U.S. patent application number 12/702536 was filed with the patent office on 2011-08-11 for wind power generation system for lighter than air (lta) platforms.
This patent application is currently assigned to Northrop Grumman Systems Corporation. Invention is credited to Roy A. Charletta, Alice DeBiasio, Donald DiMarzio, Douglas R. Frei, Theodore W. Hilgeman, Thomas J. Hunt, Michael Melnyk.
Application Number | 20110192938 12/702536 |
Document ID | / |
Family ID | 44352912 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110192938 |
Kind Code |
A1 |
DiMarzio; Donald ; et
al. |
August 11, 2011 |
WIND POWER GENERATION SYSTEM FOR LIGHTER THAN AIR (LTA)
PLATFORMS
Abstract
An apparatus includes a lighter than air platform, a reversible
propulsive/wind turbine, a deployable anchor to constrain movement
of the lighter than air platform with respect to an anchor point
allowing wind to drive the turbine, and a generator/motor coupled
to the turbine to produce electrical power when movement of the
lighter than air platform is constrained. A method performed by the
apparatus is also provided.
Inventors: |
DiMarzio; Donald;
(Northport, NY) ; Hilgeman; Theodore W.;
(Centerport, NY) ; DeBiasio; Alice; (Smithtown,
NY) ; Hunt; Thomas J.; (Centereach, NY) ;
Frei; Douglas R.; (Setauket, NY) ; Charletta; Roy
A.; (Smithtown, NY) ; Melnyk; Michael;
(Centerport, NY) |
Assignee: |
Northrop Grumman Systems
Corporation
Los Angeles
CA
|
Family ID: |
44352912 |
Appl. No.: |
12/702536 |
Filed: |
February 9, 2010 |
Current U.S.
Class: |
244/53R ;
204/242; 205/628 |
Current CPC
Class: |
B64B 1/50 20130101; B64B
1/00 20130101 |
Class at
Publication: |
244/53.R ;
204/242; 205/628 |
International
Class: |
B64B 1/00 20060101
B64B001/00; C25B 9/00 20060101 C25B009/00; C25B 1/04 20060101
C25B001/04 |
Claims
1. An apparatus comprising: a lighter than air platform; a turbine;
a deployable anchor to constrain movement of the lighter than air
platform with respect to an anchor point allowing wind to drive the
turbine; and a generator/motor coupled to the turbine to produce
electrical power when movement of the lighter than air platform is
constrained.
2. The apparatus of claim 1, further comprising: an energy storage
system for storing energy supplied by the motor/generator.
3. The apparatus of claim 1, wherein the energy storage system
supplies energy to the generator/motor to drive the turbine and
propel the lighter than air platform.
4. The apparatus of claim 1, wherein the energy storage system
comprises: a water source; an electrolysis cell for using the
electrical power to split water into hydrogen and oxygen; and a
hydrogen storage system.
5. The apparatus of claim 4, further comprising: a second turbine;
and a hydrogen engine for using the hydrogen to drive the second
turbine.
6. The apparatus of claim 1, wherein the deployable anchor
comprises: a flyable anchor.
7. The apparatus of claim 6, wherein the flyable anchor comprises:
an airfoil; an actuator for controlling the orientation of the
airfoil; a control system for controlling the actuator in response
to remote control commands; and a restraining device.
8. The apparatus of claim 7, wherein the restraining device
comprises one of: a harpoon, a grappling hook, a sail, a drogue,
and an anchor.
9. An apparatus comprising: a lighter than air platform; a turbine;
a tether to constrain movement of the lighter than air platform
with respect to an anchor point allowing wind to drive the turbine;
a generator/motor coupled to the turbine to produce electricity
when the turbine is driven by the wind; an energy storage system on
the lighter than air platform for converting the electricity into
stored energy; and a power management system for using the stored
energy to drive the generator/motor.
10. The apparatus of claim 9, wherein the energy storage system
comprises: an electrolysis system for using the electricity to
split water into hydrogen and oxygen; and a hydrogen storage
unit.
