WO2014028201A2

WO2014028201A2 - Airborne concentrated solar photovoltaic system

Info

Publication number: WO2014028201A2
Application number: PCT/US2013/052438
Authority: WO
Inventors: Leonid Goldstein
Original assignee: Leonid Goldstein
Priority date: 2012-08-16
Filing date: 2013-07-28
Publication date: 2014-02-20
Also published as: WO2014028201A3

Abstract

A photovoltaic solar system for energy production, comprising an inflatable parabolic reflector- concentrator inside of possibly lighter than air balloon and a solar panel outside of the balloon. The system tracks sun while overcoming wind impact. The system can be used in fixed or vehicular installations both in land and marine environments. Also disclosed a solar farm and an efficient air cooling system for solar cells.

Description

AIRBORNE CONCENTRATED SOLAR PHOTOVOLTAIC SYSTEM

DESCRIPTION

BACKGROUND OF THE INVENTION

This invention is generally directed to solar photovoltaic energy conversion systems and methods.

Currently, solar energy is not cost competitive with fossil fuels or even with wind energy, even in the south of the US. The solar cells are still expensive, and the concentrated solar systems are expensive as well because of the combination of relatively high costs of metal parabolic reflectors and sun tracking means. A number of patents discuss solar photovoltaic cells in combination with inflatable means, including US Patent No. 4126123 by Frederick Hall, US Patent No. 8127760 and 7997264 by Mithra Sankrithi, US Patent No. No. 8074638 by Eric Cummings. These patents do not teach how such inflatable means would cope with winds, cloud overcast, tracking complexities, overheating and other related issues. Also, they are still too costly.

There is need in a cost effective photovoltaic solar energy system that solves the problems above. This invention is directed to teaching such a system.

SUMMARY OF THE INVENTION

This invention is generally directed to solar photovoltaic energy conversion systems and methods. Further, this description discloses a device and a method for converting solar energy into electrical energy and more. Many embodiments of the invention comprise methods and devices that concentrate sun light on a solar panel, using light and inexpensive inflatable reflectors-concentrators, while protecting them from the wind forces.

One embodiment of the invention is a device for converting solar energy into electric energy, comprising: at least one reflector-concentrator, formed by an inflated body, having a transparent skin in one part of its envelope and a reflecting surface on the internal side in the opposite part of its envelope; a solar panel, placed near the focus of said reflector- concentrator; a solar tracking system, continuously aligning axis of said reflector-concentrator with direction to the sun.

The inflated body can be filled with lighter than air gas, or its internal air can be heated by solar energy. The inflated body can be streamlined, or to be a part of a (possibly streamlined) balloon, or to be enclosed in a streamlined balloon. A number of such devices can be placed close one to another and form a part of a solar farm.

Another embodiment of the invention is a device for converting solar energy into electric energy, comprising: a solar light concentrator; a non-planar solar panel with a plurality of solar cells with gaps; a fan placed to the rear of the solar panel, blowing both the solar panel's rear side and the solar panel's front side.

The description uses prior patent applications by the inventor:

International Patent Application PCT/US13/40666

Provisional US Patent Application 61/683,783 (PPA-31)

Provisional US Patent Application 61/700,317 (PPA-32)

Provisional US Patent Application 61/706,123 (PPA-33)

Provisional US Patent Application 61/707,983 (PPA-34)

that are incorporated herein by reference, except that in case of any conflicting term definitions or meanings the meaning or the definition of the term from this description prevails.

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

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:

Fig. 1 is a perspective view of one embodiment of the invention, comprising a reflector- concentrator inside of a balloon. Fig. 2 is a sectional view of some details of this embodiment and a scheme of the light reflection in it.

Fig. 3 is a sectional view of some details of this embodiment, including solar heating surfaces. Fig. 4 is a view of sun tracking motion by this embodiment.

Fig. 5A is a sectional side view of a solar farm according to another embodiment of the invention.

Fig. 5B is a top view of the solar farm according to this embodiment of the invention.

Fig. 6 is a sectional side view of another embodiment of the invention, providing a balloon with an external tail.

Fig. 7A is a sectional side view of a rail and a roller in that embodiment of the invention

Fig. 7B is a perpendicular sectional view of the rail and the roller in that embodiment of the invention.

Fig. 8 is a sectional side view of another embodiment of the invention, comprising a

streamlined balloon.

