U.S. patent application number 16/776468 was filed with the patent office on 2021-07-01 for high altitude gravity energy storage.
This patent application is currently assigned to STRATOSOLAR, INC.. The applicant listed for this patent is STRATOSOLAR. Invention is credited to ROGER ARNOLD, EDMUND J. KELLY.
Application Number | 20210197949 16/776468 |
Document ID | / |
Family ID | 1000005462756 |
Filed Date | 2021-07-01 |
United States Patent
Application |
20210197949 |
Kind Code |
A1 |
KELLY; EDMUND J. ; et
al. |
July 1, 2021 |
HIGH ALTITUDE GRAVITY ENERGY STORAGE
Abstract
The present invention is realized by apparatus and methods for
harvesting, storing, and generating energy by permanently placing a
large rigid buoyant platform high in the earth's atmosphere, above
clouds, moisture, dust, and wind. Long, strong and light tethers
can connect the buoyant structure to the ground which can hold it
in position against wind forces. Weights suspended from the buoyant
platform with cables are raised and lowered by electric winches to
store and release gravitational potential energy. High voltage
transmission lines electrically connect the platform to the earth's
surface. Electrical energy from the high voltage transmission lines
or from photovoltaic arrays on the platform can be stored as
gravitational potential energy and subsequently released as
electricity from generators driven from the stored gravitational
potential energy and used on the platform or transmitted via the
high voltage transmission lines.
Inventors: |
KELLY; EDMUND J.; (RIO
VISTA, CA) ; ARNOLD; ROGER; (SUNNYVALE, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STRATOSOLAR |
SAN ANSELMO |
CA |
US |
|
|
Assignee: |
STRATOSOLAR, INC.
SAN ANSELMO
CA
|
Family ID: |
1000005462756 |
Appl. No.: |
16/776468 |
Filed: |
January 29, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15611782 |
Jun 1, 2017 |
10569853 |
|
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16776468 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64B 1/50 20130101; Y02E
10/50 20130101; H02S 10/00 20130101; H02S 10/20 20141201; H02S
30/20 20141201; B64B 1/08 20130101 |
International
Class: |
B64B 1/50 20060101
B64B001/50; H02S 10/00 20060101 H02S010/00; H02S 30/20 20060101
H02S030/20; H02S 10/20 20060101 H02S010/20 |
Claims
1. A large rigid buoyant rectangular platform residing in the low
stratosphere having a tether to the ground, said large rigid
buoyant tethered rectangular platform comprising multiple small
rectangular platforms positioned in a rectangular configuration
forming said large rectangular platform, said large rectangular
platform comprising a ratio of buoyancy to a frontal area greater
than a ratio of buoyancy to frontal area of a small rectangular
platform.
2. A large rigid tethered buoyant rectangular platform of claim 1,
wherein said multiple small rectangular platforms are squares.
3. A large rigid tethered buoyant rectangular platform of claim 1,
said large platform comprising a square.
4. A large rigid tethered buoyant platform of claim 1, said
platform tethered to the ground by multiple tethers.
5. A large rigid tethered buoyant platform of claim 4, said
platform tethered by multiple tethers to a cable, said cable
tethered to the ground.
6. A large rigid tethered buoyant platform of claim 1, comprising a
tether comprising a high voltage cable.
7. A large rigid tethered buoyant platform of claim 1, comprising a
tether comprising a fiber optic cable.
8. A large rigid tethered buoyant platform of claim 7, wherein said
tether comprising said fiber optic cable runs from said platform in
the low stratosphere to the ground.
Description
CROSS REFERENCE TO RELATED APPLICATIONS:
[0001] This application is a continuation of USSN 15/611,782 filed
June 1, 2017 which is a continuation of 14104126 filed Dec. 12,
2013.
DESCRIPTION
1. Field
[0002] This invention generally relates to energy storage and more
particularly gravity energy storage.
2. Prior Art
[0003] An area of prior art is gravity energy storage. This uses
mechanical energy to raise a mass through a height, storing energy
as gravitational potential energy. Energy is subsequently retrieved
by lowering the mass. The most common form is pumped storage
hydroelectricity which uses an electric motor to drive a pump and
transport a mass of water from a low altitude reservoir up a hill
to a high altitude reservoir in order to store energy. Electrical
energy is subsequently recovered as water flows back down the hill
driving a turbine that drives a generator.
[0004] On a smaller scale the original "grandfather" clocks used
human mechanical energy to raise weights and store it as
gravitational potential energy. As the weights slowly descended the
recovered mechanical energy powered the mechanical clocks.
[0005] Because of the perceived need for energy storage solutions
to complement intermittent alternative energy sources such as wind
and solar energy there are several new gravity storage ideas being
pursued, though none have yet been deployed. These include using
buoyancy in the ocean as taught in US patent US20100107627, various
means of transporting mass as rock or gravel up a height using
continuous mechanical conveyors of containers and subsequently
bringing the mass back down as taught in CN2307111, and giant
pistons, usually made of rock as taught in US20120085984.
[0006] As with all energy storage solutions the central problem is
cost. A commonly perceived cost goal for economic viability is
$100/kWh capital cost. There is as yet no energy storage solution
that is close to achieving this goal. Most of the various forms of
existing and proposed gravity energy storage also suffer from
geographic constraints that limit their scale and/or location.
[0007] Another area of prior art is buoyant airships and balloons
that float in the atmosphere.