11. A method comprising: providing a lighter than air platform
including a propulsion turbine; deploying an anchor to constrain
movement of the lighter than air platform with respect to an anchor
point; using the propulsion turbine to drive a generator on the
lighter than air platform to produce electrical power; hoisting the
anchor; and using the propulsion turbine to propel the lighter than
air platform.
12. The method of claim 11, further comprising: using the
electrical power to store energy.
13. The method of claim 12, wherein the step of using the
electrical power to store energy comprises: splitting water to
generate hydrogen; and storing the hydrogen.
14. The method of claim 13, further comprising: using the hydrogen
in a buoyancy system.
15. The method of claim 13, further comprising: using the hydrogen
to generate electricity.
16. The method of claim 13, further comprising: using the hydrogen
in an internal combustion engine in a propulsion system.
17. The method of claim 12, wherein the step of using the
electrical power to store energy comprises: charging a battery.
Description
FIELD OF THE INVENTION
[0001] This invention relates to electric power generation for
lighter than air (LTA) platforms.
BACKGROUND OF THE INVENTION
[0002] Lighter than air (LTA) platforms are enjoying renewed
interest in a variety of applications. In addition to traditional
uses such as advertising and promotion, there is increased interest
in LTA platforms for both civil and military Intelligence,
Surveillance, Reconnaissance, and Communications (ISR&C)
applications.
[0003] The long endurance and low fuel consumption rates inherent
in LTA systems are attractive attributes for persistent airborne
ISR&C applications. An increasing demand for LTA platforms to
provide a significant time-on-station capability, whether they are
tethered aerostats or mobile airships, places increasing energy
demands on long term power for both its payload and propulsion
energy system. Current propulsion and electric power systems that
rely on fossil fuels provide both limited transit range and
time-on-station. The same is true for batteries as well as
conventional fuel cell powered systems. As a result of these
limitations, the full endurance potential of LTA ISR&C systems
has been difficult to realize. Recent LTA designs have included
renewable energy sources such as solar cells (i.e., photovoltaics)
to enhance both mobile LTA platform range and time-on-station
performance. Photovoltaic solutions can provide additional power to
propulsors and payloads, but have their own limitations which
include conversion efficiencies, restriction to daylight
operations, and weather and weight issues.
[0004] There is a need for an energy source for fixed and mobile
LTA platforms that can provide significant power for both
propulsion (i.e., transit and station keeping) and payload
systems.
SUMMARY OF THE INVENTION
[0005] In a first aspect, the invention provides an apparatus
including a lighter than air platform, a reversible propulsive/wind
turbine, a deployable anchor to constrain movement of the lighter
than air platform with respect to an anchor point allowing wind to
drive the turbine, and a generator/motor coupled to the turbine to
produce electrical power when movement of the lighter than air
platform is constrained.
[0006] In another aspect, the invention provides an apparatus
including a lighter than air platform, a turbine, a tether to
constrain movement of the lighter than air platform with respect to
an anchor point allowing wind to drive the turbine, a
generator/motor coupled to the turbine to produce electricity when
the turbine is driven by the wind, an energy storage system on the
lighter than air platform for converting the electricity into
stored energy, and a power management system for using the stored
energy to drive the generator/motor.
[0007] In another aspect, the invention provides a method
including: providing a lighter than air platform including a
propulsion turbine, deploying an anchor to constrain movement of
the lighter than air platform with respect to an anchor point,
using the propulsion turbine to drive a generator on the lighter
than air platform to produce electrical power, hoisting the anchor,
storing energy generated by the wind and turbines, and using the
propulsion turbine to propel the lighter than air platform.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic representation of an LTA platform with
an anchor power generation (APG) system.
[0009] FIG. 2 is a block diagram of portions of a flying anchor
system.
[0010] FIG. 3 is a schematic representation of an LTA platform with
several optional anchor systems.
[0011] FIG. 4 is a graph of atmospheric wind speeds as a function
of altitude.
[0012] FIG. 5 is a block diagram of an LTA wind turbine
generator/motor system.
