GB2624186A - An unmanned aerial vehicle and energy harvesting device - Google Patents

Abstract

An unmanned aerial vehicle and an energy harvesting device, the unmanned aerial vehicle 100 has a reversible hydrogen fuel cell 200 configured to power multiple propellers 103 and generate hydrogen fuel from the electrolysis of water; an energy harvesting device 500 of the unmanned aerial vehicle is configured to harvest energy from an environmental source to generate electricity for use by the reversible hydrogen fuel cell 200 to generate the hydrogen fuel; the energy harvesting device includes at least one impeller which is configured to harvest energy from wind to generate electricity.

Description

AN UNMANNED AERIAL VEHICLE AND ENERGY HARVESTING DEVICE

FIELD OF THE INVENTION

The invention relates to an unmanned aerial vehicle and an energy harvesting device which may be associated with the unmanned aerial vehicle. In particular, it relates to an environmentally friendly unmanned aerial vehicle and an energy harvesting device which is configured to harvest environmental energy for generating electrical energy.

BACKGROUND TO THE INVENTION

Unmanned ariel vehicles (UAVs), such as multirotor drones, have numerous applications in both industry and recreation, such as in agriculture, manufacturing, package transport, security, disaster management and videography. UAVs typically rely on gasoline, nitrogen, or hydrogen as fuel for generating power to propel the UAV. Smaller UAVs rely on batteries to supply sufficient energy for propulsion, such as common lithium polymer (Li-Po) and lithium ion (Li-Ion) batteries.

Compared to a pound of traditional fuel like gasoline, most rechargeable batteries deliver less than 3% specific energy. Batteries also add more weight to propel. Gasoline provides a 10:1 advantage over batteries in terms of energy density and efficiency. Furthermore, gasoline offers a longer flight duration compared to batteries. However, in light of the current environmental problems caused by global warming, there is a need for more sustainable and eco-friendly power solutions. The aviation industry is increasingly striving for a net zero carbon footprint and ways to reduce carbon emissions into the atmosphere. As a result, UAVs with reversible hydrogen fuel cells as the main power source are being developed. Patent publication number KR102245475 describes an energy self-supporting unmanned aerial vehicle using a water electrolysis fuel cell. United States patent number U56854688B2 describes a Solid Oxide Regenerative Fuel Cell (SORFC) incorporated into an electrically powered airplane to provide either regenerative or primary electrical energy. The main components of a reversible hydrogen fuel cell typically are a hydrogen fuel cell, a water purification unit, an electrolyser unit for generating hydrogen and oxygen from water, a hydrogen compressor, and a hydrogen storage unit. The electrolyser unit, however, requires energy to perform the water electrolysis process.

Various energy harvesting techniques are being proposed to be used in UAVs. However, the weight-to-power ratio of such energy harvesting modules still needs to be optimised. Examples of available renewable energy resources are wind and solar energy, which can be used in a hybrid power system to provide backup energy to batteries, for example. US patent number US856893832 discloses systems and methods of electric power generation in which thermoelectric generators are used with a fuel cell to generate additional electricity from the excess heat generated by the fuel cell. Wind energy harvesting techniques, such as propellor motors that generate electricity from the rotation of the propellors by airflow have been incorporated into a UAV. The electricity generated with the propeller motors may be used to recharge a battery or power the sensors of the UAV, as described in United States patent number US9550577B1.

There remains a need for sufficiently lightweight and efficient ways to generate electricity from renewable energy sources to extend the time of flight of UAVs.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided an unmanned aerial vehicle comprising a reversible hydrogen fuel cell configured to power multiple propellers of the unmanned aerial vehicle and generate hydrogen fuel from the electrolysis of water; and an energy harvesting device configured to harvest energy from an environmental source and generate electricity for use by the reversible hydrogen fuel cell, the energy harvesting device including at least one impeller which is configured to harvest energy from wind and generate electricity.

The energy harvesting device may be a triboelectric energy harvester configured to generate electricity based on the triboelectric effect and electrostatic induction upon the rotation of the impeller from wind in use.

The triboelectric energy harvester may be a wind-rolling triboelectric generator. The wind-rolling triboelectric generator may comprise the impeller surrounded by a generally circular and hollow tube or guard which houses one or more dielectric spheres and has multiple circumferentially spaced electrodes on its internal surface, the tube having an inlet and an outlet which are arranged such that air introduced into the inlet moves along a portion of an interior of the tube to the downstream outlet to create a wind passing in one direction through the tube, the wind moving the dielectric sphere within the tube to permit contact of the dielectric sphere with the electrodes to generate electricity via the triboelectric effect in use. The inlet may be defined in an inner radial surface of the tube and the outlet may be defined in an outer radial surface of the tube at a selected distance along the circumference of the tube from the air inlet. Preferably, multiple air inlets and air outlets are defined in the tube and circumferentially spaced along the inner and outer radial surfaces of the tube so that the inlets and outlets are offset to allow for air entering the inlets to move along a portion of the interior of the tube in one direction from the the to the outlets.