[0008] Balloons float freely without propulsion and are constructed
from gas tight flexible membranes, usually thin plastic like
polyethylene. They contain a lighter than air gas, sometimes
pressurized and sometimes unpressurized. A commonly used
terminology is "zero-pressure" for unpressurized balloons and
"super-pressure" for pressurized balloons. Free floating balloons
of both types are typically exploited for tracking weather or for
scientific purposes. The largest balloons have volumes of about 1
million cubic meters and can float in the stratosphere at altitudes
exceeding 40 km. They are fragile, carry small payloads and are
used for one flight.
[0009] Airships have an aerodynamic shape and a means of propulsion
and are categorized as rigid, semi rigid or blimps.
[0010] Blimps, like the Goodyear blimp, use a gas tight membrane
filled with a pressurized lighter than air gas to provide a
combination of buoyancy, structural rigidity, protection from
weather and an aerodynamic shape. This means of construction
combined with the limited strength of available membrane materials
has limited the scale of blimps to a volume of a few thousand cubic
meters. Blimps either have a means of propulsion or they are
tethered to the ground. A tethered blimp lacking means of
propulsion is usually called an aerostat. Because of their limited
volume, all blimps and aerostats have been confined to the denser
air environment of altitudes below 10 km in the troposphere. This
is because as the air becomes less dense with altitude, a given
volume provides less buoyancy. Blimps have heavy propulsion
systems, fuel and passenger or equipment payloads all of which have
to be supported by buoyancy. Aerostats lack propulsion systems, but
have tethers that are at least as heavy. In both cases it has
proven impractical to provide sufficient buoyancy or a sufficiently
light blimp to enable operation in the low stratosphere.
[0011] Rigid airships are constructed with a rigid framework that
provides structural rigidity and aerodynamic shape and contain zero
pressure gas bags within the rigid framework to provide buoyancy.
This means of construction has enabled the construction of large
craft with volumes exceeding 100,000 cubic meters. Rigid and semi
rigid airships have all been powered aircraft. Airships have only
operated at altitudes well below 10 km. To build airships that
could operate at higher altitude involves building very much larger
craft. The engineering and operational constraints of doing this
combined with the lack of an economic or military demand have meant
that this option has never been explored.
[0012] The earth's atmosphere in the low stratosphere in the region
of 20 km altitude has benign weather properties over most of the
earth's surface below latitude 60 degrees that make it attractive
for long endurance operation. This has been exploited by
reconnaissance aircraft like the U2 and Global Hawk. Weather we are
familiar with is confined to the troposphere which extends up to an
altitude from about 8 km to 12 km with a gradual transition to the
stratosphere called the tropopause. The high winds of the jet
stream occur at the tropopause. There is no moisture or clouds in
the stratosphere and turbulent weather patterns like thunderstorms
and hurricanes do not reach high enough to have effect at an
altitude of 20 km. This is well illustrated by flights by U2 and
Global Hawk over hurricanes for weather research. Winds are steady
and horizontal, mostly less than 20 meters per second, with small
episodic periods in winter of a few weeks every few years where
they can reach 50 meters per second due to excursions of the polar
vortex which circles the poles in the stratosphere in winter.
[0013] The permanently benign weather properties of the atmosphere
in the region of 20 km altitude in the low stratosphere make it a
distinct and separate operational environment which enables
practical long endurance operation as evidenced by the U2 and
global hawk aircraft. The unique low air pressure, low air density
environment requires unique aircraft designed to operate there.
Conventional aircraft are designed to operate at lower altitudes up
to around 12 km, and their aerodynamics and propulsion systems
cannot operate at altitudes around 20 km. There have been attempts
at building long endurance high altitude airships to fly at 20 km
altitude and above, but none have as yet succeeded due to the
difficult engineering challenges of limited buoyancy posed by the
thin atmosphere. In the class of buoyant aircraft, only un-tethered
and un-powered free floating weather and research balloons have
operated in the stratosphere.
[0014] No prior art airship or aerostat has been designed to stay
aloft on a permanent basis. Endurance is measured in weeks for
airships and months for aerostats. They both have limited endurance
and both must avoid bad weather.
[0015] In summary all prior art mechanisms that float in the
atmosphere have been relatively small scale and short endurance and
almost all have operated in the troposphere. There have been no
tethered buoyant rigid structures operated in the atmosphere at any
altitude.
[0016] Another feature of high altitude operation in the low
stratosphere is the large distance to the horizon. From an altitude
of 20 km, the horizon is approximately 550 km distant. This means
that observation or communication technologies that are confined to
"line of sight" operation can cover a wide area from this altitude.
This includes active technologies like radars, laser and radio
communications, and passive optical and radio surveillance. The air
is clear at 20 km which enables uninterrupted and secure laser
light communication between platforms and between platforms and
spacecraft. There have been proposals for long endurance high
altitude aircraft or airships to "station keep" and act as
communications and observation hubs, but the operating constraints
have proven too difficult. They would use solar energy during
daylight hours with batteries storing energy for nighttime.
Providing sufficient energy to station keep in the worst case winds
of around 50 m/s has proven impractical.
[0017] Another feature of the environment in the low stratosphere
is sunlight is more intense. Atmospheric scattering is much reduced
due to the much smaller mass of air in the optical path, especially
at lower sun elevation angles. This results in higher daily solar
energy incident on a surface. This can exceed a factor of three or
more times ground level solar energy at the same location depending
on latitude and tracking. Also solar energy is totally predictable
as it is not interrupted by weather or dust.
[0018] Photovoltaic solar energy systems use solar cells to convert
solar energy directly into electricity. The solar cells are usually
connected together in panels, which in turn are mounted on
mechanical supports and connected together to form arrays.
Associated with the photovoltaic panels are electrical elements
such as conductors, voltage converters, combiners, fuses, relays
surge protectors and inverters used to combine the power from the
collection of photovoltaic panels into a single power output.