DETAILED DESCRIPTION OF THE INVENTION
[0013] One source of abundant energy that LTA platforms have is the
capability of station-keeping with continual access to wind at
altitude. In order to exploit this energy resource for LTA
platforms, in one aspect, the invention employs an apparatus,
referred to herein as an Anchored Power Generation (APG) system.
The APG system concept of operation begins with a tethering or
anchoring of the LTA platform at an appropriate altitude. For a
mobile airship, an anchor line (i.e., a tether) is lowered from the
airship with an anchor at the end. Various types of anchors can be
used, wherein the selected type would be appropriate for either
maritime operations (e.g., a sand or water drag anchor) or land
operations (e.g., a grappling anchor, harpoon). For the case of an
aerostat, it is assumed that the LTA platform is already
tethered.
[0014] The APG concept includes an onboard wind turbine electric
power generation system. For an aerostat, this wind turbine
provides continuous power to onboard payload systems. For a mobile
airship, however, this energy can be converted and stored to
provide additional power for in-transit propulsion as well as
payload support. During transit, the onboard wind turbine acts in
reverse, serving as a propulsion system and consuming the energy
that was stored while the airship was anchored.
[0015] In one embodiment, for a mobile airship mode of operation,
electric energy generated by the wind turbine can be used to split
water (e.g., captured atmospheric humidity or onboard storage) in
order to generate hydrogen. Hydrogen can be stored as part of the
airship buoyancy system, and used to generate electricity via fuel
cells to power a dual mode generator-motor propulsion system. An
active hydrogen generation system compensates for buoyancy gas
leakage and significantly extends LTA range and lifting
capability.
[0016] As an alternative to fuel cell energy conversion, some of
the stored hydrogen can be directly consumed by an internal
combustion engine propulsion system that utilizes hydrogen as the
propulsive energy source. The APG system allows a mobile LTA
airship to periodically rest, regenerate hydrogen, and store the
hydrogen for energy needed for in-transit propulsion and payload
requirements (e.g., communications, radar, etc.). When the airship
is on-station it can simply lower its anchor and run all payload
electrical systems directly off of the wind turbine generator.
[0017] An airship with the APG system has potentially unlimited
range and access to operationally significant power for on-station
payload support without any ground based refueling or servicing.
This is especially important when persistent unmanned operations
are required for civilian and military ISR&C missions.
[0018] Referring to the drawings, FIG. 1 is a schematic
representation of an LTA platform 10 with an Anchor Power
Generation (APG) system. The LTA platform includes at least one
turbine 12 and 14. An anchor 16 system is used to constrain the
movement of the LTA platform with respect to an anchor point. This
limits the movement of the LTA platform with respect to winds
experienced by the platform at altitude. The wind can then be used
to drive the turbine and the turbine can be used to drive a
generator to produce electricity that can be used to power a
payload and/or can be used to store energy that can be subsequently
used to drive the turbine in a propulsive mode. The anchor can be
deployed when on-board power generation is desired.
[0019] The anchor can be a remote controlled, flyable anchor, that
includes an airfoil and an actuator needed to control the
orientation of the airfoil to direct the flight of the anchor. FIG.
2 is a block diagram of portions of a flying anchor system 18. The
flying anchor system includes an airfoil 20, an actuator 22, a
receiver 24, and a restraining device 26. The actuator and receiver
are components of a control system that may be contained in a
housing 28. The housing would be connected to the lighter than air
platform by a tether (not shown). When the flying anchor is to be
deployed, it can be lowered from the LTA platform on the tether.
Its location can be controlled by sending control signals to the
receiver through the on-board control system in the LTA platform.
These control signals are then used to activate the actuators,
which control the orientation of the airfoil to control the flight
of the anchor system. The control signals can be supplied either
wirelessly, and received by the antenna 30, or through a wire in
the tether. Once the anchor has been positioned at a desired
location, the restraining device 26 can be deployed. As used in
this description, a restraining device is a device that prevents or
resists movement of the anchor system with respect to land, water
or air, depending upon the type of anchor system. In various
embodiments, restraining devices can include, for example, anchor
rods, harpoons, grappling hooks, drogues, Danforth anchors, or
parachutes.