Fig. 9A is a schematic view of the optical subsystem in the that embodiment of the invention Fig. 9B is a schematic view of forces in that embodiment of the invention.

Fig. 10 is a schematic view of another embodiment of the invention, in which the balloon is raised to an altitude.

Fig. 11 is a schematic view of another embodiment of the invention, comprising a vehicle. Fig. 12 is a view of another embodiment of the invention with enhancements.

Fig. 13 is a view of another embodiment of the invention with rotating streamlined balloon. Fig. 14 is a view of another embodiment of the invention with multiple reflectors in a streamlined balloon.

Fig. 15 is a sectional view of another embodiment of the invention with an internal solar panel. Fig. 16 is a view of another embodiment of the invention with different placement of tethers. Fig. 17 is a view of another embodiment of the invention with low placement of a solar panel. Fig. 18 is a side sectional view of another embodiment of the invention.

Fig. 19 is a view of a surface of the solar panel in this embodiment of the invention. GLOSSARY

The term 'solar panel', as used here, includes 'solar array' and 'solar module'.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 shows general view of one embodiment of the invention. It comprises an inflated balloon 101, having transparent skin 102 in its top half and transparent or non-transparent skin 103 in its bottom half. The internal space of balloon 101 is divided into two gas tight compartments by a divider-reflector 104, made of flexible fabric and having light reflective top surface. The gas pressure in the upper compartment is slightly higher than the gas pressure in the bottom compartment, which is slightly higher than atmospheric pressure. Divider 104 is made in such form, that in presence of the pressure difference between the upper and the lower

compartments, divider 104 has a paraboloid form, with its concave side toward the upper compartment. Balloon 101 is filled with lighter than air gas, such as hot air, methane, hydrogen, helium, or some mixture of gases. Consequently, balloon 101 raises in the air, and is held by three tethers 106, connected to it at some distance one from another. The connection points are reinforced. The other ends of tethers 106 are fed into a device 107, installed on the ground. Device 107 contains actuators that can pull in and let out each tether 106

independently, changing their effective length. This can be done using small electric motors. A photovoltaic solar panel 105 is attached to the top of balloon 101 in such a way, that there is free air flow between it and the surface of balloon 101. It can be done, for example, by attaching multiple plastic raisers, in the form of small cylinders, to the bottom of solar panel 105 and gluing them to the top of balloon 101. In the top part of balloon 101, just below solar panel 105, skin 102 is replaced by a flat rigid transparent disk 109, made of a transparent and heat-resistant material, such as acrylic or glass. Solar panel 105 can be attached to disk 109. Electric wires 108 connect solar panel 105 to the electricity consumer or an inverter on the ground. Electric wires 108 are laid on the surface of balloon 101 and descend to the ground. A control system 110 is provided. Balloon 101 has an imaginary main axis, passing through the center and the top of balloon 101, and the center of reflector 104. The system tracks apparent sun movement in two axis. In operation, control system 110 changes lengths of tethers 106 in such a way, as to point the main axis in the direction of the sun. In the presence of turbulent wind, these length changes are also used to keep the main axis pointed to the sun, despite disturbance, created by the wind.

Fig. 2 helps to explain the work of the system, described above. Paraboloid reflector 104 has a focal point or focus F, which can be inside or outside of balloon 101. The sun beams, falling on reflector 104 parallel to the main axis, are reflected into the focus F. Solar panel 105 is placed slightly behind the focus F or slightly in front of it, so that the concentrated solar beams cover its surface uniformly. When concentrated solar light hits solar cells on it, solar panel 105 generates electric energy.