[0019] Current photovoltaic electricity systems suffer from several
problems. Their high capital costs make the cost of the energy they
produce uncompetitive without subsidy.
[0020] The power produced by photovoltaic panels varies by more
than a factor of two depending on their geographic location.
Large-scale systems in the best sunny geographic locations also
have high ancillary costs to compensate for the long transmission
distance from the system to the average power user.
[0021] Photovoltaic arrays need to have large entry apertures to
produce meaningful amounts of power. Utility scale systems have
apertures measured in millions of square meters. Current systems
consequently consume large areas of land and significant quantities
of construction materials like glass and steel needed to fabricate
this large aperture array.
[0022] Weather in the form of clouds, dust, wind, rain, hail, frost
and snow make power generation unpredictable and require that
structures be strong and durable which adds significantly to their
cost. Typical design wind loads are around 2000 Pa and mechanical
snow loads are around 5000 Pa.
[0023] Some current large scale systems use large arrays of
individually steered collecting elements. Robust mechanical
support, motors, gears, electrical equipment etc are needed for
each collector element, contributing significantly to overall
cost.
[0024] The cost problem is compounded by the generally low overall
energy conversion efficiency of current systems, which
consequentially requires a larger surface area and more material to
produce a given power output compared to higher conversion
efficiency systems.
[0025] There have been some proposals to attach cells to tethered
aerostats to generate power. These have all proposed current small
scale aerostats tethered at relatively low altitudes in the
troposphere. None of these proposals have been reduced to practice
because of practical constraints that make them unrealistic. At all
altitudes in the troposphere, weather can be severe and the
durability of current aerostat technology is poor. The small scale
of aerostats mean that they can at best only provide a small amount
of power, and many thousands would be needed to provide power at a
utility scale of hundreds of mega Watts. They would need to be
spaced far apart to avoid colliding. There would be a constant need
to winch them down for maintenance and to avoid weather.
SUMMARY
[0026] The present invention is realized by apparatus and methods
for placing a large rigid buoyant platform high in the atmosphere,
above clouds, moisture, dust, and wind. Long, strong and light
tether(s) can connect the buoyant structure to the ground which can
hold it in position against wind forces. The platform can serve
several uses, either individually or in any combination. These uses
include gravity energy storage implemented by using energy to power
winches and cables to raise weights supported by the platform
buoyancy to a high altitude, thus storing energy as gravitational
potential energy and subsequently lowering the weights recovering
the stored energy. Electricity output from a photovoltaic array
attached to the platform can be stored on the platform as
gravitational potential energy and can also be coupled to high
voltage transmission line(s) which connect from the platform to the
earth's surface. The high voltage transmission lines can also be
used to deliver energy from the ground to gravity energy storage on
the platform or from gravity energy storage on the platform to the
ground.
[0027] These and other objects and features of the invention will
be better understood by reference to the detailed description which
follows taken together with the drawings in which like elements are
referred to by like designations throughout the several views.
DRAWINGS
Figures
[0028] FIG. 1 is a perspective view of a platform module designed
in accordance with the present invention.
[0029] FIG. 2A is a perspective view of a buoyant platform module
with an attached tether and winch designed in accordance with the
present invention.
[0030] FIG. 2B is a perspective view of a platform module designed
in accordance with the present invention at high altitude.
[0031] FIG. 3A is a simplified perspective view of the buoyant
platform module shown in FIG. 1 and FIG. 2.
[0032] FIG. 3B is a perspective view of a small platform assembled
from three of the platform modules shown in FIG. 3A with an added
inflated nose cone and tail section.
[0033] FIG. 3C is a perspective view of a small platform assembled
from nine of the platform modules shown in FIG. 3A with an added
inflated aerodynamic edge.
[0034] FIG. 3D is a perspective view of a small platform assembled
from sixteen of the platform modules shown in FIG. 3A with an added
inflated aerodynamic edge.
[0035] FIG. 4 is a perspective view of a large platform assembled
from twenty five of the nine platform module, small platform
elements shown in FIG. 3C with an added inflated aerodynamic
edge.
[0036] FIG. 5A is a perspective view of a platform module assembled
folded flat on the ground.
[0037] FIG. 5B is a perspective view of a platform module unfolded
to about 30 degrees.
[0038] FIG. 5C is a perspective view of a platform module fully
unfolded to vertical with cross bracing and gas bag added.
[0039] FIG. 6 is a perspective view from above of a small platform
made from 16 platform modules, during vertical deployment to form
part of a large platform.
[0040] FIG. 7A is a perspective view from above of a large platform
constructed from 81, small platforms, each small platform being
constructed from 16 platform modules, as a small platform is being
added to the large platform.
[0041] FIG. 7B is a perspective view of a close up of the bottom
front left of FIG. 7A.
[0042] FIG. 7C is a perspective view of a stage in the deployment
of the small platform.
[0043] FIG. 7D is a perspective view of a subsequent stage in the
deployment of the small platform.
[0044] FIG. 8 is a schematic view of the mechanical and electrical
elements of a gravity energy storage system using a buoyant high
altitude platform.
[0045] FIG. 9A is a perspective view of a gravity storage system
using a small buoyant high altitude platform.
[0046] FIG. 9B is a perspective view of a close up view of a
gravity storage weight shown in FIG. 9A.
[0047] FIG. 10 is a perspective view of a large platform with
gravity storage.
