GB2471658A - Energy harvesting system using hydraulic circuit - Google Patents

Abstract

A device for harvesting energy from pedestrian or vehicular traffic comprises a surface element 120 for receiving pressure from the traffic, and a fluid-flow circuit including a fluid-filled resilient (compressible) tube 10. A turbine generator 50 is coupled to the circuit to generate electricity. The circuit includes an expansion bladder 30, a fluid reservoir 70, one way valves 20, 60 and 80, and a control/release valve 40. The device may be mounted within a stair tread or floor module to capture the energy from human footfall, possibly to provide energy for advertising applications.

Description

Facility:Innovate

Description:

BackQround to the Invention: The field of energy harvesting has attracted a great number of innovations in recent years.

Many of these innovations have been based on the use of piezoelectric materials and the concept of harvesting ambient vibrations. The majority of these mechanisms are aimed at the wireless sensor market and produce very small amounts of useful power. A smaller number of inventions use direct electromagnetic induction. These are usually applied to much larger scale operations such as fooffall harvesters, and vehicular traffic harvesters. The range of mechanisms employed for energy harvesting include; piezo-ceramics (PZT), active fibre composites (AFC), piezoelectric polymers (PVDF), electromagnetic induction and electrostatic generation.

There are relatively few examples of energy harvesting systems designed to be installed in a floor/stair locations. A larger number of devices have been developed for on-body use and for capturing energy from vehicular traffic.

WO/2002/054569 describes an off-body' hydraulic system used to transfer downward pressure into energy, and is loosely applied to vehicular and animal traffic.

Hydraulic shoe-sole generators incorporating separate fluid reservoirs in the sole and heel of a shoe are known in the prior art. The reservoirs in these generators are coupled via turbines so that fluid flows from heel to sole during heel strike and back to the heel when the sole is compressed.

Summary of invention:

The invention provides a device, system and method as defined in the appended independent claims to which reference should now be made. Preferred or advantageous features of the invention are set out in dependent sub-claims.

Thus, in a first aspect the invention may provide a device for harvesting energy from pedestrian or vehicular traffic comprising, a surface element for receiving pressure from the pedestrian or vehicular traffic, a fluid-flow circuit comprising a fluid-filled resilient tube, a turbine generator coupled to the fluid-flow circuit such that flow of fluid through the circuit generates electricity, in which the surface element transfers pressure from the traffic to the resilient tube to actuate fluid flow through the circuit. The device may be advantageously used for harvesting energy from pedestrian traffic.

In a preferred example, the invention according to the first aspect may provide an energy harvesting device consisting of a compressible, fluid filled, tube which can be mounted within a stair tread or floor module and which is intended to capture the energy from human fooffall.

The device may be part of a larger system intended to provide power for applications such as advertising applications.

In a second aspect the invention may provide a system for harvesting energy to power an electrical application comprising one or more devices according to the first aspect of the invention.

In a third aspect the invention may provide method of harvesting energy from pedestrian or vehicular traffic comprising the steps of, transferring pressure caused by the pedestrian or vehicular traffic over a surface to a fluid-flow circuit thereby causing fluid to flow in the circuit, and generating electricity from the flow of fluid using a turbine generator. Preferably the method of the third aspect of the invention uses a device according to the first aspect of the invention or a system according to the second aspect of the invention.

Parameters Affecting Available Energy in Footfall Energy Harvesting: Based on fundamental physical considerations, it is possible to determine the amount of energy that could potentially be extracted from fooffall. Energy is transferred by a combination of applied force and a resultant displacement. If the applied force is a constant, F, and the resultant displacement is d, then the energy, E, this represents is: E= F.d In the more general case where the reaction force varies with displacement, x, according to Fx then the energy becomes: EOdFxdx Two types of situation likely to be found in practice are the constant force, F described above where E=F.d and the situation where the force is generated by a spring (with spring constant, k) where the force is proportional to displacement (F=k.x) where the energy is E12k.d2.

Given that the available force is limited then the maximum energy is obtained for the constant force case (E=F.d).