I n one of possible embodiments, buoyancy is created by letting the sun to heat the air inside of balloon 101. M ultiple mechanisms can be used for heating. In one of them, some part of the reflector 104 is painted black or replaced with a black fabric. An example is the outer ring 301 in Fig. 3. It is heating up both upper and lower chambers of balloon 101. In another mechanism, there is a body 302, made of two cardboard rectangles, painted black and inserted one into another at right angle. Body 302 is hanging from the top of the balloon 101 on three lines 303. Body 302 has normally vertical position. When the sun is in zenith, the surfaces of body 302 are parallel to the sun beams, and very little solar energy is captured by them. The lower is the sun on the horizon, the larger becomes the projection of body 302 to a plane, perpendicular to the sun bea ms. Thus, this simple device allows to capture more sun energy inside of the balloon 101 when the sun is low in the morning and in the afternoon, and reflect more energy to sola r panel 105 in noon, when the sun is high. One more mechanism is shown in Fig. 12. I n this mechanism, a light filter 1206 is provided in the path of the reflected light that blocks some of the light in the long wavelength range of the specter that cannot be converted to electric energy by solar cells, used in solar panel 105, or can be harmful for them. Light filter 1206 is heating air inside of balloon 101 and in the same time decreases parasitic heat, generated in solar panel 105. Fans, working from the current, generated by solar panel 105, can be provided inside of upper and/or lower chambers of balloon 101 to ensure convection of heated air inside of these chambers. In this embodiment, balloon 101 can cool at night, sink to the ground, but it will raise again in the morning, when sun heats up the air in it. The upper and the lower chambers of balloon 101 can have valves to let out extra air, when air pressure exceeds pre-defined value.

Fig. 4 helps to explain sun tracking using variable length tethers in two dimensional case. The pictured system has two cables for single axis tracking. The position of balloon 101 in the beginning of the motion is in the solid lines. The left cable 106 is shorter than the right cable 106. The position in the end of the motion is shown in the dashed lines. To change the orientation of balloon 101, device 106 lets out the left tether 106, while pulling in the right cable 106.

Control system 110 directs and controls all aspects of the system operation, including sun tracking. It can comprise multiple sub-systems, attached to either mount 107 or balloon 101. Control system 110 comprises one or more processors or microcontrollers, sensors,

communication means and actuators. The sensors may include anemometers, barometers, hygrometers, thermometers, cable tension meters, cameras, light sensors, pressure sensors, altitude meters, gyroscopes and other. Control system 110 can be connected to the Internet to receive general weather information, especially warnings of extreme weather events.

Fig. 12 shows this embodiment with additional enhancements. In one of them, the circular line, at which reflector 104 is connected to the skin of balloon 101 is additionally reinforced with a steel ring or a circular tube 1201. Two or more cables 1202 connect opposite sides of ring 1201 and prevent it from deforming. This is done to minimize deformation of the form of reflector 104 in strong winds. Another enhancement is active cooling of solar panel 1205 with a top fan 1203 and/or a side fan 1204. Fans 1203 and 1204 work from DC current, produced by solar panel itself.

The sun light concentration ratios can be anywhere between 4:1 and 2,000:1. Device 107 can be installed on a ground, on a bottom of a lake, a sea or an ocean, on a buoy or on a vessel or on a moving vehicle. Balloon 101 can be deflated and folded to a very small package for transportation or storage.

Example parameters for this embodiment:

Diameter of balloon 101: 20 m

Volume of balloon 101: 4,000 m³

Reflecting area (perpendicular sunbeams): 300 m²

Concentration ratio: 25:1

Solar panel area: 12 m²

Solar module efficiency: 15%

Peak power output: 40 kW

Among advantages of this embodiment: The system allows to use much smaller amount of expensive solar cells, compared with direct photovoltaics. The reflector-concentrator is completely protected against environment impacts, such as sand, dust, dirt, flying debris wind, water etc. The reflector-concentrator and the tracking actuators are less expensive, than the corresponding parts in conventional concentrated solar systems. The solar panel and the transparent skin of the balloon are less susceptible to sand, dust, flying debris and vandalism, because they placed are at some height from the ground for most of the time. Also, the transparent skin of the balloon is less likely to accumulate dirt because of its convex form and motion in the wind.

Another embodiment of the invention is a solar farm, having multiple balloon based solar panels, connected to a common inverter and/or transformer and tied to the electric grid.

Strong winds interfere with the balloons. Therefore, it is better to place such a farm in a place with predominantly light winds. Also, it is preferable to place the balloons only slightly above the ground and sufficiently close one to another, so that each balloon is somewhat shielded from the wind by the balloons upwind from it, but sufficiently far one from another in order to avoid collision of the balloons in the turbulent air and avoid or minimize shadowing of one balloon by another, when the sun is low on the horizon. There is an advantage in tight packing balloons in the farm: the same number of balloons occupies less land, and the wind pressure on each balloon is smaller because of partial aerodynamic shading by neighboring balloons. On the other hand, in a too tight packing, balloon reflectors would partially hide sun from each other, when the sun is low on the horizon. An optimal packing of the balloons should find an optimum between these considerations. Let's call D the diameter of the balloon. In one embodiment, the balloons are placed in the vertices of a hexagonal structure with the distance between centers of the balloons, equal 3 x D, as shown in Fig. 5A and 5B. Lower point of the balloon should be at the distance 0.1-0.5 x D from the ground. To protect outside balloons from the wind, the balloon farm can be encircled by natural or artificial protection, or a combination of them. Natural protection can be hills, tall trees (comparable in height to the diameter of the balloon) etc. Artificial protection can be done in the form of an inflatable wall 501. Inflatable wall 501 comprises inflatable panels 502, filled with lighter than air gas or hot air, attached to the ground and spread by cables 503.