[0048] TABLE--US--0001
DRAWINGS--REFERENCE NUMERALS
[0049] 11 strut 12 cable cross brace 13 top surface structure 14
top surface section 15 photovoltaic panel top surface 16 interior
gas bag 21 tether-HV cable 22 winch 23 platform module 31 inflated
tail section 32 inflated nose section 33 inflated edge section 41 9
module small platform 61 deployment boom 62 16 module, small
platform 63 in guides or rails 71 16 module, small platform 72
across guides or rails 73 large platform made of 81, small
platforms 80 PV panel array 81 Electrical power conversion 82
electrical motor-generator 83 motor-gearbox shaft 84 gearbox-brake
85 gearbox-reel shaft 86 gravity cable reel 87 gravity cable 88
gravity storage weight
GLOSSARY
[0050] The specification uses several standard definitions
throughout to avoid ambiguity. These related definitions are tied
to specific aspects of the description.
[0051] Platform module: the standard and smallest unit of platform
construction.
[0052] Small platform: An assembly of platform modules.
[0053] Large platform: An assembly of small platforms.
DETAILED DESCRIPTION
[0054] FIG. 1 shows a perspective view of a buoyant platform module
23 designed in accordance with the present invention. It consists
of a rigid framework formed from struts 11, top surface 13 and
cross bracing cables 12. The interior of the framework holds a gas
bag 16, which contains the buoyancy gas, commonly hydrogen or
helium. The top surface 13 is assembled from smaller structural
sections 14. The top surface of each structural section 14 can
support an array of photovoltaic panels 15 that can either
partially or completely cover the top surface 13. The photovoltaic
panels 15 are connected electrically with wires, DC-DC voltage
converters, combiners and electricity distribution hardware to
provide high voltage (HV) power output from the platform. This HV
output can be AC or DC. In this embodiment when fully assembled,
the overall structure is a rigid cross braced cube. The length of
the cube is in the region of 100 meters. The dimensions are set by
the buoyancy available at the design altitude. The module buoyancy
supports the mass of the module and the wind loads. The buoyant
platform module 23 described can be used as a module in a modular
construction system or method used to build larger buoyant
platforms from assemblies of modules. For simplicity in the
description we subsequently refer to these cubic buoyant platform
modules as platform modules. Embodiments are not restricted to
cubes, and other geometric forms are feasible. A particular variant
has a height that is different than the width. This allows a simple
change in vertical strut length and gas bag height to provide
different buoyancies. This allows embodiments with different
payloads or operational altitudes to be easily constructed.
[0055] Equipment and materials need to operate within the
environmental constraints of the low stratosphere. Air pressure is
about 8000 Pa which affects buoyancy and the breakdown voltage. The
air temperature is around -60 degrees Celsius, and the ozone
concentration is around 2.8 ppm. These affect the choice of
materials, particularly plastics that may become more brittle or
suffer damage. The struts and top surface are lightweight, rigid
truss frameworks, typically formed from aluminum. The gas bag is
typically a thin plastic membrane. A commonly used material is
polyethylene film around 25 microns thickness. The membrane may be
a laminate or co-extrusion of several plastic and metal materials
to provide properties such as low buoyancy gas permeability,
protection from ozone, weld-ability and strength.
[0056] Photovoltaic panels are of lightweight construction,
typically weighing about 2 kg per square meter or less. Various
photovoltaic cell technologies can be employed including commonly
used crystalline and polycrystalline silicon. Given the
predominance of direct solar radiation in the low stratosphere,
concentrating photovoltaic panels that need to track the sun may
benefit. Photovoltaic panel materials need to handle the cold and
the UV, particularly the cell encapsulant material. Silicone is one
good choice. Compared to photovoltaic panels on the ground, the
need for water based weather protection is reduced as there is no
water in the low-stratosphere operating environment. Ground based
photovoltaic panels as well as handling water based weathering,
also have to handle snow loads of around 5000 Pa, hail, regular
washing, and maximum wind loads of around 2000 Pa. In contrast, in
the low-stratosphere there is no hail, snow, or significant dust,
and maximum wind loads are about 125 Pa to 150 Pa, so photovoltaic
panels can be simpler and less robust photovoltaic panels are
highly reliable, and the absence of water based weather degradation
and the low operating temperature will enhance this reliability in
the low-stratosphere.
[0057] Arrays of photovoltaic panels 15 can be formed in the same
ways they are on the ground. The simplest form is a flat array
covering the surface. Single fixed axis, one axis tracking and two
axis tracking are all also possible. Because the structural array
has a cost per unit area, optimizing the area usage is more
important than with ground based photovoltaic arrays, and is
similar to ground based commercial photovoltaic systems on roofs
that want to optimize the electricity generated for the roof area.
As with ground based photovoltaic arrays, detailed cost analysis
based on the cost of photovoltaic panels, the additional costs of
tracking apparatus and the geographic location determine what is
the most cost effective array form to deploy.
[0058] Embodiments of platform modules may not cover the entire
surface with a photovoltaic array 15, or even any photovoltaic
panels. As part of a larger platform they may serve other roles,
such as providing active and passive fire safety, by providing fire
suppressants or acting as a non flammable fire break.
[0059] They may also support other payloads such as winches and
weights to implement gravity energy storage. They may also support
wireless or laser communication systems for communication with the
ground, space, or other stratospheric platforms. They may also
support radar systems for uses such as monitoring weather, air
traffic control and military uses. Other military uses include use
as a weapons platform carrying missiles, direct energy laser
weapons or drone aircraft. They may also support observation
systems such as space telescopes and ground monitoring. They may
also support scientific payloads.
[0060] Many of these uses are enabled or enhanced by the permanence
of the platform, the large payloads that can be carried and the
large and permanent electrical power that is available. Payloads of
hundreds of tonnes are possible and power of many hundreds of mega
watts are available. Night time power can be provided from
electricity storage on the platform from batteries or gravity
storage or from the electricity grid on the ground.