Alternatively, the triboelectric energy harvester may be a rotary triboelectric generator. The rotary triboelectric generator may comprise a stator adjacent the impeller, the stator supporting at least one electrode opposite the impeller, and wherein one or more fibres extend from a blade of the impeller, the one or more fibres being configured to contact the electrode upon rotation of the impeller to generate electricity via the triboelectric effect in use.

Further alternatively, the triboelectric energy harvester may include both a rotatory triboelectric generator and a wind-rolling triboelectric generator. In one implementation, the impeller may be surrounded by a generally circular and hollow tube or guard which houses one or more dielectric spheres and has multiple circumferentially spaced internal electrodes on an internal surface of the tube, the tube having an inlet and an outlet which are arranged such that air introduced into the inlet moves along a portion of an interior of the tube to the downstream outlet to create a wind passing or travelling in one direction through the tube, the wind moving the dielectric sphere within the tube to permit contact of the dielectric sphere with the electrodes, the tube further supporting at least one external electrode opposite the impeller, and wherein one or more fibres extend from a blade of the impeller, the one or more fibres beings configured to contact the external electrode upon rotation of the impeller in use.

The reversible hydrogen fuel cell may include a hydrogen fuel cell, an electrolyser configured to generate hydrogen from water and supply the hydrogen to the hydrogen fuel cell, a hydrogen compressor and a hydrogen storage unit. The electrolyser may be configured to receive the electricity generated by the energy harvesting device.

In addition to wind, one or more further environmental sources of energy for the energy harvesting device may be solar, thermal or mechanical energy from vibrations. Accordingly the UAV may include one or more of a solar energy harvesting device, a thermal energy harvesting device or a mechanical energy harvesting device such as a piezoelectric generator configured to harvest energy from vibrations of the UAV when in use.

In accordance with a second aspect of the invention, there is provided a wind energy harvesting device, comprising an impeller with blades configured to harvest wind energy to rotate the impeller around its major axis; a generally circular and hollow tube radially surrounding the impeller; one or more dielectric spheres housed within the tube; multiple circumferentially spaced internal electrodes on an internal surface of the tube; an inlet defined in the tube; an outlet defined in the tube, wherein the inlet and the outlet are arranged such that air introduced into the inlet moves along a portion of an interior of the tube to the downstream outlet to create a wind passing in one direction through the tube, the wind moving the dielectric sphere within the tube to permit contact of the dielectric sphere with the electrodes to generate electricity from the triboelectric effect and electrostatic induction in use; at least one external electrode supported on an external surface of the tube opposite the blades of the impeller; and one or more fibres extending from a blade of the impeller, the one or more fibres being configured to contact the external electrode upon rotation of the impeller to generate electricity from the triboelectric effect and electrostatic induction in use.

The impeller may also be configured to rotate an electromagnet of a generator to generate electricity.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings: Figure 1 is a three-dimensional view of an embodiment of a multirotor unmanned aerial vehicle (UAV) with an energy harvesting device; Figure 2 is a schematic diagram of a reversible hydrogen fuel cell; Figure 3 is a top cross-sectional view of a wind-rolling triboelectric generator with arrows indicating the direction of air flow; Figure 4 is a three-dimensional view of the wind-rolling triboelectric generator of Figure 3 with arrows indicating the direction of air flow; Figure 5 is a top cross-sectional view of a rotatory triboelectric generator; Figure 6 is a top cross-sectional view of an embodiment of a wind energy harvesting device combining wind-rolling and rotatory triboelectric generators; Figure 7 is a three-dimensional view of the wind energy harvesting device of Figure 6; Figure 8 is a side view of an aerodynamic drag-reducing device; Figure 9 is a front view of the aerodynamic drag-reducing device of Figure 8; Figure 10 is a side view of an umbrella-like glider attached to a hydrogen storage unit; Figure 11 is a three-dimensional view of a hydrogen fuel cell with thermoelectric generators on an outer surface thereof; Figure 12 is a three-dimensional view of the hydrogen storage unit with a layer of photovoltaic sheets and thermoelectric generators provided on an outer surface thereof; Figure 13 is a three-dimensional view of an arm of the embodiment of the multirotor UAV of Figure 1, with a layer of photovoltaic sheets and thermoelectric generators on an outer surface thereof and piezoelectric generators within the arm; Figure 14 is a top view of a chassis of the multirotor UAV of Figure 1 with piezoelectric generators; Figure 15 is a side view of a portion of the chassis of UAV of Figure 1 with piezoelectric generators; Figure 16 is a block diagram which illustrates the connectivity between different components in the embodiment of the multirotor UAV of Figure 1; Figure 17 is a block diagram which illustrates categorised subsystems of the electronics in the embodiment of the multirotor UAV of Figure 1; Figure 18 is a block diagram which illustrates a power conditioning and control unit for the embodiment of the multirotor UAV of Figure 1; and Figure 19 is a block diagram which illustrates a control unit of the embodiment of the multirotor UAV of Figure 1