In low latitudes, the balloons can be placed in a square grid with rows along the line North-East — South-West and columns along the line South-East - North-West. The distance between the centers of the balloons in columns and rows can be 1.5-2.0 x D.

Wind has high impact on a spherical balloon because a sphere has high drag coefficient. This drag is caused mostly by the area of separated or turbulent flow and low pressure behind the sphere. Another embodiment solves this problem by providing a spherical balloon with a self- aligning tail that eliminates this area of low pressure, while allowing the sphere to freely rotate around two axes and to track the sun.

Fig. 6 is a sectional view, showing details of this embodiment. It comprises balloon 101 with reflector 104 and solar panel 105. Behind it (i.e., downwind) there is a tail 601, consisting of a thin envelope inflated with lighter than air gas, such as hot air, methane, hydrogen or helium. Tail 601 has such a form, that when it adjoins balloon 101, they together have a form with significantly lower drag coefficient, than sphere. Tail 601 is equipped with large horizontal and vertical stabilizers 602 that help it to maintain its position relative to the wind. To allow solar tracking independent of the direction of the wind, tail 601 and balloon 101 are attached through one or two semi-circular rails 603 (only one rail is shown for clarity). Two rails 603 are joined in the middle by a bar (not shown). Gap between tail 601 and the skin of balloon 101 is small compared with the diameter of balloon 101. The line, passing through the back end of tail 601, the center of its front end and the center of balloon 101 is parallel to the wind. We will call it the long axis of the device in this description. In the plane, perpendicular to the long axis, tail 601 can have round or elliptical section, with horizontal axis slightly longer than the vertical one. Most of tail 601 is made of a transparent material. Rails 603 are attached to tail 601 on a bearing 604 with a small electric motor 605, capable of rotating rails 603 around the long axis. Balloon 101 can move along rails 603 on rollers 606, described below. Rollers 606 are affixed to the skin of balloon 101, which is properly reinforced near the attachment points. The plane of rails 603 is perpendicular to the plane in which reflector 104 is attached to the skin of balloon 101. Balloon 101 can be equipped with a counterweight on the end, opposite to solar panel 105. Tail 601 is attached to a mount 607 with a front tether 608 and back tether 609. Tethers 608 and 609 can have constant length, or back tether 609 can have variable length by using an actuator in mount 607. A control system 610 is provided. Acting on stabilizers 602, wind always turns the system balloon 101 - tail 601 to have its long axis along the wind, and balloon 101 heading into the wind. Control system moves bearing 604 and rollers 606 in such way that the main axis of balloon 101 always stays pointed to the sun, despite rotation of tail 601.

Fig. 7A is a side view of roller 606. It shows a body 701, attached to balloon 101 and having four rubber wheels 702 in contact with rail 603. A small electric motor 703 drives wheels 702 on command from control system 610. Fig. 7B shows sectional view of the same device from the side of balloon 101 with body 701 removed. This embodiment has an additional advantage of lower forces, acting on balloon 101 in the wind.

In more embodiments, tail 601 can be cambered, creating vertical lift upward. Also, lift can be created by pulling tail 601 down, using tether 609. Instead of mechanism with rail 601, tail 601 can slide over surface of balloon 101.

