WO2025003714A1

WO2025003714A1 - Energy harvesting device, system and method of manufacture

Info

Publication number: WO2025003714A1
Application number: PCT/GB2024/051706
Authority: WO
Inventors: Karthikeyan Velayutham
Original assignee: Katrick Technologies Ltd
Current assignee: Katrick Technologies Ltd
Priority date: 2023-06-29
Filing date: 2024-07-01
Publication date: 2025-01-02
Anticipated expiration: 2025-12-29
Also published as: GB202309861D0; TW202517894A

Abstract

An energy harvesting device is disclosed. The energy harvesting device comprises one or more foils and a pressurised energy conversion system. The pressurised energy conversion system comprises a working fluid, one or more fluid displacement devices configured to be driven by movement of the one or more foils and one or more generators configured to be driven by the working fluid. Advantageous, the energy harvesting device can efficiently harvest energy from a turbulent fluid flow.

Description

1 Energy Harvesting Device, System and Method of Manufacture

2

3 The present invention relates to an energy harvesting device, system and method of

4 manufacture. The energy harvesting device is particularly suitable for capturing energy

5 from a turbulent fluid flow, such as ground level wind.

6

7 Background to the Invention

8

9 A conventional horizontal-axis wind turbine known in the art typically comprises three0 blades. The wind turbine converts the kinetic energy of the wind into mechanical motion1 according to the principle of aerodynamic lift. In operation, the blades rotate and drive a2 generator located within a nacelle at the top of a tower of the wind turbine. The generator3 converts the mechanical motion into electricity. 4 5 Whilst conventional horizontal-axis wind turbines are widely used in the energy industry to6 offer a source of renewable energy, there are numerous disadvantages. Horizontal-axis7 wind turbines can only operate within a narrow wind speed window. For example, if the8 wind speed is too high there is a risk of damaging the wind turbines. Conversely if the9 wind speed is too low, then there may not be enough aerodynamic lift to rotate the blades. 2 The size of horizontal-axis wind turbines has increased over time to take advantage of

3 more laminar air flows found at higher altitude. A laminar air flow results in increased

4 efficiency of a horizontal-axis wind turbine relative to a more turbulent air flow. As such,

5 commercial wind farms typically comprise large wind turbines which can presently be over

6 100 m tall. Whilst large wind turbines have a greater power output than smaller scale

7 micro wind turbines, the large wind turbines typically dominate the surrounding landscape

8 and have a negative aesthetic impact on the environment. There are further negative

9 environmental consequences as wind turbines can detrimentally affect the surrounding0 wildlife. For example, the blades of the wind turbines can kill birds. 1 2 A disadvantage of large horizontal-axis wind turbines is that they are not suitable to be3 located in urban landscapes, by motorways and especially not near airports as they tend4 to produce a significant turbulent flow in the wake of the blades. As a result, as well as5 remote land locations, wind farms comprising large wind turbines are typically located6 offshore. Yet this poses a further challenge, namely, the added complexity of transporting7 and installing such large devices in remote locations. 8 9 Another disadvantage of a conventional horizontal-axis wind turbine is that the generator is0 located within the nacelle at the top of the tower. This location makes maintenance1 challenging, particularly, for large offshore wind turbines over 100 m tall as engineers must2 climb the tower and transport any replacement parts as required. 3 4 A large offshore conventional horizontal-axis wind turbine 1 know in the art is depicted in5 Figure 1 . The wind turbine 1 comprises a tower 2, a nacelle 3 located at the top of the6 tower 2, a hub 4 about which is positioned three blades 5, and a hydraulic pump 6 located7 within the nacelle 3. In use, the hydraulic pump 6 pumps sea water 7 to a generator 88 located on a separate platform 9. Instead of being located at the top of the tower 3, the9 generator 8 is located on the platform 9, a more accessible location for maintenance.0 1 of the Invention 2 3 It is an object of an aspect of the present invention to provide an energy harvesting device4 that obviates or at least mitigates one or more of the aforesaid disadvantages of the5 energy harvesting devices known in the art. 1

2 According to a first aspect of the present invention there is provided an energy harvesting

3 device comprising:

4 one or more foils configured to respond to changes in a fluid flow with a response time

5 of less than 60 seconds; and

6 a pressurised energy conversion system, the pressurised energy conversion system

7 comprising:

8 a working fluid;

9 one or more fluid displacement devices configured to be driven by movement of the0 one or more foils; and 1 one or more generators configured to be driven by the working fluid. 2 3 Preferably, the response time may be less than 30 seconds. Preferably, the response4 time may be less than 10 seconds. Preferably, the response time may be less than 55 seconds. Most preferably, the response time may be of the order of a second. 6 7 Preferably, one or more foils may be configured to have a low inertia. 8 9 Preferably, the energy harvesting device may comprise two or more foils. 0 1 Preferably, the movement of the two or more foils may be independent. Advantageously,2 the independent motion of the two or more foils facilitates coupling energy from multiple3 locations within a turbulent flow. 4 5 Optionally, the movement of the two or more foils may be dependent. Advantageously,6 the dependent motion of two or more foils facilitates offsetting the phase of the two or7 more foils. 8 9 Preferably, the energy harvesting device further comprises one or more ducts. The one or0 more foils are located within the one or more ducts. Each of the one or more ducts1 comprises an inlet opening and an outlet opening. 2 3 Preferably, each of the one or more ducts may comprise two or more foils. 4 1 Preferably, the energy harvesting device further comprises one or more vibrational

2 members. The one or more vibrational members connect the one or more foils to the

3 pressurised energy conversion system.

4

5 Preferably, the one or more vibrational members are configured to pivot about a pivot axis

6 located between a first end and a second end of the one or more vibrational members.

7

8 Alternatively, the one or more vibrational members are configured to pivot about a pivot

9 axis at the second end of the one or more vibrational members. 0 1 Preferably, the one or more foils are configured to exhibit a pivoting motion about the pivot2 axis and a rotation motion about a rotation axis extending along the span direction of the3 one or more foils, the rotation axis being perpendicular to the pivot axis. 4 5 Preferably, the one or more fluid displacement devices may comprise a pump. The one or6 more fluid displacement devices may comprise a positive displacement pump, preferably,7 a rotary-type positive displacement pump and or a reciprocating-type positive 8 displacement pump. The one or more fluid displacement devices may comprise a piston. 9 The one or more fluid displacement devices may comprise a semi-rotary actuator. The0 one or more fluid displacement devices may comprise a swash plate piston arrangement. 1 2 Preferably, the one or more fluid displacement devices may be connected to one or more3 vibrational members. 4 5 Preferably, the energy harvesting device further comprises one or more mechanical6 connections connecting the one or more fluid displacement devices to one or more7 vibrational members. 8 9 Preferably, the one or more fluid displacement devices may be connected to the 0 vibrational member at the pivot point. Alternatively, the fluid displacement device may be1 connected to the vibrational member between the pivot point and the first end of the2 vibrational member and or between the pivot point and the second end of the vibrational3 member. 1 Optionally, the energy harvesting device further comprises a spring between the one or

2 more fluid displacement devices and the vibrational member and or mechanical

3 connection.

4

5 Optionally, there may be two or more fluid displacement devices. The two or more fluid

6 displacement devices may be fluidly connected. The two or more fluid displacement

7 devices may be connected in series or in parallel. The two or more fluid displacement

8 devices may be of different types and or size.

9 0 Preferably, the pressurised energy conversion system may further comprise one or more1 reservoirs. The one or more reservoirs may be connected to one or more fluid 2 displacement devices. 3 4 Preferably, the pressurised energy conversion system may further comprise one or more5 pressure intensifiers. The one or more pressure intensifiers may connect two or more6 reservoirs. 7 8 Optionally, each of the one or more reservoirs may comprise a diaphragm. 9 0 Optionally, the energy harvesting device further comprises one or more motors and or1 pumps. Optionally, the one or more motors and or pumps may be located between the2 two or more fluid displacement devices. Optionally, the one or more motors may be3 located between the one or more reservoirs and the one or more generators. Optionally, a4 gearbox may be connected to each of the one or more motors and or pumps. 5 6 Preferably, the pressurised energy conversion system may comprise one or more control7 valves. The control valve may be located between the one or more reservoirs and one or8 more generators. 9 0 Optionally, the pressurised energy conversion system may comprise one or more non¬1 return valves. 2 3 Optionally, the pressurised energy conversion system further comprises one or more4 proportional flow valves. 1 Optionally, the pressurised energy conversion system further comprises one or more

2 pressure dependent non-return valves.

3

4 Optionally, the pressurised energy conversion system further comprises an expansion

5 chamber. Preferably, the expansion chamber is located between the one or more fluid

6 displacement devices and the one or more reservoirs.

7

8 Optionally, the pressurised energy conversion system further comprises a pressure

9 dependent non-return valve. Preferably, the pressure dependent non-return valve may0 divert the working fluid to one of the one or more reservoirs according to the pressure and1 or flow rate of the working fluid. 2 3 Alternatively, the one or more foils are configured as one or more turbines. The one or4 more turbines are mechanically connected to one or more radial arms. The one or more5 radial arms mechanically connected to a central spindle. The one or more turbines are6 configured to rotate about one or more turbine rotation axes, rotating the radial arms and7 the central spindle. 8 9 Preferably, the pressurised energy conversion system may be a hydraulic energy0 conversion system. The working fluid may be a liquid. 1 2 Alternatively, the pressurised energy conversion system may be a pneumatic energy3 conversion system. The working fluid may be a gas. 4 5 Preferably, the energy harvesting device is a wind energy harvesting device. The fluid6 flow is wind. The one or more foils comprise one or more aerofoils. 7 8 Additionally, or alternatively, the energy harvesting device is a water flow energy 9 harvesting device. The fluid flow is a water flow. The one or more foils comprise one or0 more hydrofoils. 1 2 According to a second aspect of the present invention there is provided an energy3 harvesting system comprising two or more energy harvesting devices in accordance with4 the first aspect of the present invention. 1 Preferably, the energy harvesting system comprises a centralised reservoir and or a

2 centralised generator.