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

An unmanned aerial vehicle (UAV) is provided comprising a reversible hydrogen fuel cell configured to power one or more propellers of the unmanned aerial vehicle. The reversible hydrogen fuel cell is further configured to generate hydrogen fuel by electrolysing water. The UAV includes one or more energy harvesting devices configured to harvest energy from an environmental source and generate electricity. The electricity generated by the energy harvesting device may be used by the reversible hydrogen fuel cell to power the electrolysis process. The energy harvesting device includes at least one impeller configured to harvest energy from wind to generate electricity.

In some embodiments, the impeller of the energy harvesting device is a free-wheeling impeller with triboelectric generators associated therewith which are configured to generate electricity via the triboelectric effect and electrostatic induction upon rotation of the impeller by wind. The term "free-wheeling impeller" refers to the fad that the impeller is not connected to a load such as a generator thereby providing a more light-weight wind energy harvesting device. Alternatively, the impeller may be connected to a generator to rotate an electromagnet of the generator to generate electricity. The generator connected to the impeller may include a rotor, the electromagnet and a coil of conductive wires (stator), with the electromagnet rotating in the coil to induce a current. In some embodiments, the impeller may be connected to both a conventional wind generator or motor and to triboelectric generators configured to generate electricity via the triboelectric effect and electrostatic induction upon rotation of the impeller.

The UAV includes one or more energy harvesting devices, each being configured to harvest energy from an environmental source and generate electricity. For example, energy harvesting devices configured to harvest one or more of solar, wind, thermal or mechanical energy from a constant oscillating source such as vibrations to increase the flight time of the UAV may be provided. The electricity generated with the one or more energy harvesting devices may be directed to the electrolyser of the reversible hydrogen fuel cell for use in electrolysing water recycled from the hydrogen fuel cell. In some embodiments, the electricity generated by the one or more energy harvesting devices may be used for other purposes, such as powering specific other components of the UAV or for storage in a battery.

An embodiment of a mulfirotor UAV (100) is shown in Figure 1. The UAV (100) has one or more propellors (103), in this embodiment four propellers (103), which are powered by a reversible hydrogen fuel cell (200). Arms (109) connect the propellors (103) to a chassis (117) of the UAV.

Each arm (109) has an actuator shell (111) at a first end (113) thereof and attachment means for attaching the arm (109) to the chassis (117) at a second end (115) thereof. In other embodiments of the UAV, the arms may be integrally formed with the chassis. Actuators (119) are located within the actuator shells (111) and are configured to actuate the propellors (103), which in turn provide the necessary thrust for uplift. A second set of four arms (123) connect a wind energy harvesting device (500), also providing electricity to increase flight time, to the chassis (117) of the UAV (100). All arms (109, 123) have an aerodynamic shape, in this embodiment, a pyramidal or generally triangular cross-section.

The chassis (117) of the UAV (100) includes a base plate (105) and landing legs (107) attached thereto. The landing legs (107) increase stability and prevent damage to the UAV (100) during landing. The chassis (117) may be made of generally lightweight materials such as aluminium or a suitable composite material to reduce the overall weight of the UAV and the thrust required for flight. The base plate (105) serves as a supporting structure for a hydrogen storage unit (203) and the reversible hydrogen fuel cell (200) which are both secured thereto.

A schematic diagram of the reversible hydrogen fuel cell (200) is shown in Figure 2. The reversible hydrogen fuel cell (200) includes a hydrogen fuel cell (201), a hydrogen storage unit (203), a hydrogen compressor (205) and an electrolyser (207). The hydrogen fuel cell (201) uses hydrogen (209) as fuel and oxygen (211), which may be obtained from the surrounding air, as oxidising agent and converts the chemical energy from a pair of redox reactions into electricity (213). The electricity (213) generated by the hydrogen fuel cell (201) is used to power and control the actuation of the propellors of a UAV via a power conditioning and control unit (221). The hydrogen fuel cell produces water (215) and excess heat as by-products. The water (215) is routed to the electrolyser (207) where it can be stored and used in an electrolysis process to produce more hydrogen fuel. A separate water storage tank may be associated with the electrolyser (207). The water storage tank stores the water produced as a result of the combination of hydrogen and oxygen within the fuel cell. The weight of the water is managed by continuous conversion of water to hydrogen again with the electrolyser.