Other embodiments have simpler construction and provide even lower drag coefficient. Fig. 8 shows another embodiment in a sectional view. It comprises a streamlined balloon 801, having most of its skin made of a transparent material. Balloon 801 is filled with lighter than air gas, such as hydrogen, methane, helium or hot air. Balloon 801 is slightly asymmetrical in the vertical section. It has a slightly cambered profile and provides upward lift in the presence of the wind. Balloon 801 is equipped with an empennage 802, providing horizontal and vertical stabilizers. Because of the vertical stabilizer in empennage 802, when the direction of the wind changes, balloon 801 moves and gets aligned with the wind, with empennage 802 on the downwind. A reflector assembly 803 is attached to some structural member of balloon 801. Reflector assembly 803 has a tracking mechanism 804 with electrical engines and can rotate inside balloon 801 in two axis in the range plus/minus 180^° in the horizontal plane and plus/minus 80^° in the vertical plane. A solar panel 805 is installed on the top of balloon 801 in such a way that air flow between it and the skin of balloon 801 is permitted. Additionally, the balloon skin under solar panel is replaced with a material, having better transparency and heat resistance, such as acryl or glass. A tether 806 attaches balloon 801 to a mount 807. Mount 807 can be installed on a ground, on a bottom of a lake, a sea or an ocean, on a buoy or on a vessel or a vehicle. A control system 810 is provided. Control system 810 controls reflector assembly 803 in such a way as to ensure that it tracks sun, despite motion of balloon 801 in the changing wind. Balloon 801 has a round form in the section, perpendicular to its long axis. The dash dotted circle in Fig. 8 shows movement of the extreme points of reflector assembly 803, which comprise perimeter of the reflector. Reflector assembly 803 reflects sun light from a circle with a diameter, that is only slightly less than the diameter of the widest section of balloon 801 in the plane, perpendicular to the balloon's long axis, and the reflector's axis is always parallel to the sun beams.

Fig. 9A shows some details of reflector assembly 803 and explains how it works optically. The main reflecting surface is created by an internal surface of the lower skin 903 of an internal inflated balloon 901. Lower skin 903 has a form of paraboloid and light reflecting internal surface. Upper skin 902 is transparent. It should be noted, that the envelope of balloon 801 protects internal balloon 901, so its skins can be made from very thin and light materials. The gas pressure inside internal balloon 901 is higher than the gas pressure inside balloon 801 which is higher than outside air pressure. A rod 904 passes through internal balloon 901, and a small paraboloid mirror 905 is attached to its another end in such way, that main paraboloid reflector 901 and small paraboloid mirror 905 share the same axis and the same focal point F. A flat mirror 906 with its actuators is attached to rod 904 at the center C, around which reflector assembly 803 rotates. Solar beams fall on reflector 901 parallel to its axis, reflect and hit mirror 905, reflect again parallel to the mentioned axis and hit mirror 906. Control system 810 changes the angle of mirror 906 in two axis in such a way as to reflect the parallel beams, falling on it, onto solar panel 805. Thus, sun light is concentrated on solar panel 805 at any position of the sun and direction of the wind. It should be noted, that reflector assembly 803 is very light, and tracking mechanism 804 can be very light and inexpensive. Electric wires are present but not shown in Fig. 8. Tether 806 can split into multiple thin lines, attached to balloon 801 in many points for better force spreading.

Fig. 9B is a diagram of forces, acting on balloon 801. Buoyancy FB and weight Fw (of balloon 801 and everything it carries) are constant and the buoyancy exceeds the weight. But the aerodynamic forces are strongly dependent on the wind and can grow significantly larger than either buoyancy or weight. If the balloon has only drag, total of this drag and tether's tension FT would result in a large downward force, which would eventually overcome excess buoyancy and bring balloon 801 down. This is why this embodiment utilizes a balloon form that provides aerodynamic lift. Relation of lift FT to drag FD remains nearly constant in a wide range of wind speed. In the figure, value of FT is two times value of FD, therefore resultant aerodynamic force FA is directed at angle 60°, and tether 806 will have angle of at least 60° to the horizontal plane in any wind.

Control system 810 directs and controls all aspects of the system operation, including sun tracking. It can comprise multiple sub-systems, attached to either mount 807, balloon 801, or reflector assembly 803. Control system 810 comprises one or more processors or

microcontrollers, sensors, communication means and actuators. The sensors may include anemometers, barometers, hygrometers, thermometers, cable tension meters, cameras, light sensors, pressure sensors, altitude meters, gyroscopes and other. Control system 810 can be connected to the I nternet to receive general weather information, especially warnings of extreme weather events. Reflector assembly 803 can be equipped with a large gyroscope to maintain axis direction to the sun despite motion of ba lloon 801. I n addition to the advantages of the embodiments above, this embodiment is also resistant to the wind.