If footfall occurs at a frequency, f, then the average power is P=E.f. If it is possible to capture energy from multiple people simultaneously then the average power becomes Pn.E.f, where n is the number of simultaneous footfalls. For the constant force case, this becomes: P=n.F.d.f In order to maximise the generated power, each term in equation (1) should be maximised.

These values are limited by the nature of the pedestrian population, the effect that energy harvesting has on those pedestrians and constrains imposed by the application environment.

Displacement: The maximum displacement which a surface can undergo when stepped upon without causing an undesirable reaction from the pedestrian is not clearly defined and will probably depend on the environment. For a level surface, a step of 15mm or more is considered a trip hazard and it seems reasonable to take this as a limit in other situations. In many situations, the displacement experienced will depend on the weight of the pedestrian so that a light pedestrian will experience a smaller deflection than a heavy one. For energy harvesting purposes, it is desirable to maintain a displacement near to the acceptable maximum, irrespective of the pedestrian's weight. Preferably the surface depresses by no more than 15 mm, particularly preferably for no more than 10 mm, for example between 5 mm and 12 mm.

Reaction force: The force exerted on a walking surface depends on the weight of the person and upon their gait. In normal walking on a level surface, the vertical ground reaction force (GRF) has a maximum typically 25% above body weight while during running, this increases to 2.75-3 times body weight. The GRF varies through the gait cycle. There is a rapid initial impulse as the heel hits the ground, then the full foot comes into contact with the ground. The force then increases again as the foot lifts off. The profile during jogging and running shows a similar overall profile but the magnitude at different phases is altered.

The GRF during climbing and descending of stairs does not appear to be documented in the scientific literature but it seems reasonable to assume that the forces involved are likely to be significantly greater, particularly during climbing, than for level walking. It is proposed that a study be conducted to measure these forces in a typical staircase, as will be discussed in section.

The GRF depends on the pedestrian weight as well as on their gait. The distribution of body weight among the population depends on gender, age, ethnicity etc. Average bodyweight data for US adults is shown in. The mean weight for females in this sample is 74kg while for males it is 86kg. It may also be seen that there is a significant proportion of the population with a body weight above 100kg. These figures are intended to represent to overall adult population and this distribution may not be reflected in a particular location. For instance, in some locations there may be a large proportion of children who would have a significantly lower bodyweight. However, in the absence of specific information to the contrary, the distribution in will be assumed.

Footfall frequency: The rate of fooffall depends on the gait and physiology of the pedestrian but for normal level walking, the footfall frequency is between 2 and 2.2Hz. Given the small range of frequencies and the relatively small impact that this would have on power generation, a frequency of 2Hz will be assumed for subsequent considerations.

Number of pedestrians: As noted above, the potential for power generation increases in proportion to the number of pedestrians simultaneously walking on an energy-harvesting device. However, the device must be capable of extracting energy from each of these individuals separately if the benefit is to be gained. The ability to capture energy from multiple pedestrians depends on whether they can be constrained to remain on the harvesting device. This in turn depends on where and how the device is deployed. The intention is to divide the energy harvesting panels into 500mm wide circuits (the average width of a person standing shoulder to shoulder with another). This hot zone system' is intended to harvest the maximum available power from a crowd moving over the device.

Specific embodiments of the invention: Specific embodiments of the invention will now be described with reference to the drawings, in which; Figure 1 is an exploded view of a device and system according to an aspect of the invention.

Figure 1 illustrates an exploded view of a device for embedding into a surface such as a floor or a stair tread for harvesting energy from pedestrian traffic across that surface. Figure 1 also illustrates schematically how the device can be incorporated into a system for supplying power to an application.

The device forms a compressible floor or stair module and comprises a fluid-flow circuit having, coupled in series, a length of resilient tubing 10 containing a liquid, a first non-return valve 20, an expansion bladder 30, a release valve 40, a micro-turbine 50, a second non-return valve 60, a fluid reservoir 70 and a third non-return valve 80. The third non-return valve couples to the resilient tubing 10 to complete the circuit.

The device further comprises a tray 100 for receiving the resilient tubing, a rigid surface plate for transferring energy from pedestrian footfalls to the resilient tubing 10 and a set of leaf springs 130 biased against the rigid plate 120 to urge it away from the resilient tubing.