The electrolysis process requires electrical energy (219), which is provided by one or more renewable energy harvesters (217) such as a wind energy harvesting device which supplies at least some of the necessary energy to drive the electrolysis process for producing hydrogen (209). The wind energy harvesting device (500) of Figure 1, for example, comprises a free-wheeling impeller (121) which uses natural wind to generate electrical energy (219). The impeller blades rotate around a major axis which in turn rotates an electromagnet of a generator, generating electrical energy (219) which may be routed to and used by the electrolyser (207).

The hydrogen (209) produced by the electrolyser (207) is circulated to a hydrogen compressor (205) which is configured to compress the hydrogen. The compressor (205) may be a mechanical compressor. The compressed hydrogen (209) is then circulated to the hydrogen storage unit (203) where it is stored for later usage by the hydrogen fuel cell (201). The performance of the hydrogen fuel cell (201) is dependent on an operating pressure. The operating pressure is increased and regulated by the mechanical compressor (205) configured to increase the operating pressure of the hydrogen fuel cell (201) by releasing pre-loaded kinetic energy. The compressor may be termed a "mechanical compressor" on account of the pre-loaded kinetic energy, for example via a spring or pendulum, which does not use electrical energy and thus reduces demand for and increases availability of electric energy for other components of the UAV.

In the illustrated embodiment, the UAV includes an energy harvesting device in the form of a triboelectric energy harvester configured to generate electricity based on the triboelectric effect and electrostatic induction upon the rotation of the impeller from wind in use. The triboelectric effect is a type of contact electrification in which two materials become electrically charged after being in contact and separated. The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties. The triboelectric effect is more evident when there is relative movement during contact between the materials such that the materials become electrically charged. The triboelectric effect is considered to be related to the phenomenon of adhesion, where two materials composed of different molecules become electrostatically attracted and exchange electrons. Upon physical separation of the materials, the excess electrons in one material remain left behind, while a deficit of electrons occurs in the other material. Thus, a material can develop a positive or negative charge that dissipates after the materials separate. The exchange of electrons between the materials can be harnessed to generate an electrical current. Such generators are also called triboelectric nanogenerators (TENGS). The current generated is typically alternating current (AC).

TENGS can be used to convert kinetic mechanical energy into electrical energy by harvesting the current induced therein. In a rolling TENG, a dielectric sphere is placed within a housing having conductive electrodes attached to the internal surface thereof. Wien the dielectric sphere makes frictional contact with the electrodes there is an exchange of electrons. The dielectric sphere may consist of a material having a low conductance but able to store charges, such as expanded polystyrene (EPS) or the like. The electrode may consist of a conductive material such as a metal, or more specifically silver. The frictional contact between the dielectric sphere and the electrode forms a high potential impulse between the surfaces.

A rotary TENG may have various different configurations allowing for relative rotation between a rotator and a stator. In one configuration, a fibre of a triboelectric material may be placed at the end of a rotating blade. When air flow causes the blade to rotate the fibre may be configured to slide over an electrode on a stator, forming a high potential impulse between the surfaces of the fibre and the electrode which can be harvested.

The triboelectric energy harvester of the UAV may be a wind-rolling triboelectric generator. An embodiment of a wind-rolling triboelectric generator (300) is shown in Figures 3 and 4 and comprises an impeller (303) surrounded by a generally circular and hollow tube (305) or guard which houses one or more dielectric spheres (307) and has multiple circumferentially spaced electrodes (309) on its internal surface (311). The tube may be endless and arranged in a circular fashion so as to surround the impeller. The tube may be annular in cross-section, for example as shown most clearly in Figure 3. The tube (305) has multiple air inlets (313) defined in a radially inner surface (317) and multiple air outlets (315) defined in a radially outer surface (319) thereof.