I n more embodiments, mirror 905 can be replaced with a Fresnel lenses between reflector 901 and flat mirror 906. In other embodiments, balloon 801 can be symmetrical (non-cambered). Horizontal and/or vertical stabilizers 802 can be movable, allowing steering balloon in one or two dimensions.

Balloons 801 and 101 can have buoyancy, significantly exceeding what is necessary to keep reflectors, solar panels and tracking mechanisms in the air. Fig. 10 shows another embodiment, in which one of previously described devices is raised to a substantial altitude above the ground. It comprises balloon 801, attached by tether to mount 807. An inverter-transformer

1001 is attached from below to mount 807. It is tethered to the ground by three long tethers

1002 that are anchored in the vertices of an equilateral triangle. Such arrangement allows to keep mount 807 in the same place in any direction of wind and minimize power cable length. Electric wires from solar panel 805 enter inverter-transformer 1001. Aluminum cable 1003 exits inverter-transformer 1001, descends vertically to the ground and is connected to another piece of power conversion equipment or to an energy consumer. Inverter-transformer 1001 converts DC from solar panel 805 into AC, increases its voltage and transfers it to the ground over cable 1003. Inverter-transformer 1001 and cable 1003 are kept in the air by buoyancy and aerodynamic lift of balloon 801.

Example parameters for this embodiment:

Diameter of balloon 801 (in the plane, perpendicular to the long axis): 30 m

Length of balloon 801 (in the plane, perpendicular to the long axis): 90 m

Volume of balloon 801: 25,000 m³

Reflecting area (perpendicular sunbeams): 500 m²

Concentration ratio: 100:1

Solar panel area: 5 m²

Solar module efficiency: 20%

Peak power output: 100 kW

Additional lift capacity at 5,000 m, (hydrogen filling): 8,000 kg

Additional lift capacity can be used for inverter-transformer and/or power cable. At altitudes from 50 m and above, the solar panel and the balloon are protected from sand, dust, flying debris, vandalism and other harmful impacts that exist on the ground. This allows to make them lighter and decreases need for periodic maintenance. If balloon 801 is placed at higher altitudes (such as 3,000 to 10,000 meters), additional advantages are achieved.

1) The solar cells can be cooled more efficiently because of the lower air temperature at the altitude.

2) There is more energy in the solar radiation at the altitude, and larger part of it comes in the form of direct beams that can be efficiently concentrated (rather than diffused radiation, that cannot be concentrated). The concentrator and the solar panel can be also above most of the weather and clouds. Thus, this system can be deployed in the areas, where ground based systems are not efficient because of clouds or fog.

3) The system can track sun at lower angles, than the ground based tracking systems, and generate more energy with lower losses at such angles. This allows generating substantial power even in the high latitudes and throughout the whole day. This covers the late afternoon peak in the energy consumption, existing in most countries.

4) When the balloon is above most of the weather, energy production is regular and predictable. This allows to overcome the problem of the intermittency, which plagues scalable renewable energy sources.

5) A large number of such devices, placed in proximity one to another, can be used for local climate improvement, such as creating an oasis in a desert. It is achieved because of decrease of direct solar irradiation, reaching ground. The density of such devices should decrease from the center to the periphery, in order to decrease effect of the temperature gradient near the ground, and resultant winds.

I n some embodiments, inverter-transformer 1001 is not used, and the direct current is transformed through cable 1003 at the voltage, received from solar panel 805. In more embodiments, multiple balloons 801 are supporting a single cable 1003. In more

embodiments, balloon 101 with or without tail 601 can be used in place of balloon 801. In more embodiments, a single tether 1002 is used, com bined with cable 1003. This is especially efficient, when inverter-transformer 1001 increases voltage to a value, at which increase of length of cable 1003 does not cause significant losses.

Embodiments, shows in Fig. 1, 6, and 8, can be used in vehicles and vessels to replace fossil fuels with free solar energy. Fig. 11 shows an embodiment, in which balloon 801 is attached to a tractor 1101. Electricity, generated by solar panel 805, is transferred by wires 1102 and drives electric motor 1103, which powers tractor 1101. Electric motor 1103 can be combined with a usual diesel motor in a hybrid arrangement. When tractor 1101 is not moving, solar panel 805 on balloon 801 can be used to charge an internal or an external electric battery, to provide electric energy to consumers or to feed the grid (through an inverter). Balloon 801 can be flown at high enough altitude to avoid collisions with other vehicles and most building in rural areas. Almost any agricultural machine can be modified into solar powered one by adding the device from Fig. 8, electric engine 1103 and wires 1102. It should be noted, that device from Fig. 8 can operate completely automatically. Such sun powered equipment is especially effective in the areas, where direct sun light is available on most of days and there is little or no infrastructure for delivery of fuel and/or electricity, such as in many developing countries. Additional advantage is that balloon 801 can create substantial lift, allowing the vehicle to carry larger loads.