[0061] FIG. 2A shows a different perspective view of the platform
module shown in FIG. 1. The module is the same as in FIG. 1 with
the addition of tether/HV cable 21 and winch 22. The module is
shown during deployment, floating at about 100 meters altitude and
being held by the tether/HV cable 21. The gas bag 16 is shown in a
partially inflated condition. As the module rises in altitude and
atmospheric pressure reduces, the gas bag expands. Sufficient
buoyancy gas is added to the gas bag such that it is nearly fully
inflated at a nominal operational altitude of about 20 km.
Throughout this specification reference to 20 km altitude is meant
to be interpreted as approximately 20 km. The low stratosphere
varies in altitude and the precise operational altitude of
platforms will vary by location, and perhaps by season. The tether
may include the High Voltage (HV) cable that carries power from the
module to the ground or from the ground to the module when
necessary, such as during the night. The tether is strong and
lightweight and typically made from an aramid fiber such as Kevlar.
For efficiency and simplicity the high voltage is typically direct
current (HVDC). The combination of high voltage transmission and
aluminum conductors keeps the HV transmission cable
lightweight.
[0062] FIG. 2B shows the platform module deployed to a high
altitude, on its way to operational altitude. Winch 22 is playing
out the cable 21. The platform 23 is shown in detail in FIG. 1.
[0063] Compared to prior art airships and aerostats, a novel and
necessary feature of the platform module 23 described above is the
scale. The basic 100 meter cube module 23 has an approximate
buoyancy volume of 1,000,000 cubic meters, which far exceeds the
200,000 cubic meters of the Hindenburg, still the largest airship
ever built. The scale is necessary because the air at 20 km
altitude is very thin and a ratio of volume to top surface area of
about 100 is needed to carry the structural weight and HV cable and
platform wind loads resisted by the tether. Only flimsy disposable
balloons for science research in the high stratosphere have
approached 1,000,000 cubic meters in volume.
[0064] The rigid framework provides the support structure for the
photovoltaic panels and carries the wind induced loads. A simple
zero pressure gas bag needs no control mechanisms to adjust for
pressure changes and as an example the buoyancy gas leakage for a
gas bag of these dimensions constructed with 25 micron aluminized
PET membranes is considerably less than 1% a year. For platforms
with a design life of 20 to 30 years, buoyancy gas may not have to
be replenished for the life of the platform. Endurance measured in
decades is more accurately described as a design life, a term
normally applied to structures such as buoyant ocean platforms or
bridges.
[0065] FIGS. 3A, 3B, 3C and 3D show small platforms assembled from
platform modules 23. FIG. 3B shows a small platform constructed
from three mechanically connected platform modules 23 with an
attached inflated nose 32 and tail 31. The tether 21 attaches to
each platform module to distribute the mechanical load and combine
the HV power output from each platform module. FIG. 3C shows a
small platform constructed from nine mechanically connected
platform modules 23 with an attached inflated rounded aerodynamic
edge 33. FIG. 3D shows a sixteen platform module 23 small platform
with an inflated rounded aerodynamic edge 33. Inflated edge 33,
nose 32 and tail 31 are each gas-tight, light-weight fabric
containers filled with pressurized gas, most commonly air. The
gauge pressure might be in the region of 300 Pa to 500 Pa. Commonly
used fabrics are laminates of materials that provide various
properties. An example of such a laminate might have an exterior
layer of polyvinyl fluoride film for protection from weather, a
layer of polyester fabric for strength and an inner layer of
polyurethane film for gas tightness.
[0066] Each of these small platforms are assembled on the ground
and then deployed to 20 km altitude similar to as shown in FIG. 2B.
FIGS. 3A, 3B, 3C and 3D show small platforms deployed as small
stand alone power plants. The sixteen platform module, small
platform shown in FIG. 3D measures about 400 meters on a side. The
difficulty of manufacturing and deploying larger assemblies of
platform modules 23 leads to the method shown in FIG. 4.
[0067] FIG. 4 shows a large platform composed of 25 of the small
platforms, each constructed from 9 platform module assemblies 41
shown in FIG. 3C, mechanically connected together and deployed at
20 km altitude. As can be seen each small platform 41 has its
tether/HV cable 21 attached. Each small platform 41 is individually
assembled on the ground and then deployed to 20 km altitude using
its own tether/HV cable 21 and winch 22. On its ascent, each small
platform 41 is guided by attached booms that connect to adjacent
tethers of previously deployed small platforms 41 and use them as
guides and for horizontal support. This ensures that the deploying
small platforms 41 do not collide with adjacent tethers and also
the adjacent tethers provide mechanical support to help the
deploying small platforms 41 resist wind loads. It also ensures
that small platforms 41 can be simply and accurately guided into
their mating position within the larger platform where they can be
mechanically connected to become part of the larger platform
structure. This process is reversed to bring small platforms 41
down to the ground for maintenance or repair. The large platform
only ever exists at 20 km altitude and only small platforms 41 are
handled on the ground. This terminology distinguishing between
small and large platforms is standardized in this description.
Large platforms are always assembled from small platforms at
altitude in the low stratosphere. Small platforms are always
assembled on the ground from platform modules.
[0068] The large platform shown in FIG. 4 has 25 tethers. This
provides directional stability and redundancy. Compared to a single
small platform 41, the large platform has 25 times the buoyancy,
but only five times the frontal area, and so is deflected far less
in high winds. As large platforms grow, this effect continues and
platforms become more stable and redundant.