The air outlets (315) are circumferentially spaced along the generally circular tube (305) to be offset from the air inlets (313). Accordingly, each air outlet (315) is at a selected distance along the circumference of the tube (305) from its associated air inlet (313). An elongate passageway zone (321) is defined between each pair of offset inlets (313) and outlets (315) and in which air introduced into the inlet (313) moves along a portion of an interior of the tube (305) to one or more downstream outlets (315) so as to create a wind that moves in one direction around the endless tube (305). The wind in the tube (305) moves the free-rolling and lightweight dielectric sphere (307) in the tube (305). As a result, the lightweight dielectric sphere (307) moves or rolls within the tube (307) and makes periodic contact with the internal electrodes (309) to generate electricity via the triboelectric effect in use. The blade configuration of the impeller and the positioning of the air inlets (313) of the tube (305) relative to the impeller (303) are such that the impeller (303) may redirect air (323) into the air inlets (313) of the tube (305) when it rotates. Wind or air enters the rapidly rotating impeller (303) along its axis and is cast out by centrifugal force along its circumference through the vane tips of the impeller (303) . The action of the impeller (303) increases the air velocity and pressure and also directs it radially outward towards the tube (305). Once inside the tube (305), the air (325) flows along the passageway zone (321) to move the dielectric sphere (307) in the same direction as the air flow. The air (327) exits the tube (305) though the outlets (315).

The triboelectric generator may be a rotary triboelectric generator. An embodiment of a rotary triboelectric generator (400) is shown in Figure 5 and comprises a stator (405) adjacent to an impeller (403). The stator (405) supports one or more electrodes (407) opposite the impeller (403).

One or more triboelectric fibres (409) extend from one or more or all of the blades (411) of the impeller (403). The one or more triboelectric fibres (409) are configured (for example through a configuration of their lengths such that they span a gap between an end of the blades and the electrodes) to contact the electrodes (407) upon rotation of the impeller (403) to generate electricity via the counter triboelectric effect in use. The fibre (409) may be a natural fibre such as human hair or rabbit fur. Alternatively, the fibre (409) may be made of a triboelectric polymer such as polydimethylsiloxane or polymethyl methacrylate. The impeller blades (411) may be equally angularly spaced about the impeller's (403) axis of rotation. The impeller blades (411) may be made of a lightweight material, such that the impeller (403) has relatively low inertia and can easily rotate around the axis of rotation. The sliding friction between the electrode (407) and the fibre (405) is optimised to be extremely low. The low friction and inertia allow for the rotatory triboelectric generator (400) to generate electricity even at small wind speeds.

The triboelectric harvester may include both a rotatory triboelectric generator and a wind-rolling triboelectric generator. An embodiment of such a wind energy harvesting device (500) including both a rotatory triboelectric generator and a wind-rolling triboelectric generator is shown in Figures 6 and 7.

The wind energy harvesting device (500) includes an impeller (503) with blades (505) configured to harvest wind energy to rotate the impeller (503) around its major axis (A). The impeller (503) may be fitted to a UAV and may be configured to rotate an electromagnet of a generator upon the action of the wind to convert the mechanical rotational energy into electricity (213) in a conventional manner or may be configured to only generate electricity (213) via the triboelectric generators. A generally circular and hollow tube (507) radially surrounds the impeller (503). The tube (507) has one or more free-rolling dielectric spheres (509) housed therein and multiple circumferentially spaced internal electrodes (511) secured to an internal surface (513) of the tube (507). Air inlets (515) and air outlets (517) are defined in the tube (507). The pairs of offset air inlets (515) and air outlets (517) defined in the tube provide a passageway zone (519) for wind (523) in the interior of the tube (507). Air introduced into the inlet (515) moves along a portion of the interior of the tube (507) to one or more downstream the outlets (517) so as to create a wind that moves in one direction around the endless tube (507) in use. The wind (523) moves one or more dielectric spheres (509) within the tube (507), thereby permitting periodic or intermittent rolling contact of the one or more dielectric spheres (509) with the multiple internal electrodes (511) to generate electricity (213) from the triboelectric effect and electrostatic induction. The tube (507) further has at least one external electrode (327) secured to an external surface (529) of the tube and arranged to be adjacent the impeller and opposite the tips or ends of the radially extending blades (505) of the impeller (503). One or more fibres (531) extends from a blade (505) of the impeller (503) and have a selected length to ensure contact of the one or more fibres with the external electrode (527) upon rotation of the impeller (503). The sliding contact between the fibres and the finite electrode followed by separation of the fibre from the electrode when the impeller rotates facilitates the generation of electricity (213) from the triboelectric effect and electrostatic induction in use.

The use of triboelectric generators and static charge induction phenomena in a UAV may be considered dangerous for the ignition system and/or the hydrogen fuel cell. However, the risk may be reduced by selecting the appropriate materials for the chassis or frame of the UAV. In some embodiments, the frame of the UAV is made of or include an antistatic material to avoid charge accumulation. In other embodiments, the UAV includes one or more static dischargers or wicks which may be provided on the frame or another appropriate part of the UAV to prevent arcing and static charge build-up by removing static electricity.