[0020] FIG. 3 is a schematic representation of an LTA platform 40
with an Anchor Power Generation (APG) system. The illustrated LTA
platform includes at least one turbine 42 and 44, and a plurality
of alternative anchor systems 46, 48, 50 or 52 to constrain the
movement of the LTA platform with respect to an anchor point. The
anchor is adapted to be deployed and retrieved when the LTA
platform is at altitude. FIG. 3 shows several alternative "flying
anchor" systems that include a restraining device and an airfoil,
and are remotely piloted to guide the restraining device to an
appropriate location. The flying anchor system may include a
radio-controlled aerodynamic steering unit similar to an
aerial-refueling "flying boom", which effectively damps out
oscillations and crosswind effects. An aerodynamic deployable
anchor system enables remote autonomous mooring and wind power
generation and station keeping.
[0021] For land operations, in the example of FIG. 3, anchor system
46 includes an airfoil 54 and an anchor rod or harpoon 56. The
harpoon can be housed within a housing 58 that is flown to a
position over land, using the airfoil and actuators that can be
remotely controlled as shown in FIG. 2. Once the desired position
is reached, the harpoon can be ejected from the housing and
embedded in the land 60 to provide an anchor point. In an
alternative embodiment, the housing may contain a grappling hook
that can be ejected from the housing and used to take advantage of
rough terrain or fixed objects and materials on the ground by
engaging such land based features.
[0022] For maritime operations, the anchor will be lowered and
"flown" to a position below the sea surface. Where the depth
permits, a retraining device can be embedded in the seabed. For
deeper water, water drag anchoring can be employed. Anchor system
48 includes a restraining device 62, which may be a Danforth anchor
that can be embedded in a seabed 64 to provide an anchor point.
Anchor system 50 includes an airfoil 66 and actuators needed to
position the airfoil to direct the flight of the anchor. Anchor
system 50 further includes a restraining device such as a sea
anchor or drogue 68. In this case the restraining device does not
provide a fixed anchor point, but rather provides a moveable anchor
point which nonetheless still serves to restrain the LTA platform
that is coupled to the anchor system by the tether. It is
anticipated that a water drag (e.g., drogue) anchor system for
maritime environments will be sufficient for many LTA designs and
modes of operation.
[0023] In addition to the basic maritime and land anchoring
concepts described above, another method of "fixing" the position
of the LTA platform relative to the prevailing winds for efficient
wind turbine operation involves the deployment of large parachutes
or "air drogues" that take advantage of variation in wind speed
with different altitudes. By taking advantage of the differential
in wind speeds, the LTA platform may be slowed down enough to
enable useful power generation for LTA system and payload support.
This air-drogue concept potentially reduces tether length
requirements and may allow for power generation and energy storage
while the LTA platform is in-transit at reduced speeds.
[0024] Anchor 52 is an air anchor that includes an airfoil 70 and
actuators needed to position the airfoil to direct the flight of
the anchor. Once the air anchor is positioned at a desired
altitude, a restraining device in the form of a parachute 72 can be
deployed. In this case the restraining device does not provide a
fixed anchor point, but rather provides a moveable anchor point
that nonetheless still serves to restrain the LTA platform that is
coupled to the anchor system by the tether.
[0025] In each embodiment, the APG system includes a deployable
anchor line system of sufficient length and strength that takes
advantage of significant wind speeds found at higher altitudes, and
has a reusable restraining device appropriate for either maritime,
land based, or completely airborne operations. The anchor system
can utilize tether technology already used for aerostats with
existing anchoring systems adapted for remote operation in ocean or
land environments. Lightweight tether strap systems are available
that have both the length and strength to hold a sizable LTA
platform at high attitude. For example, holding an LTA platform at
5000 ft altitude with a tether line at a 45 degree line layout
would require 300 lb total of an 8000 lb rated line. For a 20,000
ft altitude the line weight is 1200 lbs. LTA platform tether line
capacity will depend on turbine requirements for maximum wind
speeds, which varies as a function of geographic region and
altitude.