[0069] FIGS. 5A, 5B, and 5C illustrate part of a method to
construct a platform module 23. FIG. 5A shows the module structure
assembled folded flat on the ground. This allows construction and
assembly to occur conveniently at ground level. When the assembly
of the structure including all and electrical assembly is complete
and tested at ground level, the structure is unfolded to its final
cubic configuration. Hinged joints 51 at the eight vertices of the
cube connect the structural elements and enable the unfolding from
flat to cubic. The forces used to raise the structure could be
cables and pulleys which are not shown. FIG. 5B shows an
intermediate position as the module is unfolded. FIG. 5C shows the
final position where the joints have been rigidly connected and the
hinges are locked and no longer operate. The cross bracing has been
added and the gas bag is shown added and inflated. This method of
deploying the gas bag within the rigid protective structure greatly
simplifies the deployment of such large fragile elements that could
easily be damaged by simple contact with the ground as a result of
a sudden gust of wind.
[0070] The method shown can be easily extended to unfold multiple
joined platform modules from a folded flat position using hinges at
the vertices of each cube. These small platforms can then be
deployed to high altitude and joined to form a single large multi
element structure using the method described in the description for
FIG. 4 and FIG. 7.
[0071] Another embodiment of the folding method described would
break the vertical struts with additional hinges and fold the
struts under the platform surface.
[0072] FIG. 6 shows a perspective view of a small platform 62
assembled from 16 platform modules 23 as small platform 62 is
deploying to altitude. This illustrates the method of deployment
described in the description for FIG. 4. For clarity only the
nearest neighbor tethers 21 are shown. This shows the guiding and
supporting booms 61 attaching the small platform to the adjacent
tethers 21. As a winch plays out the tether attached to small
platform 62 the small platform rises or falls vertically in a
controlled manner accurately positioned and restrained horizontally
by the booms 61.
[0073] During initial assembly of the large platform, there are few
deployed small platforms and supporting tethers for guidance.
Unique deployment methods are required using additional cables to
help guide and support deploying platforms 41 or 62.
[0074] FIGS. 7A, 7B, 7C and 7D show various perspective views
describing additional stages of small platform 71 deployment
described in the description of FIG. 6. In all views, most of the
tethers 21 are omitted for clarity.
[0075] FIG. 7A shows a perspective view of a large platform 73
floating at altitude. An assembled small platform 71 is shown at
the bottom, about to be deployed to altitude.
[0076] FIG. 7B shows a close up perspective view of small platform
71 and elements that enable its deployment. In-rails or guides 72
are used to help guide and transport small platform 71 through the
space between the tethers 21 to the location of the across-rails or
guides 63.
[0077] FIG. 7C shows a perspective view of a stage of deployment of
small platform 71 when it has completed its transport along
in-rails 72. In this embodiment across-rails 63 are shown above
in-rails 72, but they could be at the same level as in-rails 72,
with either or both at ground level or elevated using the tethers
21 as support.
[0078] FIG. 7D shows a perspective view of small platform 71 after
it has transferred via across rails 63 to the desired tether 21
location for vertical transport. The vertical stage in deployment
is shown in FIG. 6, where booms are deployed and attached to
adjacent tethers 21 and aerodynamic edges are inflated.
[0079] FIG. 8 shows a schematic view of elements attached to a
small platform 62 that implement gravity energy storage. PV panel
array 80 is electrically connected to electrical conversion and
control block 81. Electrical conversion and control block 81 is
electrically connected to HV cable-tether 21 and electrical motor
generator 82. Electrical motor generator 82 is mechanically
connected to gearbox-brake unit 84 with shaft 83. Gearbox-brake
unit 84 is mechanically connected to cable reel 86 with shaft 85.
The combination of electrical motor generator 82, gearbox-brake
unit 84, shaft 83, gearbox-brake unit 84, cable reel 86 and shaft
85 make a winch. Cable reel 86 holds long cable 87 which is
attached to gravity storage weight 88. Cable 87 is made from strong
and light material suitable for storing on reel 86. Example
materials are aramid fibers such as Kevlar or ultra high molecular
weight poly ethylene (UHMPE) such as Dyneema.
[0080] FIGS. 9A and 9B show perspective views of a small platform
that incorporates the gravity energy storage elements shown in FIG.
8. The PV array 80 is on the top surface of small platform 62. The
electrical conversion and control block 81, and winch elements are
attached to small platform 62 inside the framework and are not
visible in these views. In other embodiments these elements could
be deployed on a platform suspended below small platform 62 as a
means to evenly distribute the mechanical load. Gravity storage
weight 88 is shown in FIG. 9A and in more detail in FIG. 9B. This
illustrates the relatively small size of weight 88 relative to
small platform 62. The gravity storage weight 88 can be implemented
as a dense solid or as a granular solid such as sand or a liquid
such as water held in a container. Water and sand have the
advantage in that they are easily jettisoned in an emergency such
as a cable breaking, minimizing the hazard on the ground.
[0081] FIG. 10 shows a perspective view of a large platform 73
assembled at altitude from small platforms 62, each incorporating
gravity energy storage. This illustrates the modular, distributed
and redundant nature of high altitude gravity energy storage, with
many gravity storage weights 88 and their attendant winches and
cables. Systems can grow incrementally to very large storage
capacity, and failure of one element has little impact on overall
operation.
[0082] The magnitude of gravitational potential energy is equal to
the mass multiplied by the force of gravity multiplied by the
height. The gravity energy storage system described is unique in
that it exploits buoyancy in the atmosphere to support a large mass
and the height of approximately 20 km is much larger than the
hundreds of meters height of the prior art. Platforms described can
scale to support a mass of many thousands of tons, which when
multiplied by the 20 km altitude results in much larger potential
energy gravity storage than the prior art.