The multirotor UAV may further include a device for reducing the aerodynamic drag of the UAV.

An embodiment of such a drag-reducing device (600) is shown in Figures 8 to 10 and includes a digital anemometer (603) which may be attached to the reversible hydrogen fuel cell (200). The anemometer (603) measures the wind speed and direction and this information may be used by the drag-reducing device (600) to align the storage unit (203) and reversible hydrogen fuel cell (200) secured to the base plate (105) to reduce aerodynamic drag. In some embodiments an umbrella-like glider (605) may be secured to the storage unit (203) as shown in Figure 10. The glider (605) may have a layer of photovoltaic paint (607) to harvest solar energy and generate electricity (213). A hollow, cylindrical support (609) attaches the glider (605) to the storage unit (203). The hollow, cylindrical support (609) may vibrate in use due to wind and the vibrations may be harvested and converted into electrical energy using a microelectrochemical (MEMS) wind energy harvester (611). In this embodiment, the MEMS wind energy harvester (611) is secured between the storage unit (203) and the end of the support (609) opposite the glider (605). The MEMS wind energy harvester (611) is configured to generate electricity (213) from the wind causing drag on the glider (605).

In some embodiments, the UAV includes an energy harvesting device in the form of a thermal energy harvesting device (700) shown in Figure 11. The thermal energy harvesting device (700) includes lightweight thermoelectric generators (703), which in the embodiment of Figure 11, are attached to the outer surface (705) of the hydrogen fuel cell (201). The hydrogen fuel cell includes stacks (707) which dissipate large amounts of heat in use. The thermoelectric generators (703) convert the excess heat from the hydrogen fuel cell stacks (707) into useful electrical energy (213) which may be routed to the electrolyser, another electrical component of the UAV or a battery.

In some embodiments, the UAV includes an environmental energy harvesting device in the form of a solar energy harvesting device (800) as shown in Figure 12. The solar energy harvesting device may consist of one or more photovoltaic sheets (803), which in this embodiment are adhered to the hydrogen storage unit (203). The photovoltaic sheet (803) harvests solar energy to generate electrical energy. The solar energy harvesting device may also include photovoltaic paint configured to harvest solar energy and convert it into electricity. The embodiment shown in Figure 12 also includes thermoelectric generators (703) mounted to the outer surface of the hydrogen storage unit (203). The thermoelectric generators (703) harvest heat from the atmosphere to generate electrical energy. The combination of the photovoltaic sheets (803) with thermoelectric generators (703) allows for the generation of electricity during the day and night.

As shown in Figure 13, further thermoelectric generators (703) and photovoltaic sheets (803) may be provided on the propellor arms (109, 123) or other elongate structural parts of a UAV providing usable surface area for such sheets. The arms (109) may also include a vibration energy harvesting device in the form of piezoelectric generators (805) which are configured to generate electricity from the vibrations of the arms while the UAV is in use. The piezoelectric generators include piezoelectric elements (807) which preferably have dimensions to ensure it has more or less the same resonant frequency as the source of the vibrations to generate electricity in a continuous manner. The piezoelectric elements (807) are compressed and extended when the arms (109,123) experience vibrations, wherein the deformation and compression of the elements results in the piezoelectric material of the element (807) generating electricity. The piezoelectric material may be quartz or the like.

Similarly, the UAV may include vibration energy harvesting devices at the joints of the arms of the multirotor UAV as illustrated in Figures 14 and 15. Each arm (109, 123) extends between the chassis of the UAV and the propellor or impeller of the UAV (100). Each arm (109, 123) therefore has a first joint (1103) at a first end (113) thereof where the propellor (103) or impellor (121) is secured to the arm (109, 123). Each arm has a second joint (1105) at a second end (115) thereof where the arm (109, 123) is secured to the chassis (117), or to the base plate (105) of the chassis (117). The axial and radial oscillations at these joints experienced during use of the UAV are harvested by piezoelectric elements of piezoelectric generators in the joints (1103, 1005) to generate electric energy. The piezoelectric generators function in a similar manner to the piezoelectric actuators described above with reference to Figure 13.

Figure 16 shows a schematic (900) of the connectivity of the different components of a UAV according to aspects of the present disclosure. There is a power conditioning and control unit (221) which conditions electrical power generated by the one or more energy harvesting devices and feeds the power to one or both of an energy storage device (905) or a control unit (903). The control unit (903) may use the power provided from the power conditioning and control unit (221) to control the actuators (119) of the propellors (103).