3

4 Embodiments of the second aspect of the invention may comprise features to implement

5 the preferred or optional features of the first aspect of the invention or vice versa.

6

7 According to a third aspect of the present invention there is provided a method of

8 manufacturing an energy harvesting device comprising:

9 providing one or more foils configured to respond to changes in a fluid flow with a0 response time of less than 60 seconds; 1 providing a working fluid of a pressurised energy conversion system; 2 providing one or more fluid displacement devices of the pressurised energy 3 conversion system, the one or more fluid displacement devices configured to be4 driven by movement of the one or more foils; and 5 providing a generator configured to be driven by the working fluid. 6 7 Most preferably, the method further comprises characterising the fluid flow. 8 9 Most preferably, the method further comprises determining the optimum parameters of the0 energy harvesting device for use with the fluid flow. 1 2 Embodiments of the third aspect of the invention may comprise features to implement the3 preferred or optional features of the first and or second aspects of the invention or vice4 versa. 5 6 According to a fourth aspect of the present invention there is provided a use of an energy7 harvesting apparatus in accordance with the first aspect of the present invention, or an8 energy harvesting system in accordance with the second aspect of the present invention,9 for generating electrical energy. 0 1 Embodiments of the fourth aspect of the invention may comprise features to implement the2 preferred or optional features of the first, second and or third aspects of the invention or3 vice versa. 4 1 According to a fifth aspect of the present invention there is provided an energy harvesting

2 device comprising:

3 one or more low inertia foils; and

4 a pressurised energy conversion system, the pressurised energy conversion system

5 comprising:

6 a working fluid;

7 one or more fluid displacement devices configured to be driven by movement of the

8 one or more foils; and

9 one or more generators configured to be driven by the working fluid. 0 1 Embodiments of the fifth aspect of the invention may comprise features to implement the2 preferred or optional features of the first, second, third and or fourth aspects of the3 invention or vice versa. 4 5 According to a sixth aspect of the present invention there is provided an energy harvesting6 device comprising: 7 two or more independent foils configured to couple energy from multiple locations within8 a turbulent fluid flow; and 9 a pressurised energy conversion system, the pressurised energy conversion system0 comprising: 1 a working fluid; 2 one or more fluid displacement devices configured to be driven by movement of the3 two or more independent foils; and 4 one or more generators configured to be driven by the working fluid. 5 6 Embodiments of the sixth aspect of the invention may comprise features to implement the7 preferred or optional features of the first, second, third, fourth and or fifth aspects of the8 invention or vice versa. 9 0 According to a seventh aspect of the present invention there is provided an energy1 harvesting device comprising: 2 one or more foils; and 3 a pressurised energy conversion system, the pressurised energy conversion system4 comprising: 5 a working fluid; 1 one or more fluid displacement devices configured to be driven by movement of the

2 one or more foils; and

3 one or more generators configured to be driven by the working fluid,

4 wherein the pressurised energy conversion system is configured to dynamically vary a

5 resistive force of the pressurised energy conversion system.

6

7 Most preferably, the pressurised energy conversion system is configured to dynamically

8 vary the resistive force of the pressurised energy conversion system responsive to

9 variation in a fluid flow incident upon the one or more foils. Variation in the fluid flow may0 include variation in energy, speed, direction, and or orientation of the fluid flow, and1 response may be rapid so as to rapidly vary the resistive force responsive to such 2 variations. 3 4 In order to facilitate a generation across a large range of wind (or other moving fluid such5 as water) speeds and to have a high-degree feedback reaction to the change in the6 available energy, the present invention incorporates a dynamic resistance control whereby7 it may operate and effectively generate power in changing wind (or other moving fluid such8 as water) conditions, and may react quickly to such changes. This distinguishes from9 conventional systems which are unable to react quickly to such changing conditions.0 1 Preferably, the dynamic variation in the resistive force is to optimise the energy captured2 by the energy harvesting device. 3 4 Preferably, the dynamic variation in the resistive force is dependent on a variation in lift5 generated by the one or more foils. 6 7 Preferably, the dynamic variation in the resistive force is dependent on a variation in8 energy of the fluid flow. 9 0 Preferably, the dynamic variation of the resistive force comprises varying a flow rate of the1 working fluid displaced by the one or more fluid displacement devices. 2 3 Preferably, the dynamic variation of the resistive force comprises the pressurised energy4 conversion system further comprising two or more reservoirs configured to operate at two5 or more different pressures. 1

2 Preferably, the energy harvesting device further comprises one or more ducts, wherein the

3 one or more foils are located within the one or more ducts.

4

5 Preferably, the variation in the fluid flow, which may be a variation in the energy of the fluid

6 flow, is measured at a mid-section of the one or more ducts.

7

8 Embodiments of the seventh aspect of the invention may comprise features to implement

9 the preferred or optional features of the first, second, third, fourth, fifth and or sixth aspects0 of the invention or vice versa. In particular, those features relating to foils, vibrational1 members, fluid displacement devices, pressurised energy conversion systems and2 response times. 3 4 According to an eighth aspect of the present invention there is provided a method of5 manufacturing an energy harvesting device comprising: 6 providing one or more foils; 7 providing a working fluid of a pressurised energy conversion system; 8 providing one or more fluid displacement devices of the pressurised energy 9 conversion system, the one or more fluid displacement devices configured to be0 driven by movement of the one or more foils; and 1 providing a generator configured to be driven by the working fluid; and 2 configuring the pressurised energy conversion system to dynamically vary a resistive3 force of the pressurised energy conversion system. 4 5 As in the seventh aspect, the pressurised energy conversion system is most preferably6 configured to dynamically vary the resistive force of the pressurised energy conversion7 system responsive to variation in a fluid flow incident upon the one or more foils. 8 9 Embodiments of the eighth aspect of the invention may comprise features to implement0 the preferred or optional features of the first, second, third, fourth, fifth, sixth and or1 seventh aspects of the invention or vice versa. Likewise, in particular those features2 relating to foils, vibrational members, fluid displacement devices, pressurised energy3 conversion systems and response times. 4 5 1 Brief of Drawinos

2

3 There will now be described, by way of example only, various embodiments of the

4 invention with reference to the drawings, of which:

5

6 Figure 1 presents a schematic view of a conventional horizontal-axis wind turbine known in

7 the art;

8

9 Figure 2 presents a plot of measured wind speed in meters per second as a function of0 time in minutes for a turbulent wind flow; 1 2 Figure 3 presents a plot of percentage improvement in power output of a wind turbine, as a3 function of response time of the wind turbine; 4 5 Figure 4 presents a perspective view of an energy harvesting device in accordance with an6 embodiment of the present invention; 7 8 Figure 5 presents a schematic cross-sectional view of the energy harvesting device of9 Figure 4; 0 1 Figure 6 presents a perspective view of a foil and a vibrational member of the energy2 harvesting device of Figure 4 in (a) a first position, (b) a second position, (c) a third3 position and (d) a fourth position; 4 5 Figure 7 presents a schematic cross-sectional view of a pressurised energy conversion6 system of the energy harvesting device of Figure 4; 7 8 Figure 8 presents a schematic cross-sectional view of an alternative embodiment of the9 pressurised energy conversion system of Figure 7; 0 1 Figure 9 presents a schematic cross-sectional view of a further alternative embodiment of2 the pressurised energy conversion system of Figure 7; 3 4 Figure 10 presents a schematic cross-sectional view of another alternative embodiment of5 the pressurised energy conversion system of Figure 7; 1

2 Figure 11 presents a schematic cross-sectional view of an alternative embodiment of the

3 pressurised energy conversion system of Figure 7;

4

5 Figure 12 presents a schematic cross-sectional view of an alternative embodiment of the

6 pressurised energy conversion system of Figure 7;

7

8 Figure 13 presents a schematic cross-sectional view of an alternative embodiment of the

9 pressurised energy conversion system of Figure 7; 0 1 Figure 14 presents a schematic cross-sectional view of an alternative embodiment of the2 pressurised energy conversion system of Figure 7; 3 4 Figure 15 presents a schematic cross-sectional view of an alternative embodiment of the5 pressurised energy conversion system of Figure 7; 6 7 Figure 16 presents a schematic cross-sectional view of an alternative embodiment of the8 pressurised energy conversion system of Figure 7; 9 0 Figure 17 presents a schematic cross-sectional view of an alternative embodiment of the1 pressurised energy conversion system of Figure 7; 2 3 Figure 18 presents a schematic cross-sectional view of an alternative embodiment of the4 pressurised energy conversion system of Figure 7; 5 6 Figure 19 presents a schematic cross-sectional view of an alternative embodiment of the7 pressurised energy conversion system of Figure 7; 8 9 Figure 20(a), (b) and (c) each present schematic cross-sectional views of alternative0 embodiments of the piston of Figure 7; 1 2 Figure 21 A and 21 B presents a schematic cross-sectional view of an alternative3 embodiment of the piston of Figure 7; 4 1 Figure 22 presents a schematic cross-sectional view of an alternative embodiment of the

2 pressurised energy conversion system of Figure 7;

3

4 Figure 23 presents a schematic cross-sectional view of an energy harvesting system

5 comprising the energy harvesting device of Figure 4;

6

7 Figure 24 presents a perspective view of an alternative embodiment of the energy

8 harvesting device of Figure 4;

9 0 Figure 25 presents a perspective view of a further alternative embodiment of the energy1 harvesting device of Figure 4; and 2 3 Figure 26 presents a flow chart of the method of manufacturing the energy harvesting4 device of Figure 1. 5 6 In the description which follows, like parts are marked throughout the specification and7 drawings with the same reference numerals. The drawings are not necessarily to scale8 and the proportions of certain parts have been exaggerated to better illustrate details and9 features of embodiments of the invention. 0 1 Detailed Description of the Preferred Embodiments 2 3 Embodiments of the present invention will now be described with reference to Figures 2 to4 26. 5 6 Turbulent Wind Conditions 7 8 The present invention relates to an energy harvesting device suitable for efficiently 9 capturing energy from a relatively turbulent fluid flow as opposed to a laminar fluid flow.0 For example, instead of relatively high altitude laminar air flows, the present invention is1 suitable for use with more turbulent air flows at ground level. 2 3 A turbulent air flow is depicted in Figure 2, which is a plot of wind speed (m/s) as a function4 of time (minutes) as measured near ground level at an urban location. An urban location5 could be considered as in the vicinity of man-made structures, such as buildings, which will 1 modify the natural air flow. As can be seen there is a variation in wind speed between

2 approximately 1 and 7 m/s over a short time period, of the order of seconds. These

3 sudden peaks and troughs in wind speed are gusts and are caused by a variety of factors,

4 such as convective air currents, atmospheric pressure changes, or even the passage of

5 weather fronts. A gust of wind can be defined as a peak in wind speed approximately 4.5

6 m/s above the average prevailing wind speed with a duration of up to 60 seconds.