[0026] Another benefit to having a reusable anchoring system is
remote station keeping. This can help the LTA platform maintain a
steady position and orientation for operation of payload systems
such as radar, electro/optical/infrared (EO/IR) sensors, and
communications links. The reusable anchoring system provides a
versatile re-deployable LTA platform capability not found in
current tethered (fixed) systems, which require ground support
components. Embodiments of the invention allow for unmanned
operation in remote unprepared areas around the world.
[0027] The airborne wind turbine generator can also be integrated
into a propulsion system. Wind turbines are traditionally employed
as ground based (or offshore) stationary systems for renewable
power generation. Large blades that turn at moderate revolutions
per minute (rpms) are employed in order to maximize power
generation for the relatively slow wind speeds found near ground
level. Even with low wind speeds (.about.10 knots), megawatt power
levels can be obtained by individual wind turbine towers. Wind
turbine power goes as the cube of wind velocity, so if a wind
turbine can be operated at altitudes reached by conventional
aerostats and airships, the turbine blade diameter can be greatly
reduced and significant power can still be generated.
[0028] FIG. 4 shows average wind velocity around the globe as a
function of altitude. Winds speeds rise dramatically up to an
altitude of 40,000 ft, after which they drop before reaching the
upper stratosphere. For example, an LTA platform operating at
20,000 ft can see maximum wind speed in excess of 80 kts for
various geographic regions.
[0029] Unlike current concepts for airborne wind turbines for power
grid support that are limited by the heavy copper cables needed to
get power from the ground up to the platform, the APG system
eliminates the need for the copper cable as power is kept onboard
the LTA platform for payload consumption and propulsion. This
permits the use of much longer lightweight cable materials to
access higher wind speed at higher altitudes.
[0030] A schematic of an APG wind turbine generation/propulsion
system 80 is shown in FIG. 5. The generation/propulsion system 80
includes a wind turbine propulsor 82 coupled to a generator motor
84. The generator motor is electrically connected to a power
management and distribution (PMAD) component 86. The PMAD component
distributes electricity to on-board avionics 88, a payload 90, and
an electrolysis system 92. The electrolysis system uses the
electricity to split water from a water condenser/storage unit 94
into hydrogen and oxygen. The hydrogen is delivered to a hydrogen
storage/buoyancy system 96. The hydrogen can then be used to power
a fuel cell 98 that produces electricity that is returned to the
PMAD for further distribution. The hydrogen can also be used in a
hydrogen combustion engine 100 to drive a propulsor 102.
Photovoltaic cells 104 can be provided to produce additional
electricity that can be used to drive the generator motor or can be
distributed by the PMAD. Batteries 106 can be provided to store
electricity produced by the generator motor or fuel cell and to
supply electricity to drive the generator motor or for further
distribution by the PMAD. Batteries can also be used to store
electricity produced by the additional photovoltaic cells during
daytime operations. While FIG. 5 shows a separate propulsor 102, in
some embodiments, the motor generator can be used to drive the wind
turbine 82 to propel the LTA platform, thereby eliminating the need
for a separate propulsor.
[0031] Significant wind energy can be harvested at altitudes
accessible by LTA platforms. When the LTA is anchored, power from
the wind turbine is routed to the power management and distribution
system (PMAD). The PMAD regulates power distribution to a variety
of payload applications and energy conversion and storage systems.
When the LTA is in a transit mode, the APG system may require a
series of rest and regeneration periods depending on the range,
altitude and payload weight mission requirements. During the
regeneration period, most of the wind turbine power is routed to an
energy storage system. This could be comprised of a system of
batteries as well as to a water-to-hydrogen conversion system.