Figure 17 shows a schematic (1000) of the categorised subsystems of the electronics of a UAV according to aspects of the present disclosure. The one or more energy harvesting devices (1003) provide power to the power conditioning and control unit (221) to boost the power and reduce fuel consumption of the hydrogen fuel cell. The power conditioning and control unit (221) feeds power to and draws power from energy storage (905) depending on electricity load and supply availability. The power conditioning and control unit (221) provides electrical power to the control unit (903). A sensor unit (1005) communicates with the energy harvesters (1003) via the power conditioning and control unit (221) and the energy storage (905) and sends data to the control unit (903) to power and control the thrust provided by the actuators (119).

Figure 18 shows a schematic diagram of the power conditioning and control unit (221). Alternating current (AC) or impulses are received from the energy harvesting devices (1003) and delivered to the boost circuit (1007) and rectified by the rectifier unit (1009). After rectification, the pulsating direct current (DC) is filtered in a filtration unit (1011) to provide pure DC. The pure DC is then stored in a battery pack (1015) and/or used to charge a supercapacitor (1013), which may form part of the energy storage device (905) shown in Figure 17. The stored energy is controlled by the controller module (1017) for further transmission.

Figure 19 shows a schematic diagram of the control unit (903) which controls the actuators (119) of the propellers (103). The control unit (119) comprises a microcontroller (1019) receiving data from the drag reducing device (600), communicates with the PID controllers (1021) and controls the driver circuit (1023). Sensors collect data from the actuators and the atmosphere, and transmit the raw data to the microcontroller.

The various energy harvesting devices described herein may be used to provide energy to drive the electrolysis process of the reversible hydrogen fuel cell. UAVs are typically exposed to high wind speeds, especially at high altitudes. The triboelectric generators and wind energy harvesting devices provide a lightweight solution to increasing flight time. The aerodynamic drag reducing device reduces the amount of drag the UAV experiences due to the reversible hydrogen fuel cell. The additional lightweight environmental energy harvesting devices aid the wind energy harvesting impeller in generating electricity and further increases the flight time of the drone. The heat generated as a by-product of the hydrogen fuel cell is harvested in thermoelectric generators and aid the wind energy harvesting impeller by supplying further electrical energy to the electrolyser, or to another power-requiring component of the UAV or for storage in a battery such that it can be use when required.

The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. For example, the UAV may be in any form in terms of which flight may be achieved with one or more propellers. The UAV may be a multirotor UAV, a fixed-wing UAV or a hybrid UAV with a combination of propellers and wings. Further, only one or many of the above-described environmental energy harvesting devices may be used to generate electrical energy. The electrical energy may be used to drive the electrolysis process of the reversible or regenerative hydrogen fuel cell or used elsewhere by the UAV. A variation where the hydrogen fuel cell is not reversible is possible, with the energy harvesting device, which may be a triboelectric generator, harvesting wind or other environmental energy to supply power to small components of the UAV such as lights, frequency components, cameras and the like. In a further variation of the UAV the hydrogen fuel cell is replaced with another power supply and the energy harvesting devices such as the triboelectric generators generate backup energy in case the power supply of the UAV fails. The energy harvesting device such as the triboelectric generators may also provide power to a battery of the UAV to increase the flight time.

Any of the steps, operations, components or processes described herein may be performed or implemented with one or more hardware or software units, alone or in combination with other devices. Components or devices configured or arranged to perform described functions or operations may be so arranged or configured through computer-implemented instructions which implement or carry out the described functions, algorithms, or methods. The computer-implemented instructions may be provided by hardware or software units. In one embodiment, a software unit is implemented with a computer program product comprising a non-transient or non-transitory computer-readable medium containing computer program code, which can be executed by a processor for performing any or all of the steps, operations, or processes described. Software units or functions described in this application may be implemented as computer program code using any suitable computer language such as, for example, JavaTM, C++, or PerITM using, for example, conventional or object-oriented techniques. The computer program code may be stored as a series of instructions, or commands on a non-transitory computer-readable medium, such as a random access memory (RAM), a read-only memory (ROM), a magnetic medium such as a hard-drive, or an optical medium such as a CD-ROM. Any such computer-readable medium may also reside on or within a single computational apparatus, and may be present on or within different computational apparatuses within a system or network.

Flowchart illustrations and block diagrams of methods, systems, and computer program products according to embodiments are used herein. Each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, may provide functions which may be implemented by computer readable program instructions. In some alternative implementations, the functions identified by the blocks may take place in a different order to that shown in the flowchart illustrations.

Some portions of this description describe the embodiments of the invention in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations, such as accompanying flow diagrams, are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. The described operations may be embodied in software, firmware, hardware, or any combinations thereof.