In a preferred embodiment the device may also comprise a power conditioning unit 150 and an energy storage meansl60, for example a battery or capacitor.

A system for supplying power to an application may comprise one or more of the devices. A system may also comprise the application itself 170, for example an advertising panel or a lighting arrangement.

Further details relating to some of the elements of the device, or a system using the device, are provided below, with reference to figure 1.

The rigid tray 100 acts as a housing or container for the energy harvesting mechanism. It forms the structural section of the module and is used to contain the compressible, resilient, tube section 10 of the device. The tray defines openings 101, 102 through which the resilient tube 10 can pass.

The rigid tray 100 houses a molded tray 110 for receiving circuits of compressible pipe 10.

The molded tray 110 is used to locate and contain the resilient tube 10. Channels within the tray are one third of the depth of the compressible tube's outside diameter. This allows for the tube to be compressed by two thirds but allows the last third to remain uncompressed in order to avoid it becoming blocked when trodden on.

The rigid surface plate 120 is used for transferring energy to the resilient tubing 10. It forms the surface that a pedestrian treads on. It is preferable that the plate 120 has a non-slip upper surface. This plate fits inside of the rigid tray 100 and is mounted on a series of leaf springs 130. It is the depression of this plate that compresses the fluid filled pipe.

In an alternative, the rigid plate 120 may be replaced by any surface that allows footfall energy to be transferred to the resilient tubing. For example, the surface may be a rubber crumb surface.

The fluid -filled resilient tube or pipe 10 is the main part of the hydraulic mechanism of the device used to capture energy. It is situated under the rigid surface plate 120 and is compressed when a load (i.e. a footstep) acts on the plate.

The leaf springs 130 assist return of surface plate and help recharge the pipe. Once the system has been depressed and the load is released, the leaf springs 130 will return the rigid surface plate 120 to it's original position in order to allow the compressible tube to refill and re-expand without any extra load impeding it's re-expansion. The leaf springs 130 sit on a nylon bearing 140 that is positioned within the rigid housing 100.

The non-return valves 20, 60, 80 are coupled to the circuit at the entrance and exit openings 101, 102 of the rigid tray, as well as between the turbine 50 and the reservoir 70. Each of these valves ensures that the fluid does not slip back through the system when the pressure is released.

The expansion bladder 30 is an elastic bladder with a flow control valve 40 at it's exit and a non return valve 20 between the exit 102 on the stair tread or floor module and the entrance of the expansion bladder. The expansion bladder 30 may be charged up' with fluid from the compressible tube 10, and once it reaches a predetermined pressure, the flow control valve will release the contents through the turbine 50. The elastic nature of the expansion bladder can be used to accelerate the passage of the fluid through the turbine.

The micro hydro turbine 50 is powered by fluid from the expansion bladder 30. The micro hydro turbine is connected to a dynamo which produces electrical power and feeds it into the electrical power conditioning unit 150.

The reservoir 70 collects the fluid that passes through the turbine 50. This collected fluid' will be drawn back into the resilient tube 10 (through a non-return valve 80) as soon as the pressure on the resilient tube 10 is released and the tube is allowed to recover its shape.

The electrical power conditioning unit 150 is there to take the power from the turbine 50 and convert or condition it so that it can be effectively stored.

The electrical energy storage device 160 takes the conditioned power from the electrical power conditioning unit 150 and stores the power until it is useful. A preferable storage device is in theformofa battery or cell.

The application 170 may be any device drawing power from the energy harvesting device.

Preferable applications may consist of an electro-luminescence (EL), organic light emitting diode (OLED) or Light -Emitting Diode (LED) advertising panel, or other similar device.

A preferred method of harvesting energy from pedestrian traffic using the device illustrated in figure 1 will now be described.

As a pedestrian steps onto the module, his or her weight compresses the surface plate 120, and in turn, compresses the fluid filled tube 10. The fluid is squeezed along the tube 10 and through the first non-return valve 20 (this valve stops the fluid returning backwards through the system in an attempt to refill the tube when the pressure is released).