7

8 A dimensionless measure of the variation in the intensity of wind speed, in other words,

9 the turbulence of a fluid flow is the turbulent intensity. The turbulent intensity is defined as0 the ratio of standard deviation of fluctuating wind speed to the mean wind speed. The1 wind speed data depicted in Figure 2 has a high turbulent intensity of 41 .6%. Whilst2 Figure 2 represents the wind speed as a function of time, it is important to note that3 turbulent air flow also exhibits a spatial variation in wind speed. 4 5 If the large conventional horizontal-axis wind turbine 1 depicted in Figure 1 was relocated6 to ground level, in a turbulent air flow such as that represented in Figure 2, the variation in7 revolutions per minute of the wind turbine 1 would be a smoother function of time relative8 to the variation in wind speed. This is due to the response time of the wind turbine 19 (minutes) being greater than the time period over which the wind speed changes 0 (seconds). In other words, the inertia of the wind turbine 1 is relatively large. 1 2 Whilst the large conventional horizontal-axis wind turbine 1 in a turbulent air flow may have3 a high power output in comparison to a small wind turbine, the large wind turbine is not4 necessarily efficient. For example, when the wind speed is decelerating over a time period5 of a second as depicted in Figure 2, the large wind turbine 1 is not being driven by the lift6 generated from the incident turbulent air flow at that instant. Instead, momentum is driving7 the wind turbine at a rotation speed, specifically revolutions per minute, representative of8 the wind speed before the deceleration. As such, it will be appreciated by a person skilled9 in the art that a large wind turbine 1 cannot capture all the available energy from a 0 turbulent air flow. 1 2 The inventors have conducted yield modelling of a wind turbine. Figure 3 depicts the3 percentage improvement in power output of the wind turbine, as a function of response4 time of the wind turbine. As can be seen, there is an inverse proportionality between the5 percentage improvement in power output and the response time. This is a further 1 illustration that a wind turbine with a smaller response time, for example a second, with a

2 low inertia, will be more efficient in capturing energy from a turbulent air flow.

3

4 Turbulent air flow incident upon the large wind turbine 1 of Figure 1 will induce mechanical

5 stress due to the spatial variation in wind speed. Specifically, a first blade may experience

6 a greater wind speed, and consequently a larger induced lift, than a second blade.

7 Although the blades experience a difference in lift, the individual blades cannot rotate

8 about the hub at different speeds as they are mechanically connected via the hub,

9 resulting in stress on the components of the large wind turbine 1 . Furthermore, the larger0 induced lift exhibited by the first blade cannot be captured as the second blade acts a1 brake, limiting the efficiency of the large wind turbine 1 . 2 3 The present invention relates to an energy harvesting device with a pressurised energy4 conversion system configured to dynamically vary a resistive force. Advantageously, the5 wind energy harvesting device can efficiently capture power from a turbulent fluid flow6 without inducing mechanical stress upon the components of the device. 7 8 As explained above, a small wind turbine, such as in an urban wind system or the like,9 experiences a much smaller lift than in a large wind turbine. Moreover, the wind speed,0 direction, and orientation are more prone to changes, which can significantly affect the flow1 into a duct (discussed below), which can reduce or increase the available energy. With a2 small wind turbine there is therefore a need to be able to respond to the changing wind3 conditions to operate and effectively generate power. Embodiments of the invention4 described below are intended to be able to effectively generate power across a large5 range of wind conditions and speeds. Furthermore, embodiments of the invention 6 described below are intended to be able to react quickly to changes in wind conditions.7 8 This may be achieved by aerofoils which can go from moving in from one direction to9 another, and when hydraulically connected, constant energy transfer may be achievable0 as the aerofoils can be made to react quickly to such changes. For example, in one1 oscillation (or cycle of oscillations), an airfoil may go from one side to another, and during2 this time, it pushes a piston, pressurising a fluid (whereby the kinetic energy is transferred3 and stored as pressurised fluid), and a cycle is complete. In a next oscillation (or cycle of4 oscillations), the resistive force can be changed according to the wind conditions which are5 now different. This will not affect the previous cycle as it was completed and the energy 1 has already been stored. In a rotary system such as a large wind turbine, there will be

2 momentum stored, and as such it cannot quickly respond to the changes in wind

3 conditions and speeds as seen at ground levels.

4

5 In order to facilitate a generation across a large range of wind speeds and to have a high-

6 degree of feedback reaction to the change in the available energy, embodiments of the

7 invention described below incorporate a dynamic resistance control whereby they may

8 operate and effectively generate power in changing wind conditions, and may react quickly

9 to such changes. Specific embodiments of the present invention are illustrated below.0 1 Energy Harvesting Device 2 3 Figures 4 and 5 depict an energy harvesting device 10. The energy harvesting device 104 is suitable for harvesting energy from a fluid flow such as wind, tidal flows or even a river5 flow and specifically a turbulent fluid flow. The energy harvesting device 10 has a 6 substantially hexagonal prism shape. The energy harvesting device 10 comprises a first7 surface 11 and an opposing second surface 12 which take the form of the two hexagonal8 base surfaces of the hexagonal prism. The first and second surfaces 11 , 12 are both9 perpendicular to and centred about a central axis 13. 0 1 Generator Housing 2 3 The energy harvesting device 10 further comprises a generator housing 14 centred about4 the central axis 13. The generator housing 14 comprises an internal portion 15 and a5 cone-like portion 16, as can clearly be seen in Figure 5. The internal portion 15 of the6 generator housing 14 extends between the first and second surfaces 11 , 12 and has a7 substantially hexagonal cross-sectional shape. It will be appreciated the internal portion8 15 of the generator housing 14 may have any suitable cross-sectional shape which can9 vary between the first and second surfaces 11 , 12. The cone-like portion 16 of the0 generator housing 14 is a continuation of the internal portion 15 that protrudes from the1 first surface 11 and tapers towards the central axis 13. 2 3 Ducts 4 1 The energy harvesting device 10 further comprises ducts 17 located circumferentially

2 about the generator housing 14, as clearly shown by Figures 4 and 5. The ducts 17 take

3 the form of passageways between the first and second surfaces 11 , 12 suitable for

4 channelling a fluid flow 18 through the energy harvesting device 10. It will be appreciated

5 the fluid flow 18 could take the form of a gas flow or a liquid flow.

6

7 The cone-like portion 16 of the generator housing 14 diverts the fluid flow 18 towards the

8 ducts 17. It has been found preferable for efficient operation for the energy harvesting

9 device 10 as depicted in Figure 4 to comprise six ducts 17 located about the generator0 housing 14. Nevertheless, it will be appreciated an energy harvesting device with more or1 less ducts, for example three ducts, could also be envisaged. 2 3 Each duct 17 comprises an inlet opening 19 on the first surface 11 and a corresponding4 outlet opening 20 on the second surface 12. As can be seen in Figures 4 and 5, the ducts5 17 comprise a substantially trapezium cross-sectional shape. It will be appreciated the6 ducts 17 may have any suitable cross-sectional shape. 7 8 As shown in Figures 4 and 5, each duct 17 is uniform in size. As an alternative, it will be9 appreciated each duct 17 may have a different relative size, for example, according to the0 location of the duct 17 on the first surface 11 . 1 2 Figure 5 depicts a uniform cross-sectional shape of the duct 17 in the direction of the3 central axis 13. In other words, the cross-sectional shape does not change between the4 first and second surfaces 11 a, 12a. However, it will be appreciated there may be a5 variation in the cross-sectional shape, specifically a constriction, configured to modify the6 velocity of the fluid flow 18 through the energy harvesting device 10, in accordance with7 the Venturi effect. 8 9 Foils 0 1 The energy harvesting device 10 further comprises one or more foils 21 , located within2 each duct 17a, as shown in Figures 4 and 5. More specifically, the one or more foils 213 take the form of one or more aerofoils or one or more hydrofoils depending if the fluid flow4 18 is a gas flow or a liquid flow. 5 1 Common terms known in the art associated with a foil 21 , such as that depicted in Figures

2 4 and 5, are now defined. A foil 21 comprises a leading edge 22 and a trailing edge 23.

3 The leading edge 22, or foremost edge, is the first foil surface to meet an incident fluid flow

4 18. As such, the leading edge 22 separates the incident fluid flow 18. The trailing edge

5 23, or rearmost edge, is where the fluid flow 18 separated by the leading edge 22 meets.