The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Finally, throughout the specification and accompanying claims, unless the context requires otherwise, the word 'comprise' or variations such as 'comprises' or 'comprising' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims (14)

1. CLAIMS: 2. 3. 4. 5. 6. 7.An unmanned aerial vehicle comprising a reversible hydrogen fuel cell configured to power multiple propellers of the unmanned aerial vehicle and generate hydrogen fuel from the electrolysis of water; and an energy harvesting device configured to harvest energy from an environmental source and generate electricity for use by the reversible hydrogen fuel cell, the energy harvesting device including at least one impeller which is configured to harvest energy from wind and generate electricity.
2. The unmanned aerial vehicle as claimed in claim 1, wherein the energy harvesting device is a triboelectric energy harvester configured to generate electricity from the triboelectric effect and electrostatic induction upon the rotation of the impeller from wind in use.
3. The unmanned aerial vehicle as claimed in claim 2, wherein the triboelectric energy harvester is a wind-rolling triboelectric generator.
4. The unmanned aerial vehicle as claimed in claim 3, wherein the impeller is surrounded by a generally circular tube which houses one or more dielectric spheres and has multiple circumferentially spaced electrodes on its internal surface, the tube having an inlet and an outlet which are arranged such that air introduced into the inlet moves along a portion of an interior of the tube to the downstream outlet to create a wind passing in one direction through the tube, the wind moving the dielectric sphere within the tube to permit contact of the dielectric sphere with the electrodes to generate electricity in use.
5. The unmanned aerial vehicle as claimed in claim 4, wherein the inlet is defined in an inner radial surface of the tube and the outlet is defined in an outer radial surface of the tube at a selected distance along the circumference of the tube from the inlet.
6. The unmanned aerial vehicle as claimed in claim 4 or claim 5, wherein multiple air inlets and air outlets are defined in the tube and circumferentially spaced along the inner and outer radial surfaces of the tube with the inlets offset to the outlets.
7. The unmanned aerial vehicle as claimed in claim 2, wherein the triboelectric energy harvester is a rotary triboelectric generator.
8. 8. The unmanned aerial vehicle as claimed in claim 7, wherein the rotary triboelectric generator includes a stator adjacent the impeller, the stator supporting at least one electrode opposite the impeller, and wherein one or more fibres extend from one or more blades of the impeller, the one or more fibres being configured to contact the electrode on the stator upon rotation of the impeller to generate electricity in use.
9. The unmanned aerial vehicle as claimed in claim 2, wherein the triboelectric energy harvester includes a rotatory triboelectric generator and a wind-rolling triboelectric generator.
10. The unmanned aerial vehicle as claimed in claim 9, wherein the impeller is surrounded by a generally circular and hollow tube which houses one or more dielectric spheres and has multiple internal electrodes circumferentially spaced on an internal surface of the tube, the tube having an inlet and an outlet which are arranged such that air introduced into the inlet moves along a portion of an interior of the tube to the downstream outlet to create a wind passing in one direction through the tube, the wind moving the dielectric sphere within the tube to permit contact of the dielectric sphere with the electrodes, the tube supporting at least one external electrode opposite the impeller, and wherein one or more fibres extend from a blade of the impeller, the one or more fibres beings configured to contact the external electrode upon rotation of the impeller.
11. The unmanned aerial vehicle as claimed in any one of claims 1 to 10, wherein the reversible hydrogen fuel cell includes a hydrogen fuel cell, an electrolyser configured to generate hydrogen from water and supply the hydrogen to the hydrogen fuel cell, a hydrogen compressor and a hydrogen storage unit.
12. The unmanned aerial vehicle as claimed in claim 11, wherein the electrolyser is configured to receive the electricity generated by the energy harvesting device.
13. A wind energy harvesting device, comprising: an impeller with blades configured to harvest wind energy to rotate the impeller around its major axis; a generally circular and hollow tube radially surrounding the impeller; one or more dielectric spheres housed within the tube; multiple circumferentially spaced internal electrodes on an internal surface of the tube; an inlet defined in the tube; an outlet defined in the tube, wherein the inlet and the outlet are arranged 10. 11. 12. 13.such that air introduced into the inlet moves along a portion of an interior of the tube to the downstream outlet to create a wind passing in one direction through the tube, the wind moving the dielectric sphere within the tube to permit contact of the dielectric sphere with the electrodes to generate electricity from the triboelectric effect and electrostatic induction in use; at least one external electrode supported on an external surface of the tube opposite the blades of the impeller; and one or more fibres extending from a blade of the impeller, the one or more fibres being configured to contact the external electrode upon rotation of the impeller to generate electricity from the triboelectric effect and electrostatic induction in use.
14. 14. The wind energy harvesting device as claimed in claim 13, wherein the impeller is configured to rotate an electromagnet of a generator to generate electricity.