kites, guy wires for tall
buildings, bridge suspensions etc. jacket 603 may have dimples to
damp oscillations. The streamlined cable can be manufactured from
conventional round fiber rope by flattening it by pressure from the
sides, using the flattened rope 601 as the force bearing core, and
then wrapping jacket 603 around it, with optional foam 602 inside
of jacket 603.
[0058] Examples of using streamlined cable in this invention are
for cables 102 in FIG. 1 and FIG. 4, cable 509 in FIG. 5,
suspension cables in the kite wing in FIG. 3.
[0059] Multiple embodiments and aspects of the invention are
described with reference to ground level. The invention can be
practiced in marine environment (oceans, seas, lakes as well), in
which case water level replaces ground level.
[0060] Thus, an airborne wind energy system with enhanced power
transfer is described in conjunction with multiple specific
embodiments. While the above description contains many
specificities, these should not be construed as limitations on the
scope, but rather as exemplification of several embodiments
thereof. Many other variations are possible.
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