6

7 The foil 21 also comprises a chord 24 and span 25. The chord 24 is the distance between

8 the leading and trailing edges 22, 23. Whereas the span 25 is the distance between a first

9 side 26 and a second side 27 of the foil 21 . In addition, a chord line 28 is defined as an0 imaginary straight line connecting the leading and trailing edge 22, 23. The foil 211 comprises a uniform cross section across the span 25. 2 3 Figures 4 and 5 depict various foils 21 mounted within ducts 17. The foils 21 are 4 orientated such that the leading edge 22 is located towards the inlet opening 19 and the5 trailing edge 23 is located towards the outlet opening 20. In other words, the chord6 direction of the foil 21 is substantially parallel to the central axis 13. 7 8 In operation, a fluid flow enters the ducts 21 through the inlet openings 19, flows past the9 foils 21 inducing aerodynamic or hydrodynamic forces and then exits the ducts 21 through0 the outlet openings 20. The foils 21 exhibits movement and it is the kinetic energy from1 this movement that the energy harvesting device 10 captures, transmits, and or converts2 into electrical energy. 3 4 Vibrational Members and Pressurised Energy Conversion System 5 6 The energy harvesting device 10 further comprises a pressurised energy conversion7 system 29 and vibrational members 30 to connect the one or more foils 21 to the 8 pressurised energy conversion system 29 as depicted in Figures 6 and 7. The pressurised9 energy conversion system 29 is employed to convert movement of the one or more foils 210 into electricity. 1 2 The vibrational member 30 comprises a first end 31 and a second end 32. The first end3 31 of each vibrational member 30 is attached to a first side 26 of a foil 21 . The 4 pressurised energy conversion system 29 is located at the second end 32 of the 5 vibrational members 30. Each vibrational members 30 extends from the foil 21 , passes 1 through the generator housing 14 and extends within the generator housing 14 to the

2 pressurised energy conversion system 29.

3

4 As can be seen in Figure 6, the energy harvesting device 10 comprises a bearing axle 33

5 orientated along a pivot axis 34 in the x-y plane. The motion of the vibrational member 30

6 is constrained by the bearing axle 33 as the vibrational member 30 is configured to pivot

7 about the bearing axle 33. In addition to this pivot motion, the vibrational member 30 can

8 also rotate about an axis 35 defined by the vibrational member 30 itself. The pivot axis 34

9 can be located between the first and second ends 31 , 32 of the vibrational member 30 or0 at the second end 32 of the vibrational member 30 as will be described below in the1 context of Figures 7 and 8. The bearing axle 33 facilitates transmitting the movement of2 the foil 21 to the pressurised energy conversion system 29. 3 4 Figure 6 depicts the motion, specifically four positions, exhibited by the vibrational member5 30 and foil 21 of the energy harvesting device 10. Figure 6 defines an x, y and z axis to6 aid the description of this motion. 7 8 Figure 6a depicts a first position 36, where the vibrational member 30 is angled at -a9 relative to a central pivot position 37 of the vibrational member 30. In the context of Figure0 6, the central pivot position 37 of the vibrational member 30 is defined as when the1 vibrational member 30 is parallel to the z axis. Furthermore, in the first position 36, the foil2 21 is orientated such that the chord 24 of the foil 21 is angled at - relative to a central3 rotation position 38 of the foil 21 . The central rotation position 38 of the foil 21 is defined4 as when the chord 24 of the foil 21 is parallel to the direction of the fluid flow 18, along the5 y direction. In operation, a fluid flow 18 along the y direction is incident upon the leading6 edge 22 of the foil 21 . The angle of attack of the foil 21 generates lift (F_L) in the positive x7 direction, inducing a pivoting motion of the vibrational member 30 about the bearing 33.8 This pivoting motion is limited by a first pivot stop 39 such that the vibrational member 309 stops in a second position 40 where the vibrational member 30 is angled at +a relative to0 the z axis as depicted by Figure 6b. 1 2 When in the second position 40, the weight and or inertia of the foil 21 results in a rotating3 force (FR) inducing a rotation motion of the foil 21 an axis 35 defined by the vibrational4 member 30 itself, the axis 35 extending between the first and second ends 31 , 32. This5 rotation is limited by a first rotation stop 41 . The rotation of the foil 21 reverses the angle 1 of attack of the foil 21 such that the chord 24 of the foil 21 is angled of +p relative to the

2 central rotation position 38 as can be by Figure 6c which depicts a third position 42. It will

3 be appreciated that the position of the axis 35 relative to the foil 21 , in particular, the

4 position of the axis 35 along the chord 24 of the foil 21 , determines the relative ease at

5 which the foil 21 will rotate. For example, the axis 35 may be offset closer to the leading

6 edge 22 of the foil 21 as opposed to the trailing edge 23. As such, the position of the axis

7 35 may be optimised such to achieve the desired rotation characteristic of the foil 21 .

8

9 In the third position, the fluid flow 18 about the foil 21 generates lift (F_L) in the negative x0 direction, inducing a relative reverse pivoting motion of the vibrational member 30 about1 the bearing 33. This reverse pivoting motion is limited by a second pivot stop 43 such that2 the vibrational member 30 stops in a fourth position 44 where the vibrational member 303 angled at -a relative to the central pivot position 37 as depicted by Figure 6d. 4 5 When in the fourth position 44, the weight and or inertia of the foil 21 again results in a6 rotating force (FR) inducing in a reverse rotation motion of the foil 21 about the axis defined7 by the vibrational member 30. This rotation is limited by a second rotation stop 45. After8 which, the chord 24 of the foil 21 is angled of -p relative to the central rotation position 38,9 thereby returning the arrangement to the first position 36 as depicted by Figure 6a. The0 pivot and rotation cycle repeats. 1 2 The first and second pivot stops 39, 43 limit the pivoting range of the vibrational member3 30. The position of the first and second pivot stops 39, 43 can be adjusted according to4 the desired pivot range. The vibrational member 30 may pivot between 1 and 89° either5 side of the central pivot position 37. Preferably, the vibrational member 30 pivots between6 1° to 30° either side of the central pivot position 37. Preferably, the vibrational member 307 pivots between 1° to 15° either side of the central pivot position 37. 8 9 Similarly, the first and second rotation stops 41 , 45, limit the rotation of the vibrational0 member 30 and as such the foil 21 . The position of the first and second rotation stops 41 ,1 45 can be adjusted according to the desired rotation range, in other words, the desired2 angle of attack of the foil 21 . The vibrational member 30 and foil 21 may rotate between 13 and 89° either side of the central rotation position 38. Preferably, the combination of the4 vibrational member 30 and foil 21 rotates between 1° to 35° either side of the central5 rotation position 38. 1

2 The pressurised energy conversion system 29 located at the second end 32 end of the

3 vibrational member 30 exhibits only a pivoting motion and not a rotation motion. The

4 rotation motion is isolated to the vibrational member 30 and foil 21 . As such, the pivot

5 motion drives the pressurised energy conversion system 29 whereas the rotation motion

6 perpetuates and or assists the pivot motion.

7

8 The pressurised energy conversion systems 29 generally comprises a working fluid 46, a

9 fluid displacement device 47 and a generator 48, as can be seen in Figures 7 to 19. The0 fluid displacement device 47 is configured to be driven by the movement of the foils 21 .1 The fluid displacement device 47 is fluidly connected to the generator 47 by pipes 49. The2 fluid displacement device 47 displaces, pumps and or pressurises the fluid 46 which in turn3 drives the generator 47, thereby generating electricity. It will be appreciated that the4 generator 47 may comprise an integral impeller suitable for driving the generator 47. 5 6 In the embodiment of the pressurised energy conversion system 29a of Figure 7, the pivot7 axis 34 is located at the second end 32 of the vibrational member 30. Furthermore, the8 fluid displacement device 47 takes the form of a rotary positive displacement pump 509 mounted to the bearing axle 33. It will be appreciated by the skilled person that the fluid0 displacement device 47 could alternatively take the form of a semi-rotary actuator. 1 2 In operation, the pivoting motion of the foil 21 in the x-z plane, about the pivot axis 34,3 rotates the bearing axle 33 and thereby the rotary positive displacement pump 50. 4 Working fluid 46 is pumped by the rotary positive displacement pump 50 to a reservoir 51 ,5 also termed accumulator or pressure accumulator. The fluid pressure builds within the6 reservoir 51 as the rotary positive displacement pump 50 continues to pump the working7 fluid 46. Once the fluid pressure within the reservoir 51 reaches a threshold value, a8 control valve 52 opens, allowing the working fluid 46 to flow to and drive a generator 48. 9 After exiting the generator 48, the working fluid 46 is at atmospheric pressure and is then0 recirculated back to the rotary positive displacement pump 50, via the pipes 49, to be1 repressurised. As an alternative, it will be appreciated that the pressurised energy2 conversion system 29 may be a closed loop such that the working fluid 46 remains3 pressurised once exiting the generator 48 on the return line to the rotary positive 4 displacement pump 50. Once the reservoir 51 has been depleted the control valve 525 closes such that the reservoir 51 can be replenished with the working fluid 46 displaced by 1 the rotary positive displacement pump 50. This pulsed accumulation and release of

2 working fluid 46 within the reservoir 51 by means of the control valve 52 is repeated. In a

3 further alternative some of the pressurised work fluid can be by-passed from the cylinder

4 and or the accumulator, and or a motor could be used in a suction line to assist the aerofoil

5 in moving at lower wind speeds through re-generative action.

6

7 It will be appreciated that in an alternative embodiment, the generator 48 may be driven

8 directly by the working fluid 46 displaced by the rotary positive displacement pump 50,

9 without a reservoir 51 and control valve 52. However, depending on the configuration of0 the energy harvesting device 10, specifically, the capacity of the rotary positive 1 displacement pump 50 relative to flow and or pressure of the working fluid 46 required to2 drive the generator 48, the reservoir 51 and control valve 52 may be advantageous. For3 example, if the working fluid 46 displaced by the rotary positive displacement pump 50 is4 small relative to that required drive the generator 48, then the reservoir 51 and control5 valve 52 is required for efficient operation. Furthermore, generators 48 known in the art6 are typically more efficient and exhibit less mechanical stress when driven at a constant7 speed. The reservoir 51 and control valve 52 advantageously facilitate accumulating the8 displaced fluid and releasing the working fluid 46 in a controlled, constant flow rate and or9 pressure. 0 1 As an optional, additional feature, the reservoir 51 may comprise a flexible diaphragm 53. 2 The diaphragm 53 is distorted to accommodate an increase in working fluid 46 within the3 reservoir 51 . Furthermore, when the working fluid 46 is released by the control valve 52,4 the elasticity of the diaphragm 53 facilitates maintaining a constant flow and or pressure5 for a set time period. In other words, the diaphragm 53 pushes the working fluid 46 out of6 the reservoir 51 . 7 8 Figure 8 depicts an alternative embodiment of the pressurised energy conversion system9 29b which may comprise the same preferable and optional features as the energy 0 conversion system 29a depicted in Figure 7. In contrast to Figure 7, the pivot axis 34 is1 located between the first and second ends 31 , 32 of the vibrational member 30. 2 Furthermore, the fluid displacement device 47 takes the form of a linear positive 3 displacement pump, specifically, a piston 54. The second end 32 of the vibrational4 member 30 is connected to the piston 54 by an appropriate mechanical connection 55,5 such as a slider-crank mechanism which, in operation, converts the pivoting motion of the 1 second end 32 of the vibrational member 30 in a linear motion suitable for driving the

2 piston 54.