As the pressure from the pedestrian is released, the leaf springs 130 urge the plate 120 away from the resilient tube 10. The tube then resiliently recovers and draws fluid from the reservoir through the third non-return valve 80.

Once in the expansion bladder 30, the fluid is stored. Each consecutive step pumps more fluid through the first non-return valve 20 and into the expansion bladder 30, where it is held until such a point as the expansion bladder is full and the fluid is at a predetermined pressure. At this point the release mechanism 40 is activated and the expansion bladder 30 releases its contents through the flow control valve 40 in a short burst under its elastic pressure. This short burst of fluid is passed directly through the release valve 40, through the micro hydro-turbine 50 and through the second non-return valve 60 into the reservoir 70. The micro hydro-turbine 50 is preferably designed to operate by a magnetic coupling between the fluid part and the electrical part.

The recharging speed of the system (i.e. the time needed to be ready for the next step) may be assisted by the series of very light leaf springs 130 which act to raise the plate 120 ata slightly faster speed than the resilient tube 10 is able to re-expand -thus giving the tube minimum hindrance during re-expansion.

The micro hydro-turbine 50 produces a voltage, which can be passed through a power conditioning circuit 150 to alter the voltage and current to a desired level. The electrical energy may also, if required, be stored in a battery or capacitor 160 before being consumed by the panel, screen or device to be used for advertising or other purposes 170.

Applications: In this fast moving world, with people continually exposed to communications from every direction, it is increasingly difficult for brand owners to find effective ways of connecting with their target customers. One of the solutions which advertisers are turning to, to reach consumers on the move, is a screen-based technology. At the time of writing, the products available on the market range from small and large-scale Liquid Crystal Display (LCD) screens to animated Light -Emitting Diode (LED) displays and interactive displays.

By their very nature, these devices are positioned in areas with a substantial level of footfall such as subway stations, rail stations, bus stops and shopping centres. This sector of advertising is growing rapidly as developments in the consumer market necessitate a more pervasive and targeted approach to marketing.

At the present time these advertising solutions are hard wired into the mains, restricting both their financial viability (due to the cost of running power to each unit) and the level of power which they consume in order to keep them running. As the technology behind screen-based advertising develops and power consumption is reduced it will be possible to utilise these more advanced forms of advertising in a much wider field. The present invention, in its various aspects, provides an advantageous means of supplying power to such applications.

By harvesting energy from pedestrian traffic it is feasible to expect to see this form of advertising in such mobile or temporary applications where there are large numbers of people, for example at music festivals, field sporting events and trade shows, with no need for generators or batteries.

The emerging technologies such as OLED (organic light emitting diode), AMLCD (active matrix liquid crystal display) and EL (electro-luminescence), including TFEL (thin film electro luminescence) may advantageously be used as part of a system according to an aspect of the invention, which will generate power from peoples footsteps and eliminate the need for mains power, batteries and petrol/diesel driven generators, have the capability of providing power on demand which reduces energy consumption (you only need advertising when there is someone there to see it) and increases the mobility of the application.

Although advertising is an advantageous application for the technology outlined in this document, there are many others. For example; 1. Security metal detectors (which may be needed at music festivals or other remote locations).

2. Security lighting, bin store lighting or garage lighting activated by either footfall or door action (both of which activating the hydraulic system).

3. Lighting in general -LED, OLED etc. 4. Mobile payment terminals for credit and debit cards or barcode scanners.

5. Actuation -using the power generated to switch or actuate another system or action. For example, the opening of a door may produce a enough power for a signal which turns on CCTV or provides enough power to take a digital photograph.

6. Advertising on demand' -there is no need for an advertisement to be active if no one is there to see it. Power can be provided by the pedestrian as he/she passes the panel and the panel can remain inactive when it is not required.