Hydrogen can be stored in tanks and/or serve as part of the LTA
buoyancy system. When enough hydrogen has been generated during the
rest period, the LTA platform hoists its anchor and the hydrogen
energy is then converted by the on-board fuel cells to electricity
which subsequently powers the wind turbine generator as an electric
motor, thus providing a propulsive force. Alternatively, the stored
hydrogen can be routed directly to a hydrogen burning internal
combustion engine propulsion system. When "on-station", all payload
and avionics systems will run directly off of the wind turbine,
thus conserving any onboard energy supplies (i.e., batteries,
hydrogen, fossil fuel).
[0032] To quantitatively demonstrate the practicality for the power
generating potential of the APG system, the power output can be
calculated for a given set of LTA flight parameters including
altitude, wind speed, wind turbine blade diameter, and efficiency.
The power generated by a wind turbine is given by Equation (1):
P=1/2A.rho.V.sup.3E (1)
where P is the power in Watts, A is the area defined the blade
rotation, .rho. is the air density at altitude, V is the mean wind
velocity at altitude, and E is the turbine aerodynamic
efficiency.
[0033] As an example, consider an anchored altitude of 20,000 ft
with an air density of approximately 0.525 kg/m.sup.3. From FIG. 4,
it can be seen that from regions ranging from the South China Sea
to the Persian Gulf, and out to the Sea of Japan and the Tsushima
Strait, the mean wind velocities varies from 50 kt to 75 kt. In the
calculation to follow the use of mean wind velocities results in an
underestimate by a factor of approximately 2 of the average power
output due to the atmospheric Weibull (asymmetric) distribution of
wind velocities impacting the velocity cube dependence of the
power. Also assume a turbine blade diameter of 8 meters (an
approximate sizing for a single generator/propulsor system relative
to the LTA platform volume), and a conservative (poor) turbine
efficiency of E of 0.15. The resulting power output from one
turbine generator in this case ranges from 38 KW to 128 KW.
Doubling this due to the Weibull wind speed distribution results in
a final APG system power range at 25,000 ft that ranges from 76 KW
to 472 KW for a single wind turbine system. A dual wind turbine and
propulsion system can be used for the LTA platform, which will
effectively double this power generation capability.
[0034] Depending on regional wind speeds at altitude, the APG
system has a significant power generation capability. The available
power for anchored on-station operations is sufficient to power a
variety of demanding payload packages including communications,
EO/IR sensors and radar. This is especially true if two turbines
are used to double the power. Power output can be optimized via
moderate altitude adjustment depending on regional winds due to the
sensitive cubic power dependence on velocity.
[0035] In addition to on-station payload support, the APG system
can provide power capacity for significant energy harvesting and
storage for LTA propulsion. For the hydrogen generation and storage
concept, assuming sufficient onboard water collection and/or
storage capacity and standard electrolysis techniques with mean
winds of 80 kts at altitude, approximately 156 lb/hr (average rate
per speed distribution) of hydrogen can be generated based on the
use of two wind turbine propulsor systems. This is a significant
energy harvesting capability that also provides buoyancy gas as
needed (i.e., for leakage mitigation).
[0036] In various embodiments, the invention provides an Anchor
Power Generation (APG) system for LTA aerostats and airships for
propulsion power and/or payload power. If the anchor system
described above is replaced by a fixed tether, the invention can be
implemented as an apparatus including a lighter than air platform,
a wind turbine, a tether to constrain movement of the lighter than
air platform with respect to an anchor point allowing wind to drive
the turbine, a generator/motor coupled to the turbine to produce
electricity when the turbine is driven by the wind, an energy
storage system on the lighter than air platform for converting the
electricity into stored energy, and a power management system for
using the stored energy to drive the generator/motor.
[0037] The systems described above provide several advantages
including: continuous wind energy harvesting; continuous power for
on-station payload support; in-transit energy harvesting and
storage for propulsion; long duration unmanned on-station and
transit capability; multiple civil and military applications; and
low cost long endurance airborne platform power system. High wind
speed at altitude results in significant power for small
turbines.
[0038] While the invention has been described in terms of several
embodiments, it will be apparent to those skilled in the art that
various changes can be made to the described embodiments without
departing from the scope of the invention as set forth in the
following claims.
* * * * *