3

4 As an additional, optional feature, the piston 54 may be biased with a spring 56.

5 Advantageously, the spring 56 may assist moving the piston 54 when the pivoting motion

6 of the vibrational member 30 of insufficient force to move the piston 54 itself. The spring

7 56 facilitates operating with a low energy fluid flow incident upon the foils 21 .

8

9 As a further additional, optional feature, there may be a non-return valve 57 located in the0 pipe 49 between the piston 54 and the reservoir 51 . In operation, if there was a reverse1 fluid pressure from the reservoir 51 towards the piston 54 that exceeded driving force of2 the pivoting vibrational member 30, the non-return valve 57 would ensure the reverse fluid3 pressure did not actuate the piston 54. Similarly, as an additional or alternative feature,4 there may also be a non-return valve 57 on the return pipe 49 between the generator 485 and the piston 54 to ensure there is not a reverse fluid pressure on the generator 48.6 7 The movement of the foils 21 depicted within Figures 4 to 8 is independent. In other8 words, the movement of the foils 21 is not constrained the movement of any other foil 21 . 9 Advantageously, the independent movement of the foils 21 facilitates efficiently capturing0 the energy within a turbulent fluid flow 18 as each independent foil 21 can respond to1 localised spatial variations in the turbulent fluid flow 18. 2 3 Figure 9 depicts a further alternative embodiment of the pressurised energy conversion4 system 29c which may comprise the same preferable and optional features as the energy5 conversion systems 29a, 29b depicted in Figures 7 and 8. Figure 9 shows a hexagonal6 cross section in x-z plane of the energy harvesting device 10 and, specifically, shows four7 of the six ducts 17. As can been seen, located within each of these four ducts 17 is a foil8 21 and a vibrational member 30 mounted radially relative to the central axis 13 of the9 energy harvesting device 10. The four vibrational members 30 are all connect to a0 mechanical connection 55 located at the central axis 13. Advantageously, this 1 embodiment requires fewer components as does not require a mechanical connection 552 and a piston 54 for each vibrational members 30. Furthermore, in conditions where a3 single foil 21 does not have enough force to drive a piston 54, multiple vibrational4 members 30 may advantageously be able to drive the single piston 54 in such conditions,5 as the multiple members 30 are mechanically connected together and to the same piston 1 54. It will be appreciated that more or less than four vibrational members 30 may be

2 connect to a mechanical connection 55 and a piston 54. It will be appreciated as a further

3 alternative embodiment, multiple vibrational members 30 and associated foils 21 within a

4 single duct 17 may all be connected to a mechanical connection 55 and a piston 54.

5 Depending on the nature of the mechanical connection 55 the movement of the foils 21

6 may be dependent or independent, but it may be advantageous to maintain an angular

7 offset between each of the foils 21 .

8

9 Figure 10 depicts another alternative embodiment of the pressurised energy conversion0 system 29d which may comprise the same preferable and optional features as the energy1 conversion systems 29a, 29b, 29c, depicted in Figures 7 to 9. Figure 10 shows a 2 perspective view of a duct 17 of the energy harvesting device 10. The duct 17 comprises3 three foils 21 arranged along the z-direction, the direction of the incident fluid flow 18.4 Each foil 21 is connected to a vibrational member 30 which pivots in the x-z plane and5 drives a piston 54 via a mechanical connection 55. The three pistons 54 pump the6 working fluid 46 to one common reservoir 51 . As with previous embodiments, a control7 valve 52 releases the working fluid 46 from the reservoir 51 to drive a generator 48, after8 which the fluid is recirculated to each piston 54. The movement of the foils 21 depicted in9 Figure 10 are independent as each foil 21 connects to a separate mechanical connection0 55 and piston 54. 1 2 Figure 11 depicts another alternative embodiment of the pressurised energy conversion3 system 29e which may comprise the same preferable and optional features as the energy4 conversion systems 29a, 29b, 29c, 29d depicted in Figures 7 to 10. Similar to Figure 10,5 Figure 11 shows a perspective view of a duct 17 of the energy harvesting device 10. The6 duct 17 comprises two foils 21a, 21 b arranged along the z-direction with a first windward7 foil 21 a and a second leeward foil 21 b. The first foil 21 a is angled at +a relative to the z8 axis and the second foil 21b is angled at -a relative to the z axis. In other words, the9 phase of the pivoting motion exhibited by the first and second foils 21a is offset by half a0 cycle. This phase offset may advantageously enhance the operation and or efficiency of1 the energy harvesting device 10. 2 3 The first foil 21a is connected to a first mechanical connection 55a which is in turn4 connected to a first piston 54a. Similarly, the second foil 21 b is connected to a second5 mechanical connection 55b which is in turn connected to a second piston 54b. The phase 1 offset between the two foils 21 a, 21 b is provided by fluidly connecting the first and second

2 pistons 54a, 54b such that when the first piston 54a is exhibiting a forward stroke, the

3 second piston 54b is exhibiting a reverse stroke and vice versa.

4

5 More specifically, there are two fluid paths from the generator 48 to the reservoir 51 with

6 four non-return valves 57 to control the fluid flow. When the first piston 54a is exhibiting a

7 forward stroke and the second piston 54b is exhibiting a reverse stroke, the working fluid

8 46 will flow along the path depicted by the red dashed arrows, namely through: a non¬

9 return valve 57, the first piston 54a, the second piston 54b and a further non-return valve0 57. Conversely, when the first piston 54a is exhibiting a reverse stroke and the second1 piston 54b is exhibiting a forward stroke, the working fluid 46 will flow along the path2 depicted by the blue solid arrows, namely through: a non-return valve 57, the second3 piston 54b, the first piston 54a and a further non-return valve 57. Whilst the movement of4 the first and second foils 21 a, 21 b may be dependent, the movement of these two foils5 21 a, 21 b may be independent of other foils 21 within the energy harvesting device 10.6 7 Figure 12 depicts an alternative embodiment of the pressurised energy conversion system8 29f which may comprise the same preferable and optional features as the energy 9 conversion systems 29a, 29b, 29c, 29d, 29e depicted in Figures 7 to 11 . Similar to Figure0 8, the pivot axis 34 depicted in Figure 12 is located between the first and second ends 31 ,1 32 of the vibrational member 30 and furthermore the fluid displacement device 47 takes2 the form of a piston 54. However, in contrast to Figure 8, the piston 54 of Figure 12 is3 connected to the vibrational member 30 between the pivot point 34 and first end 31 of the4 vibrational member 30 instead of between the pivot point 34 and the second end 32 of the5 vibrational member. The piston 54 and vibrational member 30 are connected by an6 appropriate mechanical connection 55. 7 8 The piston 54 of the pressurised energy conversion systems 29b depicted in Figure 8 is9 required to exert a forward pressure towards the reservoir 51 such that there is not a0 reverse pressure acting on the piston 54. Whilst this can be mitigated with control valves1 57, it is desirable for efficient operation that the piston 54 is configured such that it can2 always provide a forward pressure to the reservoir 51 despite the variable force exhibited3 at the second end 32 of the vibrational member 30 due to a variable turbulent fluid flow 184 as now further discussed. 5 1 Dynamic Variation of the Resistive Force

2

3 The speed of the fluid flow incident upon the energy harvesting device 10 continually

4 varies, as illustrated by Figure 2. Furthermore, the direction and or orientation of the fluid

5 flow relative to the energy harvesting device 10, and particularly the ducts 17 also varies.

6 As such, there is a variation in the lift generated by the foils 21 and consequently so to the

7 generated torque. The torque represents, and is proportional to, the average hydraulic

8 pressure that could be generated by a fluid displacement device 47.

9 0 Note that direction and or orientation may be used interchangeably but are also intended1 to describe direction in the conventional sense (e.g. N, NE, E, SE, S, SW, W, NW and2 anywhere inbetween) and orientation being an angular value relative to the horizontal (e.g. 3 plus or minus x degrees). It will therefore be understood that changes in direction may or4 may not also involve a change in orientation, and vice versa. 5 6 Table I quantifies the variation in torque, the pivoting frequency and average hydraulic7 pressure of an energy harvesting device calculated for a given fluid flow speed. A 8 variation in fluid flow speed of 4 to 14 m/s, results in the torque between 1.05 Nm to 12.899 Nm and an average hydraulic pressure of 10 to 135 bar. 0 1 Table I: Projected torque, pivoting frequency and average hydraulic pressure of an energy2 harvesting device calculated for a given fluid flow speed.

1 The pressurised energy conversion system 29 exhibits a resistive force determined by, for

2 example, the configuration of the reservoir 51 or even the one or more fluid displacement

3 devices 47.