Claims (26)

1. Claims: 1. A device for harvesting energy from pedestrian or vehicular traffic comprising, a surface element for receiving pressure from the pedestrian or vehicular traffic, a fluid-flow circuit comprising a fluid-filled resilient tube, a turbine generator coupled to the fluid-flow circuit such that flow of fluid through the circuit generates electricity, in which the surface element transfers pressure from the traffic to the resilient tube to actuate fluid flow through the circuit.
2. 2. A device according to claim 1 in which the fluid-flow circuit further comprises an expansion bladder, coupled to the resilient tube via a non-return valve, and a release valve, the flow of fluid out of the expansion bladder being regulated by the release valve.
3. 3. A device according to claim 2 in which the fluid-flow circuit further comprises a reservoir for receiving fluid from the expansion bladder via a second non-return valve.
4. 4. A device according to claim 3 in which fluid is able to pass from the reservoir to the resilient tube via a third non-return valve.
5. 5. A device according to claim 2, 3, or 4 in which the turbine generator is coupled to the circuit to interact with fluid flowing out of the expansion bladder.
6. 6. A device according to any preceding claim in which the fluid and the turbine generator are magnetically coupled to generate electricity.
7. 7. A device according to any preceding claim in which the surface element is a depressible plate that squeezes the resilient tubing in response to a pressure applied to the plate by a pedestrian or vehicle.
8. 8. A device according to claim 7 in which the plate depresses by no more than 10 mm.
9. 9. A device according to any preceding claim in which the fluid-flow circuit is contained within a housing for embedding into a surface, for example a path or road.
10. 10. A device according to any preceding claim which is adapted to be embedded in a step of a set of stairs, for example as a stair tread.
11. 11. A device according to claim 10 in which the surface element provides a non-slip surface and the device is adapted to be embedded across substantially the width of the step.
12. 12. A device according to any preceding claim in which the longest dimension of the device is between 400 mm and 600 mm, preferably about 500 mm.
13. 13. A device according to any preceding claim comprising leaf springs acting to bias the surface element away from the fluid-filled tube.
14. 14. A device according to any preceding claim further comprising an electrical conditioning unit for converting energy generated by the turbine into a form in which it can be used or stored.
15. 15. A device according to any preceding claim further comprising an electrical storage means, for example a capacitor or battery.
16. 16. A system for harvesting energy to power an electrical application comprising one or more devices according to claims 1 to 15.
17. 17. A system according to claim 16 in which the electrical application is selected from the group comprising; security detectors, for example metal detectors, lighting, for example security lighting or stairwell lighting or street lighting, mobile payment terminals for credit and debit cards, mobile barcode scanners, and advertising displays.
18. 18. A system according to claim 16 or 17 comprising a plurality of devices according to claims 1 to 15 arranged beneath a sprung flooring such that traffic using the flooring results in electricity generation.
19. 19. A method of harvesting energy from pedestrian or vehicular traffic comprising the steps of, transferring pressure caused by the pedestrian or vehicular traffic over a surface to a fluid-flow circuit thereby causing fluid to flow in the circuit, and generating electricity from the flow of fluid using a turbine generator.
20. 20. A method according to claim 19 comprising the steps of, transferring pressure caused by the pedestrian or vehicular traffic to a fluid-filled resilient tube portion of the fluid-flow circuit, squeezing fluid from the resilient tube into an expansion bladder, allowing the fluid in the bladder to reach a predetermined pressure at which a release valve is actuated, passing fluid from the bladder into a reservoir, and causing fluid to be drawn from the reservoir into the resilient tube, the turbine generator being coupled to the circuit to generate electricity as fluid passes from the bladder to the reservoir.
21. 21. A method according to claim 20 in which the fluid passes through a first non return valve situated between the tube and the expansion bladder, a second non-return valve situated between the bladder and the reservoir and a third non-return valve situated between the reservoir and the tube.
22. 22. A method according to claim 20 or 21 in which fluid is drawn into the tube from the reservoir by resilient recovery of the resilient tube.
23. 23. A method according to any preceding method claim further comprising the step of conditioning and/or storing the generated electricity so that it is suitable for use.
24. 24. A method according to any preceding method claim comprising the step of using the electricity generated to power an apparatus selected from the group comprising security detectors, for example metal detectors, lighting, for example security lighting or stairwell lighting or street lighting, mobile payment terminals for credit and debit cards, mobile barcode scanners, and advertising displays.
25. 25. A device or system for energy harvesting substantially as described herein with reference to the drawings.
26. 26. A method of energy harvesting substantially as described herein with reference to the drawings.