Operation
[0083] The small platforms floating tethered in the low
stratosphere shown in FIGS. 3B, 3C and 3D, and the large platforms
shown in FIGS. 4, and 7A operate to produce photovoltaic
electricity in the manner of prior art photovoltaic power plants on
the ground. The electrical elements, including photovoltaic panels,
wires, combiner elements, DC-DC converters, DC-AC inverters are the
same but have to be designed to operate in the unique environment
in the low stratosphere, which is colder, has thinner air with low
buoyancy and a low breakdown voltage, has more ozone and has higher
intensity solar radiation with more UV. They also can be optimized
for operation in the low stratosphere, as is the case for
photovoltaic panels which don't have to handle water based weather
and are exposed to much lighter mechanical loads from wind and the
absence of snow, hail and ice.
[0084] When deployed and operating in the low stratosphere, the
small platforms like those shown in FIGS. 3A, 3B, 3C and 3D, and
the large platforms shown in FIGS. 4, and 7A operate passively to
resist wind loads and atmospheric changes. The structures move
under wind loads and buoyancy provides horizontal reaction forces
via the tethers that counteract wind forces. The volume of gas in
gas bags expands and contracts within the range of pressure changes
at the deployed altitude.
[0085] Tether/HV cables 21 are also subject to extreme wind speeds
in the troposphere, but their narrow diameter ensures that the
aerodynamic loads are small in comparison to the worst forces on
the buoyant platform and these forces are also counteracted by
platform buoyancy reaction forces.
[0086] Operation also includes deployment and maintenance and
repair. The physical scale of the buoyant structures shown in FIGS.
3A, 3B, 3C, 3D, 4, and 7A is larger than any prior art buoyant
apparatus. The apparatus and methods that enable construction and
deployment of such large scale objects is by definition new. The
design of platform modules 23 is described in the description of
FIG. 1 and FIG. 2. Each platform module is a fully functional self
contained array of photovoltaic panels, electrical systems,
structural systems, buoyancy systems and optional other use
systems. This greatly facilitates the construction of larger
structures from assemblies of these modular elements which simply
need to be mechanically connected. The method of construction of
platform modules 23 shown in FIGS. 5A, 5B, and 5C that enables all
assembly work to occur at ground level greatly simplifies the
construction process. The addition of appropriate hinges 51 at the
vertices of platform modules 23 enables this form of
construction.
[0087] The area of flat land needed along with logistical and
operational difficulties make it impractical to construct, deploy
and maintain very large platforms from the ground. The method of
small platform deployment shown in FIGS. 6, 7A, 7B, 7C, and 7D
using guide rails 63 and 72 moves the assembly process of large
platforms above the ground and then to the low stratosphere. This
process of deployment, maintenance and recovery of small platforms
that can be reasonably assembled and repaired on the ground and
joined together only in the low stratosphere makes the construction
of large platforms possible. The large platforms only ever exist as
such in the stratosphere. The assembly area on the ground is small
and if guide rails 63 and 72 are elevated, the ground under the
large array is undisturbed during operation and maintenance. Over
time with proven safety and reliability, large platforms could
become very large as the only additional impact on the ground with
large platform growth is winches and HV distribution.
[0088] The impact of HV distribution on the ground can be reduced
by using the tethers as support "towers" from which HV cables can
be suspended high above the ground, perhaps at several hundred
meters altitude. The distance between tethers is similar to the
distance 18 between HV towers in current art HV power distribution,
so cables and equipment could easily be adapted.
[0089] With low leakage gas bags and highly reliable and redundant
photovoltaic panels and electrical systems, it is likely that
platforms will stay aloft for years before maintenance or repair is
required. When necessary, the method and apparatus shown in FIGS.
6, 7A, 7B, 7C, and 7D allows small platforms to be winched down and
repaired or replaced when it is operationally convenient.
[0090] Each small platform in the large platform can have its own
tether. This, as well as allowing for maintenance and repair
provides tether redundancy and ensures that mechanical loads on the
platforms are evenly distributed. This in turn reinforces the
modular structural design as mechanical loads are constant or
reduce as the large platforms grow.
[0091] As shown in FIG. 8, FIG. 9A FIG. 9B and FIG. 10, each small
platform 62 in a large platform can implement gravity energy
storage. In operation, energy is stored by using electrical energy
to raise weight 88 using motor/generator 82 and cable 87. The
electrical energy to drive the motor generator can come from a PV
array 80 on the platform or from the ground via the platform HV
transmission cable-tether 21. In this manner, energy storage is not
necessarily tied to PV electricity generation on the small platform
62. Stored gravity energy is recovered by allowing weight 88 to
fall at a controlled rate, with attached cable 87 mechanically
driving motor generator 82, thereby producing electricity. This
electricity can be consumed by equipment on the small platform 62
and/or converted to high voltage DC by electrically connected power
convertor controller block 8 land transmitted down HV transmission
cable-tether 21.
[0092] The normal usage model envisaged is to store energy
generated during daylight for use during darkness, thus following a
daily charge-discharge cycle. However, storage and generation are
not necessarily tied to a daily cycle, and usage can vary. For
example energy stored early in the day may be recovered later,
still during daylight. If small platform 62 is at 20 km altitude,
and the weight is raised and lowered through the full 20 km
distance, the energy stored in weight 88 is approximately 54 Watt
hours per kilogram. A representative 500 tonne weight would store
approximately 25,000 kilo Watt hours of gravitational potential
energy.
[0093] Though not shown or discussed platform modules have systems
to handle static electricity and lightning. There are
instrumentation systems to monitor the electrical, structural,
buoyancy systems, gas leakage, fire environmental pressure,
temperature, sunlight and other variables. There are control
systems to handle system deployment, fire and electrical safety
systems.