4

5 Consider a pressurised energy conversion system 29 comprising a reservoir 51 with a

6 diaphragm 53 tensioned for a particular pressure, such as 70 bar. In this case, if the inlet

7 fluid flow speed is 6 m/s, which accordingly to Table I would only generate an average

8 hydraulic pressure of 25 bar, this would not be sufficient to move the 70 bar rated

9 diaphragm 53 and so the reservoir 51 would not be pressurised. In other words, the0 resistive force of the pressurised energy conversion system 29 is too high for an inlet fluid1 flow speed of 6 m/s. As such, the one or more fluid displacement devices 47, and so to2 the foils 21 , would not move. 3 4 Conversely, if the inlet fluid flow speed is 14 m/s, the average generated hydraulic 5 pressure is 134 bar according to Table I, which would readily overcome the 70 bar rated6 diaphragm 53 and pressurise the reservoir 51 . The resistive force of the pressurised7 conversion system 29 is too low for an inlet wind speed of 14 m/s. As such, the one or8 more fluid displacement devices 47, and so to the foils 21 , may move too quickly resulting9 in damage to the energy harvesting device 10. 0 1 The embodiments of the pressurised energy conversion systems presented in Figures 132 to 20 present alternative, additional and or optional features to dynamically vary the3 resistive force of the pressurised energy conversion system. The dynamic variation in the4 resistive force compensates for the variability in a turbulent fluid flow, and or maintains5 efficient operation of the energy harvesting device 10 and or maximises the energy6 harvested. 7 8 The dynamic variation in the resistive force is dependent on a variation in lift generated by9 the one or more foils. The variation in lift is due to the variability in the fluid flow incident0 upon the foils. Additionally, and or alternatively, the dynamic variation in the resistive force1 is dependent on a variation in the energy of a fluid flow incident upon the one or more foils. 2 The variation in the energy of a fluid flow is measured at a mid-section of the one or more3 ducts. The energy of the fluid flow is dependent on parameters comprising: the fluid flow4 velocity, the fluid flow direction, the fluid flow orientation as well as environmental 5 parameters such as temperature and humidity. 1

2 In operation, it is not possible to modify the resistive force of the pressurised energy

3 conversion system 29 by dynamically changing the dimensions of the one or more fluid

4 displacement devices 47, such as the diameter and or volume. Instead, these

5 embodiments change the resistive force by: (a) varying a flow rate of the working fluid

6 displaced by the one or more fluid displacement devices; and or (b) the pressurised

7 energy conversion system comprising two or more reservoirs 51 . The two or more

8 reservoirs configured to operate at two or more different pressures.

9 0 Force is proportional to the product of pressure and fluid flow rate. As such, in an instant1 of low energy fluid flow 18, where the force exhibited at the second end 32 of the 2 vibrational member 30 is relatively small, it is still possible to achieve the desired pressure3 towards the reservoir 51 by varying the flow rate of the working fluid 46. 4 5 Figure 13 depicts an alternative embodiment of the pressurised energy conversion system6 29g which may comprise the same preferable and optional features as the energy7 conversion systems 29a, 29b, 29c, 29d, 29e, 29f depicted in Figures 7 to 12. In contrast8 to Figure 8, Figure 13 depicts a spring 56 located between the mechanical connection 559 at the second end 32 of the vibrational member 30 and the piston 54. The spring 560 facilitates varying the stroke length of the piston 54 according to the variation in applied1 force at the second end 32 of the vibrational member 30. This varies the volume of2 working fluid 46 displaced by the piston 54, in other words the flow rate of the working fluid3 46. As a results, the pressure of the working fluid 46 can be varied as required. 4 5 Figure 14 depicts an alternative embodiment of the pressurised energy conversion system6 29h which may comprise the same preferable and optional features as the energy7 conversion systems 29a, 29b, 29c, 29d, 29e, 29f, 29g depicted in Figures 7 to 13. In8 contrast to Figure 13, instead of the spring 56, Figure 14 depicts a second fluid 9 displacement device 47b (also termed pre-fluid displacement device) before the main first0 fluid displacement device 47a. In Figure 14, the first and second fluid displacement1 devices 47a, 47b take the form of pistons 54a, 54b. However, it will be appreciated that2 first and second fluid displacement devices 47a, 47b may be of any type and may be of3 the same of different types. In operation, the second piston 54b modifies, for example,4 amplifies the pressure by varying the flow rate before acting upon the first piston 54a. 5 1 Figure 15 depicts an alternative embodiment of the pressurised energy conversion system

2 29i which may comprise the same preferable and optional features as the energy

3 conversion systems 29a, 29b, 29c, 29d, 29e, 29f, 29g, 29h depicted in Figures 7 to 14. In

4 contrast to Figures 14, the pressurised energy conversion system 29i of Figure 15

5 additional comprises a motor 58 between the first and second pistons 54a, 54b. As an

6 alternative embodiment it will be appreciated that there may be a motor 58 located

7 between the reservoir 51 and the generator 48 instead of, or even in addition to, the motor

8 58 between the first and second pistons 54a, 54b. Furthermore, the motor 58 may

9 alternatively take the form of a pump. Additionally, a gearbox may be attached to each0 motor and or pump. The motor(s) 58 and or pump(s) further facilitate modifying the1 pressure and or flow rate of the working fluid 76 as required accordingly to the variation in2 the turbulent fluid flow 18. 3 4 Figure 16 depicts an alternative embodiment of the pressurised energy conversion system5 29j which may comprise the same preferable and optional features as the energy 6 conversion systems 29a, 29b, 29c, 29d, 29e, 29f, 29g, 29h, 29i depicted in Figures 7 to7 15. In contrast to Figure 8, instead of the non-return valves 57, Figure 16 comprises8 proportional flow valves 59. The proportional flow valves 59 have a dynamically variable9 constriction which alters the flow rate of the working fluid 46 and thereby the pressure of0 the working fluid 46. Whilst Figure 16 depicts two proportional flow valves 59, it will be1 appreciated there may be more or less proportional flow valves 59 located within the2 pressurised energy conversion system 29j as required. It will be further appreciated that3 the proportional flow valves 59 may be controlled mechanically and or electronically.4 5 Figure 17 depicts an alternative embodiment of the pressurised energy conversion system6 29k which may comprise the same preferable and optional features as the energy 7 conversion systems 29a, 29b, 29c, 29d, 29e, 29f, 29g, 29h, 29i, 29j depicted in Figures 78 to 16. As can be seen, the embodiment of Figure 17 additionally comprises an expansion9 chamber 60 located between the piston 54 and the reservoir 51 . Additional working fluid0 46 is introduced to the working fluid 46 displaced from the piston 54 in the expansion1 chamber 60. This changes the volume of working fluid 46, modifying the flow rate and or2 pressure of the working fluid 46. 3 4 Figure 18 depicts an alternative embodiment of the pressurised energy conversion system5 29I which may comprise the same preferable and optional features as the energy 1 conversion systems 29a, 29b, 29c, 29d, 29e, 29f, 29g, 29h, 29i, 29j , 29k depicted in

2 Figures 7 to 17. In the embodiment of Figure 18, the piston 54 displaces working fluid

3 towards a pressure dependent non-return valve 61 . The pressure dependent non-return

4 valve 61 is connected to three reservoirs 51a, 51b, 51c. Each of the three reservoirs 51a,

5 51b, 51c are connected to a generator 48a, 48b, 48c. Each of the generators 48a, 48b,

6 48c have a different optimum operational pressure and or flow rates, as determined for

7 example by the tension of the diaphragm 53. In operation, the pressure dependent non¬

8 return valve 61 selectively directs displaced working fluid 46 from the piston 54 to a

9 reservoir 51 a, 51 b, 51c, and corresponding generator 48a, 48b, 48c according to the0 pressure and or flow rate of the working fluid 46. Advantageously, each generator 48a,1 48b, 48c operates within the optimum operational parameters despite the turbulent fluid2 flow 18 resulting a variation in the pressure and or flow rate of the working fluid 46. The3 resistive force of this pressurised energy conversion system 29I is modified by selecting an4 appropriate reservoir 51 to direct the working fluid 46 according to the variation in the fluid5 flow 18 incident upon the foils 21 . 6 7 Figure 19 depicts an alternative embodiment of the pressurised energy conversion system8 29m which may comprise the same preferable and optional features as the energy9 conversion systems 29a, 29b, 29c, 29d, 29e, 29f, 29g, 29h, 29i, 29j, 29k, 29I depicted in0 Figures 7 to 18. The embodiment of Figure 19 comprises a first and second piston 54a,1 54b, a first and second reservoir 51a, 51b and a first and second control valve 52a, 52b. 2 The second end 32 of the vibrational member 30 is connected the first piston 54a, which3 displaces working fluid 46 towards a first reservoir 51a. A first control valve 52a releases4 the working fluid 46 towards a second piston 54b which displaces fluid towards a second5 reservoir 52b. The second control valve 52b releases the working fluid 46 towards a6 generator 48. The components 54a, 54b, 51 a, 51b, 52a, 52b facilitate further modification7 and control of the flow rate and or pressure of the working fluid 46 directed towards the8 generator 48. 9 0 Figure 20 depicts alternative embodiments of the pistons 54 as shown in Figures 8 to 19. 1 Instead of a single piston 54, the pressurised energy conversion systems 29 may comprise2 multiple pistons 54, for example, three pistons 54a, 54b, 54c as depicted in Figure 20a.3 The three pistons 54a, 54b, 54c of Figure 20a are of equal size, in other words capacity. 4 In operation, in an instant of high energy fluid flow 18, the force at the second end 32 of5 the vibrational members 30 may be sufficient to actuate all three pistons 54a, 54b, 54c. 1 Conversely, in an instant of low energy fluid flow 18, the force at the second end 32 of the

2 vibrational members 30 may be sufficient to actuate just one of the three pistons 54a, 54b,

3 54c. In other words, multiple pistons 54a, 54b, 54c provides a means for varying the

4 volume of displaced working fluid 46 and consequently to flow rate and or pressure of the

5 working fluid 46.