Another embodiment of the invention is a solar powered blimp. It is obtained from

embodiment on Fig. 8 by deleting tether 806 and mount 807, adding an electric motor and a propeller, driven by that motor, and placing a control system on the blimp itself.

Fig. 13 shows another embodiment, in which a balloon 1301 can rotate around its long axis. Only a part 1302 of the balloon skin is transparent. The inflatable reflector rotates around one axis only, having a rotational mechanism 1303. A solar panel 1305 is installed on an arm 1304, that can change position of solar panel 1305 in two dimension in the plane of view, and rotate it in order to always put it near the focus of concentrated sun light, reflected from the inflatable reflector. Balloon 1301 is tethered by a front tether 1306F and back tether 1306B attached in such way as not to inhibit rotation of balloon 1301. In other respects, this embodiment is similar to the embodiment in Fig. 8. Fig. 14 shows another embodiment, similar to one in Fig. 8, but having elongated body and multiple reflector assemblies. The centers of the neighbor reflector assemblies are at the distance, equal two times diameter of the main reflector in the assembly. If two assemblies have different diameters, then the distance equals two times the largest diameter.

In more embodiments of the invention, solar panel 105 or 805 can be placed inside of balloons 101 and 801, correspondingly, and parasitic heat from them is used to heat the air in the balloons for buoyancy. In these embodiments, solar cells with low sensitivity for heat are preferred. One such embodiment can be similar to the embodiment in Fig. 8 with a small reflector 905 replaced by a high temperature solar panel 1505 and flat mirror 906 eliminated, as shown in Fig. 15. Typical temperature inside such balloon can be 90^°C and fans can be used to cool solar panel 1505, spreading hot air evenly inside the balloon.

Another embodiment, shown in Fig. 16, utilizes balloons 101, similar to those in Fig. 1. Instead of being attached to and moved by multiple tethers, connected to one device 107, each balloon 101 in this embodiment is attached to and moved by three or more tethers, connected to three or more devices 1607, placed at a distance, exceeding diameter of balloon 1607 from each other. Device 1607 changes available length of the tether, similarly to device 107. When multiple balloons 101 are utilized, a single device 1607 can be attached to three or four tethers, connecting three or four balloons 101, and extend or pull them in independently. In a variation of this embodiment, balloon 101 is inflated with air at ambient temperature, and rolls on the ground.

Fig. 17 shows another variant of balloon 101. The thin lines in the picture show a solar beam. The embodiment has a solar panel 1705 in the low part of an inflated balloon. The balloon has transparent skin 102 in its upper half, gas tight paraboloid reflector-concentrator 104, a paraboloid mirror 1701 on the same axis and with the focus in the same point as reflector 104. There is a transparent glass disk 1707 instead of the central part of reflector 104. The axis of the device tracks the sun. Sun beams, parallel to the axis, reflect from reflector 104, then from paraboloid mirror 1701, pass through transparent disk 1707 and hit the surface of solar panel 1705. Solar panel 1705 is equipped with a cooling device 1706, which can contain a liquid heat exchanger or a Stirling engine, utilizing heat to produce additional electric power. Reflector 104 and mirror 1701 can be replaced with a Fresnel lens. This embodiment has an advantage that the solar panel and associated cooling equipment is located low and attached to the envelope of the balloon in a place, where it does not have to be transparent and can be made from stronger material.

It should be also noted, that reflector-concentrator can have a form of a spherical cap for some small concentration ratios, and that the form of reflector-concentrator can be approximated by other curved surfaces.

In various embodiments, described above, a Fresnel lens can be used instead of the paraboloid reflector, with corresponding changes in placement of the solar panels and some other details. For example, the focus of the Fresnel lens is behind it, not in front of it, so the solar panel or a smaller Fresnel lens is placed behind the first Fresnel lens.