[0094] Also not shown are all uses of the small or large platforms
for communications or observation for civilian and military use or
as a weapons platform for military use. These uses could be added
to power platforms or be provided on platforms not primarily
designed to provide electricity.
Advantages
[0095] The gravity energy storage system enabled by the buoyant
platforms described has many advantages over prior art energy
storage systems. The round trip efficiency ratio of electrical
energy out to electrical energy in can easily exceed 90%. With
regular maintenance, round trip efficiency will stay constant for
the life of the platform which could exceed 50 years or more.
Batteries in contrast diminish in energy storage capacity with use
and have a short life.
[0096] The cost of the gravity energy storage is potentially
considerably less than $100/kWh capital cost which can result in an
added cost of less than $0.03/kWh additional cost for stored
electricity. This is far lower than any current energy storage
technology and sufficiently low to make electricity supplied from
storage competitive with electricity generated from burning fossil
fuels.
[0097] The buoyancy needed to provide gravity storage is similar to
the buoyancy needed to support PV electricity generation, which
makes them very compatible for providing a unified solution that
delivers a continuous, uninterrupted and reliable supply of low
cost electricity from solar energy.
[0098] As described, gravity energy storage can be provided in
modular increments of Mega Watt size as opposed to some
technologies like pumped storage that must be developed on a much
larger scale. These modular increments can be aggregated to provide
very large scale energy storage of many Giga Watts, far beyond any
currently deployed solution.
[0099] There is no geographic constraint on gravity energy storage
as described, compared to pumped hydro electric storage, compressed
air storage and other large scale storage technologies. Gravity
energy storage is co-located with PV energy generation and can
scale and grow with PV generation in a balanced manner.
[0100] In addition to PV power generation and gravity energy
storage, because of the benign weather free environment with
abundant reliable solar power and clear visibility to space and a
horizon exceeding 550 km radius, many synergistic new uses, either
alone or in combination, are enabled and supported by large rigid
buoyant tethered platforms floating in the low stratosphere. The
scale of the power and payload provided and the permanent nature of
the platforms enable not just new communication uses, but very
large scale, very reliable, very high bandwidth very secure
communications networks. For example the whole land area of the
mainland united states could be covered with approximately fourteen
platforms. Each platform could communicate with neighboring
platforms via laser or radio, with spacecraft with laser or radio,
and with the ground via secure fiber optic cables. If platforms are
deployed near all major urban areas to provide photovoltaic
electricity, there will be several hundred platforms in the US and
communications networks supported by them would be highly
redundant. The coverage area from each platform for radio
communications would match that of thousands of cell phone towers,
with fewer dead zones. The line of sight visibility could enable
the use of higher frequency radio bandwidth.
[0101] Because of exposure to more solar energy and the cold
operating environment that increases the efficiency of many solar
cell technologies, the photovoltaic electric power output is many
times that of a same sized prior art ground system. This means the
cost of the electricity produced is lower.
[0102] Power output is high at high latitudes, and is not affected
by clouds, dust, or bad weather. This is of particular benefit to
normally cloudy northern and mid latitude locations where most
large urban areas are located.
[0103] The combination of geographic flexibility and power
generation without the need for any fuel provides a secure and
clean energy system.
[0104] Power in the form of electricity can be provided at any
point on the earth's surface, where the definition of surface
includes the entire surface, including all land and oceans.
Offshore platforms, or platforms that straddle land and ocean could
be a particularly convenient in some locations. electricity could
be provided near mines, allowing convenient processing without
transportation of bulk ores.
[0105] The small amount of land area needed means that systems can
be located very near existing power plants, or existing
transmission and distribution networks, which reduces or eliminates
the need for new electricity transmission infrastructure.
[0106] Systems can scale to very large size. This means that fewer
platforms are needed which reduces the impact on aircraft and
airspace.
[0107] Because the land and environmental impact is small, the
platforms use commonly available materials that have no resource or
manufacturing constraint and the generated electric power is low
cost, the systems can scale to provide all needed energy.
[0108] The manufacture of synthetic fuels for transportation and
long term energy storage using the cheap electricity from the
platforms provides a complete energy solution for all current
uses.
[0109] Energy systems that do not put carbon dioxide into the
atmosphere are highly desirable. Currently all alternative energy
systems suffer from major problems: [0113] 1) They are very costly
to build [0114] 2) They are unreliable providers of electricity due
to intermittent weather effects, and so need backup generation
using alternate energy sources such as natural gas.
[0110] 3) They need large additional energy storage and
transmission infrastructure investments. [0116] 4) The most
abundant energy is located far from users, again requiring large
transmission infrastructure investments. [0117] 5) They require
large areas of land which increases their environmental impact and
limits their use to areas where both energy and land are
available.
[0111] This new system has the benefit of not producing carbon
dioxide and has none of these problems. The bottom line is clean
secure energy can be provided at much lower cost and minimal
environmental impact.
[0112] The benefits of suspending an array in the stratosphere are
the reliability of the energy source, the higher incident energy
density, and the benign stable calm low wind weather free
environment that enables permanent tethering. These benefits come
at the price of lower atmospheric density, which means less buoyant
lift and a consequent need for a large lightweight structure.
[0113] The modular manufacturing and deployment methods described
greatly reduce cost, improve quality, and speed construction. It is
envisaged that when production is mature, complete utility size
electricity generating facilities could be operational in less than
a year from breaking ground. This compares with current
technologies which require three to five or more years to
construct.
[0114] Although the present invention has been described in terms
of a first embodiment, it will be appreciated that various
modifications and alterations might be made by those skilled in the
art without departing from the spirit and scope of the
invention.
[0115] The invention should therefore be measured in terms of the
claims which follow.
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