6

7 As a further alternative to the single piston 54 as shown in Figures 8 to 19, Figure 20b

8 depicts three pistons 54a’, 54b’, 54c’ of varying size. The larger piston 54c’ displaces a

9 larger volume of working fluid 46 relative to smaller piston 54a’. As such, this facilitates0 maximising the energy harvested over a greater range of fluid flow 18 conditions. At an1 instant of very low energy fluid flow 18, there is still sufficient force to actuate the small2 piston 54a’. Whereas at an instant of very high energy fluid flow 18, there is sufficient3 force to actuate all three pistons 54a’, 54b’, 54c’, with the larger piston 54c’ maximising the4 displaced working fluid 46. 5 6 As a further alternative, instead of separate pistons 54a’, 54b’, 54c’ of varying size, the7 same functionality may be achieved with a single piston 54” with two or more openings8 62a, 62b of varying size within single piston 54” as depicted in Figure 20c. 9 0 Figures 21 A and 21 B depict an alternative embodiment of the pressurised energy 1 conversion system 29n which may comprise the same preferable and optional features as2 the energy conversion systems 29a, 29b, 29c, 29d, 29e, 29f, 29g, 29h, 29i, 29j , 29k, 29I,3 29m depicted in Figures 7 to 20. In the embodiment of Figures 20A and 20B the pivoting4 motion of the foil 21 and vibrational member 30 is converted into a rotational or semi5 rotational movement by an appropriate mechanical connection 55 at the second end 32 of6 the vibrational member 30. This rotational or semi rotational movement drives a shaft 63,7 which in turn drives the fluid displacement device 47 in the form of a swash plate piston8 arrangement 64. The swash plate piston arrangement 64 comprises a swash plate 65, a9 set of pistons 66 arranged circumferentially about a central axis 67 and a commensurate0 piston block 68. Advantageously, the pitch of the swash plate 65 relative to the central1 axis 67 can be dynamically varied to vary the volume of the working fluid 46 displaced by2 the set of pistons 66, which can been seen on comparison of Figures 20A and 20B. In3 other words, this modifies and or controls and or matches the flow rate of the working fluid4 46 directed towards the generator 48. The pitch of the swash plate 65 can be adjusted by5 a hydraulic and or a mechanical means. 1

2 Figure 22 depicts an alternative embodiment of the pressurised energy conversion system

3 29o which may comprise the same preferable and optional features as the energy

4 conversion systems 29a, 29b, 29c, 29d, 29e, 29f, 29g, 29h, 29i, 29j, 29k, 29I, 29m, 29n

5 depicted in Figures 7 to 21 . Similar to the embodiment of Figure 18, one or more pistons

6 54 displace working fluid 46 towards a pressure dependent non-return valve 61 . The

7 pressure dependent non-return valve 61 is connected to three reservoirs 51 a, 51b, 51c.

8 The reservoirs 51a, 51b, 51c are configured to operate at fluid pressures of 10 bar, 70 bar

9 and 100 bar. In operation, the pressure dependent non-return valve 61 selectively directs0 working fluid 46 displaced by the pistons 54 to one of the three reservoirs 51a, 51 b, 51c1 dependent on the pressure of the working fluid 46. The pressure dependent non-return2 valve 61 selectively directs working fluid 46 based on inputs such as the fluid flow speed at3 the inlet. The resistive force of the pressurised energy system is dynamically varied by4 selecting a different pressure rated reservoir 51a, 51b, 51c. In contrast to Figure 18, the5 embodiment of Figure 22 comprises one generator 48 suitable to be driven by the 70 bar6 reservoir 51 b. The lower (10 bar) and higher (100 bar) pressure reservoirs 51 a, 51c7 pressurise the 70 bar reservoir 51b by means of a pressure intensifier 69, which increases8 (or decreases) the pressure based on a differential piston principle where a larger 9 diameter piston pushes a smaller diameter piston (or vice versa). Advantageously, despite0 the variation in the fluid flow 18, this configuration of the pressurised energy conversion1 system 29o optimises the energy captured. 2 3 The various embodiments of the pressurised energy conversion system 29 of Figures 7 to4 22 have been described above in the context of a working fluid 46. It will be appreciated5 that the working fluid 46 may be a liquid or a gas and so the pressurised energy 6 conversion system 29 is a hydraulic or pneumatic energy conversion system. 7 8 The foils 21 of the energy harvesting device 10 may be configured to have a response9 time of less than 60 seconds or less than 30 seconds or less than 10 seconds or less than0 5 seconds or of the order of a second. In other words, the foils 21 may have a low inertia. 1 The foils may be small and light weight relative to the incident fluid flow 18. 2 3 Advantageously, the movement of the foils 21 can respond to temporal variations in a4 turbulent fluid flow 18, efficiently capturing energy. 5 1 The energy harvesting device 10 comprises a plurality of foils 21 . More specifically, Figure

2 4 depicts two foils 21 in each of the six ducts 17 of the energy harvesting device 10. It will

3 be appreciated that each duct 17 may comprise more or less foils 21 and the energy

4 harvesting device 10 may comprise more or less ducts 17. The energy harvesting device

5 10 comprises multiple vibrational members 30. A single foil 21 is attached to a single

6 vibrational member 30 which is in turn connected to the pressurised energy conversion

7 system 29. The pressurised energy conversion 29 system may comprise a single fluid

8 displacement device 47 connected to multiple vibrational members 30 or even a fluid

9 displacement device 47 connected to each vibrational member 30. The one or more fluid0 displacement devices 47 may be connected to one or more reservoirs 51 . The one or1 more fluid displacement devices 47 may drive one or more generators 48. 2 3 Energy Harvesting System 4 5 Figure 23 shows an energy harvesting system 70 comprising a plurality of energy 6 harvesting devices 10. The energy harvesting system 70 comprises more foils 21 than a7 single energy harvesting devices 10 and so has a greater capacity to harvest energy from8 a fluid flow 18. The energy harvesting system 70 may take the form of a wall, a fence,9 panels for a structure or building or even a component within a structure. The energy0 harvesting system 70 may be located in regions of high fluid flow 18, and particularly high1 turbulent fluid flow 18. 2 3 As an example, for a wind energy harvesting system 70 where the fluid of the fluid flow 184 is air, high turbulent air flow could be found near a motorway, an airport or even on a high-5 rise building. 6 7 As another example, for a liquid flow energy harvesting system 70 where the fluid of the8 fluid flow 18 is, for example water, high turbulent water flow could be found at a tidal9 barrier, a tidal estuary, a dam, river flood defences, bridge supports or even within water0 transport pipes. It will be appreciated that a liquid flow energy harvesting system 70 would1 be submerged under water. 2 3 The energy harvesting system 70 depicted in Figure 12 comprises a centralised reservoir4 51 and a centralised generator 48. More specifically, the fluid displacement devices 475 within each energy harvesting device 10 displace the working fluid 46 of the pressurised 1 energy conversion system 29 to the centralised reservoir 51 , which drives a centralised

2 generator 48. Advantageously, the energy harvesting system 70 only requires one

3 generator 48 and the generator 48 may be a high capacity generator.

4

5 Rotary Energy Harvesting Device

6

7 Figures 24 and 25 depict a rotary energy harvesting device 71 a. As can be in Figure 22,

8 the energy harvesting device 71a comprising a central spindle 72 having a central axis S.

9 Mechanically connected to the central spindle 72 is a two radial arms 73 extending radially0 from the central spindle 72. Each radial arm 73 is mechanically connected to the central1 spindle 72 through a gear arrangement 74. Each radial arm 73 has a central axis R and2 comprises two turbines 75 mechanically connected to the radial arm 73. The turbines 753 are mechanically connected to the radial arm 73 through another gear arrangement 74. 4 Each turbine 75 comprises three foils 76 radially extending from a turbine rotation axis 77. 5 6 The energy harvesting device 71 a comprises a pressurised energy conversion system 297 such as that depicted in Figures 7. A fluid displacement device 47 is mechanically8 attached to the central spindle 72. 9 0 In operation, a fluid flow 18 flows past the foils 76 inducing lift. This lift causes rotation of1 the foils 76, which rotates about the turbine rotation axis 77. Through the gear 2 arrangements 74, rotation of the turbine 75 causes rotation of the radial arm 73 about its3 central axis R and thereby rotation of the central spindle 72 about its central axis S. Thus,4 rotation of the turbine 75 drives rotation of the radial arm 73 about both its central axis R5 and the central axis S of the central spindle 72. The pressurised energy conversion6 system 29 converts movement of the central spindle 72 into electricity in a similar manner7 to that described in the context of Figure 7. 8 9 The turbine 75 comprises three foils 76, but it will be appreciated that the turbine 75 may0 comprise any suitable number of foils 76. Additionally, it will be appreciated that the exact1 shape and dimensions of the foils 76 is not critical to the invention and thus can be any2 suitable shape and dimension. 3 4 Figure 25 depicts an alternative rotary energy harvesting device 71b. This energy5 harvesting device 71b comprises all the features of the energy harvesting device 71 a 1 depicted Figure 24. In addition, the energy harvesting apparatus further comprises an

2 additional radial arm 73 and an additional turbine 75 on each radial arm 73, such that each

3 radial arm 73 comprises three turbines 75. The central spindle 72, radial arms 73 and

4 turbines 75 are located within a duct 78. The central spindle 72 is located centrally within

5 the duct 78, with each radial arm 73 extending to the internal perimeter of the duct 78.

6 Advantageously, the duct 78 acts to channel the fluid flow 18 through the energy

7 harvesting apparatus 71b.

8

9 As depicted in Figure 25, the duct 78 has a substantially circular cross-sectional shape. 0 However, it will be appreciated that the duct 78 may have any suitable cross-sectional1 shape. 2 3 As an additional, optional feature, it will be appreciated that the radial arms 73 may be4 radially distributed about the central spindle 72 and or distributed along the length of the5 central spindle 72. 6 7 The energy harvesting device 71 of Figures 24 and 25 advantageously captures a greater8 sweepable area (i.e., the cross-sectional area of a fluid flow 18 that may contact a turbine9 75) than conventional horizontal-axis wind turbines, and thus increases the efficiency of0 energy capturing. This is because the energy harvesting device 71 captures a larger1 portion of the fluid flow 18 energy incident upon the device 71 . Furthermore, as the foils2 are relatively small and or have a low inertia in comparison to a conventional horizontal¬3 axis wind turbine, the energy harvesting device 71 has a much smaller response time of4 the order of a second. This small response time facilitates efficiently capturing energy5 from a turbulent fluid flow. 6 7 Method of Manufacturing an Energy Harvesting Device 8 9 Figure 26 depicts a flow chart for a method of manufacturing an energy harvesting device0 10. The method comprises: providing one or more foils 21 configured to respond to1 changes in a fluid flow with a response time of less than 60 seconds (S1001); providing a2 working fluid 46 of a pressurised energy conversion system 29 (S1002); providing at least3 one fluid displacement device 47 of the pressurised energy conversion system 29, the at4 least fluid displacement device 47 configured to be driven by movement of the one or more 1 foils 21 (S1003); and providing a generator 48 configured to be driven by the working fluid

2 46 (S1004).