Reflectors 104 and 903 can be made of metalized BoPET, or of nylon, covered by aluminum foil, among other options. Transparent skin of balloons can be made of transparent BoPET, polyethylene, polyester, polyvinyl etc. Non-transparent parts of balloon envelopes can be made of nylon, polyethylene, BoPET or other fabric. Tethers 106, 608, 609, 806 and others can be made of strong and light synthetic fibers, such as aramids, para-aramids or ultra high molecular density polyethylene. Solar panels can use inexpensive single junction solar cells (such as silicon solar cells), multi junction solar cells or other.

Concentrated light solar panels frequently require active cooling. It is preferable to cool both front and back surfaces of the solar cells, but usual cooling means cannot be placed in front of the solar cells because they would create a shadow. The following embodiment of the invention solves this problem and provides an additional benefit of higher air speed and increased turbulence of the air near the solar panel surfaces.

Fig. 18 shows this embodiment of the invention, sectional side view. This embodiment comprises a solar concentrator 1801, a rod 1802 and a solar panel 1803, attached to rod 1802. Solar concentrator 1801 can have a paraboloid form. Solar panel 1803 comprises multiple concentric circular strips 1804 with solar cells, placed on them. Strips 1804 are connected mechanically by bars 401, which also contain electric wires, connecting solar cells from different strips 1804 into a single panel, having outgoing wires 402, as shown on Fig. 4. A fan 1806, having blades with airfoil cross section, gradually decreasing from the center to the ends, is installed on the end of rod 1802. The motor of fan 1806 is driven by electricity, generated by solar panel 1803. A conical airflow shaper is installed in front of solar panel 1803. When solar panel 1803 is lighted, the blades of fan 1806 rotate with high speed and generate strong air flow in the direction of solar panel 1803. Air flows in gaps 1903 between strips 1804, and is directed with high speed and high turbulence around both front and back surfaces of the solar cells in strips 1804, ensuring very efficient cooling. The air flow is shown in curved arrows in the right side of Fig. 18. Light reflection is shown in straight lines with arrows. In this embodiment, the focal point F of parabolic concentrator 1801 is in front of solar panel 1803, and the tilt of strips 1804 helps to put the surface of the solar cells close to normal angle to the incoming light beams.

Fig. 19 is a view of the solar module from the rear without the fan. It highlights gaps 1903 between strips 1804 of solar cells and connecting pieces 1901, holding strips 1804 together and containing power transmitting wires. It shows also an electric cable 1902, transferring electric current, generated in solar panel 1803.

Obviously, other embodiments with different placement, form and tilt of solar strips are possible. For example, in some embodiments, solar panel 1803 can be rectangular, rather than circular, with flat strips of the solar cells and multiple fans. In this variation of that

embodiment, solar concentrator 1801 can have parabolic cross section.

Thus, an airborne concentrated solar PV system is described in conjunction with one or more specific embodiments. While 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.

Claims

What is clai med is:

[Clai m 1 ] A device for converting solar energy into electric energy, comprising:

at least one reflector-concentrator, formed by an inflated body, having a transparent skin in one part of it and a reflecting surface on the internal side in the opposite part of it;

a solar panel, placed near the focus of the reflector-concentrator;

a solar tracking system, continuously aligning axis of the reflector-concentrator with direction to the sun.

[Clai m 2] The device of Claim 1, wherein the reflector-concentrator has a paraboloid form.

[Clai m 3] The device of Claim 1, wherein the inflated body is filled with a lighter than air gas.

[Clai m 4] The device of Claim 1, wherein the inflated body is filled with air, heated by solar energy.

[Clai m 5] The device of Claim 1, wherein the inflated body is aerodynamically streamlined.

[Clai m 6] The device of Claim 1, wherein the inflated body is enclosed into an

aerodynamically streamlined balloon.

[Clai m 7] A plurality of the devices of Claim 1, placed close to each other and combined into a solar farm.

[Clai m 8] A device for converting solar energy into electric energy, comprising:

a solar light concentrator;

a non-planar solar panel with a plurality of solar cells with gaps;

a fan placed to the rear of the solar panel, blowing both the solar panel's rear side and the solar panel's front side.

[Clai m 9] The device of Claim 8, wherein the solar light concentrator has a paraboloid form.

[Clai m 1 0] The device of Claim 8, wherein the solar light concentrator has a parabolic form in its cross section.