3

4 In alternative methodologies, there may be provided a method which further comprises

5 characterising the fluid flow 18. For example, this may include characterising: the mean

6 fluid flow speed, fluid flow speed distribution, turbulence, turbulent intensity, fluid flow

7 shear profile, distribution of fluid flow direction, long-term temporal fluid flow variations and

8 localised spatial variation of the fluid flow.

9 0 In alternative methodologies, there may be provided a method which further comprises1 utilising the characteristics of the fluid flow 18 to determine the optimum parameters of the2 energy harvesting device 10. For example, this optimisation process may include 3 determining: the dimensions of the energy harvesting device 10; the dimension and or4 shape of the duct(s) 17; the shape, structure, configuration and or relative positioning of5 the foils 21 ; and the configuration of the pressurised energy conversion system 29. 6 7 The energy harvesting device 10, 71 in accordance with the present invention has 8 numerous advantages. A key advantage is that the energy harvesting device 10, 719 efficiently captures energy from a turbulent fluid flow 18 as has a fast response time of less0 than 60 seconds and, more specifically, of the order of a second. In other words, the foils1 21 have a low inertia. This results in the movement of the foils 21 reflecting the fluid flow2 conditions at that instant in time instead of a previous instant in time. 3 4 Another key advantage is that the movement of at least two of the foils 21 of the energy5 harvesting device 10, 71 is independent. In other words, the independent foils 21 can6 respond to localised spatial variations in the turbulent fluid flow 18 and so more efficiently7 capture energy without inducing mechanical stress upon the components of the energy8 harvesting device 10, 71. 9 0 A further key advantage is the combination of the energy harvesting device 10, 71 with the1 pressurised energy conversion system 29. The pressurised energy conversion system 292 provides greater flexibility and simplicity when designing and implementing the energy3 harvesting device 10, 71 . For example, multiple foils 21 can easily be coupled to a4 pressurised energy conversion system 29. 5 1 Another advantage of the present invention is that one cycle of the one or more foils 21

2 equates to one cycle of the one or more fluid displacement devices 47. More specifically,

3 in the context of Figure 8, a full cycle of the pivot motion of the foil 21 equates to a full

4 stroke cycle of the piston 54. This configuration results in a responsive energy harvesting

5 device, not only due to the small response time of the foils, but also with respect to the fast

6 conversion of the kinetic energy.

7

8 Another key advantage is that the energy harvesting device of the present invention can

9 dynamically modify the resistive force of the pressurised energy conversion system to0 compensate for the variation in fluid flow speed and or direction and or orientation. This1 maximises the energy captured from a variable fluid flow as the movement of the foils is2 not limited by the pressurised energy conversion system. 3 4 An energy harvesting device is disclosed. The energy harvesting device comprises one or5 more foils and a pressurised energy conversion system. The pressurised energy 6 conversion system comprises a working fluid, one or more fluid displacement devices7 configured to be driven by movement of the one or more foils and one or more generators8 configured to be driven by the working fluid. Advantageous, the energy harvesting device9 can efficiently harvest energy from a turbulent fluid flow. 0 1 Throughout the specification, unless the context demands otherwise, the terms “comprise”2 or “include”, or variations such as “comprises” or “comprising”, “includes” or “including” will3 be understood to imply the inclusion of a stated integer or group of integers, but not the4 exclusion of any other integer or group of integers. Furthermore, unless the context clearly5 demands otherwise, the term “or” will be interpreted as being inclusive not exclusive.6 7 The foregoing description of the invention has been presented for purposes of illustration8 and description and is not intended to be exhaustive or to limit the invention to the precise9 form disclosed. The described embodiments were chosen and described in order to best0 explain the principles of the invention and its practical application to thereby enable others1 skilled in the art to best utilise the invention in various embodiments and with various2 modifications as are suited to the particular use contemplated. Therefore, further 3 modifications or improvements may be incorporated without departing from the scope of4 the invention as defined by the appended claims.

Claims

1 Claims

2

3 1 . An energy harvesting device comprising:

4 one or more foils; and

5 a pressurised energy conversion system, the pressurised energy conversion

6 system comprising:

7 a working fluid;

8 one or more fluid displacement devices configured to be driven by movement

9 of the one or more foils; and 0 one or more generators configured to be driven by the working fluid, 1 wherein the pressurised energy conversion system is configured to dynamically2 vary a resistive force of the pressurised energy conversion system responsive to3 variation in a fluid flow incident upon the one or more foils. 4 5 2. The energy harvesting device as claimed in claim 1 , wherein the dynamic variation in6 the resistive force is to optimise the energy captured by the energy harvesting device. 7 8 3. The energy harvesting device as claimed in claims 1 or 2, wherein the dynamic9 variation in the resistive force is dependent on a variation in lift generated by the one or0 more foils. 1 2 4. The energy harvesting device as claimed in claims any of the preceding claims,3 wherein the dynamic variation in the resistive force is dependent on a variation in4 energy of a fluid flow incident upon the one or more foils. 5 6 5. The energy harvesting device as claimed in any of the preceding claims, wherein the7 dynamic variation of the resistive force comprises varying a flow rate of the working8 fluid displaced by the one or more fluid displacement devices. 9 0 6. The energy harvesting devices as claimed in any of the preceding claims, wherein the1 dynamic variation of the resistive force comprises the pressurised energy conversion2 system further comprising two or more reservoirs configured to operate at two or more3 different pressures. 4 5 7. The energy harvesting device as claimed in any of the preceding claims, wherein the6 one or more foils are configured to have a low inertia.

2 8. The energy harvesting device as claimed in any of the preceding claims, wherein the

3 movement of two or more foils is independent.

4

5 9. The energy harvesting device as claimed in any of the preceding claims, wherein the

6 energy harvesting device further comprises one or more ducts, wherein the one or

7 more foils are located within the one or more ducts.

8

9 10. The energy harvesting device as claimed in claim 9, wherein the variation in the fluid0 flow is measured at a mid-section of the one or more ducts. 1 2 11 . The energy harvesting device as claimed in claims 9 or 10, wherein each of the one or3 more ducts comprises two or more foils. 4 5 12. The energy harvesting device as claimed in any of the preceding claims, wherein the6 energy harvesting device further comprises one or more vibrational members, the one7 or more vibrational members connect the one or more foils to the pressurised energy8 conversion system. 9 0 13. The energy harvesting device as claimed in claim 12, wherein the one or more1 vibrational members are configured to pivot about a pivot axis located between a first2 end and a second end of the one or more vibrational members; or 3 the one or more vibrational members are configured to pivot about a pivot axis located4 at the second end of the one or more vibrational members. 5 6 14. The energy harvesting device as claimed in claim 13, wherein the one or more foils are7 configured to exhibit a pivoting motion about the pivot axis and a rotation motion about8 a rotation axis extending along the span direction of the one or more foils, the rotation9 axis being perpendicular to the pivot axis. 0 1 15. The energy harvesting device as claimed in any of the preceding claims wherein the2 one or more fluid displacement devices comprises a pump, and or a positive 3 displacement pump, and or a rotary-positive displacement pump, and or a 4 reciprocating-type positive displacement pump and or a piston and or a semi-rotary5 actuator and or a swash plate piston arrangement. 6

1 16. The energy harvesting device as claimed in claims 12 to 15, wherein the one or more

2 fluid displacement devices are connected to one or more vibrational members.

3

4 17. The energy harvesting device as claimed in claim 16, wherein the energy harvesting

5 device further comprises one or more mechanical connections connecting the one or

6 more fluid displacement devices to the one or more vibrational members.

7

8 18. The energy harvesting device as claims in claims 13 to 17, wherein the one or more

9 fluid displacement devices are connected to the vibrational member: 0 at the pivot point; and or 1 between the pivot point and the first end of the vibrational member; and or 2 between the pivot point and the second end of the vibrational member. 3 4 19. The energy harvesting device as claimed in any of the preceding claims, wherein there5 are two or more fluid displacement devices, fluidly connected in series or in parallel;6 and or the two or more fluid displacement devices are of different types and or size.7 8 20. The energy harvesting device as claimed in any of the preceding claims, wherein the9 pressurised energy conversion system further comprises one or more pressure0 intensifiers. 1 2 21 . The energy harvesting device as claimed in any of the preceding claims, wherein the3 pressurised energy conversion system comprises one or more control valves and or4 one or more non-return valves and or one or more proportional flow valves and or one5 or more pressure dependent non-return valves. 6 7 22. The energy harvesting device as claimed in any of the preceding claims, wherein the8 pressurised energy conversion system comprises an expansion chamber. 9 0 23. The energy harvesting device as claimed in claim 1 , wherein the one or more foils are1 configured as one or more turbines, wherein the one or more turbines are mechanically2 connected to one or more radial arms, the radial arms connected to a central spindle. 3 4 24. The energy harvesting device as claimed in claim 1 , wherein the working fluid may be5 a gas or liquid. 1

2 25. An energy harvesting system comprising two or more energy harvesting devices as

3 claimed in claims 1 to 24.

4

5 26. The energy harvesting system as claimed in claim 25, wherein the energy harvesting

6 system comprises a centralised reservoir and or a centralised generator.

7

8 27. A method of a method of manufacturing an energy harvesting device comprising:

9 providing one or more foils; 0 providing a working fluid of a pressurised energy conversion system; 1 providing one or more fluid displacement devices of the pressurised energy 2 conversion system, the one or more fluid displacement devices configured to be3 driven by movement of the one or more foils; 4 providing a generator configured to be driven by the working fluid; and 5 configuring the pressurised energy conversion system to dynamically vary a resistive6 force of the pressurised energy conversion system responsive to variation in a fluid7 flow incident upon the one or more foils. 8 9 28. Use of an energy harvesting apparatus as claimed in claims 1 to 24 or an energy0 harvesting system as claimed in claims 25 and 26 for generating electrical energy. 1 2